JP2011014673A - Soi substrate and method of manufacturing the same, and method of manufacturing solid-state image pickup device with soi substrate - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide: an SOI substrate where an antireflective film or the like capable of preventing characteristics of an image sensor from deteriorating, are preformed; a method of manufacturing the same; and a method of manufacturing a solid-state image pickup device with the SOI substrate.SOLUTION: The SOI 100 includes: a silicon substrate 101; a first insulating film 102 formed on the silicon substrate 101; a second insulating film 103 formed on the first insulating film 102; a third insulating film 104 formed on the second insulating film 103; and a silicon layer 106 formed on the third insulating film 104.

Description

  The present invention relates to a back-illuminated solid-state imaging device using an SOI (Silicon on Insulator) substrate, and more particularly to an SOI substrate, a manufacturing method thereof, and a manufacturing method of a solid-state imaging device using the same.

  In recent years, such as a CMOS image sensor having a large number of two-dimensionally arranged pixels formed using an SOI substrate, each of which is provided with a photodiode as a photoelectric conversion element and a plurality of MOS transistors for reading pixel signals. Solid-state imaging devices have been developed.

  Conventionally, a surface irradiation type solid-state imaging device formed by arranging photoelectric conversion elements, MOS transistors, and various wirings on the upper surface of a semiconductor substrate has a general structure. However, in the case of the above configuration, it is necessary to dispose the light receiving region of the photoelectric conversion element away from the MOS transistor and the wiring. Therefore, when the number of pixels is increased without increasing the area of the semiconductor substrate, there is a problem that the aperture ratio of the light receiving region of each photoelectric conversion element is reduced.

  In order to avoid this, recently, a semiconductor substrate such as an SOI substrate or a silicon substrate is used, a MOS transistor or a wiring layer is formed on one surface side of the semiconductor substrate, and a photoelectric conversion element is formed on the back surface side facing the surface. A solid-state imaging device having a so-called back-illuminated configuration in which a light receiving region is formed and arranged has been developed.

  A back-illuminated solid-state imaging device formed using a conventional SOI substrate will be described below with reference to FIGS.

  FIG. 8 is a cross-sectional view for explaining the structure and manufacturing method of a conventional SOI substrate. FIG. 9 is a cross-sectional view for explaining a method of manufacturing a conventional back-illuminated solid-state imaging device.

  First, referring to FIG. 8, the structure and manufacturing method of an SOI substrate will be described below with an example of a bonding method combining a hydrogen ion implantation step and a separation step, which is one of methods for manufacturing an SOI substrate. I will explain it.

  First, as shown in FIG. 8A, a first single crystal silicon substrate 401 as a base wafer and a second single crystal silicon substrate 402 as a bond wafer are prepared.

  Next, as shown in FIG. 8B, the surface of the second single crystal silicon substrate 402 is oxidized to form a silicon oxide film 403 which is an oxide film.

  Next, as shown in FIG. 8C, hydrogen ions are implanted into the second single crystal silicon substrate 402 to form a microbubble layer (encapsulation layer) 404 at a predetermined depth from the surface.

  Next, as shown in FIG. 8D, the silicon oxide film 403 of the second single crystal silicon substrate 402 into which hydrogen ions have been implanted and the surfaces of the first single crystal silicon substrate 401 are brought into contact with each other at room temperature to be bonded.

  Next, as shown in FIG. 8E, in the above state, heat treatment is performed at a temperature of 500 ° C. or higher to separate the separation substrate 406 and the SOI substrate 407 with the microbubble layer 404 as a boundary. At this time, a damaged layer usually remains at the peeling interface of the SOI substrate 407.

  Next, as shown in FIG. 8 (f), in order to improve the bonding force between the silicon oxide film 403 of the second single crystal silicon substrate 402 of the SOI substrate 407 and the first single crystal silicon substrate 401, 1000 ° C. Heat treatment is performed at a high temperature of 1300 ° C. Thereafter, the SOI substrate 407 is manufactured by removing the damaged layer of the second single crystal silicon substrate 402 of the SOI substrate 407 (see, for example, Patent Document 1).

  Hereinafter, a method for manufacturing the backside illumination type solid-state imaging device will be specifically described with reference to FIG.

  First, as shown in FIG. 9A, a silicon layer 411, a silicon oxide layer 412 and a silicon layer 413 are laminated and formed on an upper side of an SOI substrate 410 obtained by epitaxially growing single crystal silicon on a quartz substrate. Then, a photodiode 414 is formed on the main surface of the silicon layer 413 by using an ion implantation method.

  Next, as shown in FIG. 9B, on the upper surface of the main surface of the silicon layer 413, for example, a wiring layer 415A in which a metal wiring 415 is formed, and a supporting silicon substrate 417 for improving the mechanical strength on the upper surface. Are bonded together to produce a solid-state imaging device precursor 400.

  Next, as shown in FIG. 9C, the solid-state imaging device precursor 400 is turned upside down, and the SOI substrate 410, the silicon layer 411, and the silicon oxide layer 412 are removed by, for example, an etching method, and the photodiode 414 is obtained. The silicon layer 413 formed with is exposed.

  Next, as shown in FIG. 9D, an antireflection film 418 and an electrode pad (not shown) are formed on the silicon layer 413.

  Next, as shown in FIG. 9E, a color filter 420 and an on-chip lens 421 are formed on the antireflection film 418 so as to correspond to each photodiode 414 (see, for example, Patent Document 2).

  As a result, a back-illuminated solid-state imaging device can be manufactured.

  As the configuration of the antireflection film 418, for example, a two-layer film structure including a silicon oxide film and a silicon nitride film is disclosed (for example, see Patent Document 3).

Japanese Patent Application Laid-Open No. 2000-124092 JP 2005-259828 A Japanese Patent Laid-Open No. 2005-268643

  However, in the conventional method for manufacturing a solid-state imaging device, as shown in FIG. 9C, it is necessary to once expose the silicon layer 413 and deposit the antireflection film 418. Therefore, the silicon layer 413 is contaminated by intrusion of metal impurities or the like from the surface of the silicon layer 413. Further, boron (B), phosphorus (P), or the like, which is a dopant of the silicon layer 413, is non-uniformly detached from the silicon layer 413 due to heating at the time of forming the antireflection film 418 or the like.

