JPH0457365A - Manufacture of solid-state image sensing element - Google Patents

Abstract

PURPOSE:To form micro-lenses having small radii of curvature in corresponding to a reduction in pitch in a short time and improve the light condensing property and degree of integration of a solid-state image pickup element by forming the micro-lenses by meting a transparent resist pattern. CONSTITUTION:A semiconductor substrate 21 on which a photosensitive section 26, electrodes 24 and 25, and light-shielding film 28 are formed in advance is coated with a transparent protective film 29 and the film 29 is coated with a photosensitive transparent resist film 31. Stripe- or island-like transparent resist patterns having rectangular or trapezoidal cross sections are formed so that they can face the photosensitive section 26 by patterning the resist film 31. Then micro-lenses 32 are formed by performing heat treatment on the substrate 21 after the substrate 21 is positioned, with the transparent resist pattern down side, so as to melt the resist pattern, Therefore, the micro-lenses 32 which have high heights and small radii of curvature and are excellent in light condensing property can be formed and a highly integrated solid-state image sensing element can be manufactured, because the melted transparent resist pattern becomes higher in height due to the surface tension and the gravity acting downward.

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Industrial Application Field) The present invention relates to a method of manufacturing a solid-state image sensor, and particularly to a method of manufacturing a solid-state image sensor that improves the process of forming microlenses.

(Prior Art) Conventionally, a solid-state image sensor is shown in Fig. 4 (a) as explained below.
) to (d).

First, for example, a two-layer transfer electrode 4.5 is formed on a p-type semiconductor substrate 1 via an insulating film 2.3, and then an n-type impurity is doped into the substrate 1 using the transfer electrode 5 as a mask to form a photosensitive area. An n-type diffusion layer 6 is formed. Subsequently, a transparent interlayer insulating film 7 is deposited over the entire surface. Subsequently, a light shielding film 8 made of A11 or the like is formed on the interlayer insulating film 7 so as to be located above the transfer electrode 5, and then a transparent protective film 9 is deposited on the entire surface (as shown in FIG. 4(a)). ).

Next, as shown in FIG. 2B, a photosensitive transparent resist is applied onto the protective film 9 and dried to form a photosensitive transparent resist film 10. Subsequently, this photosensitive transparent resist film 10 is exposed and developed to form a transparent resist pattern 11 having a trapezoidal cross section and a stripe shape, facing the n-type diffusion layer 6, as shown in FIG. to form. Note that in this step, a so-called island-like transparent resist pattern, which is a substantially uniform rectangular pattern or is scattered in a matrix manner, may be formed. Subsequently, the striped transparent resist pattern 11 is melted and thermally deformed by heat treatment at the melting temperature of the transparent resist, thereby forming a microlens 12 having a semi-cylindrical cross section as shown in FIG. Then, a solid-state image sensor is manufactured. Note that when the transparent resist pattern has an island shape, a hemispherical microlens is formed.

However, the above-mentioned conventional method has problems in terms of light gathering ability and miniaturization, as described below.

(2) When the transparent resist pattern 11, which has a trapezoidal cross section and a striped shape, is melted and deformed, the surface tension of the melted resist increases to a height (Hl), as shown in FIG.
), but gravity generally prevails and the angle (α
l) becomes smaller and also expands in the lateral direction, so the width (W
l) becomes wider.

As a result, the radius of curvature of the microlens 12 increases, and the light-gathering ability decreases.

(2) As shown in FIG. 6, if the width of the transparent resist pattern 11 after patterning is W1% and the pitch is dl, and the width of the formed microlens 12 is W1 and the pitch is d and -, melting occurs as described above. Since it spreads in the lateral direction when it is deformed, the relationship Wl<W, -d, >d, - is established. As a result, when forming the transparent resist pattern 11, it is necessary to widen the pitch (dl) of the transparent resist pattern 11 in advance so that d+- does not become 0. It becomes difficult to form a macro lens 12 that is compatible with the miniaturization of the diffusion layer 6 itself and the miniaturization of the pitch.

(2) For the same reason as mentioned above, thermal deformation takes time, so the time required to form the microlens becomes longer.

(Problems to be Solved by the Invention) The present invention was made in order to solve the above-mentioned conventional problems. The present invention aims to provide a method for manufacturing an image sensor.

(Means for Solving the Problems) The present invention includes a step of coating a transparent protective film on a semiconductor substrate on which a photosensitive part, an electrode, and a light shielding film have been formed in advance, and a process of coating a photosensitive transparent resist film on the protective film. a step of coating the resist film; a step of buttering the resist film to form a striped or island-like transparent resist pattern with a rectangular or trapezoidal cross section facing the photosensitive area;
A solid-state imaging device comprising the steps of arranging the substrate so that the transparent resist pattern is located on the lower side, and forming a microlens by performing heat treatment to melt the transparent resist pattern. This is a method for manufacturing an element.

(Function) According to the present invention, a semiconductor substrate on which a striped or island-like transparent resist pattern is formed to face a photosensitive area is placed upside down and heat-treated to form a melted transparent resist pattern. The surface tension not only increases the height, but also applies downward gravity, making it possible to form microlenses with a large height, small radius of curvature, and excellent light-gathering ability.

