JPH04268763A - Method of forming on-chip microlens - Google Patents

Abstract

PURPOSE:To enable a micro-lens to be lessened in noneffective region by a method wherein a first and a second resist film are etched back until the second resist film is eliminated, the first resist film is thermally deformed into lenses, and the first resist film and a lens material layer are etched back. CONSTITUTION:Resist films 4a and 3 are etched back until the resist film 4a is fully eliminated. Then, island-like resist films 3a are thermally deformed into the shapes of lenses. The resist film 3a is formed of material excellent in thermal deformation property, so that it can be deformed into a comparatively fine lens excellent in light converging property. Thereafter, the lens-shaped resist film 3a is transferred onto a lens material layer 2 through etchback.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for forming an on-chip microlens, and more particularly to a method for forming an on-chip microlens in which a large number of microlenses are formed on a chip such as a solid-state image sensor.

0002

2. Description of the Related Art A solid-state image sensing device in which microlenses made of resist or plastic are formed on each light receiving element on the surface of a semiconductor substrate is disclosed in, for example, JP-A-2-10
This method is introduced in Japanese Patent Application Publication No. 3962, Japanese Patent Application Laid-Open No. 1-270362, and the like.

[0003] Conventionally, the formation of microlenses has been
forming a lens material layer made of plastic on the surface of the solid-state image sensor, forming a resist film on the lens material layer,
The resist film is patterned by exposure and development so that rectangular islands remain independently on each light-receiving element, and by heat treatment, each rectangular island-shaped resist film is shaped into a lens (approximately convex spherical shape).
The shape of the lens was transferred to the lens material layer by thermally deforming the resist film and etching back the resist film and the lens material layer.

0004

[Problems to be Solved by the Invention] However, in the conventional method of forming microlenses, the distance between the microlenses is 1.
．． The thickness is as much as 5 μm, which poses a problem of widening the ineffective area. This is because conventionally, a resist with low resolution, such as HPR-204 (trade name), has been used to form the lenses, making it impossible to reduce the distance between the microlenses. On the other hand, if a high-resolution film is used, there is a problem that it will not be thermally deformed neatly into a lens shape during the heat treatment after patterning.

This is because a resist film has a property that if the thermal deformability is good, the resolution will be bad, and if the resolution is good, the thermal deformability will be good. That is, there is a trade-off between thermal deformability and resolution of the resist film, and this has been a major constraint on narrowing the ineffective area.

The present invention has been made to solve these problems, and its purpose is to narrow the ineffective area of the microlens.

[0007]

[Means for Solving the Problems] A method for forming an on-chip microlens according to claim 1 includes forming a first resist film having good thermal deformability on a lens material layer on a chip surface, and forming a first resist film having good thermal deformability.
A second resist film with good resolution is formed on the resist film, the second resist film is patterned, and the second resist film and the first resist film are etched back until the second resist film is removed. After that, the first
The first resist film is thermally deformed into a lens shape, and then the first resist film and the lens material layer are etched back. A method for forming an on-chip microlens according to a second aspect includes forming a first resist film on a lens material layer on a chip surface, forming a second resist film on the first resist film with poor adhesion, and The second resist film is patterned, and then the second resist film is thermally deformed into a lens shape by heat treatment, and then the first and second resist films are patterned.
The resist film and lens material layer are etched back.

[0008]

EXAMPLES Hereinafter, a method for forming an on-chip microlens according to the present invention will be explained in detail according to the illustrated examples. Figure 1 (A
) to (G) are sectional views showing one embodiment of the present invention in the order of steps. (A) First, as shown in FIG. 1A, a lens material layer (for example, CMS) 2 made of plastic is coated and formed on a substrate 1 of a solid-state image sensor. (B) Next, as shown in FIG. 1B, a first resist film having good thermal deformability [for example, H
PR-204 (trade name)] 3 is formed, and the first resist film 3 is exposed to light over the entire surface. That is, it is exposed to light without patterning.

