JP2009105150A - Solid-state imaging device and manufacturing method thereof - Google Patents

Abstract

An object of the present invention is to propose a solid-state image pickup device having an antireflection film and a method for manufacturing the solid-state image pickup device that prevents a decrease in quantum efficiency in a photoelectric conversion unit with fewer manufacturing steps than in the conventional example. .
A plurality of photoelectric conversion elements formed in a two-dimensional array on a semiconductor substrate, an oxide film formed on the semiconductor substrate on which these photoelectric conversion elements are formed, and an oxide film formed on the oxide film And the first to third color filters having different transmission wavelengths formed corresponding to the photoelectric conversion elements on the antireflection film, and the first of these color filters. The antireflection film formed under the second color filter is composed of the first antireflection film having the same film thickness, and the antireflection film formed under the third color filter is more than the first antireflection film. A solid-state imaging device comprising a second antireflection film formed to be thick.
[Selection] Figure 2

Description

  The present invention relates to a solid-state imaging device and a manufacturing method thereof, and more particularly, to a structure of an antireflection film formed on a photoelectric conversion unit and a manufacturing method thereof.

  In general, in a pixel constituting a solid-state imaging device, a P-type or N-type well is formed on a semiconductor substrate, and an impurity diffusion region having a different polarity is embedded in the well, and a photoelectric conversion unit is formed by these PN junctions. Forming. An oxide film having a refractive index of 1.4 to 1.5 is formed on the semiconductor substrate on which the photoelectric conversion portion is formed, and the antireflection made of a silicon nitride film having a refractive index of about 3.5 is formed on the oxide film. A film is formed. On this antireflection film, optical filters having different transmission wavelengths are formed corresponding to the respective photoelectric conversion units, and then microlenses are formed on the respective optical filters.

  In such a solid-state imaging device, with the recent miniaturization of elements, there is a concern about a decrease in quantum efficiency with respect to light incident on the photoelectric conversion unit. Such a decrease in quantum efficiency is caused by a high reflectivity with respect to incident light in the antireflection film. For example, the reflectance of an antireflection film made of a silicon nitride film is about 30% with respect to incident light. Here, the quantum efficiency is represented by a ratio of the number of photocurrent carriers generated with respect to the number of photons incident on the photoelectric conversion unit.

  Further, the reflectance of the antireflection film has wavelength dependency. Therefore, since the reflectance of the antireflection film formed under each color filter is different, a difference occurs in the quantum efficiency.

  In other words, if the antireflection film is formed to have a uniform film thickness regardless of the type of color filter, the reflectivity of each antireflection film formed under different color filters is not minimum, so that the quantum efficiency of the entire solid-state imaging device as a whole Further, since the reflectance differs for each color, it causes color unevenness.

Therefore, as a means to solve the above problem, a structure that prevents the decrease in quantum efficiency and color unevenness by controlling the film thickness of the antireflection film so that the reflectance to the antireflection film for each color is minimized is known. It has been. (Patent Document 1)
However, in order to form a solid-state imaging device having such a structure, the antireflection film must be formed with a different film thickness for each color. Therefore, since more manufacturing steps are required than before, there is a problem in terms of production cost.
Japanese Patent Laid-Open No. 2005-142510

  SUMMARY OF THE INVENTION An object of the present invention is to propose a solid-state imaging device having an antireflection film and a method for manufacturing the solid-state imaging device that prevents a decrease in quantum efficiency in a photoelectric conversion unit with fewer manufacturing steps than the conventional example.

  A solid-state imaging device according to the present invention includes a plurality of photoelectric conversion elements formed in a two-dimensional array on a semiconductor substrate, an oxide film formed on the semiconductor substrate on which these photoelectric conversion elements are formed, and the oxide film An antireflection film formed thereon, and first to third color filters having different transmission wavelengths formed corresponding to the photoelectric conversion elements on the antireflection film. Among them, the antireflection film formed under the first and second color filters is composed of the first antireflection film having the same film thickness, and the antireflection film formed under the third color filter is the first antireflection film. It is characterized by comprising a second antireflection film formed thicker than the antireflection film.

