WO2010006984A1 - Back surface technology imager pixel and related image sensor - Google Patents
Back surface technology imager pixel and related image sensor Download PDFInfo
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- WO2010006984A1 WO2010006984A1 PCT/EP2009/058744 EP2009058744W WO2010006984A1 WO 2010006984 A1 WO2010006984 A1 WO 2010006984A1 EP 2009058744 W EP2009058744 W EP 2009058744W WO 2010006984 A1 WO2010006984 A1 WO 2010006984A1
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- 229910021417 amorphous silicon Inorganic materials 0.000 claims abstract description 68
- 229910021419 crystalline silicon Inorganic materials 0.000 claims abstract description 60
- 238000010521 absorption reaction Methods 0.000 claims abstract description 31
- 238000003384 imaging method Methods 0.000 claims abstract description 14
- 239000000969 carrier Substances 0.000 claims description 18
- 230000005684 electric field Effects 0.000 claims description 11
- 238000002161 passivation Methods 0.000 claims description 11
- 230000000694 effects Effects 0.000 claims description 9
- 238000009792 diffusion process Methods 0.000 claims description 4
- 238000005215 recombination Methods 0.000 description 7
- 230000006798 recombination Effects 0.000 description 7
- 230000006872 improvement Effects 0.000 description 6
- 238000004519 manufacturing process Methods 0.000 description 6
- 239000004065 semiconductor Substances 0.000 description 6
- 238000000151 deposition Methods 0.000 description 5
- 239000000463 material Substances 0.000 description 5
- 230000008901 benefit Effects 0.000 description 4
- BOTDANWDWHJENH-UHFFFAOYSA-N Tetraethyl orthosilicate Chemical compound CCO[Si](OCC)(OCC)OCC BOTDANWDWHJENH-UHFFFAOYSA-N 0.000 description 3
- 230000009471 action Effects 0.000 description 3
- 230000015572 biosynthetic process Effects 0.000 description 3
- 238000006243 chemical reaction Methods 0.000 description 3
- 238000001514 detection method Methods 0.000 description 3
- XUIMIQQOPSSXEZ-UHFFFAOYSA-N Silicon Chemical compound [Si] XUIMIQQOPSSXEZ-UHFFFAOYSA-N 0.000 description 2
- 230000000295 complement effect Effects 0.000 description 2
- 230000004907 flux Effects 0.000 description 2
- 238000001465 metallisation Methods 0.000 description 2
- 230000003287 optical effect Effects 0.000 description 2
- 230000005855 radiation Effects 0.000 description 2
- 229910052710 silicon Inorganic materials 0.000 description 2
- 239000010703 silicon Substances 0.000 description 2
- OKTJSMMVPCPJKN-UHFFFAOYSA-N Carbon Chemical compound [C] OKTJSMMVPCPJKN-UHFFFAOYSA-N 0.000 description 1
- 239000011358 absorbing material Substances 0.000 description 1
- 238000010420 art technique Methods 0.000 description 1
- 229910052799 carbon Inorganic materials 0.000 description 1
- 239000013078 crystal Substances 0.000 description 1
- 230000003247 decreasing effect Effects 0.000 description 1
- 230000007547 defect Effects 0.000 description 1
- 230000001419 dependent effect Effects 0.000 description 1
- 239000003574 free electron Substances 0.000 description 1
- 230000006870 function Effects 0.000 description 1
- 229910052732 germanium Inorganic materials 0.000 description 1
- GNPVGFCGXDBREM-UHFFFAOYSA-N germanium atom Chemical compound [Ge] GNPVGFCGXDBREM-UHFFFAOYSA-N 0.000 description 1
- 238000009413 insulation Methods 0.000 description 1
- 238000005304 joining Methods 0.000 description 1
- 238000005259 measurement Methods 0.000 description 1
- 229910044991 metal oxide Inorganic materials 0.000 description 1
- 150000004706 metal oxides Chemical class 0.000 description 1
- 238000000034 method Methods 0.000 description 1
- 238000005036 potential barrier Methods 0.000 description 1
- 230000035945 sensitivity Effects 0.000 description 1
- 230000003595 spectral effect Effects 0.000 description 1
Classifications
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- H—ELECTRICITY
- H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
- H10F—INORGANIC SEMICONDUCTOR DEVICES SENSITIVE TO INFRARED RADIATION, LIGHT, ELECTROMAGNETIC RADIATION OF SHORTER WAVELENGTH OR CORPUSCULAR RADIATION
- H10F39/00—Integrated devices, or assemblies of multiple devices, comprising at least one element covered by group H10F30/00, e.g. radiation detectors comprising photodiode arrays
- H10F39/10—Integrated devices
- H10F39/12—Image sensors
- H10F39/18—Complementary metal-oxide-semiconductor [CMOS] image sensors; Photodiode array image sensors
- H10F39/182—Colour image sensors
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- H—ELECTRICITY
- H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
- H10F—INORGANIC SEMICONDUCTOR DEVICES SENSITIVE TO INFRARED RADIATION, LIGHT, ELECTROMAGNETIC RADIATION OF SHORTER WAVELENGTH OR CORPUSCULAR RADIATION
- H10F30/00—Individual radiation-sensitive semiconductor devices in which radiation controls the flow of current through the devices, e.g. photodetectors
- H10F30/20—Individual radiation-sensitive semiconductor devices in which radiation controls the flow of current through the devices, e.g. photodetectors the devices having potential barriers, e.g. phototransistors
- H10F30/21—Individual radiation-sensitive semiconductor devices in which radiation controls the flow of current through the devices, e.g. photodetectors the devices having potential barriers, e.g. phototransistors the devices being sensitive to infrared, visible or ultraviolet radiation
- H10F30/22—Individual radiation-sensitive semiconductor devices in which radiation controls the flow of current through the devices, e.g. photodetectors the devices having potential barriers, e.g. phototransistors the devices being sensitive to infrared, visible or ultraviolet radiation the devices having only one potential barrier, e.g. photodiodes
- H10F30/222—Individual radiation-sensitive semiconductor devices in which radiation controls the flow of current through the devices, e.g. photodetectors the devices having potential barriers, e.g. phototransistors the devices being sensitive to infrared, visible or ultraviolet radiation the devices having only one potential barrier, e.g. photodiodes the potential barrier being a PN heterojunction
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- H—ELECTRICITY
- H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
- H10F—INORGANIC SEMICONDUCTOR DEVICES SENSITIVE TO INFRARED RADIATION, LIGHT, ELECTROMAGNETIC RADIATION OF SHORTER WAVELENGTH OR CORPUSCULAR RADIATION
- H10F39/00—Integrated devices, or assemblies of multiple devices, comprising at least one element covered by group H10F30/00, e.g. radiation detectors comprising photodiode arrays
- H10F39/011—Manufacture or treatment of image sensors covered by group H10F39/12
- H10F39/016—Manufacture or treatment of image sensors covered by group H10F39/12 of thin-film-based image sensors
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- H—ELECTRICITY
- H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
- H10F—INORGANIC SEMICONDUCTOR DEVICES SENSITIVE TO INFRARED RADIATION, LIGHT, ELECTROMAGNETIC RADIATION OF SHORTER WAVELENGTH OR CORPUSCULAR RADIATION
- H10F39/00—Integrated devices, or assemblies of multiple devices, comprising at least one element covered by group H10F30/00, e.g. radiation detectors comprising photodiode arrays
- H10F39/10—Integrated devices
- H10F39/12—Image sensors
- H10F39/199—Back-illuminated image sensors
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- H—ELECTRICITY
- H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
- H10F—INORGANIC SEMICONDUCTOR DEVICES SENSITIVE TO INFRARED RADIATION, LIGHT, ELECTROMAGNETIC RADIATION OF SHORTER WAVELENGTH OR CORPUSCULAR RADIATION
- H10F71/00—Manufacture or treatment of devices covered by this subclass
- H10F71/10—Manufacture or treatment of devices covered by this subclass the devices comprising amorphous semiconductor material
- H10F71/103—Manufacture or treatment of devices covered by this subclass the devices comprising amorphous semiconductor material including only Group IV materials
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- H—ELECTRICITY
- H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
- H10F—INORGANIC SEMICONDUCTOR DEVICES SENSITIVE TO INFRARED RADIATION, LIGHT, ELECTROMAGNETIC RADIATION OF SHORTER WAVELENGTH OR CORPUSCULAR RADIATION
- H10F71/00—Manufacture or treatment of devices covered by this subclass
- H10F71/138—Manufacture of transparent electrodes, e.g. transparent conductive oxides [TCO] or indium tin oxide [ITO] electrodes
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- H—ELECTRICITY
- H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
