Solid-state imaging device

Abstract

The solid-state imaging device (1) includes: a semiconductor substrate (20) having a main surface (20a) provided with a plurality of light-sensing regions (3); and an insulating film (30) provided on the main surface (20a) of the semiconductor substrate (20). A plurality of concavities and convexities (R) are formed on the surface (main surface (30b)) of the insulating film (30) on the side opposite to the main surface (20a) of the semiconductor substrate (20), and in the light-sensing region (3), there are height differences of the plurality of concavities and convexities (R).

Description

Technical Field

[0001] The present invention relates to a solid-state imaging device. Background Art

[0002] In a solid-state imaging device that constitutes an image sensor such as a CMOS, there is, for example, a device having sensitivity in a wide wavelength range from the ultraviolet region to the near-infrared region. In a solid-state imaging device having sensitivity in the ultraviolet region, in order to suppress deterioration of elements caused by ultraviolet light, an insulating film such as a BPSG (Boro-phospho silicate glass) film is formed as a protective film in a light-sensitive region. In order for the insulating film to fully function as a protective film, a thickness of about 1 μm is required. In this case, it is considered that interference of incident light occurs between the upper surface of the insulating film and the main surface of the semiconductor substrate, and the spectral sensitivity becomes uneven with respect to the wavelength of the incident light. Regarding such a technical problem, in the solid-state imaging element described in, for example, Patent Document 1, by forming a base pattern formed of periodic convex portions on the surface of the light-receiving element, one or more irregularities having a height difference of about 1 wavelength or more of the incident light are formed on the surface of the insulating film.

[0003] Prior Art Documents

[0004] Patent Documents

[0005] Patent Document 1: Japanese Patent Laid-Open No. 6-125068 Summary of the Invention

[0006] Problems to be Solved by the Invention

[0007] In the solid-state imaging element described in the above Patent Document 1, by forming irregularities on the surface of the insulating film, interference of incident light in the insulating film is reduced, and unevenness of spectral sensitivity with respect to the wavelength of the incident light is reduced. However, in this conventional solid-state imaging element, the irregularity pattern appearing on the surface of the insulating film is uniform, and thus the effect of reducing interference of incident light in the insulating film is limited. Therefore, in order to effectively reduce unevenness of spectral sensitivity in a wide wavelength range including, for example, the ultraviolet region to the near-infrared region, further improvements are needed.

[0008] The present invention has been completed to solve the above problems, and an object thereof is to provide a solid-state imaging device capable of effectively reducing unevenness of spectral sensitivity in a wide wavelength range.

[0009] Means for Solving the Problems

[0010] A solid-state imaging device according to an aspect of the present invention includes: a semiconductor substrate having a main surface provided with a plurality of light-sensing regions; and an insulating film provided on the main surface of the semiconductor substrate. On the surface of the insulating film opposite to the main surface of the semiconductor substrate, a plurality of irregularities are formed, and in the light-sensing regions, there are height differences of the plurality of irregularities.

[0011] In this solid-state imaging device, in the light-sensing regions, there are a plurality of height differences among the plurality of irregularities provided on the insulating film. Due to the existence of such a plurality of height differences, when incident light enters the light-sensing regions, a plurality of interferences with different optical path lengths are generated within the insulating film. As a result, the uneven periods of the spectral sensitivity with respect to the wavelength of the incident light cancel each other out, and unevenness in sensitivity within a wide wavelength region including, for example, the ultraviolet region to the near-infrared region can be reduced.

[0012] In the light-sensing regions, when measuring the height differences of the irregularities at intervals of 0.01 μm, the maximum value of the appearance frequency of the surface height of the insulating film based on the topmost part of the insulating film may also be 5% or less. In this case, there are various height differences of the irregularities in the insulating film, and the effect of canceling out the uneven periods of the spectral sensitivity with respect to the wavelength of the incident light is improved. Therefore, unevenness in sensitivity within a wide wavelength region including, for example, the ultraviolet region to the near-infrared region can be reduced more effectively.

[0013] In the light-sensing regions, when measuring the height differences of the irregularities at intervals of 0.01 μm, the standard deviation of the appearance frequency of the surface height of the insulating film based on the topmost part of the insulating film may also be 1% or less. In this case, there are various height differences of the irregularities in the insulating film, and the effect of canceling out the uneven periods of the spectral sensitivity with respect to the wavelength of the incident light is improved. Therefore, unevenness in sensitivity within a wide wavelength region including, for example, the ultraviolet region to the near-infrared region can be reduced more effectively.

[0014] In the light-sensing regions, the height difference between the topmost part and the bottommost part of the irregularities may also be 0.5 μm or more and 0.9 μm or less. By making the height difference 0.5 μm or more, the optical path length difference of the incident light within the insulating film becomes sufficiently large, and thus the effect of canceling out the uneven periods of the spectral sensitivity with respect to the wavelength of the incident light is further improved sufficiently. In addition, since the height difference is 0.9 μm or less, the depth of the concave portion is not excessive, and a change in the absolute value of the spectral sensitivity caused by refraction and reflection of the incident light on the surface of the insulating film can be suppressed.

[0015] The main surface of the semiconductor substrate may also be a flat surface. In this case, the shape of the main surface of the semiconductor substrate is simplified, and thus cost reduction of the solid-state imaging device can be achieved.

[0016] Effects of the Invention

[0017] According to the present invention, unevenness in spectroscopic sensitivity can be effectively reduced within a wide wavelength region. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 is a plan view showing a schematic structure of a solid-state imaging device.

[0019] Figure 2 is Figure 1 a sectional view taken along line II-II.

[0020] Figure 3 is a plan view showing an uneven pattern of an insulating film.

[0021] Figure 4 is Figure 3 an enlarged view of a main part.

[0022] Figure 5 (a) of Figure 4 is a sectional view taken along line C1-C2, and (b) of Figure 4 is a sectional view taken along line C1-C3.

[0023] Figure 6 is a schematic sectional view showing a formation state of unevenness of an insulating layer.

[0024] Figure 7 is a schematic sectional view showing a relationship between heat treatment and an interval of unevenness.