  The method for manufacturing a solid-state imaging device according to the present invention includes a step of forming a plurality of photoelectric conversion elements in a two-dimensional array on a semiconductor substrate, and an oxide film is formed on the semiconductor substrate on which these photoelectric conversion elements are formed. A step of forming an antireflection film on the oxide film, and a first transmission layer having a different transmission wavelength corresponding to each photoelectric conversion element on the first and second antireflection films. And a step of forming a third color filter.

  According to the present invention, it is possible to prevent a decrease in quantum efficiency with fewer manufacturing steps than in the conventional example.

  Hereinafter, embodiments of the solid-state imaging device of the present invention will be described with reference to FIGS.

  FIG. 1 is a top view illustrating the photoelectric conversion unit of the solid-state imaging device according to the present embodiment. 2A is a cross-sectional view taken along the broken line A-A ′ shown in FIG. 1, and FIG. 2B is a cross-sectional view taken along the broken line B-B ′.

  The color filter in this example uses three kinds of color filters 11 and 12, which are a green color filter 11 that transmits green light, a red color filter 12 that transmits red light, and a blue color filter 13 that transmits blue light. , 13 are formed in a Bayer array. Further, the film thickness of the first antireflection film 15 formed under the green color filter 11 and the red color filter 12 is formed thinner than the film thickness of the second antireflection film 14 formed under the blue color filter 13. It is a structured.

  In the solid-state imaging device shown in FIGS. 1 and 2, photoelectric conversion elements 17 are formed on a semiconductor substrate 16 in a two-dimensional array. A silicon oxide film 18 is formed on the semiconductor substrate 16 on which the photoelectric conversion elements 17 are formed, and the first and second antireflection films 14 made of a silicon nitride film are formed on the silicon oxide film 18. , 15 are formed. A green color filter 11 is formed on the antireflection films 14 and 15 in a checkered pattern corresponding to each photoelectric conversion element 17 via the first planarization layer 19, and the green color filter 11 is not formed. A blue color filter 13 or a red color filter 12 is formed at the location. A microlens 21 is formed on each of the color filters 11, 12, and 13 with a second planarizing layer 20 interposed therebetween.

  Next, the manufacturing process of the solid-state imaging device shown in FIGS. 1 and 2 according to the present embodiment will be described with reference to FIGS. In addition, (a) and (b) of each figure in FIGS. 3-6 shows sectional drawing corresponding to FIG. 2 (a) and (b).

  First, as shown in FIG. 3, a silicon oxide film 18 having a refractive index of 1.4 to 1.5 is formed with a thickness of 1 to 10 nm on a semiconductor substrate 16 on which the photoelectric conversion element 17 is formed. A silicon nitride film 22 having a refractive index of 3.5 is uniformly formed with a thickness of 100 nm by a CVD (Chemical Vapor Deposition) method.

  Next, as shown in FIG. 4, a photoresist 23 is formed on the silicon nitride film 22 so as to cover only portions where the blue color filter 13 is to be formed later on the silicon nitride film 22, and exposure is performed. .

  Next, as shown in FIG. 5, ion etching is performed on the exposed silicon nitride film 22. This process causes a difference in the film thickness of the antireflection film, and the etched portion becomes the first antireflection film 15, and the unetched portion becomes the second antireflection film 14.

  Next, as shown in FIG. 6, the photoresist 23 is removed.

  Finally, the first planarizing layer 19, the color filters 11, 12, 13 and the second planarizing layer 20 are formed in this order, and then the microlens 21 is formed, as shown in FIG. 1 and FIG. A solid-state imaging device can be obtained.

  The film thicknesses of the first and second antireflection films 14 and 15 formed here are determined from FIG. 7 showing the wavelength dependency of the transmittance that varies depending on the film thickness of the antireflection films 14 and 15. That is, for example, when the film thickness of these antireflection films 14 and 15 is 55 nm, the transmittances of the green wavelength and the red wavelength are approximately the same, approximately 95%. On the other hand, the transmittance at the blue wavelength is about 80%, and this difference in transmittance causes color unevenness and a decrease in quantum efficiency. In this embodiment, the film thickness is controlled so that the transmittance of the blue wavelength matches the transmittance of the other two colors. If the film thickness is 70 nm or more, substantially the same transmittance can be realized.