- H10F—INORGANIC SEMICONDUCTOR DEVICES SENSITIVE TO INFRARED RADIATION, LIGHT, ELECTROMAGNETIC RADIATION OF SHORTER WAVELENGTH OR CORPUSCULAR RADIATION
- H10F77/00—Constructional details of devices covered by this subclass
- H10F77/10—Semiconductor bodies
- H10F77/16—Material structures, e.g. crystalline structures, film structures or crystal plane orientations
- H10F77/162—Non-monocrystalline materials, e.g. semiconductor particles embedded in insulating materials
- H10F77/166—Amorphous semiconductors
- H10F77/1662—Amorphous semiconductors including only Group IV materials
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- H—ELECTRICITY
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- H10F—INORGANIC SEMICONDUCTOR DEVICES SENSITIVE TO INFRARED RADIATION, LIGHT, ELECTROMAGNETIC RADIATION OF SHORTER WAVELENGTH OR CORPUSCULAR RADIATION
- H10F77/00—Constructional details of devices covered by this subclass
- H10F77/20—Electrodes
- H10F77/244—Electrodes made of transparent conductive layers, e.g. transparent conductive oxide [TCO] layers
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- H—ELECTRICITY
- H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
- H10F—INORGANIC SEMICONDUCTOR DEVICES SENSITIVE TO INFRARED RADIATION, LIGHT, ELECTROMAGNETIC RADIATION OF SHORTER WAVELENGTH OR CORPUSCULAR RADIATION
- H10F39/00—Integrated devices, or assemblies of multiple devices, comprising at least one element covered by group H10F30/00, e.g. radiation detectors comprising photodiode arrays
- H10F39/80—Constructional details of image sensors
- H10F39/805—Coatings
- H10F39/8053—Colour filters
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- H—ELECTRICITY
- H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
- H10F—INORGANIC SEMICONDUCTOR DEVICES SENSITIVE TO INFRARED RADIATION, LIGHT, ELECTROMAGNETIC RADIATION OF SHORTER WAVELENGTH OR CORPUSCULAR RADIATION
- H10F39/00—Integrated devices, or assemblies of multiple devices, comprising at least one element covered by group H10F30/00, e.g. radiation detectors comprising photodiode arrays
- H10F39/80—Constructional details of image sensors
- H10F39/806—Optical elements or arrangements associated with the image sensors
- H10F39/8063—Microlenses
-
- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
- Y02P70/00—Climate change mitigation technologies in the production process for final industrial or consumer products
- Y02P70/50—Manufacturing or production processes characterised by the final manufactured product
Definitions
- the invention relates to an imager pixel in backplane type technology and an associated image sensor.
- One field of application of the invention is the field of imaging. From a technological point of view, the invention applies to CMOS technology (CMOS for "COMPLEMENTARY METAL-OXIDE SEMICONDUCTOR") and to hydrogenated amorphous silicon technology.
- CMOS technology is preferred, however, as CMOS manufacturing lines are more widespread than CCD manufacturing lines.
- the conversion of photons into electron-hole pairs is the basis for the operation of image sensors.
- the digital acquisition of an image is achieved by the projection of an image on an imaging circuit, which causes the conversion at each point of the image of the luminous flux into electric charges, these charges being periodically measured by an electronic circuit and the value of this measurement converted into digital data.
- the elementary cell for converting an image sensor is the pixel.
- the thickness of material that is necessary to absorb the photons does not vary, because it depends on the wavelength of the light absorbed and the absorbing material such as, for example, crystalline silicon noted cSi.
- the absorbing material such as, for example, crystalline silicon noted cSi.
- a thickness of about 7.5 ⁇ m of crystalline silicon cSi is required.
- This large thickness is a problem of crosstalk (English language) because it is important compared to the width of the pixel.
- Crosstalk may be optical, i.e., light radiation entering the pixel non-perpendicular to the surface may become absorbed in a neighboring pixel due to the angle of incidence.
- the crosstalk can also be electronic, that is, a photogenerated electron in one area of the pixel can be collected by a neighboring pixel.
- the conversion efficiency of long wavelengths that require a substantial material thickness to be absorbed is sacrificed by decreasing the active photogeneration thickness by means of deep doping which promotes recombination or by means of a layer of buried insulation at the desired depth.
- This insulating layer is advantageously used in a back-side architecture which, by the absence of an interconnection track on the input side of the luminous flux, advantageously allows a wide angle for access to the silicon by the light rays. These large angles are necessary to increase the number of photons arriving on the sensor and to obtain the spatial resolution compatible with pixels of limited size. In return, these large angles increase the optical crosstalk.
- a complementary technique for limiting electronic cross-talk is to create weak electric fields by producing doping gradients favoring the path of the photogenerated electrons towards the collection zone of the pixel situated closest to the photogeneration site.
- the invention does not have this disadvantage.
- the invention relates to a rear-type technology imager pixel which comprises a crystalline silicon absorption layer having a single type of doping in which at least one carrier-collecting electrode is formed. on which a first potential is applied, characterized in that it further comprises:
- the amorphous silicon absorption layer fixed on one side of the crystalline silicon layer and in which a diode is formed, and a transparent electrode fixed on the amorphous silicon absorption layer and on which is applied a second potential, the potential difference between the second potential and the first potential leading to a reverse bias of the diode.
- the amorphous silicon absorption layer has a thickness of less than 50 nm. This feature allows carriers created by photoelectric effect in the amorphous silicon area to reach the crystalline silicon layer by diffusion.
- the crystalline silicon layer comprises, near the amorphous silicon absorption layer, an additional crystalline silicon layer whose doping differs from that of the crystalline silicon layer having a single type of doping.
- the additional crystalline silicon layer is located in contact with the amorphous silicon layer.
- the additional crystalline silicon layer is located at a distance from the amorphous silicon layer of less than 100 nm.
- the additional crystalline silicon layer doped with a doping different from that of the crystalline silicon layer having a single type of doping has the considerable advantage of making it possible to adjust the electronic properties of the heterostructure. More precisely, this additional crystalline silicon layer makes it possible to reduce the residual leakage current due to the electric field created by the potential difference without substantially increasing the recombination of the carriers.
- the amorphous silicon layer comprises, near the crystalline silicon absorption layer, and additionally to the diode, an amorphous silicon area whose doping is modified relative to the rest of the amorphous silicon layer.
- the amorphous silicon zone is located in contact with the crystalline silicon layer.
- the amorphous silicon zone is located at a distance from the crystalline silicon layer of less than 10 nm.
- Such a region of doped amorphous silicon with modified doping has the considerable advantage of making it possible to adjust the electronic properties of the heterostructure. More precisely, it makes it possible to reduce the residual leakage current due to the electric field created by the potential difference ⁇ V without substantially increasing the recombination of the carriers.
- the potential difference is adjusted so that carriers created by the photoelectric effect in the amorphous silicon zone reach the crystalline silicon layer having a single type of conduction doping under the effect of the electric field associated with the potential difference.
- the imager of the invention allows a much larger photon absorption than an imager pixel of the prior art. The detection of images is very significantly improved.
- FIG. 1 represents a first example of an imager pixel of the invention
- FIG. 2 represents a second example of an imager pixel of the invention
- FIG. 3 represents a third example of an imager pixel of the invention
- FIG. 4 represents a fourth example of an imager pixel of the invention.
