JP2007227636A - Semiconductor device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a semiconductor device having high photoelectric conversion rates by increasing the number of carriers to be generated, even for lights having different wavelengths such as R, G and B. <P>SOLUTION: The semiconductor device has a plurality of element portions 11<SB>B</SB>, 11<SB>G</SB>and 11<SB>R</SB>alignedly provided on a plane and executing photoelectric conversion of incident lights; and a protective film 12 for protecting the element portions 11<SB>B</SB>, 11<SB>G</SB>and 11<SB>R</SB>. In the semiconductor device, the protective films 12 are formed so as to have different thicknesses depending on the wavelengths of lights to be subjected to photoelectric conversion so that the incident strength of the lights into each of the element sections 11<SB>B</SB>, 11<SB>G</SB>and 11<SB>R</SB>may be the maximum. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a semiconductor device used for an image sensor.

  An image sensor is, for example, a cell in which a plurality of cells having one photodiode are arranged on a plane. Usually, incident light is incident on a color filter or a prism, and a red region (R region) or a green region ( G light) and blue light (B light) are divided into light of each wavelength, and the divided light is made incident on cells of the same structure to detect the incident intensity of light of each of R, G, and B wavelengths. ing. In addition, there is a type in which light of R, G, and B wavelengths is incident on the same cell by time sharing, and the incident intensity of light of each wavelength of R, G, and B is detected for each time sharing.

Japanese Patent Laid-Open No. 10-144951

FIG. 1 shows a configuration of one cell of a general image sensor.
As shown in FIG. 1, one cell (pixel) constituting an image sensor includes an N-type well 2 formed in a predetermined region of a P-type substrate 1 and an upper peripheral edge of the N-type well 2 for element isolation. The field oxide film 3 formed by the LOCOS (Local Oxidation of Silicon) method formed in the region, the high-concentration N-type region 4 for electrical connection with the N-type well 2, and the field oxide film 3 The formed interlayer insulating film 5, the wiring 6 formed through the interlayer insulating film 5 and connected to the high-concentration N-type region 4, and the interlayer insulating film 5 and the wiring 6 are formed on the upper layer to protect the element. The protective film 7 is provided. In the cell having the above configuration, one photodiode is formed by the P-type substrate 1 and the N-type well 2, and a depletion layer 8 is generated near the interface between the P-type substrate 1 and the N-type well 2. When incident light 9 is incident, carriers 10 (electron-hole pairs) are generated by the light absorbed inside the cell, and the carriers 10 generated mainly in the depletion layer 8 are respectively converted into P-type regions and N-type regions. By moving to the mold region, a current is generated and photoelectric conversion is performed.

  Generally, when light is transmitted through a transmissive film such as the protective film 7, the light transmission intensity varies depending on the film thickness of the protective film 7 and the wavelength of light. However, in the conventional image sensor, since cells having the same structure are used and transmitted through the protective film 7 and the like having the same film thickness and the same film quality, light having different wavelengths is detected for each of R, G, and B. , G, and B did not necessarily have the optimal transmission intensity for light of different wavelengths. In other words, the thickness and quality of the transmissive film such as the protective film 7 are not suitable for light having different wavelengths for R, G, and B. As a result, incident R, G, and B light with different wavelengths did not efficiently generate carriers, and incident light could not be efficiently photoelectrically converted.

  For example, in Patent Document 1, a protective film whose thickness is changed stepwise and continuously is used for one light receiving element in order to avoid interference of light in the protective film. In addition, the entire surface of the light receiving element did not function efficiently, and the photoelectric conversion efficiency was not good. In particular, with the widespread use of digital cameras and the like, there is a need for higher resolution image sensors, that is, image sensors with a high number of pixels. To increase the number of pixels without changing the overall size. The area per cell must be reduced, and even if the cell area is small, a cell having high photoelectric efficiency is required.

  The present invention has been made in view of the above problems, and an object of the present invention is to provide a semiconductor device having a high photoelectric efficiency by increasing the number of carriers generated even when light of R, G, and B has different wavelengths. To do.

