JPH04243161A - Manufacture of microlens for solid image pickup element - Google Patents

Abstract

PURPOSE:To provide the manufacture of a microlens for solid image pickup element, which can be easily formed by the use of an exposure device to be used for the formation of a solid image pickup element. CONSTITUTION:A microlens for solid image pickup element is manufactured by a process for forming a substrate-flattening layer 1 on a solid image pickup element, by a process for forming a thin film 2 in parts other than a microlens- forming part on said substrate-flattening layer 1, then by a process for forming a lens layer 4 thicker than said thin film 2 on the whole surface and further forming an upper flattening layer 5 on the lens layer, thereafter by a process for etching back said upper flattening layer 5 and lens layer 4 until the surface of said thin film 2 appears, and then by a process for forming the lens layer 4 into a lens-shape after removing said thin film 2.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of manufacturing a solid-state image sensing device, and more particularly to a method of manufacturing a microlens formed above a light receiving array in order to improve the aperture ratio and the sensitivity of the device.

0002

2. Description of the Related Art Conventionally, in solid-state imaging devices, microlenses have been formed above the light receiving array in order to improve the aperture ratio and the sensitivity of the device. A method for forming such a microlens is described in, for example, Japanese Patent Application Laid-Open No. 59-9445.
No. 6 discloses a method as shown in FIGS. 6 to 8. That is, in FIG. 6, 101 is an image sensor substrate made of P-type silicon;
High concentration n+ type diffusion regions 102 in which n type impurities are diffused are arranged above, and these P type image sensor substrate 101
By the pn junction between the pn junction and the n+ type diffusion region 102, photodiodes as photoelectric conversion sections are configured corresponding to the number of pixels. Further, an Al wiring 103 for signal detection is formed between each n+ type diffusion region 102 on the surface of the image sensor substrate 101, and a passivation film 104 is formed on the entire surface including the Al wiring 103. Passivation film 1 for optical input
04 constitutes a front-illuminated solid-state image pickup device that receives light from the light source.

[0003] When forming a micro condenser lens on the light receiving surface of this solid-state image sensor, first, the entire surface of the light receiving surface is
As shown in Figure 7, PMMA (polymethyl methacrylate), for example, is used as a material that is optically colorless, has high light transmittance, and has the function of causing chemical changes when exposed to radiation such as electron beams and X-rays, and is spin-coated. PMMA thin film 105 with a thickness of about 1 to 3 μm applied by a method such as
is formed as a thin film for forming a lens. Next, this PMM
The PMMA thin film 105 is selectively exposed to electron beams or X-rays in accordance with the planar pattern in which the micro condensing lens is to be formed, corresponding to each light-receiving portion of the A thin film 105, that is, a photodiode. Next, by developing this PMMA thin film 105 with a developer,
As shown in FIG. 8, the exposed portion is removed to form a micro condenser lens 106 made of a PMMA thin film corresponding to each photodiode.

0004

[Problems to be Solved by the Invention] As explained in the above conventional example, in order to form a microlens, the material must be optically colorless, have high light transmittance, and be resistant to electron beams and X-rays.
A material that undergoes chemical changes due to radiation such as radiation is required, and in conventional examples, materials such as PMMA are used. For this reason, as exposure equipment, I-line or G-line, which is normally used in the manufacture of semiconductor devices such as solid-state image sensors,
A line stepper could not be used, and electron beam, X-ray, or deep UV exposure equipment was required.

However, it is desirable that the microlenses also be formed by the same exposure apparatus as that used to form the solid-state image sensor below the microlenses. The reason for this is that errors in the size and distortion of images exposed by each exposure device actually exist, and furthermore, in recent years, the pixel size of solid-state image sensors has been reduced to 10 μm or less, and with this, when forming microlenses, The mask alignment error becomes severe, and from this point of view, it is desirable to use a stepper with a high precision alignment error.

[0006] In the conventional microlens forming method, after coating the lens material, a thin oxide film is spin-coated.
Coat using the On Grass method (S.O.G), etc., and then apply a regular resist on top of it to form a resist film.
After that, the uppermost resist is patterned by photolithography, then the thin oxide film is removed using the resist as a mask, and then the lens material is etched away using the remaining thin oxide film as a mask, using the so-called multilayer resist process. A method of forming microlenses is also considered, but this method has the disadvantage that the process and structure are extremely complicated.

The present invention was made in order to solve the above-mentioned problems in the conventional method of forming microlenses, and it is possible to easily form microlenses using an exposure device such as a stepper used in forming solid-state image sensors. The present invention aims to provide a possible method for forming a microlens for a solid-state image sensor.

[0008]

[Means and Effects for Solving the Problems] In order to solve the above-mentioned problems, the present invention provides a step of forming a base flattening layer on a solid-state image sensor, and a step of forming a base flattening layer on the base flattening layer. a step of forming a thin film on the entire surface, a step of forming a lens layer thicker than the thin film on the entire surface, and further forming an upper flattening layer thereon; A microlens for a solid-state imaging device is formed by a step of etching back the lens layer, and then a step of molding the lens layer into a lens shape after removing the thin film.

[0009] By using the above process, the exposure equipment normally used in the manufacture of semiconductor devices such as solid-state image sensors can be used as is, and high-precision microlenses can be easily formed with a simple process using etchback. can do.

