JP3277952B2 - Method for manufacturing solid-state imaging device and method for forming on-chip lens - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a solid-state imaging device, particularly a solid-state imaging device having an on-chip lens, and a method for forming an on-chip lens.

[0002]

2. Description of the Related Art Some solid-state image sensors have an on-chip lens formed above each light receiving element in order to improve sensitivity. Conventionally, formation of an on-chip lens is generally performed by applying a resist film, which is an organic material, performing exposure and development processing on the resist film, patterning the resist film, and then performing a reflow process on the patterned resist film. Then, the resist film was formed into a shape close to a dome.

Further, a method of transferring a lens shape by etch-back after reflow processing is often used for forming an on-chip lens. Whichever method you take,
In the past, it was essential to form a lens shape by reflow, and it was essential to use an organic material such as a resist as a lens material.

[0004]

However, the method of forming an on-chip lens in which an organic material is subjected to a reflow treatment has a problem that the controllability of the lens shape is poor. More specifically, the shape of the lens is distorted due to the subtle surface condition of the underlayer, the subtle deviation of the reflow temperature, and the like. As shown in FIG. 5, adjacent lenses stick together (lens short), and the lens floats due to surface tension. That happens.

[0005] It is needless to say that this hinders an improvement in sensitivity and causes an increase in smear and shading. This has been a factor restricting the miniaturization, high integration, and increase in the number of pixels of the solid-state imaging device.

SUMMARY OF THE INVENTION The present invention has been made to solve such a problem. In addition to improving the controllability of the lens shape of the solid-state image pickup device, the on-chip lens is formed by etch-back for forming the on-chip lens. A method for manufacturing a solid-state imaging device capable of preventing the base from being destroyed,
An object of the present invention is to provide a method for forming an on-chip lens.

[0007]

According to a first aspect of the present invention, there is provided a method of manufacturing a solid-state imaging device, wherein a first lens material serving as a core portion is selectively formed, and a second lens material is entirely formed. A method for manufacturing a solid-state imaging device in which an on-chip lens is formed by leaving a side wall on a side surface of a core by etching back a second lens material, wherein the etch back for the second lens material is performed by: The etching depth stops before the etching depth reaches a depth at which the underlayer of the second lens material is exposed in the portion between the on-chip lenses.

According to a second aspect of the present invention, there is provided a method for forming an on-chip lens, wherein a core portion made of a first lens material is selectively formed on a pixel disposition area so as to be located on a central portion of each pixel. Forming a second lens material on the pixel disposition area including the core portion so as to sufficiently cover the core portion, and then performing an etch-back process on the second lens material to form a second lens material; 2. An on-chip lens forming method in which the lens material of No. 2 is left as a sidewall on the side surface of the core, wherein the anisotropic etching of the second lens material is performed with an etching depth between each of the on-chip lenses. The stop is performed before reaching a depth at which the base of the second lens material is exposed to the portion.

[0009]

According to the method for manufacturing a solid-state imaging device of the first aspect,
Since the lens is formed by the core portion and its side wall, the size and curvature of each on-chip lens can be more accurately controlled by appropriately setting the height of the core portion and the diameter of each core portion, and the distance between adjacent lenses can be controlled. Short circuit can be prevented,
Further, since the etch-back for forming the sidewall is stopped before the underlayer of the second lens material is exposed between the on-chip lenses, the underlayer, for example, the on-chip filter is prevented from being destroyed by the etch-back. Can be.

According to the method of forming an on-chip lens according to the second aspect, since the lens is formed by the core and the sidewall thereof, the height of the core and the diameter of each core are appropriately set to more accurately. In addition, the size and curvature of each on-chip lens can be controlled, a short circuit between adjacent lenses can be prevented, and a side wall is formed before the underlayer of the second lens material is exposed between the on-chip lenses. Is stopped, it is possible to prevent the base from being destroyed by the etch back.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail with reference to the illustrated embodiments. FIG. 1 is a sectional view showing an example of the solid-state imaging device of the present invention. In the drawing, 1 is a semiconductor substrate, 2 is a thermal oxide film, 3 is a vertical transfer electrode made of polycrystalline silicon, 4 is an interlayer insulating film, 5 is a light shielding portion made of aluminum, and covers a portion other than the light receiving element in the imaging area. ing.