A semiconductor device according to a first invention for solving the above-mentioned problems is as follows.
In a semiconductor device having a plurality of element portions arranged in a plane and performing photoelectric conversion of incident light, and a protective film protecting the surface of the element portion,
The protective film is formed to have a different thickness according to the wavelength of light to be subjected to photoelectric conversion so that the incident intensity of light to each of the element portions is maximized.

A semiconductor device according to a second invention for solving the above-mentioned problem is as follows.
In the semiconductor device according to the first invention,
The protective film is formed to have a different thickness by etching a single protective film.

A semiconductor device according to a third invention for solving the above-mentioned problem is as follows.
In the semiconductor device according to the first invention,
The protective film is formed by a single protective film or a plurality of stacked protective films, each having a different thickness.

A semiconductor device according to a fourth invention for solving the above-mentioned problems is as follows.
In the semiconductor device according to any one of the first to third inventions,
When the wavelength λ of the light for performing the photoelectric conversion, the refractive index of the protective film is n, and m is an arbitrary integer,
According to the wavelength of light for photoelectric conversion, the thickness t of the protective film is t = [λ / (2n)] · m, respectively.

A semiconductor device according to a fifth invention for solving the above-mentioned problem is as follows.
In the semiconductor device according to any one of the first to third inventions,
When the wavelength of the light for performing the photoelectric conversion is at least a blue, green, and red wavelength range of visible light, and the protective film is a silicon nitride film having a refractive index of 2.05,
The thickness of the protective film with respect to the blue wavelength range of visible light is in the range of 5250 mm to 5550 mm, preferably 5400 mm, and the thickness of the protective film with respect to the green wavelength range of visible light is 6300 mm to 6700 mm. The thickness of the protective film with respect to the red wavelength region of visible light is 8150 mm or more and 8650 mm or less, preferably 8400 mm.

A semiconductor device according to a sixth invention for solving the above-mentioned problem is as follows.
In a semiconductor device having a plurality of element portions arranged in a plane and performing photoelectric conversion of incident light, and a protective film protecting the surface of the element portion,
The protective film has a different refractive index according to the wavelength of light for photoelectric conversion so that the incident intensity of light to each of the element portions is maximized.

A semiconductor device according to a seventh invention for solving the above-mentioned problem is as follows.
In the semiconductor device according to the sixth invention,
When the wavelength λ of the light for performing the photoelectric conversion, the thickness of the protective film is t, and m is an arbitrary integer,
The protective film has a refractive index n of n = [λ / (2t)] · m depending on the wavelength of light for photoelectric conversion.

A semiconductor device according to an eighth invention for solving the above-mentioned problems is as follows.
In the semiconductor device according to the sixth invention,
The wavelength of the light for performing the photoelectric conversion is at least a blue, green, red wavelength range of visible light,
When the thickness of the protective film is 5000 mm,
The refractive index of the protective film with respect to the blue wavelength range of visible light is set to 1.71 or more and 1.85 or less, preferably 1.78, and the refractive index of the protective film with respect to the green wavelength range of visible light is set to 1.78. 1.52 or more and 1.68 or less, preferably 1.60, and the refractive index of the protective film with respect to the red wavelength region of visible light is 1.94 or more and 2.18 or less, preferably 2 .06,
When the thickness of the protective film is 6000 mm,
The refractive index of the protective film with respect to the blue wavelength range of visible light is 1.79 to 1.91, preferably 1.85, and the refractive index of the protective film with respect to the green wavelength range of visible light is The refractive index of the protective film in the range of 1.70 or more and 1.86 or less, preferably 1.78, or the red wavelength region of visible light is 1.63 or more and 1.83 or less, preferably 1 .73.

  According to the present invention, since the protective films having different optimum film thicknesses and film qualities are transmitted with respect to light having different wavelengths, the number of carriers generated in each element portion by light having different wavelengths is increased. The incident light can be photoelectrically converted with high efficiency, and as a result, the detection sensitivity can be improved.