[0025] Figure 8 is a schematic sectional view showing a relationship between heat treatment and an interval of unevenness.

[0026] Figure 9 is showing Figure 4 a coordinate diagram of a height difference profile of unevenness of a pattern shown in.

[0027] Figure 10 is showing Figure 4 a coordinate diagram of an appearance frequency of a surface height of an insulating film of a pattern shown in.

[0028] Figure 11 is showing a solid-state imaging device having Figure 4 a coordinate diagram of spectroscopic sensitivity characteristics in an ultraviolet region to a near-infrared region of unevenness of a pattern shown in.

[0029] Figure 12 is a coordinate diagram showing an enlarged view of spectroscopic sensitivity characteristics in an ultraviolet region of a solid-state imaging device having Figure 4 unevenness of a pattern shown in.

[0030] Figure 13 is a plan view showing an uneven pattern of an insulating film of a comparative example.

[0031] Figure 14 is Figure 13 the enlarged view of the main part of

[0032] Figure 15 is Figure 14 the cross-sectional view of line D1-D2 of

[0033] Figure 16 is a coordinate diagram showing Figure 14 the height difference profile of the unevenness of the pattern shown

[0034] Figure 17 is a coordinate diagram showing Figure 14 the frequency of occurrence of the surface height of the insulating film of the pattern shown

[0035] Figure 18 is a coordinate diagram showing the solid-state imaging device having Figure 14 the spectral sensitivity characteristics in the ultraviolet to near-infrared regions of the unevenness of the pattern shown

[0036] Figure 19 is a coordinate diagram that magnifies and shows Figure 4 the spectral sensitivity characteristics in the ultraviolet region of the solid-state imaging device having the unevenness of the pattern shown

[0037] Figure 20 is a coordinate diagram showing the spectral sensitivity characteristics in the ultraviolet to near-infrared regions of the solid-state imaging device without unevenness of the insulating film

[0038] Figure 21 is a coordinate diagram that magnifies and shows the spectral sensitivity characteristics in the ultraviolet region of the solid-state imaging device without unevenness of the insulating film

[0039] Figure 22 is a coordinate diagram showing the relationship between the maximum value of the frequency of occurrence of the surface height of the insulating film and the peak and valley of the spectral sensitivity

[0040] Figure 23 is a coordinate diagram showing the state of the peak and valley displacement of the spectral sensitivity

[0041] Figure 24 is a coordinate diagram showing the relationship between the standard deviation of the frequency of occurrence of the surface height of the insulating film and the peak and valley of the spectral sensitivity

[0042] Figure 25 is a diagram showing the state of the peak and valley of the spectral sensitivity when the height difference between the top and bottom of the unevenness changes

[0043] Figure 26 is a schematic cross-sectional view showing the change of the unevenness before and after heat treatment

[0044] Figure 27It is a partial enlarged view showing a modified example of the concavo-convex pattern of the insulating film.

[0045] Figure 28 It is a partial enlarged view showing another modified example of the concavo-convex pattern of the insulating film.

[0046] Figure 29 It is a partial enlarged view showing another modified example of the concavo-convex pattern of the insulating film.

[0047] Figure 30 It is a partial enlarged view showing another modified example of the concavo-convex pattern of the insulating film.

[0048] Figure 31 It is a partial enlarged view showing another modified example of the concavo-convex pattern of the insulating film. Detailed Embodiment

[0049] Hereinafter, a preferred embodiment of a solid-state imaging device according to an aspect of the present invention will be described in detail with reference to the accompanying drawings.

[0050] [Schematic Structure of Solid-State Imaging Device]

[0051] Figure 1 It is a plan view showing the schematic structure of the solid-state imaging device. In addition, Figure 2 is Figure 1 a cross-sectional view taken along line II-II. The solid-state imaging device 1 includes a plurality of light-sensing regions 3, a plurality of transfer gate portions 5, a plurality of antiblooming gate portions 7, a plurality of antiblooming drain portions 9, and a shift register portion 11 as shown in Figure 1 . These structures are formed on the main surface 20a of the semiconductor substrate 20. The solid-state imaging device 1 of the present embodiment is, for example, a surface-incident type image sensor, and one light-sensing region 3 constitutes one pixel.

[0052] Each light-sensing region 3 senses the incidence of light and generates charges corresponding to the intensity of the incident light. That is, the light-sensing region 3 functions as a photoelectric conversion portion. In the present embodiment, the planar shape of the light-sensing region 3 is a rectangular shape formed by two long sides and two short sides. The plurality of light-sensing regions 3 are arranged in a second direction (a direction along the short side direction of the light-sensing region 3) orthogonal to the first direction along the long side direction of the light-sensing region 3 and are arranged in an array in one-dimensional direction. The shape of the light-sensing region 3 is not limited to the above-described substantially rectangular shape, and various shapes can be adopted.

[0053] Each transfer gate portion 5 corresponds to the light sensing region 3 respectively and is disposed on one short side of the planar shape of the light sensing region 3. That is, a plurality of transfer gate portions 5 are arranged in the second direction on one short side of the planar shape of the light sensing region 3. The transfer gate portion 5 acquires the charges generated in the light sensing region 3 and transfers the acquired charges as signal charges in the first direction. An isolation region 13 is disposed between adjacent transfer gate portions 5. The isolation region 13 realizes electrical separation between the transfer gate portions 5.

[0054] Each anti-blooming gate electrode portion 7 corresponds to the light sensing region 3 respectively and is disposed on the other short side of the planar shape of the light sensing region 3. That is, a plurality of anti-blooming gate electrode portions 7 are arranged in the second direction on the other short side of the planar shape of the light sensing region 3. The anti-blooming gate electrode portion 7 acquires the charges generated in the light sensing region 3 and transfers the acquired charges as useless charges in the first direction. The above isolation region 13 is disposed between adjacent anti-blooming gate electrode portions 7. The isolation region 13 realizes electrical separation between the anti-blooming gate electrode portions 7.