- FIG. 5 represents a cross-sectional view of a rear-type technology imager according to the prior art
- FIG. 6 represents a cross-sectional view of a first example of a rear-type technology imager according to the invention
- FIG. 7 represents a cross-sectional view of a second example of a rear-type technology imager according to the invention.
- FIG. 8 represents a cross-sectional view of a third example of a rear-type technology imager according to the invention
- FIG. 9 represents a cross-sectional view of a fourth example of a rear-type technology imager according to the invention.
- Fig. 1 shows a first exemplary imager pixel of the invention.
- the pixel comprises a support 1, a transfer layer 2, a PMD layer 3 (PMD for "Physical Media Dependent"), a crystalline silicon layer having a single doping type 4, an amorphous silicon layer 5, a transparent electrode 6, a carrier collection electrode 7 and, optionally, a passivation layer 8 which covers the transparent electrode 6.
- PMD Physical Media Dependent
- the crystalline silicon layer 4 has only one type of doping.
- crystalline silicon layer "having a single type of doping” is meant a crystalline silicon layer which only has, at equilibrium, predominant carriers of a single type (type N, or type P, or type IN , or type IP, or type I).
- a diode is formed in the amorphous silicon layer 5.
- the amorphous silicon layer 5 thus comprises, for example, an intrinsic amorphous silicon layer 5a and a P + 5b doped amorphous silicon layer.
- the thickness of the layer 5a is, for example, between 5 nm and 500 nm and the thickness of the layer 5 b between, for example for example, 5nm and 50nm.
- a first potential Vl is applied to the collecting electrode 7 and a second potential V2 to the transparent electrode 6.
- the presence of this zone devoid of free carriers commonly called depletion zone (English language), aims to avoid recombination in amorphous silicon.
- the potential difference ⁇ V is, for example, equal to -2V.
- the photogenerated electrons in the amorphous silicon zone 5 can then reach the crystalline silicon layer 4 under the action of the electric field associated with the potential difference ⁇ V.
- the photogenerated electrons reach the carrier collecting electrode 7 under the action of the electric field associated with the potential difference ⁇ V for a first part of their path and by diffusion for the remainder of their path .
- a greater potential difference ⁇ V lengthens the part of the path that is performed under the action of the electric field.
- the amorphous silicon absorption layer 5 and the crystalline silicon layer 4 form a structure which must allow the photogenerated electrons in the amorphous silicon layer 5 to reach the collector electrode of carriers 7.
- Such structure has a conduction band.
- the "conduction band" of a semiconductor is the energy band in which circulate the free electrons.
- the conduction band of the structure of the invention is therefore chosen so that there is no potential barrier preventing the photogenerated carriers from joining the crystalline silicon. In a manner known per se, this choice of the conduction band depends on the semiconductor material (amorphous or crystalline silicon), the doping of the semiconductor as well as the voltage applied to the semiconductor.
- the transfer layer 2 for example a TEOS layer (TEOS for "Tetra-Ethyl-Ortho-Silicate") makes it possible, in a manner known per se, to fix the PMD layer 3 on the support 1. itself, the carrier collection electrode 7 formed in the crystalline silicon layer 4 is connected to a signal reading circuit (not shown in the figure).
- TEOS Tetra-Ethyl-Ortho-Silicate
- the photogenerated carriers which are collected by the electrode 7 are electrons.
- the invention however relates to other embodiments in which it is the photogenerated holes that are collected by the electrode 7. These other embodiments are not detailed in the present description, because the skilled person who knows a Embodiment of the invention in which the collected carriers are electrons can transpose, without particular difficulty, the invention to embodiments where they are holes that are collected.
- Fig. 2 shows a second exemplary imager pixel of the invention.
- the amorphous silicon layer 5 has a thickness sufficiently small for the carriers created there to reach the collecting electrode 7 by diffusion.
- the potential difference ⁇ V which creates the depleted zone in the amorphous silicon does not participate here in a conduction of carriers to the electrode.
- the thickness of the layer 5 is then substantially between, for example, 2 nm and 10 nm for a crystalline silicon layer thickness 4 between 1 ⁇ m and 5 ⁇ m.
- an additional crystalline silicon layer 9 whose doping differs from doping the crystalline silicon layer 4 is placed between the crystalline silicon layer 4 and the absorption layer 5a.
- the crystalline silicon layer 9 then has an N-type doping.
- the thickness of the layer 9 is small, for example equal to 100 nm.
- the formation of the crystalline silicon layer 9 is intended to make it possible to adjust the electronic properties of the heterostructure. In particular, it makes it possible to reduce the residual leakage current due to the electric field created by the potential difference ⁇ V without substantially increasing the recombination of the carriers.
- the additional crystalline silicon layer 9 formed between the crystalline silicon layer 4 and the amorphous silicon layer 5a is a non-recombinant interface, that is to say an interface which has no defects and / or no unsaturated bonds .
- the recombination speed of carriers in layer 9 is weak (eg 10cm / s).
- the layer 9 is preferably located in contact with the amorphous silicon layer 5a, as shown in FIG. 3. According to a variant of the invention, the layer 9 is distant from the layer 5a. It is a layer made of the same material and the same doping as the layer 4 which then separates the layer 9 from the layer 5a. The distance between the layer 5a and the layer 9 is less than 100 nm.
- the amorphous silicon layer 5a is intrinsic, for example.
- the amorphous silicon layer 5a comprises, in the vicinity of the absorption layer 4, an amorphous silicon zone 10 whose doping differs from that of the layer 5a, for example an N-type doping.
- the thickness of the zone 10 is for example equal to 10 nm.
- the zone 10 is located in contact with the crystalline silicon layer 4, as shown in FIG. 4. It should be noted that, if the structure of the invention comprises a crystalline silicon layer 9 such as that described previously, the zone 10 is then in contact with the layer 9 or the layer of material which separates the layer 9 from the layer 5a.
- the zone 10 is distant from the layer 4.
- the zone 10 is then separated from the layer 4 by an amorphous silicon layer having a doping identical to the doping of the layer 5a.
- the distance between zone 10 and layer 4 is preferably less than 10 nm.
- Such an amorphous silicon zone 10 is intended to allow the electronic properties of the heterostructure to be adjusted. In particular, it makes it possible to reduce the residual leakage current due to the electric field created by the potential difference ⁇ V without substantially increasing the recombination of the carriers.
- a rear-facing image sensor
- the image sensor comprises a support 1, a transfer layer 2, a PMD layer 3 in which are integrated metallizations ml, m2, a silicon layer crystal 4 in which are formed conductive electrodes 7 electrically connected to metallizations ml and m2, a passivation layer 8 placed above the crystalline silicon layer 4, FC red, green V and blue B color filters placed above the passivation layer 8, a planarization layer P which covers the colored filters and ML micro-lenses which cover the planarization layer P.
- an image sensor manufacturing method according to the invention comprises, up to at the step of surface passivation not included, a succession of steps in accordance with those known for the manufacture of a "back-side" type image sensor of the prior art.
- FIG. 6 represents an image sensor of the invention consisting of a set of pixels such as those represented in FIG. 1.
- the image sensor manufacturing method of the invention comprises the following steps:
- a diode may be formed by combining a first intrinsic zone I (5a) and a second zone P + doped (5b) It is also possible to form a diode by a first N-doped zone, a second intrinsic zone I, and a third doped zone P);
- FC R, V, B color filters on the passivation layer 8;
- FIG. 7 represents a first improvement of the image sensor represented in FIG. 6.
- a lateral doping variation is made in the thickness of the amorphous silicon layer 5.
- the variation of lateral doping can be carried out in FIG. the entire thickness of the amorphous silicon layer or only in the thickness of the intrinsic zone of the amorphous silicon layer.
- "Lateral doping variation” means that doping varies in connection with the color filters: a first doping d1 is performed under the red color filters R, a second doping d2 is performed under the green color filters V and a third doping d3 is performed under the blue color filters B.