The semiconductor device according to the present invention performs photoelectric conversion in each cell constituting the image sensor so that light of each wavelength is transmitted with the maximum transmission intensity with respect to incident light of different wavelengths. The film thickness and film quality of the protective film and the like are optimized so as to enter the element portion with the maximum incident intensity.
Hereinafter, an embodiment of a semiconductor device according to the present invention will be described with reference to FIGS.

The semiconductor device according to the present invention has a basic configuration equivalent to that of the image sensor cell shown in FIG.
That is, as one cell (pixel) constituting the image sensor, the N-type well 2 formed in a predetermined region of the P-type substrate 1 and the upper peripheral portion of the N-type well 2 for element separation are formed. Field oxide film 3, high-concentration N-type region 4 that is electrically connected to N-type well 2, interlayer insulating film 5 formed on field oxide film 3, and interlayer insulating film 5 are formed. A wiring 6 connected to the high-concentration N-type region 4, an interlayer insulating film 5, and a protective film 7 for protecting the element are formed on the wiring 6. Note that the P-type and the N-type are not limited to the above combinations, and may be reversed.

Here, the process conditions of the cell will be described. The N-type well 2 is formed by ion-implanting phosphorus (P) into the P-type substrate 1 and then diffusing and activating it by a subsequent thermal diffusion process. 10 ¹² / cm ² . When the depth of the N-type well 2 is set to 1 μm by controlling the thermal diffusion process, the impurity concentration in the N-type well 2 is 2 × 10 ¹⁶ / cm ³ . When the depth of the N-type well 2 is 2 μm, the impurity concentration in the N-type well 2 is 1 × 10 ¹⁶ / cm ³ .

As the protective film 7, an insulating film such as a silicon oxide film (SiO ₂ ), a silicon nitride oxide film (SiON), or a silicon nitride film (Si ₃ N ₄ ) is used, and is formed using a plasma CVD apparatus.
In the case of using a silicon oxide film, two kinds of process conditions are used, ie, high frequency and low frequency as electromagnetic waves for plasma generation, and 0.62 kW for high frequency electromagnetic waves and 0.38 kW for low frequency electromagnetic waves. is doing. The pressure is 1.9 Torr, the substrate temperature is 400 ° C., and 1.8 lm / min of ethyl silicate (TEOS; tetraethoxysilane) and 4.0 slm of oxygen (O ₂ ) are supplied as raw materials to form a film. The process time is set according to the film thickness. The refractive index of the silicon oxide film formed by this process is 1.46 ± 0.01. “Slm” is a unit expressed in liters per minute at 1 atm and 0 ° C.

In the case of using a silicon nitride oxide film, two kinds of process conditions are used, ie, high frequency and low frequency as electromagnetic waves for plasma generation. The high frequency electromagnetic waves are 0.4 kW, and the low frequency electromagnetic waves are 0.4 kW. Power is being applied. The pressure is 1.9Torr, the substrate temperature was 400 ° C., as a starting material, silane (SiH ₄₎ 0.2 slm, ammonia (NH ₃₎ 2.0slm, nitrous oxide (N ₂ O) 1. 4 slm and nitrogen (N ₂ ) are supplied at 5.0 slm, and the process time is set according to the film thickness to be formed. The refractive index of the silicon nitride oxide film formed by this process is 1.85 ± 0.03.

  When a silicon nitride film is used, RF (13.56 MHz) electromagnetic waves are used as process conditions for plasma generation, and electric power of 0.58 kW is applied. The pressure is 1.5 Torr, the substrate temperature is 350 ° C., 0.8 lm of silane and 2.0 slm of ammonia are supplied as raw materials, and the process time is set according to the film thickness to be formed. The refractive index of the silicon nitride film formed by this process is 2.05 ± 0.05.