  Since the wiring layer 415A having the metal wiring 415 is already formed before the antireflection film 418 is formed, the antireflection film 418 must be formed at a relatively low temperature (400 ° C. or lower). I must. At this time, when the antireflection film 418 having a thickness of about 50 nm is formed at a low temperature by the plasma CVD method, it is necessary to set the concentration of the source gas introduced into the chamber at the time of film formation low in order to suppress the film formation rate. . However, if the concentration of the raw material gas is lowered, it is difficult to generate uniform plasma, so that the variation in the thickness of the antireflection film to be formed increases. Specifically, for example, the variation in the film thickness of the antireflection film 418 formed on the surface of the silicon layer 413 is generally 10% to 20%. Therefore, it is difficult to uniformly form the antireflection film 418 having a film thickness variation of, for example, 100 nm or less, which requires a variation in film thickness of 5% or less.

  Further, when the antireflection film is formed by the plasma CVD method, as described in detail below, the surface of the silicon layer 413 is more likely to be damaged by charge-up.

  In other words, due to the above factors, there has been a problem that image sensor characteristics deteriorate due to, for example, an increase in dark current or an increase in pixel defects, and a decrease in sensitivity or a variation in sensitivity occurs due to a variation in film thickness.

  The present invention solves the above-described problems, and provides an SOI substrate on which an antireflection film or the like is formed in advance, which can prevent deterioration of image sensor characteristics, a method for manufacturing the same, and a method for manufacturing a solid-state imaging device using the SOI substrate. For the purpose.

  In order to achieve the above-described conventional object, an SOI substrate of the present invention includes a silicon substrate, a first insulating film formed on the silicon substrate, a second insulating film formed on the first insulating film, The second insulating film includes a third insulating film formed on the second insulating film and a silicon layer formed on the third insulating film.

  With this configuration, an SOI substrate having a plurality of insulating films with little variation in film thickness can be realized. In addition, since at least one surface of the silicon layer is not exposed, a highly reliable SOI substrate capable of preventing the occurrence of crystal defects and the like in a subsequent process of forming a solid-state imaging device using the SOI substrate can be obtained.

  Further, the first insulating film is a first silicon oxide film, the second insulating film is a silicon nitride film, and the third insulating film is a second silicon oxide film. Thereby, an SOI substrate including an antireflection film with little film thickness variation can be realized.

  Further, the thickness of the silicon nitride film is 40 nm or more and 65 nm or less, and the thickness of the second silicon oxide film is more than 0 nm and 25 nm or less. Thereby, it is possible to realize an SOI substrate including an antireflection film having excellent transmittance in a predetermined range of wavelengths.

  The method for manufacturing an SOI substrate according to the present invention includes a step of forming a first insulating film on a first silicon substrate, a step of forming a second insulating film on the first insulating film, and a step of forming on the second insulating film. A step of forming a third insulating film, a step of forming a crystal defect layer inside the first surface of the second silicon substrate, a third insulating film of the first silicon substrate, and a first surface of the second silicon substrate; And a step of peeling a side opposite to the first surface of the second silicon substrate with a crystal defect layer to form a silicon layer.

  The method for manufacturing an SOI substrate according to the present invention includes a step of forming a first insulating film on the first silicon substrate, a step of forming a second insulating film on the first insulating film, and a second step of forming the second silicon substrate. A step of forming a third insulating film on one surface, a step of forming a crystal defect layer inside the first surface of the second silicon substrate, a second insulating film of the first silicon substrate, and a second silicon substrate. A step of bonding the third insulating film, and a step of peeling a side opposite to the first surface of the second silicon substrate with a crystal defect layer to form a silicon layer.

  The method for manufacturing an SOI substrate according to the present invention includes a step of forming a first insulating film on the first silicon substrate, a step of forming a third insulating film on the first surface of the second silicon substrate, and a third method. A step of forming a second insulating film on the insulating film, a step of forming a crystal defect layer inside the first surface of the second silicon substrate, a first insulating film of the first silicon substrate, and a second silicon substrate. A step of bonding the second insulating film, and a step of peeling a side opposite to the first surface of the second silicon substrate with a crystal defect layer to form a silicon layer.

  By these methods, an SOI substrate having a plurality of insulating films with little variation in film thickness can be easily manufactured. In addition, since at least one surface of the second silicon substrate is not exposed, a highly reliable SOI substrate that can prevent generation of crystal defects and the like can be formed in a subsequent process of forming a solid-state imaging device using the SOI substrate. .

  Further, the first insulating film is a first silicon oxide film, the second insulating film is a silicon nitride film, and the third insulating film is a second silicon oxide film. Accordingly, an SOI substrate including an antireflection film with little variation in film thickness can be manufactured.

  Further, the thickness of the silicon nitride film is 40 nm or more and 65 nm or less, and the thickness of the second silicon oxide film is more than 0 nm and 25 nm or less. Accordingly, an SOI substrate including an antireflection film with little variation in film thickness can be manufactured.

  The method for manufacturing a solid-state imaging device according to the present invention includes a step of forming a first insulating film on a first silicon substrate, a step of forming a second insulating film on the first insulating film, and a step on the second insulating film. Forming a third insulating film on the first silicon substrate; forming a crystal defect layer on the first surface side of the second silicon substrate; and a third insulating film of the first silicon substrate and a first surface of the second silicon substrate. Bonding, a step of peeling a side opposite to the first surface of the second silicon substrate with a crystal defect layer to form a silicon layer, a step of forming a photodiode on the silicon layer, Forming a laminated wiring on a side opposite to the first surface, removing the first silicon substrate and the first insulating film, and forming a color filter and an on-chip lens on the second insulating film; , At least.

  By this method, a solid-state imaging device with high sensitivity and little sensitivity variation can be manufactured.

