JP2007287818A - Solid imaging device and its manufacturing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a solid imaging device which can suppress the reflection and absorption of incident light in a convex inter-layer lens to effectively obtain high sensitivity. <P>SOLUTION: A photoelectric conversion part 4 is formed at a specified position on the surface layer of a silicon substrate 1, and a light shielding film 12 that has an opening exposing an upper part to the photoelectric conversion part 4 is formed. A transparent insulation layer 13 which light passes through is formed on the light shielding film 12 to embed the opening, and a convex inter-layer lens 25 and a transparent lens flattening film 26 covering the lens 25 are formed on the opening with the transparent insulation layer 13 between. The convex inter-layer lens 25 has a double-layer structure of a central lens 27 and a peripheral lens 28. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a solid-state imaging device and a method for manufacturing the same, and more particularly to a solid-state imaging device having a convex in-layer lens.

  FIG. 4 is a cross-sectional view showing a unit pixel in an example of a conventional solid-state imaging device.

  In FIG. 4, an overflow barrier 2, a well layer 3, a photoelectric conversion unit 4, a vertical transfer channel 5, a reading unit 6, and a channel stop unit 7 are formed by performing ion implantation of necessary impurities on the silicon substrate 1. .

  Further, a vertical transfer electrode 10 is formed on the silicon oxide film 8 and the vertical transfer channel 5, and a light shielding film 12 is formed so as to have an opening exposing the upper portion of the photoelectric conversion unit 4 through the silicon oxide film 11. ing.

  A transparent insulating film 13 is formed on the light shielding film 12 so as to fill the opening, and a transparent protective film 14 for protecting the pixel region and the peripheral circuit portion (not shown) is formed on the transparent insulating film 13. Is formed.

  A transparent color filter flattening film 16 is formed on the color filter layer 15 and the color filter layer 15 so as to fill a step, and a micro-on-chip lens 17 is formed on the transparent color filter flattening film 16. ing.

  In the prior art, high sensitivity has been obtained by forming the micro-on-chip lens 17 and condensing incident light on the photoelectric conversion unit 4.

  In recent years, CCD (Charge Coupled Device) type solid-state imaging devices are increasingly required to be smaller and have higher pixels due to the spread of digital still cameras, digital video cameras, camera-equipped mobile phones, and the like.

  However, with further miniaturization and higher pixel count, the size of the pixels incorporated in the solid-state image sensor is further reduced, and the light collection reaches the limit only with a micro-on-chip lens, which is one of the basic performances. It is clear that the sensitivity decreases and it becomes difficult to capture a clear image under a predetermined illuminance.

  To solve this problem, a solid-state imaging device having a configuration as shown in FIGS. 5 and 6 has been proposed. 5 and 6, members corresponding to those described in FIG. 4 are denoted by the same reference numerals, and detailed description thereof is omitted.

  That is, in the example shown in FIG. 5, in order to improve the sensitivity, in addition to the micro-on-chip lens 17, a convex in-layer lens 18 is formed between the color filter layer 15 and the photoelectric conversion unit 4, and incident light is transmitted. Furthermore, it has the structure which condenses on the photoelectric conversion part 4 efficiently (refer patent document 1).

In the example shown in FIG. 6, a film 20 made of the same material as the convex inner lens 19 is formed on the convex inner lens 19 to reduce the lens interval and reduce the ineffective region in incident light. In this structure, more incident light is collected (see Patent Document 2).
Japanese Patent Laid-Open No. 11-40787 JP 2002-76316 A

  However, the technique using the in-layer lens as in the conventional technique has the following problems.

  First, when the convex inner lenses 18 and 19 are used, before forming the color filter layer 15, an acrylic resin (refractive index: about 1. 6) or polyimide resin (refractive index: about 1.8) or the like. At this time, in order to condense incident light with the convex inner lenses 18, 19, the convex inner lenses 18, 19 are formed of a material having a higher refractive index than the resin material of the transparent lens flattening film 26. There is a need to. Patent Documents 1 and 2 describe that a plasma silicon nitride film having a refractive index of 1.9 to 2.0 or a plasma silicon oxynitride film having a refractive index of 1.5 to 1.9 is employed.

