JP2829066B2 - SOLID-STATE IMAGING ELEMENT WITH MICRO LENS AND METHOD OF MANUFACTURING THE SAME - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a solid-state imaging device and a method for manufacturing the same, and more particularly, to a solid-state imaging device characterized in that a microlens is formed by using a photoresist pattern. The present invention relates to the manufacturing method.

[Prior Art] A solid-state imaging device is usually called a CCD or MOS imaging device, and is a kind of silicon semiconductor device. The solid-state imaging device includes a light receiving area and vertical and horizontal scanning circuits for driving the light receiving area and extracting image signals. The light receiving area is made up of a large number of fine pixel components. The pixel further includes a light receiving portion and a signal portion such as a wiring for extracting an electric signal from the pixel. Although the ratio of the light receiving portion to the whole is referred to as the aperture ratio, these devices generally have a low aperture ratio, do not use light incident on the signal processing portion, and have a drawback that the light utilization ratio is low. For this reason, improvement of the light utilization rate has been considered so far.

There have been various proposals for providing a microlens for condensing light for each pixel of a solid-state imaging device.
4366, JP 57-9180, JP 57-124485, etc.
Thereafter, it can be seen in JP-A-60-60756. A method of providing a lens-shaped cap on a light-receiving element or a light-emitting element has been known in the past, and is often seen in optical devices and the like, and the application of the microlens can be said to be a proposal along this line. However, many of the methods proposed so far are difficult in terms of concrete implementation, and many have many problems from the viewpoint of yield.

For example, in a method in which lens-shaped irregularities are formed in a solid-state imaging device-like organic resin layer by pressing while being heated against a mold, it is extremely difficult to form a uniform lens without involving air bubbles in the organic resin layer, It is also difficult to prevent a phenomenon such as sticking from occurring in the mold.

Also, studies have been made on forming a V-shaped groove on the surface of a glass plate by ion etching to form a prismatic refraction diffraction element, and disposing it on a solid-state imaging device. However, in this method, it is extremely difficult to accurately bond the element onto the element, and there is a problem in practicality and mass productivity.

[Problems to be solved by the invention]

The present invention aims to eliminate the disadvantages of the prior art and to form a microlens array (microlens array) directly on a solid-state imaging device by using photolithography technology widely used in the manufacture of semiconductor devices. In particular, it is an object of the present invention to provide an excellent method in terms of productivity, yield, cost, and the like.

[Means for solving the problem]

In order to achieve the above object, as a result of examining various materials and processes, it is good to form a microlens by post-exposing a photoresist pattern formed in a rectangular shape using photolithography technology and flowing it by heat treatment. I found That is, the present invention provides a method for efficiently bleaching a specific photoresist material upon post-exposure (overall exposure), becoming almost transparent at a wavelength of 400 nm or more (transmittance: 95% or more), and a rectangular resist pattern. Is subjected to a heat treatment at a predetermined temperature, the width of the bottom of the pattern hardly changes, resulting in an almost perfect arc-shaped pattern. In addition, the arc-shaped pattern of the photoresist thus formed is collected as a lens. It is based on the discovery of having light capabilities.

Hereinafter, the method for forming a microlens of the present invention will be specifically described.

At present, in semiconductor photolithography, an alkali-developable positive photoresist comprising an alkali-soluble resin (eg, phenol novolak resin) and a photosensitizer (eg, naphthoquinonediazide compound) is used. In these, the exposed portions are solubilized in an alkali developing solution, and a positive pattern is obtained. Usually, these resists are sensitive in a wavelength range from i-line (365 nm) to g-line (436 nm) and have strong light absorption before light irradiation. However, when these resists are irradiated with light of a certain degree or more, bleaching is efficiently performed (in the sense of bleaching action,
Eliminate light absorption and improve transmittance) and 400nm
Almost transparent in the above wavelength region (transmittance: 9
5% or more). In this case, an alkali-soluble resin 40 serving as a resist matrix polymer
Some materials have light absorption in a wavelength region of 0 nm or more, and thus need to be limited as a material.

In addition, DeepUV resists that are sensitive to short wavelength light such as KrF excimer laser (248 nm)
Most are almost transparent in the wavelength region of 0 nm or more, and are suitable for the lens-forming material of the present invention.

