JPH0624232B2 - Method of manufacturing solid-state imaging device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Field of Industrial Application) The present invention relates to a method for manufacturing a solid-state imaging device in which a microlens is provided on each photosensitive portion.

(Prior Art) A solid-state imaging device has advantages such as small size and light weight, high reliability, and long life as a semiconductor element, and is free from image sticking defects such as image sticking and pattern fading. It has certain characteristics. Therefore, the color compact video camera is naturally widely used for measuring instruments, production machines, image information processing devices and the like.

The structure of a conventional color solid-state imaging device will be described with reference to the sectional view of FIG. Photodiodes 2 functioning as photoelectric conversion elements are formed at a predetermined pitch on a semiconductor substrate 1, an insulating film 3 made of an oxide film or the like is formed thereon, and a PSG film 4 functioning as a passivation film is further formed thereon. To be done. Further, an aluminum light-shielding film 5 and a smoothing layer 6 made of an acrylic resist are formed on this. The portion where the photodiode 2 is formed becomes a photosensitive portion, and the aluminum light shielding film 5 is provided with an opening portion in a region corresponding to the photosensitive portion. And PEP method (Photo Engravin
g Process) and a dyeing method to form a cyan dyeing layer 7 on a predetermined photosensitive portion, and a yellow dyeing layer 9 is formed on another predetermined photosensitive portion via an intermediate layer 8 for preventing mixing. No dyeing layer is provided on the photosensitive section that detects white light. Finally, a protective layer 10 is provided on this. The intermediate layer 8 and the protective layer 10 are also made of an acrylic resist like the smooth layer 6.

(Problems to be Solved by the Invention) In such a conventional solid-state imaging device, it is necessary to increase the number of pixels in order to increase the resolution. Therefore, the photosensitive portion area with respect to the effective pixel area is reduced, and eventually, This leads to a decrease in sensitivity. Sensitivity is an important element of a solid-state imaging device, and this decrease in sensitivity is a fatal drawback.
Performance will be reduced.

In order to solve this problem, various proposals have been made so far to provide a microlens on each photosensitive portion, but it cannot always be said that it has been sufficiently successful.

For example, JP-A-60-38989 describes a method of obtaining a microlens molded into a convex lens shape by heat-treating a pattern-developed photosensitive resin and softening it.
However, there are problems that the softened photosensitive resin is connected to the adjacent microlens, the manufacturing process is complicated, and the like.

The present invention provides a method of manufacturing a solid-state image pickup device, which enables a microlens for preventing a decrease in sensitivity to effectively exhibit its function on a photosensitive section that has been made finer by increasing the number of pixels by a simpler manufacturing process. The purpose is to provide.

[Structure of Invention]

(Means for Solving the Problems) In order to achieve the above object, a method for manufacturing a semiconductor device of the present invention is a pixel in which a plurality of photosensitive parts (2) are arranged in a matrix on a semiconductor substrate (1). In order to smooth the surface of the solid-state imaging device (2 to 9) in which the region (101) is formed, the first photosensitive resin is applied to the entire substrate to form the smooth layer (200). In the forming process, a casein-based resist is applied as a second photosensitive resin on the smoothing layer (200), and the resist is exposed and developed to form a microlens layer ( 201) is formed without applying heat treatment above the softening temperature of the resist, and a third photosensitive resin is formed on the microlens layer (201) and the smooth layer (200 or 6). Apply the protective film (202)
And a step of forming.

(Operation) A smooth layer, a microlens layer, and a surface protective film are sequentially formed on the surface of the solid-state imaging device by the first to third photosensitive resins. The second photosensitive resin that becomes the microlens layer is a casein resist. When this material is applied and pattern developed, the edges of the film are rounded as shown in FIG. This makes it possible to easily form a convex microlens on the photosensitive portion in a low temperature process.

Further, a smooth layer and a protective layer are formed of the first and third photosensitive resins. Since the microlenses are formed by a low temperature process without softening treatment by heating, the resin film once formed is not deformed by heat. For this reason,
The same kind of photosensitive resin can be used for the smooth layer, the intermediate layer, the protective layer, and the like. The laminated photosensitive resins of the same kind can simultaneously develop each layer from the surface protective layer to the smooth layer by one pattern development. As a result, the bonding pad section (second
The removal of the photosensitive resin on the openings shown in the drawing) and on the scribe (dicing) lines of the substrate can be performed collectively at the final step of patterning the protective layer.