  However, in the case of this structure, particularly incident light passing near the apex of the lens enters the high-refractive-index convex in-layer lenses 18 and 19 from the low-refractive-index transparent lens flattening film 26. Therefore, there is a problem that a reflection component is generated and the obtained sensitivity is lowered.

  In addition, the material of a general convex-shaped inner-layer lens can refract incident light reliably and can collect it, and can further reduce the curvature of the lens and can shrink the device in the thickness direction (high refractive index ( 2.0) is used, and this plasma silicon nitride film absorbs light greatly on the short wavelength side (≦ 550 nm), and light is absorbed when incident light passes through the inner lens. In particular, there is a problem that the sensitivity of the blue component (wavelength near 450 nm) is lowered.

  The present invention solves the above-mentioned conventional problems, suppresses the reflection and absorption of incident light in the convex in-layer lens, and enables realization of a solid-state imaging device capable of effectively obtaining high sensitivity and its manufacturing method. With the goal.

  In order to achieve the object, a solid-state imaging device according to the present invention is formed on a semiconductor substrate and performs photoelectric conversion, a light-shielding film having an opening that exposes an upper portion of the photoelectric conversion unit, A transparent insulating layer that is formed so as to fill the opening on the light-shielding film and transmits light, a convex inner lens formed on the opening via the transparent insulating layer, and the convex layer And a transparent lens flattening film formed so as to cover the inner lens, and the convex inner lens has a two-layer structure of a central lens portion and an outer edge lens portion.

  Further, a convex inner lens having a two-layer structure of a central lens portion having the same refractive index as that of the transparent lens flattening film and an outer lens portion in which a film having a higher refractive index is deposited and at least the lens apex film is removed. It is set as the structure provided with.

  The central lens part forms a convex lens with a refractive index equivalent to that of the transparent lens flattening film, and a transparent film having a higher refractive index than the central lens part is removed from the outer edge lens part, and at least the film at the lens apex part is removed. It is characterized by being formed.

  With this configuration, it is possible to eliminate reflection of incident light in the vicinity of the apex of the lens while securing light collection by the lens. Therefore, incident light can be efficiently collected on the photoelectric conversion unit, and as a result, a highly sensitive solid-state imaging device can be realized.

  In the solid-state imaging device according to the present invention, it is preferable that the central portion of the convex inner lens is formed of a silicon oxynitride film that hardly absorbs light. By adopting such a configuration, it is possible to suppress absorption of light when passing through the in-layer lens.

  In the solid-state imaging device according to the present invention, the outer edge lens portion of the convex inner lens is formed of a silicon nitride film having a refractive index of about 2.0 and suppressing light absorption on the short wavelength side. Is preferred. By adopting such a configuration, it is possible to reliably refract and condense light with the inner lens, and to suppress light absorption when passing through the outer edge lens portion.

  The method for manufacturing a solid-state imaging device according to the present invention includes a first step of forming a photoelectric conversion unit that performs photoelectric conversion on a semiconductor substrate, and a first step of forming a light-shielding film having an opening that exposes an upper portion of the photoelectric conversion unit. Two steps, a third step of forming a transparent insulating layer which is formed on the light shielding film so as to fill the opening, and transmits light; and a central lens on the opening via the transparent insulating layer. A fourth step of forming a convex in-layer lens having a two-layer structure of a portion and an outer edge lens portion, and a fifth step of forming a transparent lens flattening film so as to cover the convex in-layer lens, The four steps are a first step of forming a convex lens that is the central lens part, and a transparent film is formed on the central lens part and etched, so that the outer edge lens part is moved from the central lens part to the outer lens part. First to form a transparent film with a high refractive index Characterized in that it comprises a step.

  Further, the second step of forming the outer edge lens portion in the fourth step includes a step of removing a transparent film at least at the apex portion of the convex in-layer lens.

  By this method, it is possible to manufacture a solid-state imaging device capable of eliminating the reflection of incident light near the apex of the lens while securing the light collection by the lens.

