JP2017092179A - Solid state imaging device and method of manufacturing the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a solid state imaging device in which red light sensitivity is improved.SOLUTION: A solid state imaging device has a semiconductor layer 20 formed on a support substrate 10, and a plurality of photoelectric conversion elements 21 arranged on the semiconductor layer 20. On the surface of the support substrate 10 where the semiconductor layer 20 is formed, grooves 10a are formed corresponding to the photoelectric conversion elements 21, light reflection structures 14 are arranged in the grooves 10a, and the light reflection structure 14 consists of a reflection metal 11 formed along the surface of the groove 10a, and a light transmission layer 12 placed between the reflection metal 11 and semiconductor layer 20.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a technology relating to a solid-state imaging device such as a CMOS image sensor or a CCD image sensor in which a plurality of photoelectric conversion elements are arranged two-dimensionally.

A solid-state imaging device is a two-dimensional array of CMOS or CCD type photoelectric conversion elements that absorbs light and generates charges, and transfers the generated charges to the outside as electrical signals. Widely used in digital still cameras.
In general, a photoelectric conversion element on a solid-state imaging element is formed of a silicon photodiode having a pn junction. When light is applied to a pn junction to which a reverse voltage is applied, electrons generated in the depletion layer drift in the depletion layer and reach the n-type region. In a solid-state imaging device, imaging data can be obtained by reading out electrons accumulated in the n-type region of the photodiode of each pixel as signal charges.

The intensity of light incident on the photoelectric conversion element is rapidly attenuated as it goes inside because photons are absorbed in the semiconductor and generate electron-hole pairs. The rate of absorption depends on the light absorption coefficient, and the longer the wavelength of light, the smaller the rate of absorption when penetrating the same distance. Therefore, there is a problem that red light having a long wavelength is not absorbed in the semiconductor and the red sensitivity is lowered.
The prior art disclosed in Patent Document 1 is a solid-state imaging device in which a metal reflector and back electrode is formed on the back surface of the photoelectric conversion element in order to reuse infrared rays that have passed through the photoelectric conversion element. However, since the formed metal reflecting mirror is flat, the angle of the reflected light cannot be controlled, and there is a problem that it cannot efficiently re-enter the photoelectric conversion element.

  On the other hand, the prior art disclosed in Patent Document 2 is a structure in which red light that has passed through the semiconductor substrate can be efficiently re-incident on the photoelectric conversion element by forming a concave reflecting mirror on the back surface of the semiconductor substrate. Since functional elements need to be formed on both the front and back sides of the substrate, the substrate can be placed directly on the stage when forming the back surface element after forming the front surface element, or when packaging after forming the element on both sides. There is a problem that it becomes difficult to handle the substrate, for example, it becomes impossible.

JP-A-10-173998 JP 2011-119484 A

  The present invention has been made paying attention to the above problems, and an object of the present invention is to provide a solid-state imaging device with improved red light sensitivity.

  In order to solve the problem, a solid-state imaging device which is one embodiment of the present invention is a solid-state imaging device including a semiconductor layer formed over a supporting substrate and a plurality of photoelectric conversion elements arranged over the semiconductor layer. A groove corresponding to the photoelectric conversion element is formed on the surface of the support substrate on which the semiconductor layer is formed, and a light reflecting structure is disposed in the groove. And a reflective metal formed along the surface of the groove, and a light transmission layer disposed between the reflective metal and the semiconductor layer.

According to the solid-state imaging device of one embodiment of the present invention, among the light incident on the photoelectric conversion element, the red light that cannot be absorbed by the photoelectric conversion element and passes through the semiconductor layer is provided corresponding to the photoelectric conversion element. The red light sensitivity of the solid-state imaging device can be improved because it is reflected by the reflective metal having the light reflecting structure and re-enters the photoelectric conversion device.
In particular, when the surface of the reflective metal formed in the groove is a concave curved surface such as a bowl-like shape such as a bowl, the light reflected by the reflective metal of the light reflecting structure is the pixel on which the light is incident. Therefore, there is no possibility of causing color mixing due to incidence on the photoelectric conversion elements of adjacent pixels.
In addition, according to the aspect of the present invention, since it is not necessary to form an element on the back surface of the support substrate, the substrate can be directly placed on the stage during the manufacturing process, and the substrate handling is easy.

