JPH0818091A - Semiconductor photoelectric transducer with plurality of photodiodes - Google Patents

Abstract

PURPOSE:To reduce a drift due to crosstalk and light reception of a dead zone and to make photoelectric characteristics of elements uniform by diffusing an impurity of the same type as photodiodes near the p-n junction of the photodiode to form an isolation band, and providing a light shielding film on the surface of the band acceptor the photoreceiving surface of the photodiode. CONSTITUTION:Photodiodes 2-1, 2-2 and 2-3 (hereinafter referred to as '2-i') and an isolation band 3 are provided on a semiconductor substrate 1, and output terminals 4-1, 4-2 and 4-3 are provided corresponding to the photodiodes 2-i. The surface except the photoreceiving surface of the photodiode 2-i is covered with a light shielding layer 6. The band 3 is so provided the a gap to the p-n junctions of the photodiodes is reduced as much as possible. When the conductivity type of the substrate is p-type, the conductivity types of the impurity diffused layers of the photodiode 2-i and the band 3 are naturally n-type.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor photoelectric conversion device having a plurality of photodiodes.

[0002]

2. Description of the Related Art As is well known, in a photoelectric element such as a photodiode, an impurity forming a conductivity type opposite to that of a semiconductor on a semiconductor substrate is diffused into a predetermined region on the semiconductor substrate to form a pn junction. And an output terminal connected to an external circuit is provided at the pn junction and a different part from the pn junction, and those output terminals are connected to the external circuit to apply light to the pn junction. When irradiated, it generates a photocurrent according to its illuminance, so it is widely used for sensors for measuring the amount of light, optical encoders, etc., insulation between logic circuits, remote control devices, and optical communication.

As the photodiode, there is a so-called photodiode array in which a plurality of photodiodes are provided on a single chip. This photodiode array consists of a plurality of photodiodes that operate independently of each other, and is formed on a single semiconductor substrate either alone or together with their output signal processing circuits. Had two major problems.

The first problem is mutual interference between photodiodes, that is, crosstalk. This crosstalk is a phenomenon in which the output current of a specific photodiode is affected by the operating state of another adjacent photodiode, that is, the amount of light received and the impedance of an external circuit.

In a typical example, the output terminal of a specific photodiode in the central portion is connected to an ammeter with all the photodiodes evenly irradiated with light, and the photodiode is adjacent to the specific photodiode. When the output terminal of the photodiode is switched from the short-circuited state to the open state (that is, when the external impedance is changed from 0 to infinity), the photocurrent of the specific photodiode is increased by several tens to 100%. This increase is crosstalk.

This phenomenon is because when the output terminals of adjacent photodiodes are short-circuited, almost all the photocurrent of the photodiode flows through the short-circuit circuit, but when the output circuit is opened, the photocurrent is reduced. This occurs because it overflows and concentrates on the neighboring photodiodes to which the external circuit is connected.

A simple and effective method for preventing the above-described crosstalk phenomenon is disclosed in Japanese Utility Model Laid-Open No. 62-074350. This provides a separation zone region between the pn junctions,
In the same step as forming the pn junction, impurities having the same quality as the impurities diffused in the pn junction are diffused to form a separation band, and the separation band is short-circuited to the semiconductor substrate. When released, the overflowing photocurrent is circulated to the semiconductor substrate without passing through another photodiode, thereby attempting to eliminate crosstalk.

In this case, the characteristics of the separation band do not have to be completely the same as those of the pn junction, as long as they have the same conductivity type. However, if the isolation band is formed at the same time as the formation of the pn junction of the photodiode in the impurity diffusion step of forming the pn junction, the isolation band is injected into the pn junction without adding an extra step. This is advantageous because impurities of the same kind as the impurities are diffused to the same depth at the same concentration.

However, this known method can suppress the crosstalk phenomenon to some extent, but cannot completely prevent the crosstalk phenomenon. That is, this publication describes that crosstalk can be suppressed to about 10% by this method, but this is substantially reduced to 0%.
It was impossible to say.

The second problem is that, apart from this crosstalk, when light hits a region that should be a dead zone between the photodiodes, minority carriers are generated and flow into the pn junction of the adjacent photodiode, which causes This is a problem that drift occurs due to a change in the amount of light received in the dead zone.

In order to solve this problem, the above-mentioned actual exploitation 62
No. 074350 describes a technique for suppressing the generation of minority carriers by providing a light-shielding coating in the dead zone region. Although this drift is eliminated by doing so, it has been considered that such a light-shielding coating does not have the function of suppressing the crosstalk.