In the solid-state imaging device manufacturing method according to the present invention, the first step of forming the central lens portion in the fourth step has a refractive index equivalent to that of the transparent lens flattening film formed in the fifth step. The silicon oxynitride film is formed by changing the ratio of silane (SiH ₄ ) gas, nitrous oxide (N ₂ O) gas, and nitrogen (N ₂ ) gas so as to have little absorption of light. It is preferable to include a process. With such a configuration, it is possible to suppress the absorption of light when passing through the intralayer lens.

In the solid-state imaging device manufacturing method according to the present invention, the second step of forming the outer edge lens portion in the fourth step has a refractive index higher than that of the central lens portion, and emits light at a short wavelength. It is preferable to include a step of forming a silicon nitride film by changing the ratio of silane (SiH ₄ ) gas, ammonia (NH ₃ ) gas, and nitrogen (N ₂ ) gas so as to suppress absorption. With such a configuration, light can be reliably refracted and collected by the inner lens, and absorption of light when passing through the outer edge can be suppressed.

  According to the solid-state imaging device and the manufacturing method thereof of the present invention, it is possible to realize a solid-state imaging device that can effectively obtain high sensitivity by suppressing the reflection and absorption of incident light in the convex in-layer lens.

  Hereinafter, embodiments of a solid-state imaging device and a method for manufacturing the same according to the present invention will be described with reference to the drawings.

  FIG. 1 is a cross-sectional view showing a configuration of a unit pixel region of a solid-state imaging device according to an embodiment of the present invention. In the following description, members corresponding to those described in FIGS. 4 to 6 are denoted by the same reference numerals.

  The solid-state imaging device according to the present embodiment includes a plurality of photoelectric conversion units made of photodiodes arranged in a matrix on the silicon substrate 1, and a vertical transfer unit that transfers signal charges read from each photoelectric conversion unit in the column direction. And a horizontal transfer unit for transferring the signal charges transferred from the vertical transfer unit in the row direction.

  As shown in FIG. 1, an overflow barrier 2 is formed near the surface of the silicon substrate 1, and a silicon oxide film 8 is formed on the surface of the silicon substrate 1. In the well layer 3 formed between the overflow barrier 2 and the silicon oxide film 8, a photoelectric conversion unit 4 that is a photodiode in which a hole accumulation layer is provided immediately below the silicon oxide film 8 is formed.

  A vertical transfer unit 21 a is formed on one side of the photoelectric conversion unit 4 with the reading unit 6 interposed therebetween. The vertical transfer portion 21 a includes a vertical transfer channel 5 that is an impurity diffusion layer formed in the well layer 3, and an insulating film 22 and a polysilicon film 23 that are formed above the vertical transfer channel 5 via the silicon oxide film 8. And the vertical transfer electrode 10. A silicon oxide film 11 is formed on the upper surface and side surfaces of the vertical transfer electrode 10.

  On the other side of the photoelectric conversion unit 4, a vertical transfer unit 21 b that transfers a signal charge read from another adjacent photoelectric conversion unit (not shown) is formed. The photoelectric conversion unit 4 and the vertical transfer unit A channel stop portion 7 is formed between 21b.

  On the silicon oxide film 8, a light shielding film 12 having an opening in a region above the central portion of the photoelectric conversion unit 4 is formed. The light shielding film 12 covers the upper surface and side surfaces of the vertical transfer electrode 10 covered with the silicon oxide film 11 and the upper side of the outer edge of the photoelectric conversion unit 4, and light is incident on a region other than the light receiving region of the photoelectric conversion unit 4. To prevent.

  A transparent insulating film 13 made of BPSG is formed on the light shielding film 12 so as to fill the opening. On the transparent insulating film 13, a transparent protective film 24 for protecting the pixel region and the peripheral circuit portion (not shown) is formed.

  A convex inner lens 25 having a two-layer structure is formed on the transparent protective film 24 so as to collect incident light onto the photoelectric conversion unit 4. A transparent lens flattening film 26 is formed on the convex shaped inner lens 25 so as to fill the step.