[0055] Each anti-blooming photo-drain portion 9 corresponds to a plurality of anti-blooming gate electrode portions 7 respectively and is disposed adjacent to the anti-blooming gate electrode portion 7 in the first direction. That is, a plurality of anti-blooming photo-drain portions 9 are arranged in the second direction on the other short side of the planar shape of the light sensing region 3. The anti-blooming photo-drain portion 9 is connected to a prescribed fixed potential and discharges the useless charges transferred from the corresponding anti-blooming gate electrode portion 7.

[0056] The shift register portion 11 corresponds to a plurality of transfer gate portions 5 respectively and is disposed adjacent to the transfer gate portion 5 in the first direction. That is, a plurality of shift register portions 11 are arranged in the second direction on the other short side of the planar shape of the light sensing region 3. The shift register portion 11 receives the signal charges transferred from the transfer gate portions 5 respectively, transfers them in the second direction and sequentially outputs them to the readout amplifier portion 15. The signal charges output from the shift register portion 11 are converted into voltages by the readout amplifier portion 15 and output to the outside of the solid-state imaging device 1 as voltages of each light sensing region 3 arranged in the second direction.

[0057] A light-shielding film LS is disposed in a region other than the plurality of light sensing regions 3. In the present embodiment, the light-shielding film LS is disposed so as to cover the transfer gate portion 5, the anti-blooming gate electrode portion 7, the anti-blooming photo-drain portion 9, and the shift register portion 11. The light-shielding film LS can prevent light from entering these regions and prevent the generation of useless charges due to the light incident on these regions.

[0058] In the light sensing region 3, as Figure 2As shown, an insulating film 30 is provided on the main surface 20a of the semiconductor substrate 20. The semiconductor substrate 20 has a main surface 20a and a main surface 20b that face each other. In the present embodiment, both the main surface 20a and the main surface 20b are flat surfaces, and the main surface 20a serves as the light incident surface of the semiconductor substrate 20. The semiconductor substrate 20 is configured to include a p-type semiconductor region 21, a p-type semiconductor region 22, an n+-type semiconductor region 23, a p+-type semiconductor region 24, and an oxide film 25 from the main surface 20b side. In the present embodiment, the semiconductor substrate 20 is made of Si. When the semiconductor substrate 20 is made of Si, group 3 elements such as B are used as p-type impurities, and group 5 elements such as P and As are used as n-type impurities.

[0059] The oxide film 25 is, for example, a silicon oxide film. This oxide film 25 functions as a gate oxide film of a MOS transistor in the transfer gate portion 5. In addition, in the light sensing region 3, the oxide film 25 has the effect of preventing components from the insulating film 30 from invading the semiconductor substrate 20. For example, as described later, when the insulating film 30 is a BPSG film, the oxide film 25 prevents B (boron) or P (phosphorus) from the BPSG film from invading the semiconductor substrate 20.

[0060] In addition, when the oxide film 25 is provided on the semiconductor substrate 20, the surface of the oxide film 25 can be regarded as the main surface 20a of the semiconductor substrate 20. When the oxide film 25 is not provided on the semiconductor substrate 20, the surface of the p+-type semiconductor region 24 becomes the main surface 20a of the semiconductor substrate 20. The semiconductor regions constituting the semiconductor substrate 20 are not limited to Figure 2 the structure. For example, the p+-type semiconductor region 24 may not be provided, the n+-type semiconductor region 23 may be located on the p-type semiconductor region 22, and the oxide film 25 may be directly formed on the n+-type semiconductor region 23.

[0061] The insulating film 30 has a main surface 30a and a main surface 30b that face each other. The main surface 30a is the surface facing the main surface 20a side of the semiconductor substrate 20, and the main surface 30b is the surface facing the opposite side of the main surface 20a of the semiconductor substrate 20. The insulating film 30 can be formed by, for example, evaporation. The main surface 30a follows the shape of the main surface 20a of the semiconductor substrate 20 and becomes a flat surface. On the other hand, a plurality of irregularities R are formed on the main surface 30b. The irregularities R are formed into irregularities with a rectangular cross section by etching or mechanical polishing, and then a part of the irregularities with a rectangular cross section is made to flow by heat treatment, thereby becoming a smooth and continuous shape. The insulating film 30 is, for example, a BPSG (Boro-phospho silicate glass) film and also functions as an antireflection film (AR film).

[0062] The thickness of the insulating film 30 varies for each part according to the multiple unevennesses R, and is, for example, 0.5 μm to 3 μm. The lower limit value of the thickness of the insulating film 30 is a value determined in consideration of the function as a protective film, that is, sufficient ultraviolet light resistance is exhibited. In addition, the upper limit value of the thickness of the insulating film 30 is a value determined in consideration of process limitations (such as the ease of forming contact holes), etc.

[0063] [Detailed structure of unevennesses of insulating film]

[0064] Figure 3 is a plan view showing the uneven pattern of the insulating film. In addition, Figure 4 is an enlarged view of the main part thereof. Figure 3 shows the light sensing region 3 for three pixel amounts, Figure 1 in the directions shown, the first direction corresponds to the Y direction, the second direction corresponds to the X direction, Figure 2 and the thickness direction of the semiconductor substrate 20 shown corresponds to the Z direction. Figure 3 and Figure 4 show the region corresponding to the convex portion 31 of the unevenness R in solid color and the region corresponding to the concave portion 32 in dots. When the height position of the top 31a of the convex portion 31 is set to 1 and the height position of the bottom 32a of the concave portion 32 is set to 0, the region corresponding to the convex portion 31 is a region with a height position of 0.5 or more and 1 or less, and the region corresponding to the concave portion 32 is a region with a height position of 0 or more and less than 0.5.

[0065] As Figure 3 and Figure 4 show, in the light sensing region 3, on the main surface 30b side of the insulating film 30, a plurality of unevennesses R are formed by the main surface 30b of the insulating film 30 undulating in a sine wave shape. In the examples of Figure 3 and Figure 4 , the substantially square-shaped concave portions 32 are arranged in a matrix in the in-plane direction of the main surface 30b of the insulating film 30, and the other portions become the convex portions 31. For each of the X direction and the Y direction, one side of the concave portion 32 is about 3.0 μm, and the pitch between the concave portions 32, 32 is about 3.0 μm.