  Thus, in this embodiment, only the film thickness of the second antireflection film 14 under the blue color filter 13 is changed to the film of the first antireflection film 15 disposed under the other color filters 11 and 12. It is formed thicker than the thickness. In this way, by making the transmittance of the antireflection films 14 and 15 formed under the color filters 11, 12, and 13 equal, a solid-state imaging device with no color unevenness and high quantum efficiency can be obtained. Here, in this embodiment, the refractive index of the silicon oxide film 18 is 1.0 or more, and the film thickness thereof is formed in the range of 1 nm to 10 nm, and the first and second antireflection films 14 and 15 are formed. Has a refractive index of 2.0 or more, and a film thickness of 40 nm to 70 nm is formed to obtain a solid-state imaging device with high quantum efficiency.

  In addition, the film thickness of the anti-reflective films 14 and 15 in this embodiment is not restricted above, It can set freely, unless it deviates from the meaning of invention.

It is a top view which shows the photoelectric conversion part of the solid-state imaging device by this embodiment. It is sectional drawing which shows the photoelectric conversion part of the solid-state imaging device by this embodiment, the figure (a) is sectional drawing along broken line AA 'shown in FIG. 1, and the figure (b) is FIG. It is sectional drawing along the broken line BB 'shown. It is sectional drawing which shows the manufacturing process of the solid-state imaging device by this embodiment. It is sectional drawing which shows the manufacturing process of the solid-state imaging device by this embodiment. It is sectional drawing which shows the manufacturing process of the solid-state imaging device by this embodiment. It is sectional drawing which shows the manufacturing process of the solid-state imaging device by this embodiment. It is a figure which shows the wavelength dependence of the transmittance | permeability by each film thickness of a silicon nitride film.

Explanation of symbols

  11: green color filter, 12: red color filter, 13: blue color filter, 14: second antireflection film, 15: first antireflection film, 16: semiconductor substrate, 17: photoelectric conversion element, 18: silicon Oxide film, 19: first planarization layer, 20: second planarization layer, 21: microlens, 22: silicon nitride film, 23: photoresist.

Claims (5)

A plurality of photoelectric conversion elements formed in a two-dimensional array on a semiconductor substrate;
An oxide film formed on a semiconductor substrate on which these photoelectric conversion elements are formed;
An antireflection film formed on the oxide film;
On the antireflection film, the first to third color filters having different transmission wavelengths formed corresponding to the photoelectric conversion elements are provided.
Among these color filters, the antireflection film formed under the first and second color filters is composed of the first antireflection film having the same film thickness, and is formed under the third color filter. Comprises a second antireflection film formed thicker than the first antireflection film.   2. The solid-state imaging device according to claim 1, wherein the first antireflection film and the second antireflection film are formed of the same material and in the same manufacturing process, and differ only in film thickness.   The solid-state imaging device according to claim 1, wherein the antireflection film is a silicon nitride film. Forming a plurality of photoelectric conversion elements in a two-dimensional array on a semiconductor substrate;
Forming an oxide film on a semiconductor substrate on which these photoelectric conversion elements are formed;
A first antireflection film having the same film thickness is formed under the first and second color filter formation planned regions on the oxide film, and the third color filter formation planned region on the oxide film is formed under the third color filter formation planned region. Forming a second antireflection film thicker than the first antireflection film;
Forming the first to third color filters having different transmission wavelengths on the first and second antireflection films corresponding to the photoelectric conversion elements, respectively. Manufacturing method of imaging apparatus. The steps of forming the first and second antireflection films include
A step of uniformly forming a silicon nitride film on the oxide film;
Forming a photoresist on the silicon nitride film formed under the third color filter formation scheduled region;
Exposing the silicon nitride film through the photoresist;
The method for manufacturing a solid-state imaging device according to claim 4, further comprising a step of etching the region exposed by the exposing step.

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