In addition, since it is possible to prevent the transparent resist pattern in the melt state from spreading laterally, it is possible to form microlenses with the same width and pitch as when forming the transparent resist pattern, and to miniaturize the photosensitive area formed on the semiconductor substrate. Accordingly, it is possible to manufacture highly integrated solid-state imaging devices.

Furthermore, since the time for deforming the transparent resist pattern can be shortened due to the above-described effect, microlenses can be formed in a short time.

(Example) Hereinafter, an example of the present invention will be described in detail with reference to FIGS. 1(a) to (e).

First, for example, a two-layer transfer electrode 24.25 is formed on a p-type semiconductor substrate 21 via an insulating film 22.23, and then an n-type impurity is doped into the substrate 21 using the transfer electrode 25 as a mask to form a photosensitive area. An n-type diffusion layer 26 is formed. Subsequently, a transparent interlayer insulating film 27 is deposited over the entire surface.

Subsequently, a light shielding film 28 made of AJ or the like is formed on the interlayer insulating film 27 so as to be located above the transfer electrode 25, and then a transparent protective film 29 is deposited on the entire surface (as shown in FIG. 1(a)). ).

Next, as shown in FIG. 3B, a photosensitive transparent resist of, for example, polystyrene is coated on the protective film 29 and dried to form a photosensitive transparent resist film 30. Continuing,
By exposing and developing this photosensitive transparent resist film 30, a transparent resist pattern 31 having a trapezoidal cross section and a stripe shape is formed on the n-type diffusion layer 30, as shown in FIG.
Formed so as to face 6.

Next, the substrate 21 is placed upside down so that the transparent resist pattern 31 is located on the lower side (see FIG.
d) As shown). Next, the melting temperature of the transparent resist (
The striped transparent resist pattern 31 is melted and thermally deformed by heat treatment at 130 to 160°C for about 5 to 10 minutes, thereby forming a microlens 32 having a semi-cylindrical cross section as shown in FIG. to manufacture a solid-state image sensor.

According to the method of the present invention, when the transparent resist pattern 31 having a trapezoidal cross section and a stripe shape is melted and deformed, the surface tension of the resist in the melted state increases to a height (H2) as shown in FIG. ), and a downward force of gravity is applied, so it is possible to prevent horizontal expansion and increase the angle (α2). As a result, the radius of curvature of the microlens 32 can be made small, and the light gathering ability can be improved.

Further, as shown in FIG. 3, the width of the transparent resist pattern 31 after patterning is W2, the pitch is d2, and the width of the formed microlenses 32 is W2' pitch is d2-
, W2-W2- d can be prevented from spreading in the lateral direction when melting and deforming as described above.
The relationship is 2-d 2-. As a result, since the microlenses 32 can be formed with the same width and pitch as the patterned transparent resist pattern 31, the semiconductor substrate 2
It is possible to form a macro lens 32 that is compatible with the miniaturization of the diffusion layer 26 itself as a photosensitive portion formed in 1 and the miniaturization of the pitch.

Furthermore, since the deformation time of the transparent resist pattern 31 can be shortened due to the above-described effect, the microlens 31 can be formed in a short time. Specifically, compared to the conventional method, microlens formation took approximately 1/2 the processing time.

In the above embodiment, a striped transparent resist pattern was formed, but the same effect can be achieved even if an island-shaped transparent resist pattern is formed. In this case, hemispherical microlenses are formed by the melting process.

[Effects of the Invention] As detailed above, according to the present invention, a microlens with a small radius of curvature can be formed in a short time in response to the miniaturization of the photosensitive area itself and the miniaturization of the pitch, and as a result, the light-gathering performance is improved. This brings about remarkable effects such as the ability to mass-produce highly integrated solid-state imaging devices.

[Brief explanation of the drawing]

FIGS. 1(a) to (e) are cross-sectional views showing the manufacturing process of a solid-state image sensor in an example of the present invention, FIG. 2 is a schematic view showing a microlens formed in this example, and FIG. Schematic diagram for explaining the effects of this embodiment, FIG. 4(a)-
(d) is a cross-sectional view showing the manufacturing process of a solid-state image sensor by the conventional method, FIG. 5 is a schematic diagram showing a microlens formed by the conventional method, and FIG. 6 is a schematic diagram for explaining the problems with the conventional method. It is a diagram. 21...p-type semiconductor substrate, 24.25...-transfer electrode, 26...n-type diffusion layer (photosensitive part), 28...shielding film, 29...protective film, 31...transparent Resist pattern, 32...microlens. Applicant's agent Patent attorney Takehiko Suzue

Claims (1)

[Claims] A process of coating a transparent protective film on a semiconductor substrate on which a photosensitive area, an electrode, and a light-shielding film have been formed in advance, a process of coating a photosensitive transparent resist film on this protective film, and a process of patterning this resist film to form stripes. a step of forming a transparent resist pattern having a rectangular or trapezoidal cross section and facing the photosensitive area; and a step of arranging the substrate so that the transparent resist pattern is located on the lower side. 1. A method for manufacturing a solid-state image sensor, comprising the steps of: forming a microlens by melting the transparent resist pattern through heat treatment.