[0066] In the light sensing region 3, there are height differences of a plurality of unevennesses R. For example, when observing a cross section from the center C1 of one concave portion 32 to the centers C2 of two adjacent concave portions 32 in the Y direction (refer to Figure 4 ), as shown in (a) of Figure 5 , the thickness T1 of the insulating film 30 at the bottom 32a of the concave portion 32 is about 0.85 μm, and the height difference of the unevenness R (the thickness from the bottom 32a of the concave portion 32 to the top 31a of the convex portion 31) T2 is about 0.7 μm. The maximum thickness of the insulating film 30 (= T1 + T2) is about 1.55 μm.

[0067] Further, for example, when observing a cross-section from the center C1 of a concave portion 32 to the center C3 of two adjacent concave portions 32 in the X and Y directions (refer to Figure 4 ), as shown in Figure 5 (b), the thickness T1 of the insulating film 30 at the bottom 32a of the concave portion 32 is approximately 0.85 μm, and the height difference of the unevenness R (the thickness from the bottom 32a of the concave portion 32 to the top 31a of the convex portion 31) T2 is approximately 0.9 μm. The maximum thickness of the insulating film 30 (= T1 + T2) is approximately 1.75 μm.

[0068] Further, the height difference F between the top and bottom of the unevenness R (refer to Figure 9 ) is 0.5 μm or more and 0.9 μm or less. The topmost part refers to the top 31a among the tops 31a of the plurality of convex portions 31 with the highest height from the main surface 20a of the semiconductor substrate 20, and the bottommost part refers to the bottom 32a among the bottoms 32a of the plurality of concave portions 32 with the lowest height from the main surface 20a of the semiconductor substrate 20.

[0069] The unevenness R of the insulating film 30 is formed by, for example, dry etching and heat treatment. First, as shown in Figure 6 (a), on the main surface 30b of the insulating film 30, a resist 33 corresponding to the formation position of the convex portion 31 is formed by photolithography. Next, as shown in Figure 6 (b), the portion of the insulating film 30 where the resist 33 is not formed is dry-etched to form the concave portion 32. After forming the concave portion 32, the resist 33 is removed. Then, by heat-treating the insulating film 30, a part of the cross-section rectangular-shaped unevenness R flows, and as shown in Figure 6 (c), a smooth and continuous unevenness R is formed on the main surface 30b side of the insulating film 30.

[0070] According to the above manufacturing method, since the flow amount of the unevenness R during heat treatment is fixed, the higher the position of the top 31a of the convex portion 31 becomes as the distance between the concave portions 32, 32 before heat treatment increases, and the lower the position of the top 31a of the convex portion 31 becomes as the distance between the concave portions 32, 32 before heat treatment decreases. That is, the height difference T2 of the concave portion 32 can be adjusted using the distance between the concave portions 32, 32 before heat treatment.

[0071] Figure 7 In the example of Figure 7 (a), in the state before heat treatment, the width W1 of the convex portion 31 and the width W2 of the concave portion 32 are both set to 3.0 μm, and the thickness T2 from the bottom 32a of the concave portion 32 to the top 31a of the convex portion 31 is set to 1.4 μm. In this case, in the state after heat treatment, as shown in Figure 7 (b), the width W1 of the convex portion 31 and the width W2 of the concave portion 32 both remain at 3.0 μm, and the height difference T2 of the concave portion 32 is 0.7 μm. On the other hand,Figure 8 In the example of (a), in the state before heat treatment, the width W1 of the convex portion 31 and the width W2 of the concave portion 32 are both set to 4.2 μm, and the thickness T2 from the bottom 32a of the concave portion 32 to the top 31a of the convex portion 31 is set to 1.4 μm. In this case, in the state after heat treatment, as shown in Figure 8 (b), the width W1 of the convex portion 31 and the width W2 of the concave portion 32 both remain at 4.2 μm, and the height difference T2 of the concave portion 32 is 0.9 μm.

[0072] Figure 9 is a coordinate diagram showing the height difference profile of the unevenness of the pattern shown in Figure 4 . In this diagram, the horizontal axis represents the position in the X direction, and the vertical axis represents the height position of the insulating film 30. In the vertical axis, the height position of the top 31a of the convex portion 31 is used as a reference (=0 μm). The height difference profile of the unevenness R is obtained by scanning a depth gauge along the scanning line G1 on the diagonal line of the light sensing region 3 set to one pixel amount. By scanning the depth gauge along the scanning line G1, a height difference profile equivalent to the case of depth measurement by inclined sliding scanning of one concave portion 32 and the surrounding convex portions 31 is obtained.

[0073] As shown in Figure 9 , in the pattern of the unevenness R shown in Figure 4 , the height position of the top 31a of the convex portion 31 is 0 μm at the center in the scanning direction, gradually decreases from the center to the ends in the scanning direction, and is -0.2 μm at both ends in the scanning direction. In addition, the height position of the bottom 32a of the concave portion 32 is -0.2 μm at the center in the scanning direction, gradually decreases from the center to the ends in the scanning direction, and is -0.9 μm at both ends in the scanning direction. From the results of Figure 9 , it can be seen that the difference in the height positions between the top position and the bottom position of one amplitude of the height difference profile is small at the center in the scanning direction and gradually increases from the center to the ends. That is, it can be considered that in the light sensing region 3, there are height differences of the unevenness R of the main surface 30b in the plurality of insulating films 30.