In addition to the above problems, in the conventionally known photodiode, BCl ₃ is generally used as the impurity diffusion source to form the pn junction, but these diffusion sources are used. Since the photodiode array manufactured in this way has a poor yield and the above drifts are not constant and vary widely, there are variations in the photoelectric characteristics of many photodiodes formed on one semiconductor substrate (wafer). Therefore, there is a problem in that the photoelectric conversion characteristics greatly vary between chips and also between light receiving portions having the same effective light receiving area in the same chip.

[0013]

SUMMARY OF THE INVENTION The present invention has been made from the above viewpoint, and its purpose is to:
It is an object of the present invention to provide an integrated circuit including a high-quality photodiode in which a crosstalk phenomenon and a drift due to light reception in a dead zone are extremely small, and photoelectric conversion characteristics of constituent elements are uniform.

[0014]

The reason why the crosstalk cannot be completely suppressed in the above-mentioned separation band is that the separation band itself is a photodiode, and when receiving light, a considerable amount of photocurrent is generated. In addition, it has been found that the current capacity of the separation band circuit is insufficient to completely absorb the overflow current from the adjacent original photodiode and return it to the semiconductor substrate.

That is, since the current capacity of the separation band circuit is insufficient, in addition to the photocurrent generated by the separation band itself, the overflow current from the original photodiode adjacent to the separation band circuit is completely absorbed, so that the semiconductor substrate is formed. Can't be refluxed, so
Excessive current overflows in the photodiode connected to the external circuit, which causes crosstalk.

Therefore, if a light-shielding coating is applied to this separation band so that it does not function as a photodiode itself and does not generate a photocurrent, there is a margin in the current capacity of the separation band circuit. It has been found that the overflow current from the photodiode can be completely absorbed and can be circulated back to the semiconductor substrate, so that the crosstalk can be completely suppressed.

Therefore, the above-mentioned object of the present invention is to diffuse the impurities of the same type as the pn junction into the vicinity of the pn junction forming a plurality of photodiodes formed on one semiconductor substrate to separate the photodiodes. This is achieved by providing a band and applying a light-shielding coating on the surface of the separation band.

More specifically, the above object of the present invention is to:
This can be achieved more reliably by a semiconductor photoelectric conversion device having a plurality of photodiodes including the following components. (A) Semiconductor substrate. (B) In a plurality of independent regions on the surface of the semiconductor substrate,
It is formed by diffusing impurities of a conductivity type opposite to that of the semiconductor substrate, and each of the plurality of p functions as a photodiode.
n-junction. (C) A separation band formed by diffusing impurities of the same quality as the impurities diffused in the pn junction into a separation band region defined so as to surround each region of the pn junction with a minute gap. (D) An output terminal electrically connected to each of the plurality of pn junctions. (E) An oxide layer covering the surfaces of at least a plurality of pn junctions and separation bands except for contact holes for output terminals. (F) A light-shielding layer that covers at least the surface of the separation band except the light-receiving surfaces of the plurality of pn junctions. (G) An electrode provided on the back surface of the semiconductor substrate.

The present invention will be described in detail below with reference to the drawings. 1 is a plan view showing the configuration of a semiconductor photoelectric conversion device having a plurality of photodiodes according to the present invention, FIG. 2 is a sectional view taken along line II-II of the semiconductor photoelectric conversion device shown in FIG. 1, and FIG. It is a III-III sectional view of the semiconductor photoelectric conversion element shown.

In the figure, 1 is a semiconductor substrate, 2-1,
2-2 and 2-3 (hereinafter, referred to as 2-i) are photodiodes provided on the substrate 1, 3 is a separation band, 4-1, 4
-2 and 4-3 (hereinafter referred to as 4-i) are output terminals 5 respectively provided corresponding to the photodiode 2-i.
Is an oxide layer, 6 is a light-shielding layer that covers a portion other than the light-receiving surface of the photodiode 2-i, 7 is an electrode provided on the back surface of the semiconductor substrate, and 8 is a connection terminal for short-circuiting the separation band 3 to the electrode 7. .

Output terminals 4-i are provided in the light receiving portions of the photodiodes 2-i, and they are respectively connected to the electrodes 7 through external circuits (not shown).
It is desirable that the separation band 3 be provided so as to completely surround the light receiving surface of the photodiode 2-i and that the gap between the separation band 3 and the pn junction is as small as possible.
When the n-junctions are arranged in a line, it is sufficient to provide them so that the photocurrent circuit between them can be cut off. Thus, the separation band 3 is short-circuited to the electrode 7 by a contact hole or the like (not shown).