  Further, the first insulating film is a first silicon oxide film, the second insulating film is a silicon nitride film, and the third insulating film is a second silicon oxide film. Thereby, it is possible to manufacture a solid-state imaging device with small sensitivity variations and excellent reliability.

  Further, the thickness of the silicon nitride film is 40 nm or more and 65 nm or less, and the thickness of the second silicon oxide film is more than 0 nm and 25 nm or less. Thereby, a highly sensitive solid-state imaging device can be produced.

  According to the present invention, it is possible to obtain an SOI substrate that realizes a high-performance solid-state imaging device having high sensitivity and extremely small variations in sensitivity and spectral characteristics, a manufacturing method thereof, and a manufacturing method of a solid-state imaging device using the same. .

Sectional drawing explaining the structure of the SOI substrate in Embodiment 1 of this invention The figure explaining the characteristic of the anti-reflective film provided in the SOI substrate in Embodiment 1 of this invention Sectional drawing explaining the manufacturing method of the SOI substrate in Embodiment 1 of this invention Sectional drawing explaining the manufacturing method of the SOI substrate in Embodiment 2 of this invention Sectional drawing explaining the manufacturing method of the SOI substrate in Embodiment 3 of this invention Sectional drawing explaining the manufacturing method of the solid-state imaging device in Embodiment 4 of this invention Schematic diagram explaining the mechanism of image sensor characteristics degradation Sectional drawing explaining the structure and manufacturing method of the conventional SOI substrate Sectional drawing explaining the manufacturing method of the conventional back irradiation type solid-state imaging device

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. The same elements will be described with the same reference numerals.

(Embodiment 1)
Hereinafter, the structure and manufacturing method of the SOI substrate according to the first embodiment of the present invention will be described with reference to the drawings.

  FIG. 1 is a cross-sectional view illustrating the structure of an SOI substrate according to Embodiment 1 of the present invention.

As shown in FIG. 1, an SOI substrate 100 includes a silicon substrate 101 made of single crystal silicon, a first insulating film 102 made of a first silicon oxide film (SiO ₂ ), and a second made of a silicon nitride film (SiN). The insulating film 103, the third insulating film 104 made of a second silicon oxide film (SiO ₂ ), and the silicon layer 106 made of single crystal silicon are laminated. An antireflection film 105 formed, for example, on the light receiving side of the solid-state imaging device is constituted by at least a two-layer film structure of the second insulating film 103 and the third insulating film 104. Furthermore, the silicon layer 106 is a layer in which, for example, a photodiode that is a light receiving element of a solid-state imaging device is formed. At this time, the silicon layer 106 has a film thickness of, for example, 5 μm to 15 μm, and is formed by, for example, an epitaxial growth method or bonding of single crystal silicon.

  Note that when the antireflection film is formed by the two-layer film structure of the second insulating film 103 and the third insulating film 104, it is important to have a film structure with as high a transmittance as possible.

  Therefore, an optimum film thickness configuration of the second insulating film and the third insulating film constituting the antireflection film used in the solid-state imaging device or the like will be described below with reference to FIG.

FIG. 2 is a diagram for explaining the characteristics of the antireflection film provided on the SOI substrate in the first embodiment of the present invention. FIG. 2 shows the transmittance of visible light having a wavelength of 400 nm to 650 nm when the thickness of the silicon nitride film (SiN) that is the second insulating film 103 is changed. At this time, the thickness of the second silicon film (SiO ₂ ) as the third insulating film 104 is shown as a parameter.

  As shown in FIG. 2, the film thickness of the second insulating film 103 is, for example, 40 nm to 65 nm, preferably 45 nm to 65 nm, and more preferably 50 nm to 60 nm. The film thickness of the third insulating film 104 is, for example, more than 0 nm and 25 nm or less, preferably 5 nm to 15 nm, more preferably 5 nm to 10 nm. As an example, when the silicon nitride film is 50 nm, in order to realize a transmittance of 95% or more, the silicon oxide film may be formed with a thickness of 5 nm.

  This is because when the thickness of the second insulating film 103 is 40 nm or less, reflection of incident light on the surface of the silicon substrate becomes remarkable, and when it is 65 nm or more, the transmittance of incident light to the silicon substrate deteriorates. This is because the characteristics deteriorate. Further, when the film thickness of the third insulating film 104 is 0 nm, the interface state is formed at the interface between the silicon nitride film (SiN) as the second insulating film 103 and the silicon substrate, so that the image quality of the image sensor is deteriorated. When the thickness exceeds 25 nm, reflection of incident light on the surface of the silicon substrate becomes remarkable.

  According to this embodiment, an SOI substrate having an antireflection film in advance can be realized. Moreover, the film thickness variation of the antireflection film having at least a two-layer film structure can be reduced. Further, since a silicon layer is provided on the antireflection film, for example, when a solid-state imaging device is formed using this SOI substrate, at least one surface (the third insulating film 104 side) of the silicon layer is not exposed. As a result, an SOI substrate that can prevent the occurrence of crystal defects in the silicon layer can be realized.

  In the present embodiment, the silicon oxide film (SiO) / silicon nitride film (SiN) structure is described as an example of the antireflection film, but the present invention is not limited to this. For example, a silicon oxide film (SiO) / silicon oxynitride film (SiON) structure or a silicon nitride film (SiN) / silicon oxynitride film (SiON) structure may be used, and similar effects can be obtained.

  Below, the manufacturing method of the SOI substrate in Embodiment 1 of this invention is demonstrated in detail using drawing.

  FIG. 3 is a cross-sectional view illustrating the method for manufacturing the SOI substrate in the first embodiment of the present invention. In addition, the same code | symbol is attached | subjected and demonstrated to the same component as FIG. Further, the first silicon substrate 101 is used as the silicon substrate of the SOI substrate, the first silicon oxide film 102 is used as the first insulating film, the silicon nitride film 103 is used as the second insulating film, and the second silicon oxide film 104 is used as the third insulating film. explain.