[0074] In addition, in the light sensing region 3, when measuring the height difference of the unevenness R at intervals of 0.01 μm, the maximum value of the appearance frequency of the surface height of the insulating film 30 based on the topmost part of the insulating film 30 becomes 5% or less. Figure 10 is a coordinate diagram showing the appearance frequency of the surface height of the insulating film of the pattern shown in Figure 4 . In this diagram, the horizontal axis represents the surface height of the insulating film, and the vertical axis represents the appearance frequency. The depth resolution when calculating the appearance frequency is set to 0.01 μm. As shown in this diagram, Figure 4In the concavo-convex R pattern shown, the surface height of the insulating film is widely distributed in the range of 0 μm to -0.9 μm, and the peak of the appearance frequency is located near -0.2 μm. The appearance frequency is also about 4% around the peak position of -0.2 μm, in the range of -0.2 μm to 0 μm and -0.2 μm to -0.3 μm, it is about 1.5% - 4%, and in the range of -0.4 μm to -0.9 μm, it is below 1%. From this result, it can be known that Figure 4 In the concavo-convex R of the pattern shown, the height difference of the concavo-convex does not deviate to a specific value, and to a certain extent, it uniformly includes height differences of various values.

[0075] [Function and effect of the concavo-convex of the insulating film]

[0076] In the solid-state imaging device 1 having the above structure, since in the light-sensing region 3, there are multiple height differences in the concavo-convex R provided on the main surface 30b side of the insulating film 30, when incident light enters the light-sensing region 3, multiple interferences with different optical path lengths are generated in the insulating film 30. As a result, the uneven periods of the spectral sensitivity with respect to the incident light wavelength cancel each other out. For example, the sensitivity unevenness in a wide wavelength region including the ultraviolet region to the near-infrared region can be reduced.

[0077] In addition, in the solid-state imaging device 1, in the light-sensing region 3, when measuring the height difference of the concavo-convex R at intervals of 0.01 μm, the maximum value of the appearance frequency of the surface height of the insulating film based on the topmost part of the insulating film 30 becomes 5% or less. As a result, there are various height differences in the concavo-convex R in the insulating film 30, and the effect of canceling out the uneven periods of the spectral sensitivity with respect to the incident light wavelength is improved. Therefore, for example, the sensitivity unevenness in a wide wavelength region including the ultraviolet region to the near-infrared region can be more effectively reduced.

[0078] In addition, in the solid-state imaging device 1, in the light-sensing region 3, the height difference F between the topmost part and the bottommost part of the concavo-convex R is 0.5 μm or more and 0.9 μm or less. Since the height difference F is 0.5 μm or more, the optical path length difference of the incident light in the insulating film 30 becomes sufficiently large, so the effect of canceling out the uneven periods of the spectral sensitivity with respect to the incident light wavelength is further sufficiently improved. In addition, since this height difference F is 0.9 μm or less, the depth of the concave portion 32 is not excessive, and the absolute value change of the spectral sensitivity caused by the refraction and reflection of the incident light on the surface of the insulating film 30 can be suppressed.

[0079] In addition, in the solid-state imaging device 1, the main surface 20a of the semiconductor substrate 20 provided with the insulating film 30 is a flat surface. As a result, the shape of the main surface 20a of the semiconductor substrate 20 is simplified, and the cost reduction of the solid-state imaging device 1 is sought.

[0080] Figure 11 andFigure 12 is a coordinate diagram showing the spectral sensitivity characteristics of a solid-state imaging device having unevenness of a pattern as shown Figure 4 . Figure 11 It shows the spectral sensitivity characteristics in a wide wavelength range from the ultraviolet region to the near-infrared region, Figure 12 and magnifies and shows the spectral sensitivity characteristics in the ultraviolet region. Figure 11 And Figure 12 , in which the horizontal axis represents the wavelength, the vertical axis represents the sensitivity, and the spectral sensitivity characteristics related to four samples having the same structure as the above-described embodiment are overlapped and plotted. As Figure 11 And Figure 12 shown, it can be confirmed that in the examples, by canceling out the uneven periods of the spectral sensitivity with respect to the incident light wavelength, no peaks and valleys are generated in the spectral sensitivity profile, and the unevenness of the spectral sensitivity in a wide wavelength range from the ultraviolet region to the near-infrared region can be effectively reduced. In addition, it can be confirmed that the unevenness of the spectral sensitivity characteristics between the samples is very small.

[0081] On the other hand, Figure 13 is a top view showing the uneven pattern of the insulating film of the comparative example. In addition, Figure 14 is an enlarged view of a main part thereof. Figure 13 And Figure 14 In the example of, the unevenness R has a convex portion 31 extending in a strip shape in the X direction and a concave portion 32 extending in a strip shape in the Y direction when viewed from above, and the convex portion 31 and the concave portion 32 are formed by being alternately arranged in the Y direction. The widths of the convex portion 31 and the concave portion 32 in the Y direction are both 3.0 μm.

[0082] In this comparative example, for example, when observing a cross section from the center D1 of one concave portion 32 to the center D2 of two adjacent concave portions 32 in the Y direction (refer to Figure 14 ), as Figure 15 (a) shown, the thickness T1 of the insulating film 30 at the bottom 32a of the concave portion 32 is about 0.85 μm, and the height difference of the unevenness R (the thickness from the bottom 32a of the concave portion 32 to the top 31a of the convex portion 31) T2 is about 0.9 μm. The maximum thickness of the insulating film 30 (= T1 + T2) is about 1.75 μm.

[0083] Figure 16 is a coordinate diagram showing the height difference profile of the unevenness of the pattern as shown Figure 14 . The height difference profile of the unevenness R is obtained by scanning a depth gauge along a scanning line G2 set in the Y direction of a light sensing region of one pixel amount (refer to Figure 13 ). Figure 14In the concavo-convex R pattern shown, the height position of the top 31a of the convex portion 31 is 0 μm near the center in the Y direction of the convex portion 31, and the height position of the bottom 32a of the concave portion 32 is -1 μm near the center in the Y direction of the concave portion 32. From Figure 16 the results, it can be seen that Figure 14 in the pattern shown, the height difference of the concavo-convex R is single.

[0084] Figure 17 is a coordinate diagram showing the frequency of occurrence of the surface height of the insulating film of the pattern shown in Figure 14 . In this diagram, similar to the case of Figure 10 , the depth resolution when calculating the frequency of occurrence is set to 0.01 μm. As shown in this diagram, Figure 14 in the concavo-convex R pattern shown, the frequency of occurrence of the surface height of the insulating film is concentrated in the range of 0 μm to -0.1 μm. Among the peaks of the frequency of occurrence near 0 μm, the frequency of occurrence reaches about 7%. From this result, it can be seen that Figure 14 in the concavo-convex R of the pattern shown, the height difference of the concavo-convex is biased towards a specific value.