0010

[Example] Next, an example will be explained. 1 to 5 are manufacturing process diagrams for explaining an embodiment of a method for manufacturing a microlens for a solid-state image sensor according to the present invention. Note that the configuration of the solid-state imaging device below the microlens is the same as the conventional one, so illustration and explanation will be omitted, and illustration and explanation will be given starting from the base flattening layer formed above. In Figure 1,
1 is a base flattening layer, for example, PMMA or the like is spin-coated several times on the wafer on which the solid-state imaging device is formed, and then heat treatment is performed at a temperature higher than the thermal softening point to flatten the surface. Form it so that it does. The thickness of the base flattening layer 1 is adjusted during the coating process so that it becomes the optimum value as a result of lens optical design.

Next, S. O. After forming a thin film 2 made of G or the like on the entire surface of the underlying flattening layer 1, a resist is applied to the thin film 2.
A desired resist pattern 3 is formed using the exposure equipment used to form the solid-state image sensor, and using this resist pattern 3 as a mask, only the thin film 2 is etched using a reactive ion etching method or the like. Only the thin film 2 is anisotropically removed under the conditions that the underlying planarizing layer 1 and the resist pattern 3 are not etched. When this step is completed, the cross-sectional structure shown in FIG. 1 is obtained. Note that the thickness of the thin film 2 is set to be approximately equal to the final thickness of the lens layer, which will be described later.

Next, the resist pattern 3 is removed, and as shown in FIG.
As shown in FIG. 2, a lens material such as PMMA is applied to the entire surface of the wafer to a thickness that is at least thicker than the thin film 2 to form a lens layer 4. Thereafter, an upper flattening layer 5 is formed on top of the above lens material, or a material having an etching rate equivalent to the lens material when dry etching is performed later, to flatten the uppermost part of the wafer. I do. This step is necessary for the subsequent etch-back step.

Next, the upper flattening layer 5 and the lens layer 4 are
Etch back is performed using a reactive ion etching method or the like. At this time, as mentioned earlier, the upper planarization layer 5
So that the etching rate of lens layer 4 and lens layer 4 are the same,
It is necessary to adjust their constituent materials or etching conditions. When this etching process is completed, the state shown in FIG. 3 is that the surface of the thin film 2 is not covered with the lens layer 4, and the lens layer 4 is equal to the thickness of the thin film 2.
It is in a state where the thickness is formed.

Next, as shown in FIG. 4, only the thin film 2 is removed. Various methods can be considered for this step, such as wet processing or dry etching, but the point is that only the thin film 2 needs to be removed without etching the base planarizing layer 1 and the lens layer 4.

Next, by performing treatment for a desired period of time at a temperature higher than the thermal softening point of the material constituting the lens layer 4, the lens layer 4 is formed into a lens shape as shown in FIG. 5, and a microlens is formed. 6 is obtained.

Although the embodiments have been described above, the present invention is equally applicable to cases in which a color filter is provided below a base flattening layer, or to cases in which a color filter is formed on a lens.

Furthermore, in the above embodiments, materials such as PMMA are used as the materials for the underlying flattening layer 1 and the lens layer 4, but these constituent materials are transparent in the light reception wavelength region of the solid-state image sensor. It is not necessary to have the characteristic of being sensitive to radiation as in the conventional example. Therefore, the range of selection of lens materials is widened, and materials with good light transmittance and lens properties can be selected, and highly reliable and stable lenses can be formed in a simple process. Further, in this embodiment, the constituent material of the thin film 2 is S. O. Although G is shown as a constituent material of the thin film 2, it has a good etching selectivity when etching back the lens layer 4, and
Various materials can be used as long as they are hardly etched and the constituent materials of the underlying flattening layer 1 and lens layer 4 are not removed in the step of removing the thin film 2. O. It is not limited to G.

[0018]

[Effect of the invention] As explained above based on the embodiments,
According to the present invention, using various lens materials that can be used with an exposure apparatus used in the process of forming a solid-state image sensor,
Microlenses with high reliability and good characteristics can be formed in a simple process.

[Brief explanation of the drawing]

FIG. 1 is a manufacturing process diagram for explaining an embodiment of a method for manufacturing a microlens for a solid-state image sensor according to the present invention.

FIG. 2 is a diagram showing a manufacturing process following FIG. 1.

FIG. 3 is a diagram showing a manufacturing process following FIG. 2;

4 is a diagram showing a manufacturing process following FIG. 3. FIG.

5 is a diagram showing a manufacturing process following FIG. 4. FIG.

FIG. 6 is a manufacturing process diagram showing a conventional method for manufacturing a microlens for a solid-state image sensor.

7 is a diagram showing a manufacturing process following FIG. 6. FIG.

8 is a diagram showing a manufacturing process following FIG. 7. FIG.

[Explanation of symbols]

1 Base planarization layer 2 Thin film 3 Resist pattern 4 Lens layer 5 Upper planarization layer 6 Micro lens

Claims (1)

[Claims] 1. A step of forming a base flattening layer on a solid-state image sensor, a step of forming a thin film on the base flattening layer in a portion other than the microlens forming portion, and then forming a lens layer thicker than the thin film on the entire surface. forming a layer and further forming an upper planarizing layer thereon, etching back the upper planarizing layer and the lens layer until the surface of the thin film is exposed, and then removing the thin film and then forming the lens layer. 1. A method for manufacturing a microlens for a solid-state image sensor, comprising the steps of: molding the microlens into a lens shape.