As a result, the steps required to form the microlenses in the solid-state imaging device are simplified and the number of steps is reduced. It is possible to avoid the problem that an extra step of molding the resist for pattern-developed micro-resist to be softened (fluidized) by heat treatment and molded into a convex lens shape is required.
The problem that the pattern of the resist fluidized by the heat treatment spreads is also avoided.

Further, in the smoothing layer forming step, since the smoothing layer is not pattern-developed due to the opening of the bonding pad portion and the like,
The next resist can be coated on the smooth layer having no steps, and resist unevenness (striation) does not occur. As a result, a manufacturing process with good quality and yield can be realized.

(Example) Hereinafter, the present invention will be described in detail based on an illustrated example.

FIG. 1D shows a horizontal sectional view of an embodiment of the color solid-state imaging device according to the present invention.

Photodiodes 2 are formed on the surface of the semiconductor substrate 1 at a predetermined pitch, and only the portions corresponding to the photodiodes 2 are thinly formed on the surface of the semiconductor substrate 1, the PSG film 4, and the photodiodes 2. An aluminum light-shielding film 5 having an opening only in a portion, a smoothing layer 6, a cyan dyeing layer 7 formed only in a portion corresponding to a predetermined photodiode 2,
A transparent first intermediate layer 8 for preventing color mixing and a yellow dyeing layer 9 formed only in a portion corresponding to a predetermined photodiode 2 are formed as in the conventional device.

The transparent second intermediate layer 200 is formed on the yellow layer 9, and the microlens layer 201 is formed on the portion corresponding to each photodiode 2 thereon. A protective layer 202 is provided on the microlens 201.

FIG. 2 is a plan view of this solid-state imaging device.

The photodiodes 2 (not shown) are arranged in the pixel region 101 on the substrate surface in a plurality of rows in a horizontal direction X along a horizontal register (not shown) and in a plurality of columns in a vertical direction Y along a vertical register (not shown). Are formed in a matrix.

An enlarged view of this pixel region 101 is shown in FIG.

As described above, the openings 102 of the light-shielding film are arranged in a matrix in the horizontal direction X and the vertical direction Y corresponding to the arrangement of the photodiodes 2 (not shown). The microlens layer 201 is formed in a stripe shape in the vertical direction at a position corresponding to each column in the vertical direction of the opening 102, and has a width slightly larger than the width of the opening 102 in the horizontal direction X. . This striped microlens layer is
It is formed of a casein-based resist.

Next, a manufacturing process of such a color solid-state image pickup device will be described with reference to the sectional view shown in FIG.

First, the photodiodes 2 which are photoelectric conversion elements are formed on the surface of the semiconductor substrate 1 at a predetermined pitch. Subsequently, an insulating film 3 such as an oxide film is formed on the substrate 1, and a passivation film such as a PSG film 4 is formed thereon. Then
An aluminum light-shielding film 5 having an opening corresponding to the photodiode 2 is formed on the PSG film 4 by vapor deposition and patterning. Then, a smooth layer 6 made of a transparent polymer resin layer such as acrylic resin is formed on the entire surface by spin coating.
Is formed with a film thickness of 2 μm (FIG. 1 (a)).

Next, a water-soluble resist having a film thickness of 1.0 μm is spin-coated on the smooth layer 6. Examples of the water-soluble resist material include proteins such as gelatin and casein, or polyvinyl alcohol to which 1% ammonium dichromate as a photosensitizer is added. Subsequently, this water-soluble resist is pre-baked at 70 ° C. for 40 minutes, and then exposed under a condition of 50 mJ / cm ² through a predetermined mask using a high pressure mercury lamp. After that, the substrate 1 is immersed in pure water for 10 seconds and then post-baked to leave only a portion of the water-soluble resist layer corresponding to a predetermined photodiode (which becomes a cyan photosensitive portion).

Subsequently, the residual water-soluble resist layer is dyed by immersing the substrate 1 in a cyan dyeing solution kept at 60 ° C. for 2 minutes, washing it with pure water, and then drying it to form a portion corresponding to a predetermined photodiode. A cyan dyed layer 7 is formed on the surface (FIG. 1 (b)).