[0085] Figure 18 and Figure 19 are coordinate diagrams showing the spectral sensitivity characteristics of a solid-state imaging device having the concavo-convex of the pattern shown in Figure 4 . Figure 18 shows the spectral sensitivity characteristics in a wide wavelength range including the ultraviolet region to the near-infrared region, Figure 19 and magnifies and shows the spectral sensitivity characteristics in the ultraviolet region. Figure 18 and Figure 19 show, similar to the cases of Figure 11 and Figure 12 , the spectral sensitivity characteristics related to four samples having the same structure as the comparative example are overlapped and plotted. As can be seen from Figure 18 and Figure 19 , in the comparative example, the effect of canceling out the uneven periods of the spectral sensitivity with respect to the incident light wavelength is not easily generated, and compared with the embodiment, peaks and valleys are generated in the spectral sensitivity profile. It can also be seen that compared with the embodiment, the unevenness of the spectral sensitivity characteristics among the samples becomes larger.

[0086] In addition, Figure 20 and Figure 21 are coordinate diagrams showing the spectral sensitivity characteristics of the solid-state imaging device of the reference example. In this reference example, the spectral sensitivity characteristics related to four samples having no concavo-convex provided on the insulating film are overlapped and plotted. As can be seen from Figure 20 and Figure 21As can be seen, in the reference example, the effect of canceling out the uneven periods of the spectral sensitivity with respect to the incident light wavelength was not exhibited. Compared with the comparative example, larger peaks and valleys were generated in the spectral sensitivity profile, and the unevenness of the spectral sensitivity characteristics among samples further increased.

[0087] [Study on the unevenness of the insulating film]

[0088] In the above-described embodiment, the maximum value of the appearance frequency of the surface height of the insulating film 30 based on the topmost portion of the insulating film 30 is 5% or less. When calculating the maximum value of the appearance frequency of the surface height of the insulating film 30, the relationship between the maximum value of the appearance frequency of the surface height of the insulating film 30 and the peaks and valleys of the spectral sensitivity was studied. Here, the peaks and valleys of the spectral sensitivity are set as the average value of the absolute values of the unevenness amounts of the spectral sensitivity at each wavelength in the entire wavelength region (200 nm to 1000 nm). The absolute value of the unevenness amount of the spectral sensitivity at each wavelength is a value calculated as ΔS / S×100 (%) when the average value of the spectral sensitivity at a certain wavelength is set as S, and the difference between the maximum value or the minimum value of the spectral sensitivity at a certain wavelength and S is set as ΔS.

[0089] Figure 22 is a coordinate diagram showing the relationship between the maximum value of the appearance frequency of the surface height of the insulating film and the peaks and valleys of the spectral sensitivity. In this figure, the horizontal axis represents the maximum value of the appearance frequency of the surface height of the insulating film, and the vertical axis represents the peaks and valleys of the spectral sensitivity. As Figure 22 can be seen, there is a certain correlation between the maximum value of the appearance frequency of the surface height of the insulating film and the peaks and valleys of the spectral sensitivity. The larger the maximum value of the appearance frequency of the surface height of the insulating film, the smaller the peaks and valleys of the spectral sensitivity. According to Figure 22 the results, within the range where the maximum value of the appearance frequency of the surface height of the insulating film is 5% or less, the peaks and valleys of the spectral sensitivity are suppressed to 1% or less. Therefore, it can be confirmed that the maximum value of the appearance frequency of the surface height of the insulating film being 5% or less is a condition meaningful for reducing the unevenness of the spectral sensitivity.

[0090] The reason for setting the depth resolution when calculating the appearance frequency of the surface height of the insulating film to 0.01 μm is that the peaks and valleys of the spectral sensitivity shift by changing the height difference of the unevenness. Figure 23 is a coordinate diagram showing the shift of the peaks and valleys of the spectral sensitivity. As shown in this figure, the peaks and valleys of the spectral sensitivity reverse when the waveform of the spectral sensitivity shifts by 1 / 2 cycle. For example, at a wavelength of 200 nm, if the height difference of the unevenness changes by 0.04 μm, correspondingly, the waveform of the spectral sensitivity shifts by 1 / 2 cycle. Therefore, by measuring the depth of the unevenness with a resolution of 1 / 4 of 0.04 μm, that is, 0.01 μm, the phenomenon of the reversal of the peaks and valleys of the spectral sensitivity can be calculated as the appearance frequency.

[0091] A wavelength of 200 nm is near the lower limit of the measurement band of a general light-receiving sensor. On the longer wavelength side, the height difference of the unevenness required to shift the waveform of the spectral sensitivity by 1 / 2 cycle becomes a larger value. Therefore, if the depth resolution when calculating the occurrence frequency is specified based on a wavelength of 200 nm, sufficient resolution is also achieved in a solid-state imaging device that targets incident light on the longer wavelength side.

[0092] In addition, in the light-sensitive region 3, when measuring the height difference of the unevenness R at intervals of 0.01 μm, the standard deviation of the occurrence frequency of the surface height of the insulating film 30 based on the topmost part of the insulating film 30 can also be 1% or less. In this case, there are also various height differences of the unevenness R in the insulating film 30, enhancing the effect of canceling out each other the uneven periods of the spectral sensitivity with respect to the incident light wavelength. Therefore, it is possible to more effectively reduce the sensitivity unevenness in a wide wavelength region including, for example, the ultraviolet region to the near-infrared region.