(C) Next, as shown in FIG. 1C, a second resist film [for example, PFR (trade name)] 4 with good resolution is coated on the first resist film 3 with good thermal deformability. Form by applying. (D) Next, as shown in (D) of FIG. 1, the second resist film 4 with good resolution is patterned by exposure (exposure through a mask) and development to form each light receiving element (not shown).
Island-shaped resist films 4a, 4a, . . . , which are rectangular when viewed from above and are independent from the others, are formed at positions corresponding to .

(E) Next, the resist films 4a, 4a, . . . and the resist film 3 are etched back until the resist films 4a, 4a, . FIG. 1E shows the state after this etchback. As a result of this etchback, island-shaped resist films 3a, 3a, which are rectangular when viewed from above and are independent of each other, are formed at positions corresponding to each light receiving element, and this pattern is formed by the exposure in step (D). , the pattern of the resist films 4a, 4a, . . . formed by development is exactly the same. That is, the patterns of the resist films 4a, 4a, . . . are transferred as they are to the resist films 3a, 3a, . It goes without saying that it is preferable that the etching rates of the first resist film 3 and the second resist film 4 be as similar as possible to ensure that this transfer is performed clearly.

(F) Next, each island-shaped resist film 3a, 3a, . . . is thermally deformed into a lens shape as shown in FIG. 1(F) by heat treatment. Since the resist films 3a, 3a, . . . are originally made of a material with good thermal deformability, they are formed into a relatively clean lens shape and have good light focusing characteristics. (G) Thereafter, by etching back, the shapes of the lens-shaped resist films 3a, 3a, . . . are transferred to the lens material layer 2 as shown in FIG. 1(G). As a result, microlenses 2a, 2a, . . . are formed in the lens material layer 2.

According to such an on-chip microlens formation method, patterning for forming microlenses is performed by exposing and developing the second resist film 4 with good resolution, so that each microlens 2a, 2
The interval between a can be narrowed. Specifically, conventional 1
．． The distance between the microlenses, which could not be reduced to 5 μm or less, could be reduced to about 1.0 μm. Since the distance between the microlenses can be narrowed, the ineffective area can be narrowed, and the degree of integration of the solid-state image sensor can be increased. In addition, since the shape of the microlens is obtained by thermally deforming the second resist film, which has good thermal deformability, it is possible to form a microlens with a good shape, and as a result, the light focusing property can be improved. . Therefore, it becomes possible to reduce the ineffective area without deteriorating the light collection characteristics.

FIGS. 2A to 2F are cross-sectional views showing another embodiment of the method for forming an on-chip microlens according to the present invention in the order of steps. (A) First, as shown in FIG. 2A, a lens material layer (for example, CMS) 2 made of plastic is coated and formed on a substrate 1 of a solid-state image sensor. (B) Next, as shown in FIG. 2B, a first resist film [for example, HPR-204 (
(trade name)] 3 is formed, and the first resist film 3 is exposed to light over the entire surface. That is, it is exposed to light without patterning.

(C) Next, as shown in FIG. 2 (C),
A second resist film 4 made of, for example, the same material is coated on the first resist film 3 with poor adhesion. Unlike the embodiment shown in FIG. 1, the second resist film 4 does not need to have high resolution, but rather needs to have good thermal deformability. (D) Next, as shown in FIG. 2(D), the second resist film 4 is patterned by exposure and development, so that the second resist film 4 is patterned at positions corresponding to each light-receiving element (not shown) from above, independently from each other. Island-shaped resist films 4a, 4a, . . . having a rectangular shape when viewed are formed.

(E) Next, each island-shaped resist film 4a, 4a is thermally deformed into a lens shape by performing a heat treatment. Then, as shown in FIG. 2(E), each resist film 4a,
The peripheral edges of resist films 4a are shifted, and the peripheral edges of adjacent resist films 4a, 4a come into substantially contact with each other. This is because the process (B
), the second resist film 3 was formed on 2 with poor adhesion. Therefore, the ineffective area can be reduced to approximately 0 to extremely small, and the effective aperture ratio can be increased.