Then, by the same method as the smoothing layer, 0.5 μ
A first intermediate layer 8 made of an acrylic resist is formed to a film thickness of m (FIG. 1 (b)). The intermediate layer 8 functions as a color mixing prevention film.

Then, in the same manner as in the cyan dyeing layer forming step described above, a water-soluble resist layer is formed only on a predetermined photosensitive portion (which becomes a yellow photosensitive portion), and then the substrate 1 is kept at 60 ° C. in a yellow dyeing liquid. It is immersed for 3 minutes in water, washed with pure water and dried to form a yellow dyed layer 9 (FIG. 1 (c)).

The steps up to this point are the same as the manufacturing steps of the conventional device.
The subsequent steps are the features of the present invention.

Next, similarly to the step of forming the first intermediate layer 8, the second intermediate layer 200 is formed on the entire surface of the substrate using an acrylic resist (FIG. 1 (d)). The intermediate layer 200 also functions as a smooth layer with respect to the microlens layer 201 formed later. Then, a casein-based resist, for example, caseinin containing 1% ammonium dichromate is applied to the substrate 1 to a film thickness of 1.0 μm, and after the pre-baking, predetermined steps are performed in the same manner as the dyeing layer forming step. Then, the substrate is immersed in pure water and then post-baked to form a stripe-shaped microlens layer 201 as shown in FIG. (FIG. 1 (d)).

Finally, the protective layer 202 made of an acrylic resist is formed by the PEP method (Phot method) in the same manner as the steps of forming the smooth layer and the intermediate layer.
o Engraving Process). As described above, since each of the smooth layer, the intermediate layer and the protective layer is formed of an acrylic resist, when the surface protective layer is subjected to the pattern development by the PEP method, the intermediate layer and the smooth layer underneath thereof are formed. Are also developed at the same time. Therefore, it is possible to collectively remove an unnecessary portion of the resist layer from the protective film 202 of the microlens to the passivation (PSG film) 4 for protecting the elements on the substrate surface. Then, the color solid-state imaging device according to the present invention is completed.

FIG. 4 is an enlarged cross-sectional view of the main part of FIG. 1 (d).

Microlens layer 20 formed in a stripe pattern
1 has a width slightly larger than the opening size of the aluminum light shielding film 5.

FIG. 5 shows the actual measurement results of the effect of the spread amount δ (per one side) of the microlens width on the light-shielding film opening size on the relative sensitivity of the photosensitive portion. Here, the relative sensitivity of 100% is the sensitivity when there is no microlens.

As can be seen from the figure, the microlens layer 201 exhibits the highest effect of improving the sensitivity when the microlens layer 201 is spread to both sides by about 1 μm with respect to the opening of the light shielding film. It is considered that this is because the optical function mainly based on the cross-sectional shape of the microlens layer 201 condenses most light into the opening when the light slightly spreads from the opening. That is,
When the lens width is smaller than that, the amount of light incident on the lens decreases, and when the lens width is too large, the cross-sectional shape of the effective part of the lens becomes close to a flat plate shape, and the light collecting function as the lens deteriorates. It is thought to be because.

The value of δ = 1 μm, which gives the maximum sensitivity shown in FIG. 5, is considered to change somewhat depending on the size of the opening of the light-shielding film and the distance between the opening and the microlens layer. It is important to form it slightly larger.

As described above, in order to obtain a high sensitivity improving effect, it is necessary to accurately control the width dimension of the microlens layer 201 and accurately align the microlens layer 201 and the light shielding film opening. Particularly when the number of pixels is increased and the definition is increased, extremely high accuracy is required.

In the present invention, since the microlens layer 201 is formed of the casein-based resist, the casein-based resist has a higher microfabrication resolution than other lens materials, so that it forms a microlens layer having high dimensional accuracy. be able to. Further, since the microlens layer 201 is formed in a stripe shape in the vertical direction, there is almost no positional deviation of the light shielding film opening in the vertical direction as compared with the horizontal direction. The alignment with and can be performed with high accuracy.