First, as shown in FIG. 3A, the first silicon substrate 101 is heat-treated in an oxygen atmosphere at a temperature of, for example, 900 ° C. or more, so that the surface of the first silicon substrate 101 has a thickness of 200 nm, for example. A silicon oxide film 102 is formed. Thereafter, a silicon nitride film 103 is formed on the first silicon oxide film 102 to a thickness of, for example, 50 nm by using a low pressure CVD method. At this time, a silicon nitride film is deposited using dichlorosilane (SiH ₂ Cl ₂ ) gas and ammonia (NH ₃ ) gas at a temperature of about 750 ° C. as a film forming condition of the low pressure CVD method. As a result, the silicon nitride film 103 having a refractive index (N = 2.02) different from the refractive index of the first silicon oxide film 102 (for example, N = 4.047) is formed. Similarly, a second silicon oxide film 104 is formed on the silicon nitride film 103 with a film thickness of, for example, 5 nm by using a low pressure CVD method. At this time, the second silicon oxide film 104 is deposited using a monosilane (SiH ₄ ) gas and a nitrous oxide (N ₂ O) gas at a temperature of about 800 ° C. as a film forming condition of the low pressure CVD method. Thereby, an antireflection film 105 having a two-layer structure of the silicon nitride film 103 and the second silicon oxide film 104 is formed.

  Note that the low-pressure CVD method uses high-temperature heat energy of 700 ° C. or higher to form a film by reactive vapor deposition of each source gas, so that a dense and excellent film thickness uniformity can be formed. . Specifically, the silicon nitride film 103 and the second silicon oxide film that need to be formed with a film thickness of 100 nm or less can be formed with a film thickness variation of 5% or less. Therefore, it is possible to greatly suppress the film thickness variation, which has been a problem in the conventional plasma CVD method for forming an antireflection film at a low temperature. Further, as will be described later with reference to FIG. 7, when an antireflection film is formed on a silicon layer on which a photodiode is formed, damage due to charge-up of the silicon layer or the like caused by plasma in the plasma CVD method is obviated. It can be avoided. As a result, the surface stability and reliability of the silicon layer can be greatly improved.

Next, as shown in FIG. 3B, hydrogen ions are ion-implanted from the first surface 107A of the second silicon substrate 107 at a dose of 10 ¹⁶ to 10 ¹⁷ atoms / cm ² and an acceleration energy of about 2000 KV. Inject. At this time, for example, acceleration of ions to be implanted is performed so that the concentration of hydrogen ions implanted into the second silicon substrate 107 becomes maximum from the first surface 107A of the second silicon substrate 107 at a depth of, for example, 5 μm to 15 μm. Ion implantation is performed with energy set. As a result, a crystal defect layer 108 having a thickness of 1 μm to 2 μm, for example, is formed in the second silicon substrate 107.

  Next, as shown in FIG. 3C, the surface of the second silicon oxide film 104 formed on the first silicon substrate 101 shown in FIG. 3A and the hydrogen ions shown in FIG. The first surface 107A of the second silicon substrate 107 on the implanted side is bonded at room temperature. In this state, heat treatment is performed at 400 ° C. to 500 ° C., for example, to form a large number of high-density void layers 109 in the crystal defect layer 108. The temperature of the heat treatment for forming the void layer 109 is set such that the implanted hydrogen ions are rapidly diffused as hydrogen gas and maintained below the critical temperature released from the second silicon substrate 107. The

  Then, in the above process, as shown in FIG. 3D, the second silicon substrate 107 is cleaved by the high-density void layer formed in the crystal defect layer, and the second silicon substrate on the opposite side to the first surface. 107 is peeled off. Thus, a silicon layer 106 is formed on the second silicon oxide film 104 of the first silicon substrate 101 by separating from the second silicon substrate 107 of the single crystal silicon substrate and separating it.

  Next, for example, heat treatment is performed at 1000 ° C. or higher for several hours, thereby firmly bonding the bonding surfaces of the second silicon oxide film 104 and the silicon layer 106.

  Then, the cleaved surface of the silicon layer 106 is mirror-polished by, for example, mechanical polishing or a CMP method, whereby the SOI substrate 100 is manufactured. Thereby, the silicon layer 106 having a film thickness of about 3 μm to 15 μm is formed. The film thickness of the silicon layer 106 is set in consideration of the thickness for removing the crystal defect layer or the like, for example, greater than the thickness necessary for forming the photodiode of the solid-state imaging device.

  According to the manufacturing method of the present embodiment, an SOI substrate 100 having a plurality of insulating films with little variation in film thickness and including the antireflection film 105 formed in advance by the structure of the insulating film can be easily manufactured. In addition, since at least one surface (first surface 107A) of the silicon layer 106 is not exposed, it has excellent reliability capable of preventing the occurrence of crystal defects and the like in a subsequent process of forming a solid-state imaging device using the SOI substrate 100. The SOI substrate 100 can be manufactured.

(Embodiment 2)
Below, the manufacturing method of the SOI substrate in Embodiment 2 of this invention is demonstrated in detail using drawing.

  FIG. 4 is a cross-sectional view illustrating a method for manufacturing an SOI substrate according to Embodiment 2 of the present invention.

  The SOI substrate manufacturing method according to the present embodiment is implemented in that the first insulating film and the second insulating film are formed on the first silicon substrate, and the third insulating film is formed on the second silicon substrate. This is different from the manufacturing method of the SOI substrate of mode 1. As in the first embodiment, the silicon substrate of the SOI substrate is the first silicon substrate 201, the first insulating film is the first silicon oxide film 202, the second insulating film is the silicon nitride film 203, and the third insulating film is the first insulating film. The two-silicon oxide film 204 will be described as an example.

First, as shown in FIG. 4A, the first silicon substrate 201 is heat-treated in an oxygen atmosphere at a temperature of, for example, 900 ° C. or more, so that the first silicon substrate 201 has a thickness of, for example, 200 nm on the surface of the first silicon substrate 201. A silicon oxide film 202 is formed. Thereafter, a silicon nitride film 203 is formed on the first silicon oxide film 202 with a film thickness of, for example, 50 nm by using a low pressure CVD method. At this time, a silicon nitride film is deposited using dichlorosilane (SiH ₂ Cl ₂ ) gas and ammonia (NH ₃ ) gas at a temperature of about 750 ° C. as a film forming condition of the low pressure CVD method.