Each of these positive photoresists has a temperature of a few hundred degrees Celsius.
When heat treatment is performed after patterning into a rectangular shape, a polka dot lens pattern is obtained. The effect of improving the light utilization rate by forming a lens by liquefying a solid rectangular pattern is disclosed in
Since it is described in detail in 60756, although omitted here, it is shown that the effect of improving the light utilization is about 1.55.

Hereinafter, the present invention will be described using specific materials and processes.

A solid-state image sensor silicon substrate 1 comprising a light receiving unit 2 for performing photoelectric conversion, a scanning unit 3 for extracting an electric signal generated by the light receiving unit, a passivation film 4 for protecting the light receiving unit and the scanning unit, and a color filter layer 5 ( This is shown in Fig. 1. This figure is a schematic cross-sectional view for explaining the function.) The lens fixing layer 6 is provided thereon. The material of the lens fixing layer is not particularly limited, but is preferably an organic polymer material such as polyglycidyl methacrylate and polymethyl methacrylate. The lens fixing layer is formed by spin-coating a solution of the organic polymer material (for example, using ethyl cellosolve acetate or the like as a solvent).

The microlens forming layer 7 is formed thereon by spin coating. As the material of the microlens forming layer, a positive photoresist material is desirable, and in particular, a high resolution positive photoresist material which is an alkali development type is desirable. It should be particularly noted that the alkali-soluble polymer, which is the matrix polymer of the positive photoresist material, has a transmittance of 95% or more at 400 nm, and that the resist comprising the polymer and the photosensitizer can be efficiently irradiated with light. Bleaching (400n after light irradiation)
m must have a transmittance of 95% or more). As such materials, an organic silicon-based positive photoresist using ladder silicone as a matrix polymer (RU-1600P manufactured by Hitachi Chemical), a high-resolution i-line (365 nm) to g-line (436 nm) positive photoresist (Tokyo Ohka) TSMR-V3
), KrF (248nm) excimer laser, etc.
Deep UV resist and the like can be mentioned.

Patterning of the microlens forming layer is performed by ordinary photolithography technology. That is, Kr
Irradiation with F (248 nm) excimer laser, i-line (365 nm), or g-line (436 nm), development using an alkaline developer, and rinsing with running water can obtain a microlens forming layer pattern. . ((Fig. 2 (b))
Subsequently, a large excess of light is irradiated on the entire surface of the microlens forming layer pattern, and bleaching is efficiently performed by post-exposure so that light absorption is almost eliminated at 400 nm or more. Next, the microlens forming layer pattern is subjected to a heat treatment at a predetermined temperature (for example, 100 ° C. to 150 ° C./several tens of minutes), and is subjected to thermal fluidization to form a microlens as shown in FIG. 2 (c). In order to prevent thermal deformation of the microlenses formed in this manner, it is also effective to lightly ashing with oxygen plasma thereafter.

Although the manufacturing method of the present invention has been described using actual materials and processes, the present invention is not limited to this.

[Action]

In the manufacturing method of the solid-state imaging device with microlenses of the present invention, since the photolithography technology used in semiconductor manufacturing is used, the solid-state imaging device can be manufactured with high productivity and high yield. It is. It is also an excellent method from the viewpoint of high resolution.

〔Example〕

 Hereinafter, the present invention will be described with reference to specific examples.

Example 1 A lens fixing layer 6 is mainly formed of a PGMA (polyglycidyl methacrylate) or the like on a solid-state imaging device substrate (shown in FIG. 1, which is a schematic cross-sectional view for explaining the function). Formed relatively thick with colorless and transparent organic resin as a component. In this example, 2,2 ', 4,4'-
The one to which 1% by weight of tetrahydroxybenzophenone was added was used. The PGMA film was formed by spin coating, baked at 200 ° C. for 30 minutes, and thermally crosslinked. On this, the microlens forming layer 7 was formed by spin coating using an organic silicon-based positive photoresist (RU-1600P manufactured by Hitachi Chemical) using alkali-soluble ladder silicone as a matrix polymer. The film of the microlens forming layer was 1.2 μm, and was prebaked at 90 ° C. for 30 minutes. In addition, a 2/3 inch solid-state imaging device substrate having a pixel pitch of 23 μm was used for the solid-state imaging device, and the thickness of the lens fixing layer was set to several to 10 μm. FIG. 2A shows this state.