- the doping is carbon doping or germanium.
- this doping modifies the absorption capacity of the light by the amorphous silicon, which favors the wavelengths selected by the color filters and disadvantages the other wavelengths, thus increasing the selectivity of the color filters.
- FIG. 8 represents a second improvement of the image sensor represented in FIG. 6.
- the transparent electrode 6 is not formed of a single block but of three distinct electrode blocks distributed in connection with the colored filters.
- a first electrode block is associated with the red color filter R
- a second electrode block is associated with the green color filter V
- a third electrode block is associated with the blue color filter B.
- Different potentials can then be applied to the different electrode blocks. It advantageously follows a spectral selectivity effect that enhances the effect of the color filter.
- Figure 9 shows a cross-sectional view of an image sensor according to a third improvement of the invention.
- the third improvement of the invention there is no amorphous silicon layer under the blue B color filters while this layer is present, as previously described, under the green V and R red color filters. Only the passivation layer 8 then separates the blue B color filters from the crystalline silicon layer 4.
- Such a structure advantageously makes it possible to benefit from the weakest crystalline silicon absorption, sufficient absorption for the short wavelengths but insufficient for the long wavelengths, which consequently favors the detection of blue compared to the detection of green and red.
- the various image sensors of the invention function advantageously with a maximum reflection on the lower structure which, for the low thicknesses accessible thanks to the amorphous silicon aSi, can then be optimized in thickness or index for each pixel, thus favoring the absorption according to the color detected by the pixel.
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Abstract
Description
PIXEL D' IMAGEUR EN TECHNOLOGIE FACE ARRIERE ET CAPTEUR D'IMAGE ASSOCIE PIXEL OF IMAGER IN REAR-BACK TECHNOLOGY AND IMAGE SENSOR
DESCRIPTIONDESCRIPTION
Domaine technique et art antérieurTechnical field and prior art
L' invention concerne un pixel d' imageur en technologie de type face arrière et un capteur d' image associé . Un domaine d'application de l'invention est le domaine de l'imagerie. D'un point de vue technologique, l'invention s'applique à la technologie CMOS (CMOS pour « COMPLEMENTARY METAL-OXIDE SEMICONDUCTOR ») et à la technologie à silicium amorphe hydrogéné.The invention relates to an imager pixel in backplane type technology and an associated image sensor. One field of application of the invention is the field of imaging. From a technological point of view, the invention applies to CMOS technology (CMOS for "COMPLEMENTARY METAL-OXIDE SEMICONDUCTOR") and to hydrogenated amorphous silicon technology.
A l'heure actuelle, la réalisation de capteurs d' image est basée soit sur la technologie CCD (CCD pour « Charge Coupled Device ») , soit sur la technologie CMOS. La technologie CMOS est toutefois privilégiée, du fait que les lignes de fabrication CMOS sont plus répandues que les lignes de fabrication CCD. La conversion des photons en paires électrons-trous est à la base du fonctionnement des capteurs d'image. De façon générale, l'acquisition numérique d'une image est réalisée par la projection d'une image sur un circuit imageur, qui provoque la conversion en chaque point de l'image du flux lumineux en charges électriques, ces charges étant périodiquement mesurées par un circuit électronique et la valeur de cette mesure convertie en données numériques. La cellule élémentaire de conversion d'un capteur d'image est le pixel. Alors que les pixels occupent une surface de plus en plus réduite, avec un pas sensiblement inférieur à 2μm, l'épaisseur de matériau qui est nécessaire pour absorber les photons ne varie pas, car elle dépend de la longueur d' onde de la lumière absorbée et du matériau qui absorbe tel que, par exemple, le silicium cristallin noté cSi. Ainsi, pour absorber 90% du rayonnement à une longueur d'onde de 625nm (couleur rouge), il faut une épaisseur de environ 7,5μm de silicium cristallin cSi. Cette forte épaisseur pose un problème de diaphonie (« crosstalk » en langue anglaise) car elle est importante comparée à la largeur du pixel. La diaphonie peut être optique, c'est-à-dire qu'un rayonnement lumineux qui entre dans le pixel de façon non perpendiculaire à la surface peut se retrouver absorbé dans un pixel voisin du fait de l'angle d'incidence. La diaphonie peut également être électronique, c'est-à-dire qu'un électron photogénéré dans une zone du pixel peut être collecté par un pixel voisin . Pour limiter les effets de la diaphonie, le rendement de conversion des grandes longueurs d'ondes qui demandent une épaisseur de matériau importante pour être absorbées est sacrifié en diminuant l'épaisseur active de photogénération au moyen de dopages profonds qui favorisent la recombinaison ou au moyen d'une couche d'isolant enterré à la profondeur désirée. Cette couche d' isolant est utilisée avec bénéfice dans une architecture de type face arrière ("back-side" en langue anglaise) qui, par l'absence de piste d'interconnexion sur la face d'entrée du flux lumineux, permet avantageusement un grand angle pour l'accès au silicium par les rayons lumineux. Ces grands angles sont nécessaires pour augmenter le nombre de photons arrivant sur le capteur et pour obtenir la résolution spatiale compatible avec des pixels de taille limitée. En contrepartie, ces grands angles augmentent la diaphonie optique.At present, the production of image sensors is based on either CCD (Charge Coupled Device) technology or CMOS technology. CMOS technology is preferred, however, as CMOS manufacturing lines are more widespread than CCD manufacturing lines. The conversion of photons into electron-hole pairs is the basis for the operation of image sensors. In general, the digital acquisition of an image is achieved by the projection of an image on an imaging circuit, which causes the conversion at each point of the image of the luminous flux into electric charges, these charges being periodically measured by an electronic circuit and the value of this measurement converted into digital data. The elementary cell for converting an image sensor is the pixel. As pixels occupy a growing surface reduced, with a pitch substantially less than 2μm, the thickness of material that is necessary to absorb the photons does not vary, because it depends on the wavelength of the light absorbed and the absorbing material such as, for example, crystalline silicon noted cSi. Thus, to absorb 90% of the radiation at a wavelength of 625 nm (red color), a thickness of about 7.5 μm of crystalline silicon cSi is required. This large thickness is a problem of crosstalk (English language) because it is important compared to the width of the pixel. Crosstalk may be optical, i.e., light radiation entering the pixel non-perpendicular to the surface may become absorbed in a neighboring pixel due to the angle of incidence. The crosstalk can also be electronic, that is, a photogenerated electron in one area of the pixel can be collected by a neighboring pixel. To limit the effects of crosstalk, the conversion efficiency of long wavelengths that require a substantial material thickness to be absorbed is sacrificed by decreasing the active photogeneration thickness by means of deep doping which promotes recombination or by means of a layer of buried insulation at the desired depth. This insulating layer is advantageously used in a back-side architecture which, by the absence of an interconnection track on the input side of the luminous flux, advantageously allows a wide angle for access to the silicon by the light rays. These large angles are necessary to increase the number of photons arriving on the sensor and to obtain the spatial resolution compatible with pixels of limited size. In return, these large angles increase the optical crosstalk.
Une technique complémentaire pour limiter la diaphonie électronique est de créer des champs électriques faibles en réalisant des gradients de dopage favorisant le parcours des électrons photogénérés vers la zone de collection du pixel situé au plus près du lieu de photogénération.A complementary technique for limiting electronic cross-talk is to create weak electric fields by producing doping gradients favoring the path of the photogenerated electrons towards the collection zone of the pixel situated closest to the photogeneration site.
Toutes ces techniques de l'art antérieur assurent un compromis médiocre entre la diaphonie et la sensibilité des pixels.All of these prior art techniques provide a poor compromise between crosstalk and pixel sensitivity.
L' invention ne présente pas cet inconvénient .The invention does not have this disadvantage.