It is a schematic diagram for demonstrating an example of schematic structure of the solid-state image sensor which concerns on embodiment based on this invention. It is a schematic diagram for demonstrating the manufacturing process of the solid-state image sensor which concerns on embodiment based on this invention. It is a schematic diagram for demonstrating the manufacturing process of the solid-state image sensor which concerns on embodiment based on this invention. It is a schematic diagram for demonstrating the manufacturing process of the solid-state image sensor which concerns on embodiment based on this invention. It is a schematic diagram for demonstrating the manufacturing process of the solid-state image sensor which concerns on embodiment based on this invention. It is a schematic diagram for demonstrating the manufacturing process of the solid-state image sensor which concerns on embodiment based on this invention. It is a schematic diagram for demonstrating the manufacturing process of the solid-state image sensor which concerns on embodiment based on this invention. It is a schematic diagram for demonstrating the manufacturing process of the solid-state image sensor which concerns on embodiment based on this invention. It is a schematic diagram for demonstrating the manufacturing process of the solid-state image sensor which concerns on embodiment based on this invention. It is a schematic diagram for demonstrating the manufacturing process of the solid-state image sensor which concerns on embodiment based on this invention. It is a schematic diagram for demonstrating the manufacturing process of the solid-state image sensor which concerns on embodiment based on this invention. It is a schematic diagram for demonstrating the effect of the solid-state image sensor which concerns on embodiment based on this invention.

Hereinafter, embodiments of the present invention will be described with reference to the drawings. However, the present invention is not limited to this.
As shown in FIG. 1, the solid-state imaging device of this embodiment includes a semiconductor layer 20 formed on a support substrate 10 and a plurality of photoelectric conversion elements 21 arranged on the semiconductor layer 20. On the surface of the support substrate 10, a groove 10 a is formed corresponding to the photoelectric conversion element 21, that is, at a position where it can face the photoelectric conversion element 21 in the thickness direction (up and down), and the reflective metal 11 is formed in the groove 10 a. A light reflection structure 14 made of the light transmission layer 12 is formed.

The light reflection structure 14 includes a reflective metal 11 formed along the surface of the groove 10a, and a light transmission layer 12 disposed between the reflective metal 11 and the semiconductor layer 20, that is, filled with the groove 10a.
The surface shape of the reflective metal 11 is preferably composed of a concave curvature curve having no sharp curvature portion (curvature steep portion) such as a circular arc cross section. For example, the surface shape of the reflective metal 11 is a bowl-like shape such as a hemisphere. Further, it is preferable that the area of the light reflection structure 14 is larger than the area of the photoelectric conversion element 21 in plan view, and the formation area of the photoelectric conversion element 21 is completely within the formation area of the light reflection structure 14 in plan view. . The circular arc is not limited to a part of a perfect circle, and may be a concave curvature shape made up of an ellipse or a part of a parabola.
Further, the photoelectric conversion element 21 has an interlayer insulating layer 22 and a wiring 23 disposed in the interlayer insulating layer 22. On the interlayer insulating layer 22, a color filter 24 and a microlens 25 are arranged in this order. Is formed.

Next, a method for manufacturing a solid-state imaging device will be described with reference to FIGS. However, the present invention is not limited to these.
First, as shown in FIG. 2, a processing pattern is formed on the support substrate 10 using a photoresist 13 for forming the groove 10 a for the light reflecting structure 14. As the support substrate 10, it is desirable to use a substrate made of quartz from the viewpoint of adaptability to a semiconductor processing process in a later step and easy processing of the groove 10 a having a concave bottom surface, but this embodiment is not limited thereto. is not.

Next, as shown in FIG. 3, grooves 10 a are formed on the surface of the support substrate 10 using the photoresist 13 as a mask. The shape of the groove 10a may be a rectangular cross section, but a shape that is rounded into a concave shape such as a bowl shape (such as a hemisphere) is more desirable. By performing isotropic etching using a processing means such as wet etching or isotropic dry etching, the groove 10a having a concave curved surface shown in FIG. 3 can be formed.
In order to collect the incident light reflected by the light reflecting structure 14 at the center of the photoelectric conversion element 21, the refractive index of the material of the light transmission layer 12 formed in a later step is also taken into consideration. Although it is desirable to design a concave shape, in order to improve the sensitivity of red light, the reflected light does not necessarily have to be collected at the center of the photoelectric conversion element 21 and is re-entered into the depletion layer in the pixel. Therefore, in this embodiment, it is not necessary to strictly design the concave shape formed by the groove 10a.