  The convex inner lens 25 having a two-layer structure includes a central lens portion 27 having a convex shape made of a silicon oxynitride film having a refractive index equivalent to that of the transparent lens flattening film 26 and hardly absorbing light, and a central lens. The outer lens portion 28 is made of a silicon nitride film having a refractive index higher than that of the portion 27 and suppressing light absorption at a short wavelength and removing at least the film at the lens apex portion.

  A color filter layer 15 is formed on the transparent lens flattening film 26, and a transparent color filter flattening film 16 is formed on the color filter layer 15 so as to fill a step, and the transparent color filter flattening film 16 is formed. A micro-on-chip lens 17 is formed on the top.

  In the present embodiment, the convex inner lens 25 having a two-layer structure has a central lens portion 27 made of a silicon oxynitride film having a refractive index equivalent to that of the transparent lens flattening film 26 and an outer edge lens portion 28 made a central lens portion. Since it is formed of a silicon nitride film having a refractive index higher than 27, it is possible to eliminate reflection of incident light in the vicinity of the apex of the lens while ensuring condensing by the in-layer lens.

  Further, since the central lens portion 27 is formed of a silicon oxynitride film that hardly absorbs light and the outer edge lens portion 28 is formed of a silicon nitride film that suppresses light absorption at a short wavelength, it passes through the inner lens. It is possible to suppress the absorption of light when doing so. As a result, high sensitivity can be obtained effectively.

  Next, the manufacturing method of the solid-state image sensor of this embodiment will be described.

  As in the conventional case, p-type impurities are implanted into a predetermined position in the surface layer portion of the silicon substrate 1 to form the overflow barrier 2. Subsequently, the reading unit 6 and the channel stop unit 7 are formed at predetermined intervals, respectively. Next, an n-type impurity is implanted, the photoelectric conversion unit 4 is formed between the readout unit 6 and the channel stop unit 7, and the vertical transfer channel 5 is formed outside the readout unit 6 and the channel stop unit 7, respectively. .

  Next, a silicon oxide film 8 is formed on the surface of the silicon substrate 1 by a thermal oxidation method or a CVD method. Subsequently, an insulating film 22 and a polysilicon film 23 made of silicon nitride and silicon oxide are sequentially formed on the silicon oxide film 8. The formed insulating film 22 and polysilicon film 23 are patterned by a known lithography technique and etching technique to form the vertical transfer electrode 10 on the upper side of the vertical transfer channel 5, and then the surface of the vertical transfer electrode 10 is subjected to a thermal oxidation method or the like. Thus, the silicon oxide film 11 is formed. After the insulating film 22 formed above the photoelectric conversion unit 4 is removed by a known wet etching technique, a p-type impurity is implanted into a relatively shallow position of the surface layer portion of the silicon substrate 1, and the photoelectric conversion unit 4 A hole accumulating portion is formed on the upper portion.

  Next, after depositing a metal film such as aluminum or tungsten by sputtering or CVD, patterning is performed by a known lithography technique or etching technique to cover the vertical transfer electrode 10 and photoelectric conversion on the silicon oxide film 8. A light shielding film 12 having an opening is formed above the center of the portion 4.

  Next, a transparent insulating film 13 made of BPSG is deposited on the light shielding film 12 by a CVD (chemical vapor deposition) method so as to fill the opening, and is further planarized by a reflow process. A transparent protective film 24 is formed on the transparent insulating layer 13 as a peripheral circuit part protective layer.

  An example of a method for forming the convex in-layer lens 25 thereafter will be described with reference to FIGS.

  A silicon oxynitride film 31 is formed on the transparent protective film 24 by a plasma CVD method, a resist is applied thereon to form a resist layer 32, and a rectangular shape corresponding to each photoelectric conversion unit 4, Patterning into a square shape or a circular shape (FIG. 2A), the resist layer 32 is melted by reflow treatment at a temperature of about 140 ° C. to 180 ° C., and then solidified to form on the silicon oxynitride film 31. A resist pattern 32 ′ having a convex spherical shape is generated (FIG. 2B). Using this resist pattern 32 'as a mask, the silicon oxynitride film 31 is etched to form a convex central lens portion 27 (FIG. 2- (c)).