Exposé de l'invention En effet, l'invention concerne un pixel d' imageur en technologie de type face arrière qui comprend une couche d'absorption en silicium cristallin ayant un seul type de dopage dans laquelle est formée au moins une électrode collectrice de porteurs sur laquelle est appliqué un premier potentiel, caractérisé en ce qu' il comprend, en outre :SUMMARY OF THE INVENTION Indeed, the invention relates to a rear-type technology imager pixel which comprises a crystalline silicon absorption layer having a single type of doping in which at least one carrier-collecting electrode is formed. on which a first potential is applied, characterized in that it further comprises:
— une couche d'absorption en silicium amorphe fixée sur une face de la couche de silicium cristallin et dans laquelle est formée une diode, et - une électrode transparente fixée sur la couche d'absorption en silicium amorphe et sur laquelle est appliquée un second potentiel, la différence de potentiel entre le second potentiel et le premier potentiel conduisant à une polarisation inverse de la diode . Selon une caractéristique supplémentaire de l'invention, la couche d'absorption en silicium amorphe a une épaisseur inférieure à 50nm. Cette caractéristique permet aux porteurs créés par effet photoélectrique dans la zone de silicium amorphe d'atteindre la couche de silicium cristallin par diffusion .An amorphous silicon absorption layer fixed on one side of the crystalline silicon layer and in which a diode is formed, and a transparent electrode fixed on the amorphous silicon absorption layer and on which is applied a second potential, the potential difference between the second potential and the first potential leading to a reverse bias of the diode. According to a further characteristic of the invention, the amorphous silicon absorption layer has a thickness of less than 50 nm. This feature allows carriers created by photoelectric effect in the amorphous silicon area to reach the crystalline silicon layer by diffusion.
Avantageusement, la couche de silicium cristallin comporte, à proximité de la couche d'absorption en silicium amorphe, une couche de silicium cristallin supplémentaire dont le dopage diffère de celui de la couche de silicium cristallin ayant un seul type de dopage.Advantageously, the crystalline silicon layer comprises, near the amorphous silicon absorption layer, an additional crystalline silicon layer whose doping differs from that of the crystalline silicon layer having a single type of doping.
Préférentiellement , la couche de silicium cristallin supplémentaire est située au contact de la couche de silicium amorphe.Preferably, the additional crystalline silicon layer is located in contact with the amorphous silicon layer.
Avantageusement, la couche de silicium cristallin supplémentaire est située à une distance de la couche de silicium amorphe inférieure à 100 nm.Advantageously, the additional crystalline silicon layer is located at a distance from the amorphous silicon layer of less than 100 nm.
La couche de silicium cristallin supplémentaire dopée avec un dopage différent de celui de la couche de silicium cristallin ayant un seul type de dopage présente l'avantage considérable de permettre d'ajuster les propriétés électroniques de 1' hétérostructure . Plus précisément, cette couche de silicium cristallin supplémentaire permet de diminuer le courant de fuite résiduel dû au champ électrique créé par la différence de potentiel sans augmenter sensiblement la recombinaison des porteurs.The additional crystalline silicon layer doped with a doping different from that of the crystalline silicon layer having a single type of doping has the considerable advantage of making it possible to adjust the electronic properties of the heterostructure. More precisely, this additional crystalline silicon layer makes it possible to reduce the residual leakage current due to the electric field created by the potential difference without substantially increasing the recombination of the carriers.
Avantageusement, la couche de silicium amorphe comporte, à proximité de la couche d'absorption en silicium cristallin, et additionnellement à la diode, une zone de silicium amorphe dont le dopage est modifié par rapport au reste de la couche de silicium amorphe .Advantageously, the amorphous silicon layer comprises, near the crystalline silicon absorption layer, and additionally to the diode, an amorphous silicon area whose doping is modified relative to the rest of the amorphous silicon layer.
Préférentiellement, la zone de silicium amorphe est située au contact de la couche de silicium cristallin .Preferably, the amorphous silicon zone is located in contact with the crystalline silicon layer.
Avantageusement, la zone de silicium amorphe est située à une distance de la couche de silicium cristallin inférieure à 10 nm. Une telle zone de silicium amorphe dopée avec un dopage modifié présente l'avantage considérable de permettre d'ajuster les propriétés électroniques de 1' hétérostructure . Plus précisément, elle permet de diminuer le courant de fuite résiduel dû au champ électrique créé par la différence de potentiel ΔV sans augmenter sensiblement la recombinaison des porteurs.Advantageously, the amorphous silicon zone is located at a distance from the crystalline silicon layer of less than 10 nm. Such a region of doped amorphous silicon with modified doping has the considerable advantage of making it possible to adjust the electronic properties of the heterostructure. More precisely, it makes it possible to reduce the residual leakage current due to the electric field created by the potential difference ΔV without substantially increasing the recombination of the carriers.
Selon une autre caractéristique supplémentaire de l'invention, la différence de potentiel est ajustée de façon que des porteurs créés par effet photoélectrique dans la zone de silicium amorphe atteignent la couche de silicium cristallin ayant un seul type de dopage par conduction sous l'effet du champ électrique associé à la différence de potentiel . Pour des pixels d' imageur ayant des épaisseurs de semi-conducteur identiques, un pixel d' imageur de l'invention permet une absorption de photons beaucoup plus importante qu'un pixel d' imageur de l'art antérieur. La détection des images s'en trouve très sensiblement améliorée.According to another additional characteristic of the invention, the potential difference is adjusted so that carriers created by the photoelectric effect in the amorphous silicon zone reach the crystalline silicon layer having a single type of conduction doping under the effect of the electric field associated with the potential difference. For imaging pixels having identical semiconductor thicknesses, one pixel The imager of the invention allows a much larger photon absorption than an imager pixel of the prior art. The detection of images is very significantly improved.
Brève description des figuresBrief description of the figures
D'autres caractéristiques et avantages de l'invention apparaîtront à la lecture d'un mode de réalisation préférentiel fait en référence aux figures jointes parmi lesquelles :Other features and advantages of the invention will appear on reading a preferred embodiment with reference to the appended figures among which:
- La figure 1 représente un premier exemple de pixel d' imageur de l'invention ;FIG. 1 represents a first example of an imager pixel of the invention;
- La figure 2 représente un deuxième exemple de pixel d' imageur de l'invention ; - La figure 3 représente un troisième exemple de pixel d' imageur de l'invention ;FIG. 2 represents a second example of an imager pixel of the invention; FIG. 3 represents a third example of an imager pixel of the invention;
- La figure 4 représente un quatrième exemple de pixel d' imageur de l'invention ;FIG. 4 represents a fourth example of an imager pixel of the invention;
- La figure 5 représente une vue en coupe transversale d'un imageur en technologie de type face arrière selon l'art antérieur ;FIG. 5 represents a cross-sectional view of a rear-type technology imager according to the prior art;
- La figure 6 représente une vue en coupe transversale d'un premier exemple d' imageur en technologie de type face arrière selon l'invention ; - La figure 7 représente une vue en coupe transversale d'un deuxième exemple d' imageur en technologie de type face arrière selon l'invention ;FIG. 6 represents a cross-sectional view of a first example of a rear-type technology imager according to the invention; FIG. 7 represents a cross-sectional view of a second example of a rear-type technology imager according to the invention;
- La figure 8 représente une vue en coupe transversale d'un troisième exemple d' imageur en technologie de type face arrière selon l'invention ; - La figure 9 représente une vue en coupe transversale d'un quatrième exemple d' imageur en technologie de type face arrière selon l'invention ;FIG. 8 represents a cross-sectional view of a third example of a rear-type technology imager according to the invention; FIG. 9 represents a cross-sectional view of a fourth example of a rear-type technology imager according to the invention;
Description détaillée de modes de mise en œuyre de 1' inventionDETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION
La figure 1 représente un premier exemple de pixel d' imageur de l'invention.Fig. 1 shows a first exemplary imager pixel of the invention.