Further, in the method for manufacturing a solid-state imaging device of the present invention, it is positively used for forming the microlens layer that the edge of the casein resist after pattern development is rounded as shown in FIG. In order to make the microlens more spherical, the microlens layer 201 is not heat-treated to be softened (reflowed). Therefore, there does not occur such a problem that the bottoms of the microlenses are widened and the lens arrays are connected to each other as in the heat softening treatment. Without such heat treatment, the smooth layer, the intermediate layer, the protective layer, the color filter and the like which are already laminated and formed of the resist do not have to be thermally deformed. Since the difference in softening temperature is not required between the resist materials used for each layer, it is possible to use the same kind of photosensitive resin as a smooth layer, an intermediate layer and a protective layer.

In this way, the solid-state imaging device according to the present invention can maintain high sensitivity even when the definition is increased.

Although the color solid-state image pickup device having the color filters of cyan, yellow, and white has been described in the above embodiment, the present invention is applicable to, for example, a complementary color system of cyan, yellow, green, and magenta, or three types of red, green, and blue. It is needless to say that the present invention can be applied to a color solid-state image pickup device in which primary color type color filters are laminated and a monochrome solid-state image pickup device.

In this case, the smoothing layer 6 to form the color filter
The dyeing layer 9 becomes unnecessary. Further, not only the CCD type solid-state image pickup device but also the MOS type, the BBD type (bucket relay type image pickup device) and the CID type (charge injection type image pickup device) are applicable.

〔The invention's effect〕

As described above, in the method for manufacturing a solid-state imaging device of the present invention, the microlens layer is formed by utilizing the property that the edges of the casein-based resist are rounded after pattern development. Therefore, it is possible to avoid the conventional heat treatment step of softening the microlens layer by heat treatment and molding it into a convex lens shape.

As a result, in order to carry out the conventional heat treatment step, an indispensable condition for the film to be used, that is, "even if the microlens layer (photosensitive resin) is softened, other layers (photosensitive resin) are not softened" The conditions are not imposed on the respective materials such as the smooth layer, the intermediate layer, the filter layer, the microlens layer and the protective layer in the process of the present invention. Therefore, there is a high degree of freedom in selecting the photosensitive resin material. For example, as in the embodiment shown in FIG. 1, the same kind of photosensitive resin can be used for the smooth layer, the intermediate layer and the protective layer. In such a case, there is an advantage that these layers of the same material can be subjected to pattern development collectively at a time. Therefore, according to the present invention, it becomes possible to form the microlens layer with high dimensional control and alignment accuracy by a simpler manufacturing process.

[Brief description of drawings]

FIG. 1 is a sectional view showing an embodiment of a manufacturing process and structure of a solid-state image pickup device according to the present invention, FIG. 2 is a plan view of the solid-state image pickup device of FIG. 1, and FIG. 3 is a part of FIG. FIG. 4 is an enlarged view, FIG. 4 is a partially enlarged view of FIG. 1 (d), FIG. 5 is a view showing the effect of the spread amount of the microlens width with respect to the aperture size of the light-shielding film, on the sensitivity improvement, and FIG. Sectional drawing which shows the structure of an imaging device. 1 ... Semiconductor substrate, 2 ... Photodiode, 3 ... Insulating film, 4 ... Passivation film, 5 ... Aluminum light-shielding film, 6 ... Smoothing layer, 7 ... Cyan dyeing layer, 8 ... Intermediate layer, 9: yellow dye layer, 101: pixel area, 1
02: light-shielding film opening, 201: microlens layer,
202 ... a protective layer.

Claims (2)

[Claims] 1. A surface of a solid-state imaging device (2 to 9) having a plurality of photosensitive regions (2) arranged in a matrix on a semiconductor substrate (1) and having a smooth surface. To be the first
The smoothing layer forming process of forming the smoothing layer (200) by applying the photosensitive resin of 2) to the entire substrate, and applying a casein resist as the second photosensitive resin on the smoothing layer (200), After exposure and development, a microlens layer (201) is formed on the plurality of photosensitive parts (2).
A microlens layer forming process for forming the same without applying a heat treatment above the softening temperature of the resist, and applying a third photosensitive resin on the microlens layer (201) and the smoothing layer (200). And a step of forming a protective film (202), and a method for manufacturing a solid-state imaging device. 2. The method for manufacturing a solid-state image pickup device according to claim 1, wherein the first and third photosensitive resins are both acrylic resists.