(F) After that, the second resist films 4a, 4
a,..., by etching back the first resist film 2 and the lens material layer 2, the second resist film 2 is etched back as shown in FIG. 2(F).
The resist films 4a, 4a, . . . are transferred onto the lens material layer 2 to form microlenses 2a, 2a, .

According to the present on-chip microlens forming method, the island-shaped resist films 4a, 4a consisting of the second resist film 4 formed on the first resist film 3 with poor adhesion are thermally deformed to form a microlens. Therefore, during thermal deformation, the peripheral edges of the adjacent resist films 4a, 4a shift outward, eliminating or narrowing the ineffective area. Therefore, the effective aperture ratio can be increased.

[0018]

The method for forming an on-chip microlens according to claim 1 includes forming a lens material layer on a chip surface, forming a first resist film having good heat deformability on the lens material layer, and A second resist film with good resolution is formed on the first resist film, and by exposing and developing the second resist film, the film is formed into an island shape for each microlens forming area. The second resist film and the first resist film are etched back until the second resist film is removed, and then the first resist film is thermally deformed by heat treatment. The method is characterized in that the first resist film and the lens material layer are etched back. Therefore, according to the method for forming an on-chip microlens according to the first aspect, the width of the ineffective region can be determined by the first resist film having good resolution, and thus can be made narrower. Since the shape of the microlens is formed by thermally deforming the second resist film having good thermal deformability through heat treatment, it is possible to obtain a microlens with a good shape. Therefore, the shape of the microlens can be improved and the ineffective area can be reduced. The method for forming an on-chip microlens according to claim 2 includes forming a lens material layer on the chip surface, forming a first resist film on the lens material layer, and forming a second resist film on the first resist film. forming a resist film with poor adhesion, and patterning the second resist film so that each microlens formation region exists independently in the form of an island by subjecting the second resist film to exposure and development; Thereafter, the second resist film is thermally deformed into a lens shape by heat treatment, and then the first and second resist films and the lens material layer are etched back. Therefore, according to the on-chip microlens forming method of claim 2,
Since the island-like resist film consisting of the second resist film formed on the first resist film with poor adhesion is thermally deformed to create the shape of a microlens, the periphery of each island-like resist film shifts outward at that time. The gap between the resist films is reduced,
Invalid area is reduced. Therefore, the effective aperture ratio can be increased.

[Brief explanation of the drawing]

1A to 1G are cross-sectional views showing one embodiment of the method for forming an on-chip microlens according to the present invention in the order of steps;

FIGS. 2A to 2F are cross-sectional views showing another embodiment of the method for forming an on-chip microlens according to the present invention in the order of steps;

[Explanation of symbols]

1 Chip 2 Lens material layer 2a Micro lens 3 First resist film 4 Second resist film

Claims (2)

[Claims] 1. A lens material layer is formed on a chip surface, a first resist film with good thermal deformability is formed on the lens material layer, and a second resist film with good resolution is formed on the first resist film. forming a resist film, and patterning the second resist film so that it exists independently in the form of islands for each microlens forming region by subjecting the second resist film to exposure and development; The second resist film and the first resist film are etched back until the second resist film is removed, and then the first resist film is thermally deformed into a lens shape by heat treatment.
A method for forming an on-chip microlens, comprising etching back a resist film and a lens material layer. 2. A lens material layer is formed on a chip surface, a first resist film is formed on the lens material layer, and a second resist film is formed on the first resist film with poor adhesion. , the second resist film is subjected to exposure treatment and development treatment to pattern the second resist film so that each microlens formation region is independently formed into an island shape, and then heat treatment is performed to form the second resist film as described above. The second resist film is thermally deformed into a lens shape, and then the first and second resist films are
A method for forming an on-chip microlens, comprising etching back a resist film and a lens material layer.