Next, as shown in FIG. 4B, a second silicon oxide film 204 is formed on the first surface 207A of the second silicon substrate 207 with a film thickness of, for example, 5 nm by using a low pressure CVD method. At this time, the second silicon oxide film 204 is deposited using monosilane (SiH ₄ ) gas and nitrous oxide (N ₂ O) gas at a temperature of about 800 ° C. as a film forming condition of the low pressure CVD method.

Next, as shown in FIG. 4 (c), 10 ¹⁶ to 10 ¹⁷ atoms / cm ² from the surface of the second silicon oxide film 204 formed on the second silicon substrate 207 into the second silicon substrate 207. Hydrogen ions are implanted by an ion implantation method at a dose of about 2000 KV and an acceleration energy of about 2000 KV. At this time, for example, acceleration of ions to be implanted is performed so that the concentration of hydrogen ions implanted into the second silicon substrate 207 becomes maximum from the first surface 207A of the second silicon substrate 207 at a depth of, for example, 5 μm to 15 μm. Ion implantation is performed with energy set. As a result, a crystal defect layer 208 having a thickness of, for example, 1 μm to 2 μm is formed in the second silicon substrate 207.

  Next, as shown in FIG. 4D, the surface of the silicon nitride film 203 formed on the first silicon substrate 201 shown in FIG. 4A and the second silicon substrate 207 shown in FIG. The surface of the second silicon oxide film 204 formed thereon is bonded at room temperature. In this state, heat treatment is performed at 400 ° C. to 500 ° C., for example, to form a large number of high-density void layers 209 in the crystal defect layer 208.

  Then, in the above process, as shown in FIG. 4E, the second silicon substrate 207 is cleaved by the high-density void layer formed in the crystal defect layer, and the second silicon on the opposite side to the first surface 207A. The substrate 207 is peeled off. Thereby, the silicon layer 206 is separated from the second silicon substrate 207 of the single crystal silicon substrate via the second silicon oxide film 204 on the silicon nitride film 203 of the first silicon substrate 201, and is separated and laminated. .

  Next, the bonded surface of the silicon nitride film 203 and the second silicon oxide film 204 is firmly bonded by performing a heat treatment at 1000 ° C. or higher for several hours, for example. At this time, the antireflection film 205 is formed by the silicon nitride film 203 and the second silicon oxide film 204.

  Then, the cleaved surface of the silicon layer 206 is mirror-polished by, for example, mechanical polishing or a CMP method, whereby the SOI substrate 200 on which the silicon layer 206 having a thickness of about 3 μm to 15 μm is formed. At this time, the film thickness of the silicon layer 206 is set in consideration of, for example, the thickness for removing the crystal defect layer, which is equal to or greater than the thickness necessary for forming the photodiode of the solid-state imaging device.

  According to the manufacturing method of the present embodiment, an SOI substrate 200 having a plurality of insulating films with little variation in film thickness and having an antireflection film 205 formed in advance by the structure of the insulating film can be easily manufactured. In addition, since at least the first surface 207A of the silicon layer 206 is not exposed, a highly reliable SOI substrate capable of preventing the occurrence of crystal defects and the like in a subsequent process of forming a solid-state imaging device using the SOI substrate 200. 200 can be manufactured.

  In this embodiment, the film thickness of the silicon nitride film is 50 nm and the film thickness of the second silicon oxide film is 5 nm. However, the present invention is not limited to this. For example, as in the first embodiment, the thickness of the silicon nitride film 203 is, for example, in the range of 40 nm to 65 nm, and the thickness of the second silicon oxide film 204 is, for example, in the range of more than 0 nm to 25 nm or less. The same effect can be obtained.

(Embodiment 3)
Below, the manufacturing method of the SOI substrate in Embodiment 3 of this invention is demonstrated in detail using drawing.

  FIG. 5 is a cross-sectional view illustrating a method for manufacturing an SOI substrate according to Embodiment 3 of the present invention.

  The SOI substrate manufacturing method according to the present embodiment is implemented in that the first insulating film is formed on the first silicon substrate, and the second insulating film and the third insulating film are formed on the second silicon substrate. This is different from the manufacturing method of the SOI substrate of mode 1. As in the first embodiment, the first silicon substrate 301 is used as the silicon substrate of the SOI substrate, the first silicon oxide film 302 is used as the first insulating film, the silicon nitride film 303 is used as the second insulating film, and the first silicon oxide film 302 is used as the third insulating film. An explanation will be given by taking the 2-silicon oxide film 304 as an example.

  First, as shown in FIG. 5A, the first silicon substrate 301 is heat-treated in an oxygen atmosphere at a temperature of, for example, 900 ° C. or more, so that the surface of the first silicon substrate 301 has a thickness of, for example, 200 nm. A silicon oxide film 302 is formed.

Next, as shown in FIG. 5B, a second silicon oxide film 304 is formed on the first surface 307A of the second silicon substrate 307 by using a low pressure CVD method, for example, with a film thickness of 5 nm. At this time, the second silicon oxide film 304 is deposited using monosilane (SiH ₄ ) gas and nitrous oxide (N ₂ O) gas at a temperature of about 800 ° C. as a film forming condition of the low pressure CVD method. Thereafter, a silicon nitride film 303 is formed on the second silicon oxide film 304 with a film thickness of, for example, 50 nm by using a low pressure CVD method. At this time, a silicon nitride film is deposited using dichlorosilane (SiH ₂ Cl ₂ ) gas and ammonia (NH ₃ ) gas at a temperature of about 750 ° C. as a film forming condition of the low pressure CVD method. Thereby, an antireflection film 305 composed of the silicon nitride film 303 and the second silicon oxide film 304 is formed.