  Next, a silicon nitride film 28 'is formed on the surface of the central lens portion 27 by plasma CVD (FIG. 2- (d)), and the entire surface is etched to remove the silicon nitride film 28' at least at the lens apex portion. The outer edge lens portion 28 is formed. Thus, a convex inner lens 25 having a two-layer structure is formed (FIG. 2- (e)).

  Thereafter, as shown in FIG. 1, a transparent lens flattening film 26 is formed on the convex-shaped inner lens 25 so as to fill the steps, and the color filter layer 15, the transparent color filter flattening film 16, and the micro-on-chip lens. 17 are formed sequentially.

In the present embodiment, the central lens portion 27 is a silicon oxynitride film, and has, for example, a refractive index equivalent to that of the transparent lens flattening film 26 (refractive index 1.6) and hardly absorbs light. In addition, the ratio of silane (SiH ₄ ) gas, nitrous oxide (N ₂ O) gas, and nitrogen (N ₂ ) gas is changed. This makes it possible to suppress the absorption of light when passing through the intralayer lens.

The outer edge lens portion 28 is a silicon nitride film. For example, a silane (SiH ₄ ) gas and ammonia (so that it has a higher refractive index than the central lens portion 27 and suppresses light absorption at a short wavelength. It is formed by changing the ratio of NH ₃ ) gas and nitrogen (N ₂ ) gas. As a result, light can be reliably refracted and condensed by the inner lens, and absorption of light when passing through the outer edge lens portion 28 can be suppressed.

  FIG. 3 shows an example of the refractive index and absorption coefficient of the silicon oxynitride film, silicon nitride film, and general silicon nitride film formed in this embodiment.

  In the present embodiment, the silicon oxynitride film forming the central lens portion 27 has a refractive index of 1.54 to 1.59 in the visible light region, and is almost a transparent lens flattening film (refractive index 1.6 in this example). A refractive index equivalent to that of H.26 is realized, and reflection of light in the vicinity of the lens apex can be suppressed. Also, the absorption coefficient is 0, and light absorption is also suppressed.

  In the present embodiment, the silicon nitride film that forms the outer lens portion 28 has a refractive index of 1.97 to 2.03 in the visible light region, and a transparent lens flattening film (with a refractive index of 1.6 in this example). The light is refracted by the difference in refractive index and can be reliably collected. Further, the absorption coefficient is greatly reduced on the low wavelength side in the visible light region as compared with a general silicon nitride film, and the absorption of light when light passes is also suppressed.

  The convex inner lens 25 formed in the present embodiment is formed of a silicon oxynitride film and a silicon nitride film. However, since a plasma CVD method generally used in a semiconductor process is used, an appropriate refractive index is obtained. It is possible to form a film using a material having the same.

  The solid-state imaging device and the manufacturing method thereof according to the present invention can realize a solid-state imaging device that can effectively obtain high sensitivity by suppressing the reflection and absorption of incident light in the convex-shaped inner lens, and in particular, has a two-layer structure. It is useful as a solid-state imaging device having a convex in-layer lens and a method for manufacturing the same.

Sectional drawing which shows the unit pixel of the solid-state image sensor which concerns on embodiment of this invention. Sectional drawing for demonstrating the convex-shaped inner-layer lens formation method of the solid-state image sensor in this embodiment Sectional drawing for demonstrating the convex-shaped inner-layer lens formation method of the solid-state image sensor in this embodiment Sectional drawing for demonstrating the convex-shaped inner-layer lens formation method of the solid-state image sensor in this embodiment Sectional drawing for demonstrating the convex-shaped inner-layer lens formation method of the solid-state image sensor in this embodiment Sectional drawing for demonstrating the convex-shaped inner-layer lens formation method of the solid-state image sensor in this embodiment The figure which shows an example of the refractive index and absorption coefficient of the silicon oxynitride film | membrane and silicon nitride film which were formed in this embodiment, and a general silicon nitride film Sectional drawing which shows the unit pixel in an example of the conventional solid-state image sensor. Sectional drawing which shows the unit pixel in an example of the conventional solid-state image sensor. Sectional drawing which shows the unit pixel in an example of the conventional solid-state image sensor.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Silicon substrate 2 Overflow barrier 3 Well layer 4 Photoelectric conversion part 5 Vertical transfer channel 6 Reading part 7 Channel stop part 8, 11 Silicon oxide film 10 Vertical transfer electrode 12 Light-shielding film 13 Transparent insulating film 21a, 21b Vertical transfer part 22 Insulating film 23 Polysilicon film 24 Transparent protective film 25 Convex-shaped inner lens 26 Transparent lens flattening film 27 Central lens part 28 Outer lens part