  The cells having the above-described configuration are formed independently to detect the wavelengths R, G, and B of visible light, and a plurality of these cells are arranged on a plane to constitute an image sensor. Although not shown, a spectral member (for example, a color filter) that splits incident light into R, G, and B wavelengths is disposed above each cell. Light of a wavelength is incident on each of the R, G, and B cells.

  In the present embodiment, in each of the R, G, and B cells, the protective film 7 has an optimum film thickness so that the transmission intensity of light of each wavelength is maximized. Here, FIG. 2 shows a graph of a change in signal intensity when the thickness of the protective film is changed for light of each wavelength of R, G, and B, that is, a graph of a change in intensity correlated with the transmission intensity. The optimum film thickness for each wavelength will be described. In the graph of FIG. 2, a silicon nitride film is used as a protective film, and a refractive index of 2.05 is used. R, G, and B wavelengths have a center wavelength of R of 6900 mm and G of 5350cm, B uses 4450cm. The signal intensity is a plot of the relative change with the signal intensity when the thickness of the protective film is 0 (zero) as 1.

  In general, when the thickness of the permeable membrane is changed, the change in the intensity of light transmitted through the permeable membrane is strengthened each time the wavelength of light is shifted by half a wavelength due to the interference effect in the transmissive membrane (transmitted). The absorption of the film is minimized), and its intensity undergoes a periodic change represented by a cosine function. The period of change in intensity differs depending on the wavelength of light, and the intensity for each wavelength of R, G, and B changes as shown in FIG.

  Usually, in order to ensure the function as a protective film, a film thickness of at least 4000 mm, preferably 5000 mm or more is necessary, which is the lower limit of the protective film. In consideration of the stress of the protective film, in the case of the silicon nitride film, 15000 to 20000 mm (1.5 to 2.0 μm) is the upper limit value of the protective film.

  Therefore, when attention is paid to the signal intensity of the G-band light and the R-band light at the thickness of 5400 mm where the signal intensity of the B-band light becomes approximately 1 at a film thickness larger than 5000 mm, the G-band light is about 0.9, Light has a signal intensity of about 0.8. Similarly, when attention is paid to the signal intensity of the B-band light and R-band light at a thickness of 6500 mm where the signal intensity of the G-band light is approximately 1, the B-band light is approximately 1, whereas the R-band light is Focusing on the signal intensities of the B-band light and G-band light at a thickness of 8400 mm where the signal intensity of the R-band light is approximately 1, the signal intensity of the R-band light is about 0.7, The local light has a signal intensity of about 0.5. In this way, the signal intensity does not become substantially 1 for light of all color gamut wavelengths in one film thickness. From this, the film thickness is changed according to the wavelength of light. It turns out that is good.

  Therefore, when a silicon nitride film having a refractive index of 2.05 is used as the protective film, the protective film thickness is in the range of 5250 mm or more and 5550 mm or less (5400 mm ± 5 for the B cell, as shown in FIG. 3400), preferably 5400 mm, for G cells, 6300 mm or more and 6700 mm or less (6500 mm ± 3%), preferably 6500 mm, for R cells 8150 mm or more , 8650 mm or less (about 8400 mm ± 3%), preferably 8400 mm, the relative value of the signal intensity is 0.9 or more.

Next, a method for forming a protective film with an optimum film thickness in each cell will be described with reference to FIG. In FIG. 3, for simplicity of description, the element portions are denoted by reference numerals 11 _B , 11 _G , and 11 _R , and the protective film is denoted by reference numeral 11.

In this embodiment, in order to form the protective film with the optimum film thickness for the light in the wavelength range detected by each cell, first, after the formation of the element portions 11 _B , 11 _G , 11 _R , A protective film 12 is deposited with a thick film thickness. Protective film 12 of the large thickness, the maximum thickness used in the element portion _{11 B, 11 G, 11 R} , for example, referring to FIG. 2, a 8400Å of an optimal thickness T _R in the element portion 11 _R What is necessary is just to deposit (refer Fig.3 (a)).