Next, as shown in FIG. 5C, from the surface of the silicon nitride film 303 of the antireflection film 305 formed on the second silicon substrate 307, into the second silicon substrate 307, 10 ¹⁶ to 10 ¹⁷ atoms / Hydrogen ions are implanted by an ion implantation method with a dose of cm ² and an acceleration energy of about 2000 KV. At this time, for example, acceleration of ions to be implanted is performed so that the concentration of hydrogen ions implanted into the second silicon substrate 307 becomes maximum from the first surface 307A of the second silicon substrate 307 at a depth of, for example, 5 μm to 15 μm. Ion implantation is performed with energy set. As a result, a crystal defect layer 308 having a thickness of 1 μm to 2 μm, for example, is formed in the second silicon substrate 307.

  Next, as shown in FIG. 5 (d), the surface of the first silicon oxide film 302 formed on the first silicon substrate 301 shown in FIG. 5 (a) and the second silicon shown in FIG. 5 (c). The surface of the silicon nitride film 303 formed on the substrate 207 is bonded at room temperature. In this state, heat treatment is performed at 400 ° C. to 500 ° C., for example, to form a large number of high-density void layers 309 in the crystal defect layer 308.

  Then, in the above process, as shown in FIG. 5E, the second silicon substrate 307 is cleaved by the high-density void layer formed in the crystal defect layer, and the second silicon on the side opposite to the first surface 307A is obtained. The substrate 307 is peeled off. Thus, the silicon layer 306 is separated from the second silicon substrate 307 of the single crystal silicon substrate via the silicon nitride film 303 and separated from the first silicon oxide film 302 of the first silicon substrate 301. .

  Next, the bonded surface of the silicon nitride film 303 and the first silicon oxide film 202 is firmly bonded by performing a heat treatment at 1000 ° C. or higher for several hours, for example.

  Then, the cleaved surface of the silicon layer 306 is mirror-polished by, for example, mechanical polishing or CMP to produce the SOI substrate 300 on which the silicon layer 306 having a thickness of about 3 μm to 15 μm is formed. At this time, the film thickness of the silicon layer 306 is set in consideration of the thickness for removing the crystal defect layer or the like, for example, greater than the thickness necessary for forming the photodiode of the solid-state imaging device.

  According to the manufacturing method of this embodiment, an SOI substrate 300 having a plurality of insulating films with little variation in film thickness and including an antireflection film 305 formed in advance by the structure of the insulating film can be easily manufactured. In addition, since at least the first surface 307A of the silicon layer 306 is not exposed, a highly reliable SOI substrate capable of preventing the occurrence of crystal defects or the like in a subsequent process of forming a solid-state imaging device using the SOI substrate 300. 300 can be manufactured.

  In this embodiment, the film thickness of the silicon nitride film is 50 nm and the film thickness of the second silicon oxide film is 5 nm. However, the present invention is not limited to this. For example, as in the first embodiment, the thickness of the silicon nitride film 303 is, for example, in the range of 40 nm to 65 nm, and the thickness of the second silicon oxide film 304 is, for example, in the range of more than 0 nm to 25 nm or less. The same effect can be obtained.

(Embodiment 4)
Below, the manufacturing method of the solid-state imaging device in Embodiment 4 of this invention is demonstrated in detail using FIG. That is, in the present embodiment, a solid-state imaging device is manufactured using the SOI substrate 100 described in FIG. 3 of the first embodiment. Therefore, description of the structure and manufacturing method of the SOI substrate is omitted. Therefore, a manufacturing method of the solid-state imaging device after forming the SOI substrate will be described in detail.

  FIG. 6 is a cross-sectional view illustrating a method for manufacturing a solid-state imaging device according to Embodiment 4 of the present invention. In addition, the same code | symbol is attached | subjected and demonstrated to the same component as Embodiment 1. FIG.

  First, as shown in FIG. 6A, a photodiode 111 that performs photoelectric conversion composed of an n-type impurity diffusion layer is formed in the silicon layer 106 by ion implantation of arsenic (As) or phosphorus (P). To do. At this time, the light receiving portion of the photodiode 111 is formed toward the second silicon oxide film 104 side. Note that the photodiode 111 is formed using an n-type single crystal silicon substrate used as the second silicon substrate 107 on which the silicon layer 106 is formed. An n-type region that continues from the photodiode 111 to the n-type single crystal silicon substrate is a photoelectric conversion region. At this time, as the thickness of the silicon layer 106, as described above, the silicon layer 106 is formed to have a film thickness of 5 μm to 15 μm that can photoelectrically convert visible light.

  Next, as shown in FIG. 6B, a gate electrode 112 made of polysilicon, for example, and a multilayer metal wiring 113 made of aluminum or copper are formed on the silicon layer 106 through a gate oxide film. A wiring layer 113A is formed. At this time, since the back-illuminated solid-state imaging device does not have a structure for capturing incident light from the wiring layer 113A side, the gate electrode, the metal wiring, and the like on the formation region of the photodiode 111 can be arbitrarily routed and laid out. it can. For this reason, the degree of freedom in designing the wiring layer is increased, and the pixel itself composed of the photodiode can be miniaturized. Even if the number of wiring layers 113A is increased (usually five or more), a solid-state imaging device can be easily manufactured using the latest CMOS process with advanced miniaturization technology.

  Then, after the wiring layer 113A is formed, an interlayer insulating film 114 made of, for example, a silicon nitride film is formed thereon with a thickness of about 100 nm to 300 nm. Thereafter, a support member 115 made of a silicon substrate or the like having a thickness of several hundreds of μm is further bonded through the interlayer insulating film 114 to produce a solid-state imaging device precursor 150A. Thereby, the mechanical strength is improved, and a solid-state imaging device precursor 150A that is easy to handle is obtained. In addition to the silicon substrate, glass or an organic film may be used as the support member.

  Next, as shown in FIG. 6C, the solid-state imaging device precursor 150A is turned upside down, and the first silicon substrate 101 is subjected to, for example, a CMP method, and the first silicon oxide film 102 is further subjected to a wet etching method. To remove. Note that the CMP method and the wet etching method may be used in combination.

  At this time, as the etching method of the first silicon oxide film, the wet etching method using buffered hydrofluoric acid as a chemical solution is used to etch the first silicon oxide film 102 to be etched and the silicon nitride film 103 to be the base. The selection ratio can be increased to about 200, for example. As a result, the silicon nitride film 103 can be left with a predetermined film thickness (40 nm to 65 nm).