Reference numeral 6 denotes a passivation film that entirely covers the imaging area, 7 denotes a flattening film, 8 denotes an on-chip color filter for color separation formed on the flattening film 7, and 9 denotes a first lens material, for example, A core made of silicon dioxide SiO ₂ , 1
Reference numeral 0 denotes a side wall made of a second lens material, for example, silicon nitride Si ₃ N ₄ formed on the side surface of the core portion 9, and an on-chip lens formed by the core portion 9 and the side wall 10 formed on the side surface thereof. 11 are constituted.

The core 9 of each on-chip lens 11 is located on the opening of each light receiving element,
Is formed by making full use of, for example, a sidewall technique used for manufacturing a MOSIC having a lightly doped drain structure. Therefore, the controllability of the lens shape is extremely high. Therefore, by appropriately setting the height of the core and the diameter of each core, the size and curvature of each on-chip lens can be more accurately controlled, and short-circuiting between adjacent lenses can be prevented. Since the core 9 and the sidewalls 10 forming the on-chip lens 11 are both made of an inorganic material such as SiO ₂ and Si ₃ N _4, there is no danger that the shapes will be lost due to the heat treatment.

Further, Si ₃ N which is a sidewall material
No. ₄ has a larger refractive index than the second lens material which is the core material. Therefore, since the peripheral portion of the on-chip lens has a high refractive index, light incident on a portion distant from the central portion of the on-chip lens can be refracted more and incident on the light receiving element. Can be further enhanced, and the sensitivity can be improved.

FIGS. 2A and 2B and FIGS. 3A to 3C show the main parts of the method for manufacturing the solid-state image sensor shown in FIG. 1 in the order of steps. 3B are cross-sectional views illustrating a method of forming the core of the on-chip lens in the order of steps, and FIGS. 3A to 3C are cross-sectional views illustrating a method of forming the sidewalls of the lens in the order of steps. . First,
A method for forming the core 9 of the on-chip lens 11 will be described with reference to FIGS.

(A) A light-receiving element, a transfer electrode 3, a light-shielding film 5, a passivation film 6, and the like in an imaging area are formed by a known technique, a flattening film 7 is formed, and an on-chip filter 8 is formed. Thereafter, an SiO ₂ film 9 as a first lens material is deposited on the filter 8. Then, S
A resist film 12 is selectively formed on each portion of the surface of the iO ₂ film 9 where a core is to be formed, specifically, on a portion above the opening of each light receiving element. Needless to say, this is performed by coating and forming the resist film 12 and performing exposure and development processing. FIG. 2A shows a state after the resist film 12 is selectively formed.

(B) Next, the SiO ₂ film 9 is selectively etched by RIE using the resist film 12 as a mask, and then the resist film 12 is removed. FIG. 2B shows a state after the removal of the resist film 12. This step (B)
Thus, the core 9 of each on-chip lens 11 is formed above the opening of the light receiving element. Next, a method of forming the sidewall 10 of the on-chip lens 11 will be described with reference to FIGS.

(A) As shown in FIG. 3A, Si ₃ N _{4 as} a second lens material is formed on the on-chip filter 8 including the core 9.
The film 10 is formed thick enough to cover the core 9 sufficiently. (B) Next, as shown in FIG. 3B, the Si ₃ N ₄ film 10 is formed.
Etch back all over. FIG. 3B is in the middle of the etch back.

(C) Then, as shown in FIG.
When the surface of the core 9 made of SiO _{2 as} the first lens material is exposed, the etch-back is completed. Then, the solid-state imaging device shown in FIG. 1 having the on-chip lens 11 in which the side wall 10 made of the second lens material is formed on the side surface of the core portion 9 is obtained.

FIG. 4 is a sectional view showing a modification of the solid-state image pickup device of FIG. When the etch-back is performed until the upper surface of the core portion 9 is exposed as in the solid-state imaging device of FIG. 1, the surface of the on-chip filter may be slightly broken between adjacent on-chip lenses due to the etch-back. Therefore, in order to prevent such a fear, the etchback is terminated immediately before the upper surface of the core 9 is exposed. Further, as shown by the two-dot chain line in FIG. 4, after the formation of the on-chip filter 8 and before the deposition of the first lens material, the protective film 13 is formed to prevent the surface of the on-chip filter 8 from being broken by the etch back. Prevent it.