Next, the above-mentioned organosilicon-based positive photoresist, RU-1600P, used as a microlens forming layer was patterned by ordinary photolithography technology. That is, about 200 mJ / cm ^{2 was} irradiated using a g-line (436 nm) stepper, developed using an alkali developing solution (0.66 wt.% -NMD-3), and rinsed with running water to form a microlens forming layer pattern. Obtained. (FIG. 2 (b)) FIG. 3 (a) shows the light transmittance of the microlens forming layer in this state.
Light absorption at 400 nm or more is large, making it unsuitable as a microlens.

Subsequently, the microlens forming layer pattern was irradiated with a large excess of light over the entire surface (post-exposure, for example, irradiation of about 2000 mJ / cm ² ). The light transmittance of the microlens forming layer in this state is shown in FIG. 3 (b). There is almost no light absorption at 400 nm or more, and bleaching is efficiently performed by post-exposure.
It can be seen that the lens is in a state suitable for a micro lens. Next, this microlens forming layer pattern was
A heat treatment was carried out at a temperature of 20 ° C./20 minutes, and a microlens as shown in FIG. When a microlens is formed in this way, the light utilization factor is about
It was confirmed that it was improved by 50%, and it was confirmed that a solid-state imaging device having extremely excellent characteristics was obtained.

Example 2 A high-resolution positive photoresist (TSMR-V3 manufactured by Tokyo Ohka Co., Ltd.) was used on a solid-state image sensor substrate on which a lens fixing layer made of PGMA was formed in the same manner as in Example 1, and the microlens was formed by spin coating. A formation layer was formed. The thickness of the microlens forming layer was 1.3 μm, prebaked at 90 ° C. for 30 minutes, and the same solid-state imaging device substrate as in Example 1 was used. Next, the above positive photoresist, TSMR-V3, was contact-exposed using a mercury lamp and irradiated with light of about 30 mJ / cm ² (UV intensity measured at 365 nm). Subsequently, development was performed using an alkali developing solution (2.38 wt.% -NMD-3), and rinsing was performed with running water to obtain a microlens forming layer pattern. The light transmittance of the microlens forming layer in this state is shown in FIG. 4 (a). The light absorption at 400 nm or more is large, and is not suitable as a microlens.

Subsequently, the entire surface of the microlens forming layer pattern was exposed using a mercury lamp, and was exposed to about 200 mJ / cm ² (UV intensity was 365 nm
). The light transmittance of the microlens forming layer in this state is shown in FIG. 4 (b). There is almost no light absorption at 400 nm or more, the bleaching is efficiently performed by post-exposure, and the state is suitable for a microlens. You can see that. Next, the microlens forming layer pattern was heat-treated at 150 ° C. for 20 minutes, and was subjected to thermal fluidization to form a microlens. When the microlens was formed in this manner, it was confirmed that the light utilization factor was improved by about 50%, and it was confirmed that a solid-state imaging device having extremely excellent characteristics was obtained.

Example 3 In the same manner as in Example 1, a microlens forming layer was formed by spin coating using a positive photoresist (AZ-2400 manufactured by Shipley Co., Ltd.) on a solid-state imaging device substrate on which a lens fixing layer made of PGMA was formed. The thickness of the microlens forming layer was set to 1.2 μm, and a pre-baked at 90 ° C./30 minutes, and the same solid-state imaging device substrate as in Example 1 was used.

Next, the above positive photoresist, AZ-2400, was contact-exposed using a mercury lamp, and was exposed to about 20 mJ / cm ² (UV intensity
(Measured at 365 nm). Subsequently, development was performed using an alkali developing solution (2.38 wt.% -NMD-3), and rinsing was performed with running water to obtain a microlens forming layer pattern. The light transmittance of the microlens forming layer in this state is shown in FIG. 5 (a). The light absorption at 400 nm or more is large, and is not suitable as a microlens.

Subsequently, the entire surface of the microlens forming layer pattern was exposed using a mercury lamp, and was exposed to about 200 mJ / cm ² (UV intensity was 365 nm
). The light transmittance of the microlens forming layer in this state is shown in FIG. 5 (b). There is almost no light absorption at 400 nm or more, the bleaching is efficiently performed by post-exposure, and the state is suitable for a microlens. You can see that. Next, the microlens forming layer pattern was heat-treated at 140 ° C./30 minutes, and was subjected to thermal fluidization to form a microlens. When the microlens was formed in this manner, it was confirmed that the light utilization factor was improved by about 50%, and it was confirmed that a solid-state imaging device having extremely excellent characteristics was obtained.