The light-shielding layer 6 completely covers the separation band 3,
In addition to shielding the light, the dead zone around the light receiving portion of the photodiode 2-i is provided so as to completely cover and shield the light as much as possible. There is no problem even if the light shielding layer 6 slightly overlaps the peripheral portion of the light receiving portion of the photodiode 2-i. The oxide layer 5 is provided in order to prevent the metal ions from penetrating and diffusing into the semiconductor substrate 1 when the light shielding layer 6 is formed.

The method of manufacturing such a photodiode array and the result of a comparative test with a conventionally known method will be described below. When manufacturing the photodiode according to the present invention, when the conductivity type of the semiconductor substrate is n-type, a normal manufacturing process (thermal oxidation, oxide film window opening, p-type impurity diffusion, contact hole opening, Al vapor deposition, Al etching, When a photodiode array is manufactured by rear surface electrode deposition), a separation band composed of a p-type impurity diffusion layer is provided between each pn junction. When the conductivity type of the semiconductor substrate is p-type, the conductivity type of the impurity diffusion layer of the photodiode 2-i and the separation band 3 is naturally n-type.

Next, an example of manufacturing the photodiode array according to the present invention will be described by taking the case where the conductivity type of the semiconductor substrate is n-type as an example. An oxide film (SiO ₂ ) is grown to a thickness of several thousand angstroms on the light receiving surface side of a semiconductor substrate having a specific resistance of 0.001 to 1000 Ωcm and an n type conductivity by a thermal oxidation method. Thermal oxidation is performed in the range of 600 to 1200 ° C., and wet O ₂ or dry O ₂ is used as the oxidizing atmosphere.

Next, in order to diffuse the p-type impurities,
A window is formed in a portion of the oxide layer that is necessary to form a photodiode. To open the window, first, a photoresist (photosensitive resin) is applied thinly and uniformly on the oxide layer, and a photomask consisting of a portion opaque to UV light and a transparent portion is placed on the wafer. In the photomask, the portion forming the photodiode and the portion forming the separation band are opaque light-shielding portions.

This is irradiated with UV light and developed to remove the photoresist in the portion not irradiated with UV light. This is an example of using a negative type as the photoresist, but there is no problem even if the positive type is used. This wafer is etched with a hydrofluoric acid (HF) -based processing solution to remove the SiO ₂ in the window portion, and unnecessary photoresist is removed with an organic solvent.

Next, p-type impurities are diffused inside the n-type semiconductor substrate by a thermal diffusion method to form a pn junction portion and a separation band of the photodiode. Polyboron film as a diffusion source, BN, using _{B 2 H 6, B 2 O} 3 or the like, is diffused in an atmosphere of 1000 to 1200 ° C. in a diffusion furnace. There is BCl ₃ as a p-type impurity diffusion source, but this diffusion source causes a reduction in yield and is not recommended.

Simultaneously with the diffusion, the surface of Si is again thermally oxidized to form an SiO ₂ oxide layer on the entire surface. At this time, since a B glass layer (BSG) is formed on the surface, the surface of SiO ₂ is etched using a hydrofluoric acid-based treatment liquid after taking out from the diffusion furnace. Next, using a photomask different from that for opening a window, a contact hole is formed in a necessary portion of the p-type layer (a portion to be a light receiving portion and a portion to be a separation band). This step is the same as the window opening step for the oxide layer.

Next, Al is vapor-deposited on the entire surface of the wafer on the light-receiving surface side by using a vacuum vapor deposition method, an electron beam vapor deposition method, a sputtering method or the like on the surface of the wafer. After vapor deposition of Al, an Al mask is used to form wiring, electrodes (pads for wire bonding) and light-shielding parts, and unnecessary Al is used.
Is removed. After removing the unnecessary portion, heat treatment is performed to achieve ohmic contact with Si. Since the eutectic temperature of Al and Si is 577 ° C., the heat treatment is performed below this temperature.

Next, in order to form electrodes on the back surface of the light receiving surface,
The back surface of the wafer is acid-etched, and a metal material is vapor-deposited by a method equivalent to Al vapor deposition. As the metal material, for example, Au,
Although there are Ni, Ti-Au, Ni-Au, etc., there is no problem in using any of them. After vapor deposition of the metal material, heat treatment is performed in the same manner as the Al vapor deposition step in order to achieve ohmic contact.