Claims (11)

A photoelectric conversion unit that is formed on a semiconductor substrate and performs photoelectric conversion;
A light-shielding film having an opening exposing the upper portion of the photoelectric conversion unit;
A transparent insulating layer that is formed on the light-shielding film so as to fill the opening and transmits light;
A convex in-layer lens formed on the opening via the transparent insulating layer;
A transparent lens flattening film formed so as to cover the convex in-layer lens,
A solid-state imaging device, wherein the convex inner lens has a two-layer structure of a central lens portion and an outer edge lens portion.   The solid-state imaging device according to claim 1, wherein a refractive index of the outer edge lens portion is set higher than a refractive index of the central lens portion.   3. The solid-state imaging device according to claim 1, wherein the central lens portion is formed as a convex lens having a refractive index equivalent to that of the transparent lens flattening film.   The solid-state imaging device according to claim 1, wherein the central lens portion is formed of a silicon oxynitride film.   5. The solid-state imaging device according to claim 1, wherein the outer edge lens portion is formed by removing a transparent film at least at a vertex portion of the convex in-layer lens.   6. The solid-state imaging device according to claim 1, wherein the outer edge lens portion is formed of a silicon nitride film that suppresses absorption of light on a short wavelength side. A plurality of the photoelectric conversion parts are formed in a matrix on the semiconductor substrate,
A vertical transfer unit that transfers signal charges read from each photoelectric conversion unit in the column direction, and a horizontal transfer unit that transfers signal charges transferred from the vertical transfer unit in the row direction,
The solid-state imaging device according to claim 1, which functions as a CCD (Charge Coupled Device) type solid-state imaging device. A first step of forming a photoelectric conversion unit that performs photoelectric conversion on a semiconductor substrate;
A second step of forming a light shielding film having an opening exposing the upper portion of the photoelectric conversion unit;
A third step of forming a transparent insulating layer that is formed on the light shielding film so as to fill the opening and transmits light;
A fourth step of forming a convex in-layer lens having a two-layer structure of a center lens portion and an outer edge lens portion via the transparent insulating layer on the opening;
A fifth step of forming a transparent lens flattening film so as to cover the convex in-layer lens,
The fourth step includes a first step of forming a convex lens that is the central lens portion, and a transparent film is formed on the central lens portion and etched to form the central lens on the outer lens portion. And a second step of forming a transparent film having a higher refractive index than the part.   9. The solid-state imaging device according to claim 8, wherein the second step of forming the outer edge lens portion in the fourth step includes a step of removing a transparent film at least at the apex portion of the convex inner lens. Manufacturing method. The first step of forming the central lens portion in the fourth step has a refractive index equivalent to that of the transparent lens flattening film formed in the fifth step, and silane is hardly absorbed. 9. The solid according to claim 8, comprising a step of forming a silicon oxynitride film by changing a ratio of (SiH ₄ ) gas, nitrous oxide (N ₂ O) gas, and nitrogen (N ₂ ) gas. Manufacturing method of imaging device. The second step of forming the outer edge lens portion in the fourth step has a higher refractive index than the central lens portion, and silane (SiH ₄ ) gas so as to suppress light absorption at a short wavelength. 10. The method of manufacturing a solid-state imaging device according to claim 8, further comprising a step of forming a silicon nitride film by changing a ratio of ammonia (NH ₃ ) gas and nitrogen (N ₂ ) gas.

Images