Next, after masking this portion with a resist or the like so that the protective film 12 in the element portion 11 _R region is not etched, the protective film 12 in the region of the other element portions 11 _B and 11 _G is etched by dry etching or the like. To reduce the film thickness. At this time, the film thickness to reduce the optimum film thickness in the element unit 11 _G, for example, referring to FIG. 2, so that the 6500Å an optimum thickness T _G in the element unit 11 _G, etched ( (Refer FIG.3 (b)).

Finally, these portions are masked so that the protective film 12 in the element portions 11 _R and 11 _G regions is not etched, and then the protective film 12 in the element portion 11 _B region is etched by dry etching or the like to obtain a film thickness. Reduce. At this time, the film thickness to reduce the optimum thickness to the element portion 11 _B, for example, referring to FIG. 2, so that the 5400Å an optimum thickness T _B to the element portion 11 _B, etched ( (Refer FIG.3 (c)). The procedure shown in FIG. 3B and the procedure shown in FIG. 3C may be reversed.

In this manner, a protective film having an optimum film thickness is formed corresponding to each element unit 11 _B , 11 _G , 11 _R that detects different wavelength ranges. In the cell having such a configuration, when incident light is incident, the influence of the interference of the protective film is reduced as much as possible, and the incident light is generated by a depletion layer generated near the interface between the P-type substrate and the N-type well. A large amount will be reached, and therefore more carriers will be generated in the depletion layer. As a result, it is possible to achieve high-efficiency photoelectric conversion with respect to incident light and improve detection sensitivity.

  In this embodiment, a single protective film is formed in advance, and the protective film of each cell is formed to an optimum thickness by reducing the thickness of the single protective film. The protective film of each cell may be formed in advance, and the protective film of each cell may be formed to an optimum film thickness by reducing the thickness of one or both of the multilayer protective films. .

As in the first embodiment, the semiconductor device according to the present embodiment is such that the protective film has a different optimum film thickness in each cell. However, in this embodiment, a method for forming a protective film having a different film thickness is different from that in Embodiment 1, and this forming method will be described with reference to FIG. In FIG. 4, the element portions are represented by reference numerals 11 _B , 11 _G , and 11 _R and the protective film is represented by reference numerals 13 to 15 in order to simplify the description.

In the present embodiment, in order to form the protective film with the optimum film thickness for the light in the wavelength band detected by each cell, first, after the formation of the element portions 11 _B , 11 _G , 11 _R , A protective film 13 is deposited on the entire surface with a predetermined film thickness T ₁ . The protective film 13 having the predetermined film thickness T ₁ may be deposited to a film thickness used in the element portion 11 _B , for example, an optimum film thickness of 5400 mm in the element portion 11 _B (see FIG. 4A). ).

Next, the protective film 14 is laminated on the protective film 13 with a predetermined thickness T ₂ in a region other than the element portion 11 _B , that is, in the regions of the element portion 11 _G and the element portion 11 _R. Here, the sum of the film thickness T ₁ of the protective film 13 and the film thickness T ₂ of the protective film 14 is the film thickness used in the element portion 11 _G , for example, the optimum film thickness for the element portion 11 _G with reference to FIG. The protective film 14 may be laminated so as to be 6500 mm (see FIG. 4B).

Finally, the protective film 15 is laminated on the protective film 14 with a predetermined film thickness T ₃ only in the region other than the element portion 11 _B and the element portion 11 _G , that is, the region of the element portion 11 _R. Here, the sum of the film thickness T ₁ of the protective film 13, the film thickness T ₂ of the protective film 14 and the film thickness T ₃ of the protective film 15 is the film thickness used in the element portion 11 _R , for example, referring to FIG. The protective film 15 may be stacked so as to have an optimum film thickness of 8400 mm for the element portion 11 _R (see FIG. 4C).