In the above embodiment, the present invention is applied to a solid-state imaging device having an on-chip color filter. However, the present invention can be applied to a solid-state imaging device having no on-chip color filter. . In such a solid-state imaging device, the on-chip lens 11 is formed on the flattening film 7, and there is no need to consider protection of the on-chip color filter.

[0022]

According to the first aspect of the present invention, there is provided a method of manufacturing a solid-state image sensor.
A first lens material to be a core portion is selectively formed, a second lens material is entirely formed, and the second lens material is etched back so as to remain as a sidewall on a side surface of the core portion. A method of manufacturing a solid-state imaging device for forming an on-chip lens by etching back the second lens material, exposing a base of the second lens material at a portion between the on-chip lenses having an etching depth. It is characterized by stopping before reaching the depth.

Therefore, according to the method of manufacturing a solid-state imaging device of the first aspect, since the lens is formed by the core and the side wall thereof, the height of the core and the diameter of each core are appropriately set. The size and curvature of each on-chip lens can be controlled more accurately, a short circuit between adjacent lenses can be prevented, and a side wall is formed between the on-chip lenses before the base of the second lens material is exposed. Is stopped, so that a base, for example, an on-chip filter, can be prevented from being destroyed by the etch back.

According to a second aspect of the present invention, there is provided a method for forming an on-chip lens, wherein a core portion made of a first lens material is selectively formed on a pixel disposition area so as to be located on a central portion of each pixel. Forming a second lens material on the pixel disposition area including the core so as to sufficiently cover the core, and then performing an etch-back process on the second lens material to form a second lens material; 2. An on-chip lens forming method in which the lens material of No. 2 is left as a sidewall on the side surface of the core, wherein the anisotropic etching of the second lens material is performed with an etching depth between each of the on-chip lenses. The stop is performed before reaching a depth at which the base of the second lens material is exposed to the portion.

Therefore, according to the on-chip lens forming method of the second aspect, since the lens is formed by the core and the side wall thereof, the height of the core and the diameter of each core are appropriately set. The size and curvature of each on-chip lens can be controlled more accurately, a short circuit between adjacent lenses can be prevented, and a side wall is formed between the on-chip lenses before the base of the second lens material is exposed. Is stopped, so that the base can be prevented from being destroyed by the etch back.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view illustrating an example of a solid-state imaging device manufactured by a method for manufacturing a solid-state imaging device according to the present invention.

FIGS. 2A and 2B are cross-sectional views illustrating a method of forming a core of an on-chip lens of the solid-state imaging device of FIG.

FIGS. 3A to 3C are cross-sectional views illustrating a method of forming a sidewall of an on-chip lens of the solid-state imaging device in FIG.

FIG. 4 is a sectional view showing a modified example of the solid-state imaging device of FIG. 1;

FIG. 5 is a sectional view showing a problem to be solved by the invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Semiconductor substrate 7 Planarization film 8 On-chip filter 9 Core part 10 Side wall 11 On-chip lens

Claims (2)

(57) [Claims] 1. A core made of a first lens material is selectively formed on a flattening film in an imaging region or on an on-chip filter on the surface of the flattening film so as to be located on the center of each light receiving element. Next, a second lens material is formed on the flattening film in the imaging region including the core portion or on the on-chip filter on the surface of the flattening film so as to sufficiently cover the core portion. A method of manufacturing a solid-state imaging device in which the second lens material is subjected to an etch-back process so that the second lens material remains as a sidewall on the side surface of the core. A method of manufacturing a solid-state imaging device, comprising: stopping anisotropic etching before an etching depth reaches a depth at which a base of a second lens material is exposed in a portion between each on-chip lens. 2. A core portion made of a first lens material is selectively formed on a pixel disposition area so as to be located on a central portion of each pixel, and then the pixel disposition including the core portion is performed. A second lens material is formed on the region so as to sufficiently cover the core portion, and then the second lens material is subjected to an etch-back process so that the second lens material is applied to the side surface of the core portion. A method of forming an on-chip lens that remains as a side wall, wherein anisotropic etching of the second lens material is performed, and an underlayer of a second lens material is formed in an etching depth between the on-chip lenses. A method for forming an on-chip lens, comprising: stopping before reaching an exposed depth.