Le pixel comprend un support 1, une couche de report 2, une couche PMD 3 (PMD pour « Physical Media Dépendent ») , une couche de silicium cristallin ayant un seul type de dopage 4, une couche de silicium amorphe 5, une électrode transparente 6, une électrode de collecte de porteurs 7 et, éventuellement, une couche de passivation 8 qui recouvre l'électrode transparente 6.The pixel comprises a support 1, a transfer layer 2, a PMD layer 3 (PMD for "Physical Media Dependent"), a crystalline silicon layer having a single doping type 4, an amorphous silicon layer 5, a transparent electrode 6, a carrier collection electrode 7 and, optionally, a passivation layer 8 which covers the transparent electrode 6.
La couche de silicium cristallin 4 a un seul type de dopage. Par couche de silicium cristallin « ayant un seul type de dopage », on entend une couche de silicium cristallin qui ne présente, à l'équilibre, que des porteurs majoritaires d'un seul type (type N, ou type P, ou type I-N, ou type I-P, ou type I) . Une diode est formée dans la couche de silicium amorphe 5. La couche de silicium amorphe 5 comprend ainsi, par exemple, une couche de silicium amorphe intrinsèque 5a et une couche de silicium amorphe dopée P+ 5b. Pour une couche de silicium cristallin 4 dont l'épaisseur est comprise, par exemple, entre lμm et 5μm, l'épaisseur de la couche 5a est comprise, par exemple, entre 5nm et 500nm et l'épaisseur de la couche 5b entre, par exemple, 5nm et 50nm. Un premier potentiel Vl est appliqué à l'électrode collectrice 7 et un second potentiel V2 à l'électrode transparente 6. La différence de potentiel ΔV (ΔV = V2-V1) polarise la diode en inverse, créant ainsi, dans le silicium amorphe, une zone dépourvue de porteurs libres. La présence de cette zone dépourvue de porteurs libres, communément appelée zone déplétée (« depletion zone » en langue anglaise), a pour but d'éviter les recombinaisons dans le silicium amorphe. La différence de potentiel ΔV est, par exemple, égale à -2V. Pour une amplitude suffisante de la différence de potentiel ΔV, les électrons photogénérés dans la zone de silicium amorphe 5 peuvent alors atteindre la couche de silicium cristallin 4 sous l'action du champ électrique associé à la différence de potentiel ΔV. Une fois la couche de silicium cristallin atteinte, les électrons photogénérés atteignent l'électrode collectrice de porteurs 7 sous l'action du champ électrique associé à la différence de potentiel ΔV pour une première partie de leur trajet et par diffusion pour le reste de leur trajet. Une différence de potentiel ΔV plus importante rallonge la partie du trajet qui est effectuée sous l'action du champ électrique.The crystalline silicon layer 4 has only one type of doping. By crystalline silicon layer "having a single type of doping" is meant a crystalline silicon layer which only has, at equilibrium, predominant carriers of a single type (type N, or type P, or type IN , or type IP, or type I). A diode is formed in the amorphous silicon layer 5. The amorphous silicon layer 5 thus comprises, for example, an intrinsic amorphous silicon layer 5a and a P + 5b doped amorphous silicon layer. For a crystalline silicon layer 4 whose thickness is, for example, between 1 μm and 5 μm, the thickness of the layer 5a is, for example, between 5 nm and 500 nm and the thickness of the layer 5 b between, for example for example, 5nm and 50nm. A first potential Vl is applied to the collecting electrode 7 and a second potential V2 to the transparent electrode 6. The potential difference ΔV (ΔV = V2-V1) polarizes the diode in reverse, thus creating, in the amorphous silicon, a zone devoid of carriers free. The presence of this zone devoid of free carriers, commonly called depletion zone (English language), aims to avoid recombination in amorphous silicon. The potential difference ΔV is, for example, equal to -2V. For a sufficient amplitude of the potential difference ΔV, the photogenerated electrons in the amorphous silicon zone 5 can then reach the crystalline silicon layer 4 under the action of the electric field associated with the potential difference ΔV. Once the crystalline silicon layer has been reached, the photogenerated electrons reach the carrier collecting electrode 7 under the action of the electric field associated with the potential difference ΔV for a first part of their path and by diffusion for the remainder of their path . A greater potential difference ΔV lengthens the part of the path that is performed under the action of the electric field.
Il est à noter que la couche d'absorption en silicium amorphe 5 et la couche de silicium cristallin 4 forment une structure qui doit permettre aux électrons photogénérés dans la couche de silicium amorphe 5 d'atteindre l'électrode collectrice de porteurs 7. Une telle structure présente une bande de conduction. De façon connue, la « bande de conduction » d'un semi-conducteur est la bande d'énergie dans laquelle circulent les électrons libres. La bande de conduction de la structure de l'invention est en conséquence choisie pour qu'il n'y ait pas de barrière de potentiel empêchant les porteurs photogénérés de rejoindre le silicium cristallin. De façon connue en soi, ce choix de la bande de conduction dépend du matériau semi-conducteur (silicium amorphe ou cristallin) , du dopage du semi-conducteur ainsi que de la tension appliquée au semi-conducteur. La couche de report 2, par exemple une couche de TEOS (TEOS pour « Tetra-Ethyl-Ortho- Silicate ») permet de fixer, de façon connue en soi, la couche de PMD 3 sur le support 1. Egalement de façon connue en soi, l'électrode de collecte des porteurs 7 formée dans la couche de silicium cristallin 4 est connectée à un circuit de lecture de signal (non représenté sur la figure) .It should be noted that the amorphous silicon absorption layer 5 and the crystalline silicon layer 4 form a structure which must allow the photogenerated electrons in the amorphous silicon layer 5 to reach the collector electrode of carriers 7. Such structure has a conduction band. In known manner, the "conduction band" of a semiconductor is the energy band in which circulate the free electrons. The conduction band of the structure of the invention is therefore chosen so that there is no potential barrier preventing the photogenerated carriers from joining the crystalline silicon. In a manner known per se, this choice of the conduction band depends on the semiconductor material (amorphous or crystalline silicon), the doping of the semiconductor as well as the voltage applied to the semiconductor. The transfer layer 2, for example a TEOS layer (TEOS for "Tetra-Ethyl-Ortho-Silicate") makes it possible, in a manner known per se, to fix the PMD layer 3 on the support 1. itself, the carrier collection electrode 7 formed in the crystalline silicon layer 4 is connected to a signal reading circuit (not shown in the figure).
Selon l'exemple décrit ci-dessus, les porteurs photogénérés qui sont collectés par l'électrode 7 sont des électrons. L'invention concerne toutefois d'autres modes de réalisation dans lesquels ce sont les trous photogénérés qui sont collectés par l'électrode 7. Ces autres modes de réalisation ne sont pas détaillés dans la présente description, car l'homme du métier qui connaît un mode de réalisation de l'invention dans lequel les porteurs collectés sont des électrons sait transposer, sans difficulté particulière, l'invention à des modes de réalisation où ce sont des trous qui sont collectés. La figure 2 représente un deuxième exemple de pixel d' imageur de l'invention. Selon ce deuxième exemple, la couche de silicium amorphe 5 a une épaisseur suffisamment faible pour que les porteurs qui y sont créés atteignent par diffusion l'électrode collectrice 7. La différence de potentiel ΔV qui crée la zone déplétée dans le silicium amorphe ne participe pas ici à une conduction des porteurs vers l'électrode. L'épaisseur de la couche 5 est alors sensiblement comprise, par exemple, entre 2nm et lOnm pour une épaisseur de couche de silicium cristallin 4 comprise entre lμm et 5μm.According to the example described above, the photogenerated carriers which are collected by the electrode 7 are electrons. The invention however relates to other embodiments in which it is the photogenerated holes that are collected by the electrode 7. These other embodiments are not detailed in the present description, because the skilled person who knows a Embodiment of the invention in which the collected carriers are electrons can transpose, without particular difficulty, the invention to embodiments where they are holes that are collected. Fig. 2 shows a second exemplary imager pixel of the invention. According to this second For example, the amorphous silicon layer 5 has a thickness sufficiently small for the carriers created there to reach the collecting electrode 7 by diffusion. The potential difference ΔV which creates the depleted zone in the amorphous silicon does not participate here in a conduction of carriers to the electrode. The thickness of the layer 5 is then substantially between, for example, 2 nm and 10 nm for a crystalline silicon layer thickness 4 between 1 μm and 5 μm.