Then, diamond scribing,
Dividing into individual photodiode array chips by using dicing or the like. When the conductivity type of the reference semiconductor substrate is p-type, n-type impurities are diffused to form a pn junction and a photodiode isolation band. As a diffusion source, POCl ₃ , PH ₃ , P ₂ O ₅ or the like is used, and 900 to 1200 ° C.
It suffices to diffuse in an atmosphere of, and the same as above except the impurity diffusion step.

The results of tests conducted to confirm the performance of the photodiode array according to the present invention will be described below. The photodiode arrays used in the test are the following three types. A: Those having a separator according to the present invention. B: A known material having no separator. C: The conductivity type of the part that should be the separation band is opposite to that of the present invention. Three samples were prepared for each sample, and the same experiment was performed on all the samples.

These samples were manufactured in exactly the same manner except the part of the separation zone, and the photodiode, the insulating layer and the light shielding layer were all the same in structure. As the Si substrate, an n-type (dopant is P) wafer having a size of 4 inches and a thickness of 450 μm was used. This is a standard type wafer with a specific resistance of 2 to 10 Ωcm and a crystal axis <111>, the surface of which is mirror-finished. This wafer was
It is placed in a furnace in a wet O ₂ atmosphere, and an insulating layer made of SiO ₂ is formed on the surface to a thickness of 6800 to 7800 Å.

Next, in order to diffuse the p-type impurities, a window is formed in the pn junction of the photodiode and the portion that will be the photodiode separation band. A negative type (40 cp) was used for the photoresist, a glass mask was used for the photomask, and buffered hydrofluoric acid (BHF, hydrofluoric acid + ammonium fluoride) was used for removing unnecessary SiO ₂ after development.

A polyboron film (PBF, liquid methylcellosolve, water, organic polymer, boric anhydride) was used as a diffusion source of p-type impurities, and was uniformly coated on the entire surface of the wafer by a spin coater, and then at 1100 ° C. , In an N ₂ atmosphere for 15 minutes to diffuse to a depth of 1.8 to 2.2 μm. Hydrofluoric acid (HF) is used to remove the BSG layer.
2000 Angstrom etched.

After opening the contact holes, a light-shielding layer made of Al was vapor-deposited on the surface of the wafer using an electron beam (E-Gun) to a thickness of 1.8 to 2.2 μm. The deposition rate is 35 Å / sec. The unnecessary portion of the light-shielding layer was removed using an Al liquid. After that, Si and A
The sample was heated at 450 ° C. for 30 minutes to measure ohmic contact with 1.

Next, in order to form a back surface electrode, the back surface of the wafer is acid-etched by about 0.5 μm, and a metal material A is used.
u ・ As-Au totaling 3500 Å (Au ・ A
s2000 angstrom, Au1500 angstrom)
It was vapor-deposited. It was heated at 420 ° C. for 15 minutes to form an ohmic contact of the back surface electrode. The n-type impurity concentration of the portion corresponding to the separation zone of the sample C is higher than that of the substrate. This manufacturing method is the same as the manufacturing conditions of the sample A except that the step of diffusing the n-type impurity in the separation zone is added. The diffusion of the n-type impurity was performed after the diffusion of the p-type impurity.

POCl ₃ was used as a diffusion source of n-type impurities, and it was left in a diffusion furnace at 1050 ° C. in an N ₂ / O ₂ atmosphere for 30 minutes to diffuse to a depth of 3.0 to 4.0 μm. In this way, the photodiode array as shown in FIG.
The comparative product was manufactured and an experiment on the crosstalk phenomenon was conducted. The size of each light receiving part is 0.2 × 0.7 mm, the distance between each light receiving part is 0.1 mm, and the distance between the light receiving part and the light shielding layer is 10 μ.
The distance between the m, pn junction and the separation band is 30 μm.

In this experiment, a tungsten lamp was used as a light source, and the entire surface of the photodiode array was 1000
Light is emitted so as to be Lx, and output terminals 4-1 and 4-
3 is short-circuited with the back electrode, or open, and output terminal 4
A current value of −2 was measured. The results of this experiment are shown in Table 1. When the output terminals 4-1 and 4-3 are switched from the state in which they are short-circuited to the back electrode to the open state, the increase in the output from the output terminal 4-2 is crosstalk. The crosstalk values in this table correspond to the amount of increase in the photocurrent from the output terminal 4-2 when the output terminals 4-1 and 4-3 are switched to the open state from the state where the output terminals 4-1 and 4-3 are short-circuited, and the current at the time of short circuit. It is a percentage. In the case of the product of the present invention, the crosstalk is a value recognized to be 0 within the measurement error range, and it can be seen that there is no crosstalk phenomenon.