In this manner, as in the first embodiment, a protective film having an optimum film thickness is formed corresponding to each element unit 11 _B , 11 _G , 11 _R that detects different wavelength regions. In the cell having such a configuration, when incident light is incident, the influence of the interference of the protective film is reduced as much as possible, and the incident light is generated by a depletion layer generated near the interface between the P-type substrate and the N-type well. Therefore, more carriers are generated and more carriers are generated in the vicinity of the depletion layer. As a result, it is possible to achieve high-efficiency photoelectric conversion with respect to incident light and improve detection sensitivity.

Unlike the first and second embodiments, the semiconductor device of this example is formed not to have a protective film thickness but to have an optimum film quality of the protective film for light in the wavelength range detected by each cell. Is. This forming method will be described with reference to FIG. In FIG. 5, the element portions are represented by reference numerals 11 _B , 11 _G , and 11 _R and the protective film is represented by reference numeral 16 in order to simplify the description.

In this embodiment, in order to form the film quality of the protective film with respect to the light in the wavelength band detected by each cell, the film thickness of the protective film is optimized, so that a predetermined film thickness is formed after the formation of the element portions 11 _B , 11 _G and 11 _R After the protective film 16 is deposited, a predetermined amount of ions of a predetermined type are implanted into the protective film 16 in accordance with the element portions 11 _B , 11 _G , and 11 _R , so that the film quality of the protective film 16, for example, the refractive index The optical characteristics such as these are optimized. In the case of the present embodiment, there is no order of the element portions for ion implantation, and any order may be used. However, here, as an example, the description is given in the order of the element portions 11 _B , 11 _G , 11 _R. Do.

First, this portion is masked with a resist 17 so that the protective film 16 in the element portions 11 _G and 11 _R regions is not ion-implanted, and then a predetermined amount and a predetermined type of protective film 16 in the region of the element portion 11 _B are formed. Ions 18 are implanted. At this time, as the ion species, for example, if the protective film 16 is a silicon oxide film (SiO ₂ ), silicon (Si) or oxygen (O) is used, and if the protective film 16 is a silicon nitride oxide film (SiON). If silicon (Si), oxygen (O) or nitrogen (N) is used and the protective film 16 is a silicon nitride film (Si ₃ N ₄ ), silicon (Si) or nitrogen (N) is used. Further, the injection amount is a desired optical characteristic, that is, an injection amount that provides a film quality having a refractive index characteristic that maximizes the signal intensity (transmission intensity) of the B-band light in the protective film 16 having a predetermined film thickness. (See FIG. 5A).

Next, the resist 17 is removed, and this portion is masked with a resist 19 so that the protective film 16 in the region of the element portions 11 _B and 11 _R is not ion-implanted, and then the protective film 16 in the region of the element portion 11 _G is formed. A predetermined amount of ions 20 of a predetermined type are implanted. Also at this time, as the ion species, for example, if the protective film 16 is a silicon oxide film, silicon or oxygen is used. If the protective film 16 is a silicon nitride oxide film, silicon, oxygen, or nitrogen is used, and the protective film 16 is used. If is a silicon nitride film, silicon or nitrogen is used. Also, as the injection amount, the desired optical characteristic, that is, the injection amount that provides a film quality having a refractive index characteristic that maximizes the signal intensity (transmission intensity) of the G light in the protective film 16 having a predetermined film thickness. (See FIG. 5B).

Finally, the resist 19 is removed, and this portion is masked with a resist 21 so that the protective film 16 in the region of the element portions 11 _B and 11 _G is not ion-implanted, and then the protective film 16 in the region of the element portion 11 _R is formed. A predetermined amount of ions 22 of a predetermined type are implanted. Also at this time, as the ion species, for example, if the protective film 16 is a silicon oxide film, silicon or oxygen is used. If the protective film 16 is a silicon nitride oxide film, silicon, oxygen, or nitrogen is used, and the protective film 16 is used. If is a silicon nitride film, silicon or nitrogen is used. Also, as the injection amount, the desired optical characteristic, that is, the injection amount that provides a film quality having a refractive index characteristic that maximizes the signal intensity (transmission intensity) of the R region light in the protective film 16 having a predetermined film thickness. (See FIG. 5C).