Further, in the subsequent process, in order to accurately arrange the photoelectric conversion elements 21 corresponding to the respective light reflection structures 14 arranged two-dimensionally above the light reflection structures 14, the pattern of the photoelectric conversion elements 21 by photolithography is used. When forming the alignment mark, an alignment mark needs to be formed on the support substrate 10. Therefore, although not shown, it is desirable to form alignment marks at the same time when the grooves 10a are formed on the surface of the support substrate 10.
After forming the groove 10a, a reflective metal 11 is formed on the surface of the support substrate 10 and the photoresist 13 as shown in FIG. The reflective metal 11 is a metal thin film having a high reflectance such as aluminum, silver, chromium, tantalum, tungsten, titanium, and alloys thereof. Moreover, since it is exposed to a high temperature in a subsequent manufacturing process, it is desirable that the material does not melt by heat treatment at least at 500 to 600 ° C. The reflective metal 11 is formed by means such as vapor deposition or sputtering.

  After the reflective metal 11 is formed, the photoresist 13 is peeled off. Since the photoresist 13 is covered with a metal thin film, it is difficult to remove the photoresist 13 using a remover. Therefore, by polishing means such as CMP (Chemical Mechanical Polishing), the surface of the support substrate 10 is polished, the reflective metal film on the photoresist 13 is removed, and after the photoresist 13 is exposed, a stripper treatment is performed. The photoresist 13 can be peeled off. The metal thin film adhering to the side surface of the photoresist 13 is also removed by the peeling process, so that a structure in which the reflective metal 11 is formed only on the surface of the groove 10a as shown in FIG. That is, the reflective metal 11 is formed along the surface of the groove 10a.

Next, as shown in FIG. 6, the material of the light transmission layer 12 is formed on the support substrate 10. The light transmission layer 12 is a layer for filling a gap between the groove 10 a formed in the support substrate 10 and the semiconductor layer 20, which is generated by bonding the support substrate 10 and the semiconductor substrate in a later process. The material of the light transmission layer 12 is preferably a material such as silicon nitride or undoped silicon oxide that has transparency and is resistant to a high temperature environment used in a later semiconductor process. Further, although the light transmissive layer 12 is formed by a method such as atmospheric pressure CVD (Chemical Vapor Deposition) or PE-CVD (Plasma Enhanced-CVD), the present embodiment is not limited thereto.
After the light transmissive layer 12 is formed, the surface of the light transmissive layer 12 is polished by a polishing means such as CMP until the surface of the support substrate 10 other than the grooves 10a is exposed as shown in FIG. Through the above steps, the light reflecting structure 14 including the reflective metal 11 and the light transmitting layer 12 can be formed on the surface of the support substrate 10.

Next, as shown in FIG. 8, a semiconductor layer 20 made of p-type or n-type silicon is formed on the support substrate 10 on which the light reflecting structure 14 is formed, thereby forming a substrate for manufacturing a solid-state imaging device.
As a method for forming the semiconductor layer 20 on the support substrate 10, there is a smart cut method. In this method, hydrogen ions are implanted into a semiconductor substrate, and the surface of the semiconductor substrate into which hydrogen ions are implanted or the surface of the support substrate 10 is activated by plasma treatment or ozone treatment. This is a forming method in which the semiconductor substrate is thermally peeled from the hydrogen ion implantation interface by being attached and heat-treated at 500 ° C., and the semiconductor thin film remains on the support substrate 10.

  As a method for peeling the semiconductor substrate from the bonded substrate, there is a method in which physical stimulation is applied in the vicinity of the hydrogen ion implantation interface in addition to the heat treatment. When this method is adopted, high-temperature heat treatment is not required, so that peeling from the bonding interface and cracking of the substrate due to different thermal expansion coefficients of the support substrate 10 and the semiconductor substrate can be prevented. In addition to the method of injecting hydrogen ions to form a peeling interface, after the silicon substrate and the support substrate 10 are bonded together, the silicon is shaved using a grinder and then the surface is polished by CMP. There are methods for forming the semiconductor layer 20 on the support substrate 10, but the embodiment of the present invention is not limited thereto.