  In addition, by applying wet etching instead of dry etching using plasma that causes charge-up damage to semiconductor substrates forming photodiodes and implantation of impurity ions such as metals, It is possible to remove the first silicon oxide film 102 without causing deterioration of image sensor characteristics (increase in dark current or increase in pixel defects) due to damage caused by charge-up or implantation of impurities such as metal. Become.

  At least a second silicon oxide film 104 having a thickness of more than 0 nm and not more than 25 nm and a silicon nitride film 103 having a thickness of 40 nm to 65 nm provided on the silicon layer 106 on which the photodiode 111 is formed, A laminated film having a two-layer structure is formed as the antireflection film 105.

  Next, as shown in FIG. 6D, a planarizing film 120 made of a transparent organic film such as an acrylic resin is deposited on the silicon nitride film 103 at a thickness of 0.5 μm, for example, using a spin coating method. . Further, color filters 121 and on-chip lenses 122 are formed on the planarizing film 120 so as to correspond to the photodiodes 111 formed on the silicon layer 106. Note that the planarization film is not necessarily formed as long as the antireflection film is flat, and this step may be omitted.

  Through the above process, the solid-state imaging device 150 including an image sensor having a CMOS structure is manufactured.

  That is, according to the present embodiment, an insulating film having a different refractive index between the first silicon substrate 101 and the silicon layer 106 of the SOI substrate 100 (the first silicon oxide film 102, the silicon nitride film 103, and the A second silicon oxide film 104) is formed in advance. Then, a photodiode 111 is formed on the silicon layer 106 of the SOI substrate 100, and a wiring layer 113A such as a gate electrode 112 and a metal wiring 113 is formed thereon. Thereafter, the first silicon substrate 101 and the first silicon oxide film 102 of the SOI substrate 100 are removed, and two layers of insulating films (second silicon oxide film 104 and silicon oxide having different refractive indexes) are formed on the light irradiation surface of the solid-state imaging device. A solid-state imaging device 150 is manufactured by forming an antireflection film made of the nitride film 103).

  As a result, the solid-state imaging device can be formed without exposing the surface of the silicon layer on which the photodiode is formed before forming the antireflection film, which was a problem in the manufacture of the conventional solid-state imaging device.

  Therefore, the effect obtained by not exposing the silicon layer will be specifically described.

  First, the mechanism of image sensor characteristic deterioration (pixel characteristic variation, dark current increase, pixel defect increase) that occurs when an antireflection film is formed with the silicon layer exposed will be described with reference to FIG. .

  FIG. 7 is a schematic diagram for explaining a mechanism of deterioration of image sensor characteristics.

  That is, conventionally, it has been necessary to form a silicon oxide film and a silicon nitride film constituting the antireflection film at a low temperature by the plasma CVD method with the surface of the silicon layer exposed.

  Therefore, as shown in FIG. 7A, when the plasma treatment is performed with the surface of the silicon layer exposed, heavy metal atoms (for example, nickel, iron, etc.) generated from the wall surface of the plasma CVD apparatus or the plasma generating electrode are generated. The silicon layer is driven by the electric field generated by the plasma. The implanted heavy metal atoms diffuse in the silicon layer and cause crystal defects in the silicon layer.

  In addition, when charged particles (for example, hydrogen ions) are taken in the vicinity of the surface of the silicon layer by plasma treatment, so-called charge-up damage is generated in which charge generation centers are generated in the silicon layer. This charge generation center has an effect similar to that of the above-described crystal defect because it acts to take in or release the charge generated inside the silicon layer.

  That is, as shown in FIG. 7B, crystal defects and charge generation centers generated in the silicon layer cause an increase in dark current and an increase in pixel defects. Specifically, the thermally excited electrons generate a minute leakage current that moves from the valence band to the conduction band via crystal defects and charge generation centers caused by heavy metals in the silicon layer. Even when no light enters (dark state), a minute current is generated. As a result, white dots or linear image defects are generated on the screen output from the image sensor. Therefore, annealing treatment is usually performed at a high temperature of 800 ° C. or higher in order to restore the function by relaxing the crystal defects and charge generation centers. However, in the conventional method for manufacturing a solid-state imaging device, the metal wiring having a melting point lower than 800 ° C. is already formed before the antireflection film is formed, so that the annealing process cannot be performed, and the pixel characteristics are improved by the annealing process. Is impossible.

  Further, as shown in FIG. 7A, due to the temperature rise of the silicon layer during the plasma CVD process, dopants such as arsenic and phosphorus in the silicon layer are desorbed to the outside of the silicon layer, and the n-type impurity concentration of the silicon layer Vary locally. As a result, variation in photoelectric conversion characteristics of the photodiode when light is incident occurs, resulting in variation in sensitivity for each pixel.

  However, as described above, according to the manufacturing method of the present embodiment, the surface (first surface) of the silicon layer on which the photodiode is formed is not exposed through the manufacturing process of the antireflection film. In addition, since the second silicon oxide film and silicon nitride film that serve as antireflection films are formed in advance in the SOI substrate, the surface of the silicon layer that serves as the surface of the photodiode is not exposed to plasma. Therefore, the crystal treatment does not cause crystal defects in the silicon layer due to penetration of heavy metal atoms. As a result, image sensor characteristics are not deteriorated (increase in dark current and increase in pixel defects).

  In addition, since the surface of the silicon layer is not exposed to high temperatures due to plasma treatment, boron and phosphorus, which are dopants in the silicon layer, do not leave the silicon layer to the outside, so that variations in pixel characteristics (photoelectric conversion characteristics for each pixel) occur. It can be greatly reduced.

  Further, according to the manufacturing method of the present embodiment, it is not necessary to form an antireflection film that requires high-temperature treatment after forming a wiring layer such as a metal wiring. Therefore, an anti-reflective film having a thin film thickness of more than 0 nm and not more than 100 nm is formed uniformly with a film thickness variation of 5% or less by a low pressure CVD method capable of realizing a dense and highly uniform film formation. be able to.

