JPH04278582A - Solid-state image sensing device and manufacture thereof - Google Patents

Abstract

PURPOSE:To make incidence light condense efficiently on photodiodes in a solid-state image sensing device having microlens layers by a method wherein the steps between the upper surfaces of the photodiodes and the upper surfaces of charge transfer parts are lessened. CONSTITUTION:A solid-state image sensing device adopts a two-stage constitution that a first microlens layer 11 is first provided having in combination a role to lessen the steps between the upper surfaces of photodiodes 2 and the upper surfaces of charge transfer parts 3 and moreover, a second microlens layer 13 is provided on the layer 11 holding a smooth layer 12 between the layers 11 and 13.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a highly sensitive solid-state imaging device used in video cameras and the like, and a method for manufacturing the same.

0002

[Background Art] In recent years, solid-state imaging devices have advantages such as small size, light weight, high reliability, and long life. etc., are widely used.

An example of a conventional solid-state imaging device will be explained based on FIG. 3. On the surface of the semiconductor substrate 1, photodiodes 2 functioning as photoelectric conversion elements are formed in a matrix, and between the photodiodes 2 there is a charge transfer section 3 that transfers signals photoelectrically converted by the photodiodes 2. is made of polysilicon or the like. Further above this, an aluminum light shielding film 4 and a silicon nitride film 5 are provided as a passivation film.

In a high-sensitivity solid-state imaging device, a smooth layer 6 is formed on the top surface of the silicon nitride film 5, a microlens layer 7 is provided on the top surface of the smooth layer 6 and above the photodiode 2, and This upper surface is covered with a protective film 8,
The microlens layer 7 focuses light onto the photodiode 2 to improve sensitivity.

[0005]

[Problems to be Solved by the Invention] However, although the microlens layer 7 is formed on the top surface of the smooth layer 6, the surface of the smooth layer 6 is different from the top surface of the photodiode 2 and the top surface of the charge transfer section 3. Since there is a step, unevenness occurs along this, and the microlens layer 7 is formed in a shape along this, which causes the problem that incident light is diffused and sensitivity is reduced.

[0006] The present invention solves the above-mentioned problems of the prior art, and is a microstructure that eliminates and flattens the unevenness caused by the difference in level between the top surface of the photodiode and the charge transfer section, and focuses incident light on the photodiode to improve sensitivity. An object of the present invention is to provide a solid-state imaging device having a lens layer and a method for manufacturing the same.

[0007]

[Means for Solving the Problems] In order to achieve this object, the solid-state imaging device of the present invention first forms a first microlens layer on the top surface of the photodiode with a thickness corresponding to the difference in level from the charge transfer portion. After forming and flattening the surface,
The structure is such that a smooth layer is further deposited on the upper surface, and a second microlens layer is formed on the upper surface.

[0008]

[Operation] With this structure, since the surface of the first microlens layer is flattened, the second microlens layer can be easily formed in a semi-convex shape above it. Furthermore, since both microlens layers condense incident light onto the photodiode, sensitivity can be improved.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS A solid-state imaging device which is an embodiment of the present invention is shown in FIG. In FIG. 1, 1 to 5 are the same as those in the conventional example shown in FIG. 3, so the same numbers are given and the explanation will be omitted.

That is, the feature of the present invention is that the water-soluble casein film is large enough to cover at least the photodiode 2 and is buried in the step of the silicon nitride film 5 formed between the upper part of the photodiode 2 and the upper part of the aluminum light-shielding film 4. This is achieved by providing the eyeball-shaped first microlens layer 11 made of resin. By forming this first microlens layer 11, more light can be collected by the photodiode 2 and the amount of light can be increased. Further, in order to smooth the silicon nitride film 5 and the first microlens layer 11 above the aluminum light shielding film 4, a smoothing layer 12 of acrylic transparent resin is formed, and at least the first microlens layer 1
A semi-convex second microlens layer 13 made of water-soluble casein is provided on the upper surface of the smooth layer 12 with a size larger than 1 and including a part above the aluminum light-shielding film 4. 14 is a protective layer.