  The semiconductor thin film remaining on the support substrate 10 is polished by a method such as CMP to smooth the surface, thereby forming the semiconductor layer 20 shown in FIG. The film thickness of the semiconductor layer 20 is determined by the implantation depth of hydrogen ions implanted into the semiconductor substrate before bonding. In order to increase the sensitivity to incident light, it is desirable that the semiconductor layer 20 is thicker. However, when the semiconductor layer 20 is too thick, incident light reflected by the light reflecting structure 14 is not only applied to pixels in which light is incident but also to adjacent pixels. Can result in color mixing. Therefore, the film thickness of the semiconductor layer 20 is desirably 3 to 5 μm.

Next, as shown in FIG. 9, a plurality of photoelectric conversion elements 21 arranged in a two-dimensional manner are formed on the semiconductor layer 20. The photoelectric conversion element 21 is formed so as to be disposed above the light reflecting structure 14. In addition, it is preferable that the center of the photoelectric conversion element 21 coincides with the center of the light reflecting structure 14 in plan view, and the outer edge position of the photoelectric conversion element 21 in plan view is as shown in FIG. In addition, it is preferable to arrange the light reflecting structure 14 so as to be located inside the outer edge position.
A photogate, a photodiode, or the like is used as the photoelectric conversion element 21. It is desirable to use an embedded photodiode because of high charge transfer rate. Although not shown, the photoelectric conversion element 21 is formed, and at the same time, an element necessary for driving the solid-state imaging element is formed in the pixel. For example, in the case of a CCD image sensor, a vertical transfer CCD is formed together with the photoelectric conversion element 21. On the other hand, in the case of a CMOS image sensor, elements such as a floating diffusion layer amplifier and a charge transfer transistor are formed together with the photoelectric conversion element 21.

Next, as shown in FIG. 10, after the photoelectric conversion element 21 and other elements are formed, wirings 23 for transferring signal charges and signal voltages or for driving transistors are formed. Further, depending on the structure of the solid-state imaging device, a plurality of wiring layers are required, and therefore an interlayer insulating layer 22 is formed between the wiring layers.
The material of the interlayer insulating layer 22 is a low dielectric constant material having transparency such as undoped silicon oxide. The interlayer insulating layer 22 is formed by a method such as atmospheric pressure CVD or PE-CVD. The wiring 23 is made of aluminum, copper, chromium, alloys thereof, and the like, and a wiring pattern is formed by the wiring 23 using a manufacturing process suitable for these materials, whereby the interlayer insulating layer 22 and the wiring shown in FIG. 23 can be formed.

  Next, a color filter 24 is formed as shown in FIG. Although not shown, before the color filter 24 is formed, an organic film having planarity may be formed on the interlayer insulating layer 22 and the surface may be smoothed before the color filter 24 is formed. The color filter 24 can form a pattern by photolithography using a photosensitive resin in which a pigment is dispersed. Further, a non-photosensitive resin in which a pigment is dispersed is applied on the interlayer insulating layer 22 or a planarizing film formed thereon, and a photoresist is applied on the applied non-photosensitive resin, and photolithography is performed. It is also possible to perform pattern processing of the color filter 24 by performing dry etching after forming a pattern. The color arrangement of the color filter 24 is a three-color Bayer Array of Red (R), Green (G), and Blue (B) or other arrangements using RGB, and other colors other than RGB, such as white, cyan, and yellow A color filter array in which filters such as magenta are arrayed may be used, but the present embodiment is not limited thereto.

  After forming the color filter 24, the microlens 25 is formed on the color filter 24, whereby the solid-state imaging device of this embodiment shown in FIG. 1 is completed. The microlens 25 can be formed in a lens shape by applying a photosensitive resin on the color filter 24 and forming a lens-to-lens gap for each pixel by photolithography, followed by heat flow. Alternatively, a resin is applied on the color filter 24, a photosensitive resin is applied thereon, a lens shape is formed by photolithography and heat flow, and then dry etching is performed using the photosensitive resin film having the lens shape as a sacrificial film. The microlens 25 can also be formed by a method of processing the resin formed on the color filter 24 into a lens shape.