[Table 1] I ₀ is the output current of terminal 4-2 when output terminals 4-1 and 4-3 are opened. I _S is the output current of terminal 4-2 when output terminals 4-1 and 4-3 are short-circuited to back electrode 7.

In Comparative Example A, that is, the known one having no separation zone, even if the light-shielding layer is present in the dead zone, it is about 10
It was confirmed that there was as much crosstalk as possible. Furthermore, in Comparative Example B, that is, in the photodiode array in which the conductivity type of the part that is the separation band is n-type, the crosstalk increases to 14.3% on average, and conversely the crosstalk phenomenon increases. Further, in the present invention, there is also an effect that the photoelectric characteristics of the photodiode formed as shown in Table 2 are extremely stable and the variation is reduced to about 1/20.

[Table 2]

[0041]

As described above, according to the present invention, the crosstalk phenomenon and the drift due to the irradiation light in the dead zone can be almost completely suppressed by the simple structure, and the photoelectric conversion characteristics of the photodiode can be made uniform. it can. Further, since this photodiode can be manufactured only by the conventional method, the manufacturing cost is almost the same as that of the conventional product.

[Brief description of drawings]

FIG. 1 is a plan view showing a configuration of a semiconductor photoelectric conversion element having a plurality of photodiodes according to the present invention.

FIG. 2 is a view of the semiconductor photoelectric conversion element II- shown in FIG.
It is a II sectional view.

FIG. 3 is a diagram of the semiconductor photoelectric conversion element shown in FIG.
-III is a sectional view.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Semiconductor substrate 2-1, 2-2, 2-3 ... Photo die auto 3 ... Separation band 4-1, 4-2, 4-3 ... Output terminal 5 ... Oxidation Layer 6 ... Shading layer 7 ... Backside electrode 8 ... Separation band short-circuit connection terminal

Continuation of front page (51) Int.Cl. ⁶ Identification number Office reference number FI Technical indication location H01L 31/0232 H01L 27/14 Z 31/02 D (72) Inventor Kenji Miyaji Kazuga Sekizo, Chiyoda-ku, Tokyo 2-5 Mitsui Toatsu Chemicals Co., Ltd. (72) Inventor Makoto Konagai 6-18-1-437 Minamioi, Shinagawa-ku, Tokyo

Claims (4)

[Claims] 1. In a semiconductor photoelectric conversion device having a plurality of photodiodes, p forming each photodiode.
The semiconductor photoelectric conversion device as described above, wherein an impurity of the same type as that is diffused in the vicinity of the n-junction portion to form a separation band, and at least the surface of the separation band except the light receiving surface of each photodiode is provided with a light-shielding coating. 2. A semiconductor photoelectric conversion device having a plurality of photodiodes comprising the following constituent elements. (A) Semiconductor substrate (1). (B) A plurality of pn junctions, which are formed by diffusing impurities of a conductivity type opposite to that of the semiconductor substrate (1) into a plurality of independent regions on the surface of the semiconductor substrate (1), each of which functions as a photodiode. (2-1, 2-2, 2-3). (C) The pn junction (2-1) is formed in a separation band region defined so as to surround each region of the pn junction (2-1, 2-2, 2-3) with a minute gap. 2-2, 2
Separation band (3) formed by diffusing impurities of the same quality as the impurities diffused in -3). (D) Output terminals (4-1, 4-) electrically connected to each of the plurality of pn junctions (2-1, 2-2, 2-3).
2, 4-3). (E) Excluding contact holes for the output terminals (4-1, 4-2, 4-3), at least a plurality of pn junctions (2-1, 2-2, 2-3) and separation bands (3). An oxide layer (5) covering the surface of (F) A light-shielding layer (6) that covers at least the surface of the separation band (3) except the light-receiving surfaces of the plurality of pn junctions (2-1, 2-2, 2-3). (G) An electrode (7) provided on the back surface of the semiconductor substrate (1). 3. The semiconductor substrate (1) is Si, an oxide layer (5)
A semiconductor photoelectric conversion device having a plurality of photodiodes according to claim ₂ , wherein is made of SiO ₂ . 4. A semiconductor photoelectric conversion device having a plurality of photodiodes according to claim 2, wherein the separation band (3) is short-circuited to the electrode (7).