[0011] By forming this second microlens layer 13, it becomes possible to condense the light above the aluminum light shielding film 4 onto the photodiode 2, and together with the first microlens layer 11, the light is increased. can be used to improve sensitivity.

Hereinafter, a cross-sectional view of the manufacturing process of a solid-state imaging device, which is an embodiment of the present invention, will be explained with reference to FIG. Figure 2 (a
) shows a cross-sectional view of the solid-state imaging device, in which the semiconductor substrate 1
On the surface of the photodiode 2, which functions as a photoelectric conversion element, are formed at a predetermined pitch, and in the charge transfer section 3 of the insulating layer between the photodiodes 2, a transfer electrode that controls this is formed of polysilicon or the like. has been done.

Furthermore, on top of this, an aluminum light shielding film 4 is provided.
and a silicon nitride film 5 functioning as a passivation film.

Next, as shown in FIG. 2(b), the upper surface of the silicon nitride film 5 is coated with, for example, a water-soluble casein resin 11A. Next, after pre-baking this, mask 15
Expose to light.

Next, as shown in FIG. 2C, development and post-baking are performed to form and planarize the first microlens layer 11 in the shape of an eye-shaped lens only above the photodiode 2. Since the second microlens layer 13 is formed above the layer whose surface has been flattened in this manner, the second microlens layer 13 can be easily formed into a semi-convex shape.

[0016] On this upper surface, a smooth layer 12 of about 2 μm is deposited, for example, from an acrylic transparent resin. Next, a water-soluble casein resin 13A is applied onto the smooth layer 12, and after pre-baking, it is exposed to light using a mask 16, followed by development and post-baking. Then, as shown in FIG. 2(d), a semi-convex lens-shaped second microlens layer 13 is formed. Note that the size of this semi-convex lens may be larger than the photodiode 2 and may also include the area of the charge transfer section 3.

Then, as shown in FIG. 2E, an acrylic resin is applied to a thickness of, for example, about 1.0 μm onto the substrate on which the semi-convex lens-shaped second microlens layer 13 is formed. , the protective film 14 is formed by exposing through a predetermined mask and using a special developer all at once.

[0018]

As described above, the present invention flattens the surface of the first microlens layer and forms the second microlens layer on the flat layer above the first microlens layer. The layers can be easily formed into a semi-convex shape, and a solid-state imaging device with high sensitivity can be provided by collecting a large amount of light with both microlens layers and increasing the amount of light condensed on the photodiode.

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional view of a solid-state imaging device according to an embodiment of the present invention.

[Figure 2] Cross-sectional view of the manufacturing process of the solid-state imaging device

[Figure 3] Cross-sectional view of a conventional solid-state imaging device

[Explanation of symbols] 1 Semiconductor substrate 2 Photodiode 3 Charge transfer section 4. Light shielding film 5 Silicon nitride film (insulating film) 11 First microlens layer 12 Smooth layer 13 Second microlens layer 14 Protective film

Claims (2)

[Claims] 1. A photodiode formed on a semiconductor substrate, a charge transfer section that transfers signal charges converted by the photodiode, and a light shielding film that blocks light incident on the charge transfer section. In the solid-state imaging device, a first microlens layer formed above the photodiode and having a size that flattens the surface level difference between the photodiode and the charge transfer section and covers the photodiode; a smoothing layer for further smoothing the step between the surface of the first microlens layer and the upper surface of the light shielding film formed on the entire surface including the surface of the microlens layer; and the upper part of the smoothing layer above the photodiode. 1. A solid-state imaging device comprising at least a second microlens layer formed on the surface of the photodiode and having a larger area than the photodiode. 2. Photodiodes are formed in a matrix on a semiconductor substrate, and a charge transfer section for transferring signal charges on the semiconductor substrate between the photodiodes via an insulating film, and the charge transfer section are shielded from light. After forming the light shielding film, a step of flattening the surface and forming a first microlens layer for condensing light on the upper surface of the photodiode, and a step of forming a first microlens layer on the entire surface including the surface of the first microlens layer. It is characterized by comprising at least the steps of forming a smooth layer to further improve surface smoothness, and forming a second microlens layer having a size that at least covers the photodiode on the smooth layer. A method for manufacturing a solid-state imaging device.