Then, removing the resist 21, as shown in FIG. 5 (d), depending on the element unit 11 _B, 11 _G, 11 _R for detecting the respective wavelength regions A _B optimum optical properties, A _G, A A protective film 16 having _R is formed. In the cell having such a configuration, when incident light is incident, the influence of the interference of the protective film is reduced as much as possible, and the incident light is generated in the depletion layer generated near the interface between the P-type substrate and the N-type well. As a result, more carriers are generated in the depletion layer. As a result, it is possible to achieve high-efficiency photoelectric conversion with respect to incident light and improve detection sensitivity.

  In general, even if the film thickness of the transmissive film is constant, if the refractive index of the transmissive film is changed, the change in the intensity of the light transmitted through the transmissive film is caused by the effect of interference in the transmissive film. Each time it deviates by half a wavelength, it strengthens and its intensity changes periodically represented by a cosine function. The period of change in intensity differs depending on the wavelength of light, and the intensity for each wavelength of R, G, and B changes as shown in FIGS. In FIGS. 6 and 7, the relative change is illustrated with the maximum intensity being 1.

  Specifically, the relative value of the signal intensity is proportional to COS (2π × t / (L / 2)), where t is the thickness of the protective film and L is the wavelength in the light film. When the refractive index of the protective film is n and the wavelength of light in the air is λ, L = λ / n, and the relative value of the signal intensity is proportional to COS (2π × 2nt / λ). When (2nt / λ) becomes an integer, the relative value of the signal intensity takes the maximum value. When m is an arbitrary integer, the refractive index n of the protective film is n = [λ / (2t)].・ It is calculated by m. Therefore, a desired refractive index characteristic may be obtained using this equation in accordance with the wavelength of light for photoelectric conversion. In the above calculation process, when the film thickness t of the protective film is obtained, the film thickness t can be obtained by t = [λ / (2n)] · m. Thus, a desired film thickness may be obtained according to the wavelength of light for performing photoelectric conversion.

  When the wavelength of light to be subjected to photoelectric conversion is set to the blue, green, and red wavelength ranges of visible light and the thickness of the protective film is set to 5000 mm, as shown in FIG. The refractive index of the protective film with respect to the central wavelength 4450 mm is set to 1.71 or more and 1.85 or less, preferably 1.78, and the refractive index of the protective film with respect to the green wavelength region of visible light (central wavelength 5350 mm) is set. 1.52 or more and 1.68 or less, preferably 1.60, and the refractive index of the protective film with respect to the red wavelength region of visible light (center wavelength 6900 mm) is 1.94 or more and 2.18 or less. If the range, preferably 2.06, the relative value of the signal intensity is 0.9 or more.

  When the thickness of the protective film is 6000 mm, as shown in FIG. 7, the refractive index of the protective film with respect to the blue wavelength region of visible light (center wavelength 4450 mm) is 1.79 or more and 1.91. The following range, preferably 1.85, and the refractive index of the protective film with respect to the green wavelength region of visible light (center wavelength 5350 mm) is 1.70 or more and 1.86 or less, preferably 1.78, If the refractive index of the protective film with respect to the red wavelength region of visible light (center wavelength 6900 mm) is in the range of 1.63 or more and 1.83 or less, preferably 1.73, the relative value of the signal intensity is 0.7. 9 or more.

  In this embodiment, ion implantation is performed on the protective film so that the film quality of the protective film is optimum for each cell. However, the supply of raw materials is performed under the above-described protective film process conditions in the plasma CVD apparatus. By changing the ratio or the like, a protective film having an optimum film quality for each cell may be formed at the time of forming the protective film.