  In addition, according to the manufacturing method of the present embodiment, the refractive index of the silicon nitride film or silicon oxide film constituting the antireflection film is uniform and reproducible as compared with the plasma CVD method which is a conventional film forming method. It can be formed well. For this reason, it is possible to reduce the film thickness of the antireflection film and the variation in film quality (refractive index) required to increase the sensitivity. As a result, it is possible to realize a solid-state imaging device such as a high-performance image sensor having high sensitivity and extremely small variations in sensitivity and spectral characteristics.

  In this embodiment, the solid-state imaging device using the SOI substrate of Embodiment 1 is described as an example, but the present invention is not limited to this. For example, a solid-state imaging device may be manufactured using the SOI substrate of Embodiment 2 or Embodiment 3, and similar effects can be obtained.

  In the present embodiment, a CMOS image sensor has been described as an example of the solid-state imaging device. However, the same effect can be obtained even when applied to a CCD solid-state imaging device.

  According to the present invention, an SOI substrate constituting a back-illuminated solid-state imaging device for which improvement in sensitivity to incident light and reduction in sensitivity variation are desired, a manufacturing method thereof, a manufacturing method of a solid-state imaging device using the SOI substrate, etc. Useful for technical fields.

100, 200, 300 SOI substrate 101, 201, 301 Silicon substrate 102, 202, 302 First silicon oxide film (first insulating film)
103, 203, 303 Silicon nitride film (second insulating film)
104, 204, 304 Second silicon oxide film (third insulating film)
105, 205, 305 Antireflection film 106, 206, 306 Silicon layer 107, 207, 307 Second silicon substrate 107A, 207A, 307A First surface 108, 208, 308 Crystal defect layer 109, 209, 309 Void layer 111 Photodiode DESCRIPTION OF SYMBOLS 112 Gate electrode 113 Metal wiring 113A Wiring layer 114 Interlayer insulation film 115 Support member 120 Planarization film 121 Color filter 122 On-chip lens 150 Solid-state imaging device 150A Solid-state imaging device precursor 400 Solid-state imaging device precursor 401 1st single crystal silicon substrate 402 Second single crystal silicon substrate 403 Silicon oxide film 404 Microbubble layer (encapsulation layer)
406 Release substrate 407, 410 SOI substrate 411, 413 Silicon layer 412 Silicon oxide layer 414 Photo diode 415 Metal wiring 415A wiring layer 417 Support silicon substrate 418 Antireflection film 420 Color filter 421 On-chip lens

Claims (11)

A silicon substrate;
A first insulating film formed on the silicon substrate;
A second insulating film formed on the first insulating film;
A third insulating film formed on the second insulating film;
An SOI substrate comprising a silicon layer formed on the third insulating film. 2. The SOI substrate according to claim 1, wherein the first insulating film is a first silicon oxide film, the second insulating film is a silicon nitride film, and the third insulating film is a second silicon oxide film. . 3. The SOI substrate according to claim 2, wherein the thickness of the silicon nitride film is 40 nm or more and 65 nm or less, and the thickness of the second silicon oxide film is more than 0 nm and 25 nm or less. Forming a first insulating film on the first silicon substrate;
Forming a second insulating film on the first insulating film;
Forming a third insulating film on the second insulating film;
Forming a crystal defect layer inside the first surface of the second silicon substrate;
Bonding the third insulating film of the first silicon substrate and the first surface of the second silicon substrate;
Peeling the side opposite to the first surface of the second silicon substrate with the crystal defect layer to form a silicon layer;
A method for manufacturing an SOI substrate, comprising: Forming a first insulating film on the first silicon substrate;
Forming a second insulating film on the first insulating film;
Forming a third insulating film on the first surface of the second silicon substrate;
Forming a crystal defect layer inside the first surface of the second silicon substrate;
Bonding the second insulating film of the first silicon substrate and the third insulating film of the second silicon substrate;
Peeling the side opposite to the first surface of the second silicon substrate with the crystal defect layer to form a silicon layer;
A method for manufacturing an SOI substrate, comprising: Forming a first insulating film on the first silicon substrate;
Forming a third insulating film on the first surface of the second silicon substrate;
Forming a second insulating film on the third insulating film;
Forming a crystal defect layer inside the first surface of the second silicon substrate;
Bonding the first insulating film of the first silicon substrate and the second insulating film of the second silicon substrate;
Peeling the side opposite to the first surface of the second silicon substrate with the crystal defect layer to form a silicon layer;
A method for manufacturing an SOI substrate, comprising: 7. The method according to claim 4, wherein the first insulating film is a first silicon oxide film, the second insulating film is a silicon nitride film, and the third insulating film is a second silicon oxide film. The manufacturing method of the SOI substrate of any one of Claims 1. 8. The method for manufacturing an SOI substrate according to claim 7, wherein the silicon nitride film has a thickness of 40 nm or more and 65 nm or less, and the second silicon oxide film has a thickness of more than 0 nm and 25 nm or less. Forming a first insulating film on the first silicon substrate;
Forming a second insulating film on the first insulating film;
Forming a third insulating film on the second insulating film;
Forming a crystal defect layer inside the first surface of the second silicon substrate;
Bonding the third insulating film of the first silicon substrate and the first surface of the second silicon substrate;
Peeling the side opposite to the first surface of the second silicon substrate with the crystal defect layer to form a silicon layer;
Forming a photodiode in the silicon layer;
Forming a laminated wiring on a side opposite to the first surface of the silicon layer;
Removing the first silicon substrate and the first insulating film;
Forming a color filter and an on-chip lens on the second insulating film;
A method for manufacturing a solid-state imaging device, comprising: 10. The solid-state imaging according to claim 9, wherein the first insulating film is a first silicon oxide film, the second insulating film is a silicon nitride film, and the third insulating film is a second silicon oxide film. Device manufacturing method. 11. The method of manufacturing a solid-state imaging device according to claim 10, wherein the silicon nitride film has a thickness of 40 nm to 65 nm and the second silicon oxide film has a thickness of more than 0 nm and 25 nm or less.

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