According to the solid-state imaging device of the embodiment, among the light incident on the photoelectric conversion element 21, red light that has not been absorbed by the photoelectric conversion element 21 and has passed through the semiconductor layer 20 is provided corresponding to the photoelectric conversion element 21. The red light sensitivity of the solid-state imaging device can be improved because it is reflected by the reflective metal 11 of the light reflecting structure 14 and re-enters the photoelectric conversion device 21.
In particular, when the surface of the groove 10a, that is, the surface of the reflective metal 11 is a curved surface having a smooth concave curvature such as a bowl, the light reflected by the reflective metal of the light reflecting structure 14 is the pixel on which the light is incident. Therefore, there is no possibility of causing color mixing due to incidence on the photoelectric conversion element 21 of an adjacent pixel.
In addition, since it is not necessary to form an element on the back surface of the support substrate 10, the substrate can be directly placed on the stage during the manufacturing process, and the substrate handling is easy.

Examples of the present invention will be described below, but the present invention is not limited thereto.
(Formation of the light reflecting structure 14)
A pattern for forming the light reflecting structure 14 was formed by applying a photoresist 13 to a quartz substrate having a thickness of 0.5 mm, which is the support substrate 10, using a spin coater, and performing exposure and development. Next, wet etching treatment was performed on the support substrate 10 using hydrofluoric acid to form bowl-shaped grooves 10a.
Then, the reflective metal 11 was formed by forming an aluminum thin film on the surface of the support substrate 10 by sputtering. The reflective metal 11 was formed on one surface so as to cover the groove 10 a formed in the support substrate 10 and the photoresist 13.

Next, the surface of the support substrate 10 is polished by CMP, and the reflective metal 11 covering the photoresist 13 is removed to expose the surface of the photoresist 13. Then, using a stripping solution for the photoresist 13, The photoresist 13 formed on the support substrate 10 was stripped. With the peeling, the reflective metal 11 formed on the side surface of the photoresist 13 was also removed, so that the reflective metal 11 remaining after the peeling process was only the film formed in the groove 10a.
After removing the photoresist 13, an undoped silicon oxide film was formed on the surface of the support substrate 10 by atmospheric pressure CVD. After film formation, the light-transmitting layer 12 was formed in the groove 10a by polishing the surface by CMP and smoothing the surface. The light reflecting structure 14 including the reflective metal 11 and the light transmitting layer 12 was formed on the support substrate 10 through the above steps.

(Formation of the semiconductor layer 20 on the support substrate 10)
Using a high energy ion implantation apparatus for bonding to the support substrate 10 on which the light reflecting structure 14 is formed, a dose amount of 7.0 × 10 ¹⁶ ions / cm ² and an implantation energy of 500 keV is applied to the surface of the p-type silicon substrate. Hydrogen ions were implanted under the conditions. After the hydrogen ion implantation, the surface of the silicon substrate was subjected to ozone treatment to activate the surface, and was attached to the surface of the support substrate 10 on which the light reflecting structure 14 was formed.
After the silicon substrate was bonded to the support substrate 10, heat treatment was performed at 500 ° C., whereby the semiconductor substrate was thermally peeled from the hydrogen ion implantation interface, and the semiconductor thin film remained on the support substrate 10. Next, the semiconductor thin film surface was polished by CMP, and the semiconductor layer 20 was formed by smoothing the surface. After forming the solid-state imaging device, the cross section of the device was observed with a scanning electron microscope S4800 (manufactured by Hitachi High-Technologies Corporation). As a result, the film thickness of the semiconductor layer 20 was 4 μm.