[0093] Figure 24 It is a coordinate diagram showing the relationship between the standard deviation of the occurrence frequency of the surface height of the insulating film and the peak-to-valley of the spectral sensitivity. In this diagram, the horizontal axis represents the standard deviation of the occurrence frequency of the surface height of the insulating film, and the vertical axis represents the peak-to-valley of the spectral sensitivity. As Figure 24 shown, there is a certain correlation between the standard deviation of the occurrence frequency of the surface height of the insulating film and the peak-to-valley of the spectral sensitivity. The smaller the standard deviation of the occurrence frequency of the surface height of the insulating film, the smaller the peak-to-valley of the spectral sensitivity. According to Figure 24 the results, within the range where the standard deviation of the occurrence frequency of the surface height of the insulating film is 1% or less, the peak-to-valley of the spectral sensitivity is suppressed to 1% or less. Therefore, it can be confirmed that the standard deviation of the occurrence frequency of the surface height of the insulating film being 1% or less is a significant condition for reducing the spectral sensitivity unevenness.

[0094] In addition, in the above-described embodiment, the height difference F (refer to Figure 9 ) between the topmost part and the bottommost part of the unevenness R is 0.5 μm or more and 0.9 μm or less. Regarding this point, Figure 25 shows the state of the peak-to-valley of the spectral sensitivity when the height difference F is changed. As shown in this diagram, when the height difference F is 0.1 μm, since the optical path length difference of the incident light in the insulating film is small, the displacement amount of the spectral sensitivity based on each optical path length difference becomes small. Therefore, it is considered that the effect of canceling out each other the uneven periods of the spectral sensitivity occurs only in a limited wavelength region. In contrast, when the height difference F is 0.5 μm and 0.9 μm, since the optical path length difference of the incident light in the insulating film is sufficiently large, the displacement amount of the spectral sensitivity based on each optical path length difference becomes large. Therefore, the effect of canceling out each other the uneven periods of the spectral sensitivity with respect to the incident light wavelength is enhanced, and the peak-to-valley of the spectral sensitivity can be further reduced.

[0095] When the height difference F exceeds 0.9 μm, it is considered that the optical path length difference of the incident light in the insulating film will further increase. On the other hand, the depth of the concave portion will become excessive, and the refraction and reflection of the incident light on the surface of the insulating film will cause a change in the absolute value of the spectral sensitivity. Therefore, when the height difference F is in the range of 0.5 μm or more and 0.9 μm or less, such a problem of change in the absolute value of the spectral sensitivity will not occur, and the sensitivity unevenness in a wide wavelength range including, for example, the ultraviolet region to the near-infrared region can be reduced.

[0096] The interval of the unevenness R in the state before heat treatment is preferably 2 μm to 4 μm. As Figure 26 shown, when the interval of the unevenness R before heat treatment is 1.0 μm (here, the width of the convex portion 31 and the width of the concave portion 32 are both 1.0 μm), the flow amount of the insulating film 30 from the convex portion 31 to the concave portion 32 during heat treatment is excessive, and as a result, the main surface 30b of the insulating film 30 after heat treatment tends to be flattened. When the interval of the unevenness R before heat treatment is 3.0 μm (here, the width of the convex portion 31 and the width of the concave portion 32 are both 3.0 μm), the flow amount of the insulating film 30 from the convex portion 31 to the concave portion 32 during heat treatment is appropriate, and the main surface 30b of the insulating film 30 after heat treatment has a sinusoidal undulation, forming Figure 3 and Figure 4 the unevenness R shown.

[0097] On the other hand, when the interval of the unevenness R before heat treatment is 5.0 μm (here, the width of the convex portion 31 and the width of the concave portion 32 are both 5.0 μm), the flow amount of the insulating film 30 from the convex portion 31 to the concave portion 32 during heat treatment is insufficient, and as a result, although unevenness occurs in the insulating film 30 after heat treatment, there is a tendency to leave a flat portion at the top 31a of the convex portion 31 or the bottom 32a of the concave portion 32. In this case, it is considered that the occurrence frequency of each height difference of the unevenness R tends to deviate to a specific value. Therefore, as described above, by setting the interval of the unevenness R in the state before heat treatment to 2 μm to 4 μm, various height differences of the unevenness R in the insulating film 30 are likely to exist. In addition, it is considered that the flow amount of the insulating film 30 from the convex portion 31 to the concave portion 32 during heat treatment also varies depending on the temperature during heat treatment or the impurity concentration in the insulating film 30, but as long as this heat treatment uses the manufacturing process of a standard solid-state imaging device, the appropriate range of the interval of the above-mentioned unevenness R can be generalized.

[0098] [Deformation examples of the unevenness of the insulating film]

[0099] Various variations can be applied to the unevenness R of the insulating film 30. For example, Figure 3 and Figure 4 In, the substantially square-shaped concave portions 32 are arranged in a matrix in the in-plane direction of the main surface 30b of the insulating film 30, but it can also be as Figure 27As shown in (a) of [reference], the concave portions 32 that are substantially circular in plan view are arranged in a matrix in the in-plane direction of the main surface 30b of the insulating film 30. Further, as Figure 27 shown in (b) of [reference], the concave portions 32 that are substantially equilateral triangular in plan view may also be arranged in a matrix in the in-plane direction of the main surface 30b of the insulating film 30. As Figure 27 shown in (c) of [reference], the concave portions 32 that are substantially regular hexagonal in plan view may also be arranged in a matrix in the in-plane direction of the main surface 30b of the insulating film 30.

[0100] Further, as Figure 28 shown in (a) of [reference], with respect to the structure of Figure 3 and Figure 4 , the shape and position of the convex portions 31 and the concave portions 32 may be reversed. That is, the convex portions 31 that are substantially square in plan view may be arranged in a matrix in the in-plane direction of the main surface 30b of the insulating film 30. In this case, it is also considered that when the distance between the convex portions 31, 31 is large, the flow amount of the insulating film 30 during heat treatment is insufficient. Therefore, as Figure 28 shown in (b) of [reference], it is preferable to reduce the distance between the convex portions 31, 31 while maintaining the area of the convex portions 31, and to sufficiently ensure the area of the convex portions 31 relative to the photosensitive region 3.