Selon une variante de l'invention telle que représentée en figure 3, une couche de silicium cristallin supplémentaire 9 dont le dopage diffère du dopage la couche de silicium cristallin 4 est placée entre la couche de silicium cristallin 4 et la couche d'absorption 5a. Pour une couche de silicium cristallin 4 ayant un dopage de type P, la couche de silicium cristallin 9 a alors un dopage de type N. L'épaisseur de la couche 9 est faible, par exemple égale à 100 nm. La formation de la couche de silicium cristallin 9 est destinée à permettre d'ajuster les propriétés électroniques de l' hétérostructure . En particulier, elle permet de diminuer le courant de fuite résiduel dû au champ électrique créé par la différence de potentiel ΔV sans augmenter sensiblement la recombinaison des porteurs. La couche de silicium cristallin supplémentaire 9 formée entre la couche de silicium cristallin 4 et la couche de silicium amorphe 5a est une interface non recombinante, c'est-à-dire une interface qui ne présente pas de défauts et/ou pas de liaisons insaturées. La vitesse de recombinaison des porteurs dans la couche 9 est faible (par exemple 10cm/s) .According to a variant of the invention as represented in FIG. 3, an additional crystalline silicon layer 9 whose doping differs from doping the crystalline silicon layer 4 is placed between the crystalline silicon layer 4 and the absorption layer 5a. For a crystalline silicon layer 4 having a P-type doping, the crystalline silicon layer 9 then has an N-type doping. The thickness of the layer 9 is small, for example equal to 100 nm. The formation of the crystalline silicon layer 9 is intended to make it possible to adjust the electronic properties of the heterostructure. In particular, it makes it possible to reduce the residual leakage current due to the electric field created by the potential difference ΔV without substantially increasing the recombination of the carriers. The additional crystalline silicon layer 9 formed between the crystalline silicon layer 4 and the amorphous silicon layer 5a is a non-recombinant interface, that is to say an interface which has no defects and / or no unsaturated bonds . The recombination speed of carriers in layer 9 is weak (eg 10cm / s).
La couche 9 est préférentiellement située au contact de la couche de silicium amorphe 5a, comme cela est représenté sur la figure 3. Selon une variante de l'invention, la couche 9 est distante de la couche 5a. C'est une couche faite avec le même matériau et le même dopage que la couche 4 qui sépare alors la couche 9 de la couche 5a. La distance entre la couche 5a et la couche 9 est inférieure à 100 nm.The layer 9 is preferably located in contact with the amorphous silicon layer 5a, as shown in FIG. 3. According to a variant of the invention, the layer 9 is distant from the layer 5a. It is a layer made of the same material and the same doping as the layer 4 which then separates the layer 9 from the layer 5a. The distance between the layer 5a and the layer 9 is less than 100 nm.
Selon une variante telle que représentée à la figure 4, la couche de silicium amorphe 5a est intrinsèque, par exemple. La couche de silicium amorphe 5a comporte, au voisinage de la couche d'absorption 4, une zone de silicium amorphe 10 dont le dopage diffère de celui de la couche 5a, par exemple un dopage de type N. L'épaisseur de la zone 10 est par exemple égale à 10 nm.According to a variant as shown in Figure 4, the amorphous silicon layer 5a is intrinsic, for example. The amorphous silicon layer 5a comprises, in the vicinity of the absorption layer 4, an amorphous silicon zone 10 whose doping differs from that of the layer 5a, for example an N-type doping. The thickness of the zone 10 is for example equal to 10 nm.
Préférentiellement, la zone 10 est située au contact de la couche de silicium cristallin 4, comme cela est représenté sur la figure 4. Il est à noter que, si la structure de l'invention comporte une couche de silicium cristallin 9 telle que celle décrite précédemment, la zone 10 est alors située au contact de la couche 9 ou de la couche de matériau qui sépare la couche 9 de la couche 5a.Preferably, the zone 10 is located in contact with the crystalline silicon layer 4, as shown in FIG. 4. It should be noted that, if the structure of the invention comprises a crystalline silicon layer 9 such as that described previously, the zone 10 is then in contact with the layer 9 or the layer of material which separates the layer 9 from the layer 5a.
Selon une variante, la zone 10 est distante de la couche 4. La zone 10 est alors séparée de la couche 4 par une couche de silicium amorphe ayant un dopage identique au dopage de la couche 5a. La distance entre la zone 10 et la couche 4 est préférentiellement inférieure à 10 nm.According to a variant, the zone 10 is distant from the layer 4. The zone 10 is then separated from the layer 4 by an amorphous silicon layer having a doping identical to the doping of the layer 5a. The distance between zone 10 and layer 4 is preferably less than 10 nm.
La formation d'une telle zone de silicium amorphe 10 est destiné à permettre d'ajuster les propriétés électroniques de l' hétérostructure . En particulier, elle permet de diminuer le courant de fuite résiduel dû au champ électrique créé par la différence de potentiel ΔV sans augmenter sensiblement la recombinaison des porteurs. Un capteur d'image de type face arrièreThe formation of such an amorphous silicon zone 10 is intended to allow the electronic properties of the heterostructure to be adjusted. In particular, it makes it possible to reduce the residual leakage current due to the electric field created by the potential difference ΔV without substantially increasing the recombination of the carriers. A rear-facing image sensor
(« backside ») de l'art connu est représenté en figure 5. Le capteur d'image comprend un support 1, une couche de report 2, une couche PMD 3 dans laquelle sont intégrées des métallisations ml, m2, une couche de silicium cristallin 4 dans laquelle sont formées des électrodes conductrices 7 électriquement reliées aux métallisations ml et m2, une couche de passivation 8 placée au-dessus de la couche de silicium cristallin 4, des filtres colorés FC rouge R, vert V et bleu B placés au-dessus de la couche de passivation 8, une couche de planarisation P qui recouvre les filtres colorés et des micro-lentilles ML qui recouvrent la couche de planarisation P. Concrètement, un procédé de fabrication de capteur d'image selon l'invention comprend, jusqu'à l'étape de passivation de surface non incluse, une succession d'étapes conforme à celles connues pour la fabrication d'un capteur d'image de type « back-side » de l'art antérieur.("Backside") of the known art is shown in FIG. 5. The image sensor comprises a support 1, a transfer layer 2, a PMD layer 3 in which are integrated metallizations ml, m2, a silicon layer crystal 4 in which are formed conductive electrodes 7 electrically connected to metallizations ml and m2, a passivation layer 8 placed above the crystalline silicon layer 4, FC red, green V and blue B color filters placed above the passivation layer 8, a planarization layer P which covers the colored filters and ML micro-lenses which cover the planarization layer P. In practice, an image sensor manufacturing method according to the invention comprises, up to at the step of surface passivation not included, a succession of steps in accordance with those known for the manufacture of a "back-side" type image sensor of the prior art.