It is a figure which shows the structure of one cell of an image sensor. It is a graph which shows the change of signal intensity when the thickness of a protective film is changed with respect to the light of each wavelength of R, G, and B. It is a figure explaining an example (Example 1) of the formation method of the semiconductor device which concerns on this invention. It is a figure explaining other examples (Example 2) of the formation method of the semiconductor device which concerns on this invention. It is a figure explaining other examples (Example 3) of the formation method of the semiconductor device which concerns on this invention. It is a graph which shows the change of signal intensity when changing the refractive index of a protective film (film thickness 5000mm) with respect to the light of each wavelength of R, G, and B. It is a graph which shows the change of signal intensity when changing the refractive index of a protective film (film thickness of 6000 mm) with respect to the light of each wavelength of R, G, and B.

Explanation of symbols

1 P-type substrate 2 N-type well 3 Field oxide film 4 High-concentration N-type region 5 Interlayer insulating film 6 Wiring 7, 12, 13, 14, 15, 16 Protective film 8 Depletion layer 9 Incident light 10 Carrier 11 _R , 11 _G , 11 _B element portion 17, 19, 21 resist 18, 20, 22 ion

Claims (8)

In a semiconductor device having a plurality of element portions arranged in a plane and performing photoelectric conversion of incident light, and a protective film protecting the surface of the element portion,
2. A semiconductor device according to claim 1, wherein the protective film is formed to have a different thickness in accordance with a wavelength of light for photoelectric conversion so that an incident intensity of light to each of the element portions is maximized.   The semiconductor device according to claim 1, wherein the protective film is formed to have a different thickness by etching each of the protective films of one layer.   2. The semiconductor device according to claim 1, wherein the protective film is formed to have a different thickness by a single protective film or a plurality of stacked protective films. When the wavelength λ of the light for performing the photoelectric conversion, the refractive index of the protective film is n, and m is an arbitrary integer,
4. The film thickness t of the protective film is set to t = [λ / (2n)] · m, respectively, according to the wavelength of light to be subjected to photoelectric conversion. A semiconductor device according to 1. The wavelength of the light for performing the photoelectric conversion is at least a blue, green, red wavelength range of visible light,
When the protective film is a silicon nitride film having a refractive index of 2.05,
The thickness of the protective film with respect to the blue wavelength range of visible light is in the range of 5250 mm to 5550 mm, preferably 5400 mm, and the thickness of the protective film with respect to the green wavelength range of visible light is 6300 mm to 6700 mm. The thickness of the protective film with respect to the red wavelength region of visible light is 8150 mm or more and 8650 mm or less, preferably 8400 mm. The semiconductor device according to any one of the above. In a semiconductor device having a plurality of element portions arranged in a plane and performing photoelectric conversion of incident light, and a protective film protecting the surface of the element portion,
A semiconductor device characterized in that the protective film has a different refractive index according to the wavelength of light for photoelectric conversion so that the incident intensity of light to each of the element portions is maximized. When the wavelength λ of the light for performing the photoelectric conversion, the thickness of the protective film is t, and m is an arbitrary integer,
7. The semiconductor device according to claim 6, wherein the refractive index n of the protective film is set to n = [λ / (2t)] · m, respectively, according to the wavelength of light for performing photoelectric conversion. The wavelength of the light for performing the photoelectric conversion is at least a blue, green, red wavelength range of visible light,
When the thickness of the protective film is 5000 mm,
The refractive index of the protective film with respect to the blue wavelength range of visible light is set to 1.71 or more and 1.85 or less, preferably 1.78, and the refractive index of the protective film with respect to the green wavelength range of visible light is set to 1.78. 1.52 or more and 1.68 or less, preferably 1.60, and the refractive index of the protective film with respect to the red wavelength region of visible light is 1.94 or more and 2.18 or less, preferably 2 .06,
When the thickness of the protective film is 6000 mm,
The refractive index of the protective film with respect to the blue wavelength range of visible light is 1.79 to 1.91, preferably 1.85, and the refractive index of the protective film with respect to the green wavelength range of visible light is The refractive index of the protective film in the range of 1.70 or more and 1.86 or less, preferably 1.78, or the red wavelength region of visible light is 1.63 or more and 1.83 or less, preferably 1 The semiconductor device according to claim 6, wherein the semiconductor device is .73.

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