(Manufacture of solid-state image sensors)
Next, an embedded photodiode to be the photoelectric conversion element 21 was formed on the semiconductor layer 20 by a CMOS manufacturing process. In addition, a floating diffusion layer amplifier, a charge transfer transistor selection transistor, a reset transistor, and a source follower amplifier, which are functional elements for driving the CMOS image sensor, were formed in the pixel simultaneously with the photoelectric conversion element 21.
After forming the photoelectric conversion element 21 and other elements, the wiring 23 was formed. An interlayer insulating layer 22 was formed between the wiring layers. The interlayer insulating layer 22 was formed by depositing undoped silicon oxide by atmospheric pressure CVD. The wiring 23 was formed by forming a thin aluminum film by sputtering and then processing the wiring pattern by photolithography.

Next, a color filter 24 was formed on the interlayer insulating layer 22 so as to form a Bayer array using three types of photosensitive resins each containing green, blue, and red pigments. A photosensitive resin containing a pigment was applied by spin coating, and then exposed and developed to form a pattern for each color.
After the color filter 24 was formed, a non-photosensitive resin was applied on the color filter 24 and baked to form a planarizing film. Next, a positive photosensitive resin is applied on the planarizing film by a spin coating method, and a photolithography is performed to form a gap between the lenses of each pixel. The microlens 25 was formed. In addition, the lens shape of the microlens 25 is designed so as to be condensed near the center of the photoelectric conversion element 21 when light in the visible light region is incident.
After forming the microlens 25, post-processing such as formation of a protective film, dicing of the support substrate, and wiring bonding was performed to obtain a solid-state imaging device.

Next, the behavior that is incident on the solid-state imaging device of the above-described embodiment manufactured according to the present invention will be described with reference to FIG.
The light incident perpendicularly toward the solid-state image sensor is refracted in the microlens 25 and collected toward the center of the photoelectric conversion element 21. Light having a short wavelength undergoes photoelectric conversion on the surface or inside of the photoelectric conversion element 21 to form electron-hole pairs, but most of the red light passes through the semiconductor layer 20 without being photoelectrically converted, and the light reflecting structure 14 Reflected by the reflective metal 11 inside. Further, not only the light vertically incident from the apex of the lens 25 but also the light obliquely incident on the light reflecting structure 14 after being condensed on the photoelectric conversion element 21, the surface of the reflective metal 11 has a concave shape such as a hemisphere. Therefore, the light is efficiently reflected toward the center of the photoelectric conversion element 21 and is incident again. For this reason, the sensitivity with respect to red light improves the solid-state image sensor of the structure of a present Example.

DESCRIPTION OF SYMBOLS 10 Support substrate 10a Groove 11 Reflective metal 12 Light transmissive layer 13 Photoresist 14 Light reflective structure 20 Semiconductor layer 21 Photoelectric conversion element 22 Interlayer insulating layer 23 Wiring 24 Color filter 25 Micro lens

Claims (6)

A solid-state imaging device having a semiconductor layer formed on a support substrate and a plurality of photoelectric conversion elements arranged on the semiconductor layer,
A groove corresponding to the photoelectric conversion element is formed on the surface of the support substrate on which the semiconductor layer is formed, and a light reflecting structure is disposed in the groove.
The solid-state imaging device, wherein the light reflecting structure includes a reflective metal formed along a surface of the groove, and a light transmission layer disposed between the reflective metal and the semiconductor layer.   2. The solid-state imaging device according to claim 1, wherein the surface of the reflective metal is formed of a concave curvature curve having no curvature steep portion.   The solid-state imaging device according to claim 1, wherein the surface shape of the reflective metal is a circular arc shape in cross section.   The solid-state image pickup device according to any one of claims 1 to 3, wherein a material of the support substrate is quartz.   The solid-state imaging device according to any one of claims 1 to 4, wherein a material of the light transmission layer is undoped silicon oxide. A method for producing a solid-state imaging device in which a semiconductor layer is formed on a support substrate, and a plurality of photoelectric conversion elements are arranged on the semiconductor layer,
A plurality of grooves are formed on the surface of the support substrate, a reflective metal is formed along the surface of the grooves and a light transmission layer is filled in the grooves to form a light reflecting structure,
A semiconductor substrate is bonded to the surface of the support substrate on which the light reflecting structure is formed, and further, the semiconductor thin film surface is peeled off while the semiconductor thin film is left, and then the semiconductor thin film surface is polished. Forming a semiconductor layer,
A method for producing a solid-state imaging element, comprising forming a photoelectric conversion element on the semiconductor layer.

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