La figure 6 représente un capteur d' image de l'invention constitué d'un ensemble de pixels tels que ceux représentés en figure 1. Au-delà de la succession d'étapes connues mentionnée précédemment, le procédé de fabrication de capteur d' image de l'invention comprend les étapes suivantes :FIG. 6 represents an image sensor of the invention consisting of a set of pixels such as those represented in FIG. 1. Beyond the sequence of known steps mentioned above, the image sensor manufacturing method of the invention comprises the following steps:
- dépôt de la couche de silicium amorphe 5 avec formation de diodes dans la couche de silicium amorphe (comme cela a été mentionné précédemment, une diode peut être formée par association d'une première zone intrinsèque I (5a) et d'une deuxième zone dopée P+ (5b) ; II est également possible de former une diode par une première zone dopée N, une deuxième zone intrinsèque I, et une troisième zone dopée P) ;depositing the amorphous silicon layer 5 with formation of diodes in the amorphous silicon layer (as mentioned above, a diode may be formed by combining a first intrinsic zone I (5a) and a second zone P + doped (5b) It is also possible to form a diode by a first N-doped zone, a second intrinsic zone I, and a third doped zone P);
- dépôt d'une électrode transparente 6 sur la couche de silicium amorphe 5 ;depositing a transparent electrode 6 on the amorphous silicon layer 5;
- dépôt d'une couche de passivation 8 sur l'électrode transparente 6 ;depositing a passivation layer 8 on the transparent electrode 6;
- dépôt de filtres colorés FC : R, V, B sur la couche de passivation 8 ;depositing FC: R, V, B color filters on the passivation layer 8;
- dépôt d'une couche de planarisation P sur les filtres colorés R, V, B ; - dépôt de micro-lentilles ML sur la couche de passivation P.depositing a planarization layer P on the color filters R, V, B; deposit of micro-lenses ML on the passivation layer P.
La figure 7 représente un premier perfectionnement du capteur d' image représenté en figure 6. Selon ce premier perfectionnement, une variation de dopage latérale est réalisée dans l'épaisseur de la couche de silicium amorphe 5. La variation de dopage latérale peut être effectuée dans toute l'épaisseur de la couche de silicium amorphe ou seulement dans l'épaisseur de la zone intrinsèque de la couche de silicium amorphe. Par « variation de dopage latérale », il faut entendre que le dopage varie en liaison avec les filtres de couleur : un premier dopage dl est effectué sous les filtres colorés rouge R, un deuxième dopage d2 est effectué sous les filtres colorés vert V et un troisième dopage d3 est effectué sous les filtres colorés bleu B. A titre d'exemple non limitatif, le dopage est un dopage au carbone ou au germanium. Avantageusement, ce dopage modifie la faculté d'absorption de la lumière par le silicium amorphe, ce qui favorise les longueurs d'ondes sélectionnées par les filtres colorés et défavorise les autres longueurs d'ondes, augmentant ainsi la sélectivité des filtres colorés.FIG. 7 represents a first improvement of the image sensor represented in FIG. 6. According to this first improvement, a lateral doping variation is made in the thickness of the amorphous silicon layer 5. The variation of lateral doping can be carried out in FIG. the entire thickness of the amorphous silicon layer or only in the thickness of the intrinsic zone of the amorphous silicon layer. "Lateral doping variation" means that doping varies in connection with the color filters: a first doping d1 is performed under the red color filters R, a second doping d2 is performed under the green color filters V and a third doping d3 is performed under the blue color filters B. As a non-limiting example, the doping is carbon doping or germanium. Advantageously, this doping modifies the absorption capacity of the light by the amorphous silicon, which favors the wavelengths selected by the color filters and disadvantages the other wavelengths, thus increasing the selectivity of the color filters.
La figure 8 représente un deuxième perfectionnement du capteur d' image représenté en figure 6. Selon ce deuxième perfectionnement, l'électrode transparente 6 n'est pas formée d'un seul bloc mais de trois blocs d'électrode distincts répartis en liaison avec les filtres colorés. Un premier bloc d'électrode est associé au filtre coloré rouge R, un deuxième bloc d'électrode est associé au filtre coloré vert V et un troisième bloc d'électrode est associé au filtre coloré bleu B. Des potentiels différents peuvent alors être appliqués sur les différentes blocs d'électrodes. Il s'en suit avantageusement un effet de sélectivité spectrale qui renforce l'effet du filtre coloré .FIG. 8 represents a second improvement of the image sensor represented in FIG. 6. According to this second improvement, the transparent electrode 6 is not formed of a single block but of three distinct electrode blocks distributed in connection with the colored filters. A first electrode block is associated with the red color filter R, a second electrode block is associated with the green color filter V and a third electrode block is associated with the blue color filter B. Different potentials can then be applied to the different electrode blocks. It advantageously follows a spectral selectivity effect that enhances the effect of the color filter.
La figure 9 représente une vue en coupe transversale d'un capteur d'image selon un troisième perfectionnement de l'invention. Selon le troisième perfectionnement de l'invention, il n'y a pas de couche de silicium amorphe sous les filtres colorés bleu B alors que cette couche est présente, comme décrit précédemment, sous les filtres colorés vert V et rouge R. Seule la couche de passivation 8 sépare alors les filtres colorés bleu B de la couche de silicium cristallin 4. Une telle structure permet avantageusement de bénéficier de l'absorption de silicium cristallin la plus faible, absorption suffisante pour les faibles longueurs d'ondes mais insuffisante pour les longueurs d'ondes élevées, ce qui favorise en conséquence la détection du bleu comparativement à la détection du vert et du rouge.Figure 9 shows a cross-sectional view of an image sensor according to a third improvement of the invention. According to the third improvement of the invention, there is no amorphous silicon layer under the blue B color filters while this layer is present, as previously described, under the green V and R red color filters. Only the passivation layer 8 then separates the blue B color filters from the crystalline silicon layer 4. Such a structure advantageously makes it possible to benefit from the weakest crystalline silicon absorption, sufficient absorption for the short wavelengths but insufficient for the long wavelengths, which consequently favors the detection of blue compared to the detection of green and red.
Les différents capteurs d' image de l'invention fonctionnent avantageusement avec une réflexion maximale sur la structure inférieure qui, pour les épaisseurs faibles accessibles grâce au silicium amorphe aSi, peut alors être optimisée en épaisseur ou en indice pour chaque pixel, favorisant ainsi l'absorption selon la couleur détectée par le pixel . The various image sensors of the invention function advantageously with a maximum reflection on the lower structure which, for the low thicknesses accessible thanks to the amorphous silicon aSi, can then be optimized in thickness or index for each pixel, thus favoring the absorption according to the color detected by the pixel.
Claims
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| FR0854829A FR2934084B1 (en) | 2008-07-16 | 2008-07-16 | IMAGER PIXEL IN REAR-BACK TECHNOLOGY AND IMAGE SENSOR |
| FR0854829 | 2008-07-16 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| WO2010006984A1 true WO2010006984A1 (en) | 2010-01-21 |
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Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| PCT/EP2009/058744 WO2010006984A1 (en) | 2008-07-16 | 2009-07-09 | Back surface technology imager pixel and related image sensor |
Country Status (2)
| Country | Link |
|---|---|
| FR (1) | FR2934084B1 (en) |
| WO (1) | WO2010006984A1 (en) |
Citations (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US20070152250A1 (en) * | 2005-12-29 | 2007-07-05 | Magnachip Semiconductor, Ltd. | CMOS image sensor with backside illumination and method for manufacturing the same |
-
2008
- 2008-07-16 FR FR0854829A patent/FR2934084B1/en not_active Expired - Fee Related
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| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US20070152250A1 (en) * | 2005-12-29 | 2007-07-05 | Magnachip Semiconductor, Ltd. | CMOS image sensor with backside illumination and method for manufacturing the same |
Non-Patent Citations (2)
| Title |
|---|
| KNIPP D ET AL: "Amorphous silicon based nipiin structure for color detection", JOURNAL OF APPLIED PHYSICS, AMERICAN INSTITUTE OF PHYSICS. NEW YORK, US, vol. 83, no. 3, 1 February 1998 (1998-02-01), pages 1463 - 1468, XP012044594, ISSN: 0021-8979 * |
| TUCCI M ET AL: "Variable spectral response photodetector based on crystalline/amorphous silicon heterostructure", JOURNAL OF NON-CRYSTALLINE SOLIDS, NORTH-HOLLAND PHYSICS PUBLISHING. AMSTERDAM, NL, vol. 198-200, 1 May 1996 (1996-05-01), pages 1189 - 1192, XP004243222, ISSN: 0022-3093 * |
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| Publication number | Publication date |
|---|---|
| FR2934084B1 (en) | 2010-10-15 |
| FR2934084A1 (en) | 2010-01-22 |
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