[0101] Further, the concavo-convex R pattern of the insulating film 30 is not necessarily a two-dimensional pattern, and a one-dimensional concavo-convex R may also be used. For example, Figure 29 in the example of (a) of [reference], the concavo-convex R has convex portions 31 that extend in a band shape in the X direction in plan view, and concave portions 32 that extend in a band shape in the Y direction. The convex portions 31 and the concave portions 32 are formed by being alternately arranged in the Y direction. In the example of (a) of this Figure 29 , different from the comparative examples shown in Figure 13 and Figure 14 , pairs of convex portions 31 and concave portions 32 with a width of 3.0 μm in the Y direction and pairs of convex portions 31 and concave portions 32 with a width of 2.5 μm in the Y direction are alternately arranged in the Y direction.

[0102] Furthermore, as Figure 29 shown in (b) of [reference], it may be set such that in the one-dimensional concavo-convex R, the width in the Y direction of the convex portions 31 and the concave portions 32 varies in the X direction. In the example of (b) of this Figure 29 , the width in the Y direction of the convex portions 31 gradually increases from 2.5 μm to 3.5 μm in the X direction, and conversely, the width in the Y direction of the concave portions 32 gradually decreases from 3.5 μm to 2.5 μm in the X direction.

[0103] In these methods, since there are multiple height differences in the unevenness R provided on the main surface 30b side of the insulating film 30, when incident light enters the light sensing region 3, multiple interferences with different optical path lengths are generated within the insulating film 30. Therefore, the uneven periods of the spectral sensitivity with respect to the incident light wavelength cancel each other out, and unevenness in sensitivity within a wide wavelength region including, for example, the ultraviolet region to the near-infrared region can be reduced.

[0104] In addition, as Figure 30 shown, in the unevenness R of the one-dimensional pattern, the height positions of the bottoms 32a of the concave portions 32 can also be different. Figure 30 In the example of, the widths of the convex portion 31 and the concave portion 32 in the Y direction are both 3.0 μm. In addition, the concave portion A with a relatively low height position of the bottom 32a and the concave portion 32B with a relatively high height position of the bottom 32a are alternately arranged with the convex portion 31 interposed therebetween. In this case, since the height positions of the concave portions 32 are uneven, even if the convex portion 31 and the concave portion 32 are arranged at uniform intervals in the Y direction, there may be multiple height differences in the unevenness R. The concave portions 32A and 32B with different height positions of the bottom 32a can be easily fabricated, for example, by changing the dry etching amount of the insulating film 30 before heat treatment. Figure 29 and Figure 30 In the methods of, crosstalk to adjacent pixels caused by refraction at the interface between the convex portion 31 and the concave portion 32 can be suppressed. In addition, when the pitch in the X direction of the light sensing region 3 becomes smaller, it is also easy to form the unevenness R.

[0105] Figure 29 and Figure 30 In the example of, unevenness with a one-dimensional pattern is arranged in the Y direction, and the unevenness R with a one-dimensional pattern can also be arranged in the X direction as Figure 31 shown. Figure 31 In the example of, the unevenness R is formed by uneven rows 35A in which the convex portion 31 and the concave portion 32 with a width of 3.0 μm in the X direction are arranged in the X direction, uneven rows 35B in which the convex portion 31 and the concave portion 32 with a width of 2.5 μm in the X direction are arranged in the X direction, uneven rows 35C in which the convex portion 31 and the concave portion 32 with a width of 2.0 μm in the X direction are arranged in the X direction, and uneven rows 35D in which the convex portion 31 and the concave portion 32 with a width of 1.5 μm in the X direction are arranged in the X direction. For the Y direction, the uneven rows 35A to 35D are arranged in sequence from both end sides of the light sensing region 3, and in the center, the uneven rows 35D are adjacent to each other. Between the respective uneven rows 35A to 35D, the convex portion 31 is arranged with a width of 1 μm.

[0106] Among these methods, since there are also multiple height differences in the unevenness R provided on the main surface 30b side of the insulating film 30, when incident light enters the light sensing region 3, multiple interferences with different optical path lengths are generated within the insulating film 30. Therefore, the periods of the unevenness of the spectral sensitivity with respect to the incident light wavelength cancel each other out, and unevenness of sensitivity within a wide wavelength region including, for example, the ultraviolet region to the near-infrared region can be reduced.

[0107] Description of symbols

[0108] 1... solid-state imaging device, 3... light sensing region, 20... semiconductor substrate, 20a... main surface, 30... insulating film, 30b... main surface, R... unevenness.

Claims

1. A solid-state imaging device, wherein: Comprising: A semiconductor substrate having a main surface provided with a plurality of light-sensing regions; and An insulating film provided on the main surface of the semiconductor substrate, On the surface of the insulating film opposite to the main surface of the semiconductor substrate, a plurality of concavo-convex portions having a smooth and continuous shape are formed, In the light-sensing region, there are a plurality of height differences corresponding to the length from the bottom to the top of the concavo-convex portions, In the light-sensing region, when measuring the height differences of the concavo-convex portions at an interval of 0.01 μm, the maximum value of the appearance frequency of the surface height of the insulating film based on the topmost portion of the insulating film becomes 5% or less.

2. A solid-state imaging device, wherein: Comprising: A semiconductor substrate having a main surface provided with a plurality of light-sensing regions; and An insulating film provided on the main surface of the semiconductor substrate, On the surface of the insulating film opposite to the main surface of the semiconductor substrate, a plurality of concavo-convex portions having a smooth and continuous shape are formed, In the light-sensing region, there are a plurality of height differences corresponding to the length from the bottom to the top of the concavo-convex portions, In the light-sensing region, when measuring the height differences of the concavo-convex portions at an interval of 0.01 μm, the standard deviation of the appearance frequency of the surface height of the insulating film based on the topmost portion of the insulating film becomes 1% or less.

3. The solid-state imaging device according to claim 1 or 2, wherein: In the light-sensing region, the height difference between the topmost portion and the bottommost portion of the concavo-convex portions becomes 0.5 μm or more and 0.9 μm or less.

4. The solid-state imaging device according to claim 1 or 2, wherein: The main surface of the semiconductor substrate is a flat surface.

5. The solid-state imaging device according to claim 3, wherein: The main surface of the semiconductor substrate is a flat surface.

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