Examples 4 to 6 In the same manner as in Example 1, a high-resolution positive photoresist, JSR-7750 made by Nippon Synthetic Rubber (Example 4) was formed on a solid-state image sensor substrate on which a lens fixing layer made of PGMA was formed.
A microlens forming layer was formed using JSR-7950 made by Nippon Synthetic Rubber (Example 5) and RI-7179 made by Hitachi Chemical (Example 6). The thickness of the microlens forming layer is 1.2
μm, and prebaked at 90 ° C. for 30 minutes.

Next, a g-line (436 nm) is added to the positive photoresist.
Each was irradiated with about 300 mJ / cm ² using a stepper, developed using an alkali developing solution (0.66 wt.% -NMD-3), and rinsed with running water to obtain a microlens forming layer pattern. Subsequently, the entire surface of the microlens forming layer pattern is irradiated (post-exposure, for example, about 1000 mJ / cm ² ),
It was confirmed that the microlens formation was improved by heat treatment at 150 ° C. for 10 minutes and thermal fluidization.

Example 7 In the same manner as in Example 1, an organic silicon-based positive Deep UV resist using alkali-soluble ladder silicone as a matrix polymer was spin-coated on a solid-state imaging device substrate on which a lens fixing layer made of PGMA was formed. A microlens forming layer was formed. The thickness of the microlens forming layer was 1.2 μm, and prebaked at 90 ° C. for 30 minutes.
The same solid-state imaging device substrate as in Example 1 was used.

Next, the above positive DeepUV resist was contact-exposed using a KrF excimer laser, and irradiated with light of about 300 mJ / cm ² . Subsequently, an alkaline developer (0.66 wt.%-NMD-
Developing using 3) and rinsing with running water to obtain a microlens forming layer pattern. The microlens forming layer in this state hardly absorbed light above 400 nm, and was suitable as a microlens.

In this case, it is not necessary to perform post-exposure. Next, the microlens forming layer pattern was heat-treated at 140 ° C./30 minutes, and was subjected to thermal fluidization to form a microlens. When the microlens was formed in this manner, it was confirmed that the light utilization factor was improved by about 50%, and it was confirmed that a solid-state imaging device having extremely excellent characteristics was obtained.

Comparative Example 1 A general-purpose positive photoresist, OFPR-800 (manufactured by Tokyo Ohka) was spin-coated on a solid-state imaging device substrate on which a lens fixing layer made of PGMA was formed to form a microlens forming layer. The thickness of the microlens forming layer was 1.2 μm,
Prebaked at 0 ° C / 30 minutes.

Next, the OFPR-800 film was irradiated with about 200 mJ / cm ² using a g-line (436 nm) stepper to obtain an alkaline developer (0.66 wt.%-
It was developed using NMD-3) and rinsed with running water to obtain a microlens forming layer pattern. The light transmittance of the microlens forming layer in this state is shown in FIG. 6 (a), and light absorption at 400 nm or more is large.

Subsequently, the entire surface of the microlens forming layer pattern was irradiated with light of about 2000 mJ / cm ² . The light transmittance of the microlens forming layer in this state is shown in FIG.
Even at 0 nm or more, light absorption was observed, and even when bleaching was performed by post-exposure, it did not become transparent as in the example, and it was confirmed that the film was unsuitable as a microlens.

〔The invention's effect〕

According to the present invention, a microlens can be easily formed on a solid-state imaging device substrate by ordinary photolithography. That is, the technology used in the present invention is a technology used for manufacturing a silicon semiconductor, and it is expected that cost reduction and improvement in yield can be achieved with mass productivity.

Further, the present invention is useful for increasing the resolution, and is extremely useful for manufacturing future high-resolution solid-state imaging devices.

[Brief description of the drawings]

FIG. 1 is a schematic sectional view of a solid-state imaging device substrate. DESCRIPTION OF SYMBOLS 1 ... Silicon substrate 2 ... Light receiving part 3 ... Light shielding part 4 ... Passivation layer 5 ... Color filter layer FIG. 2 shows the micro lens formation process of this invention. 6 Lens fixing layer 7 Microlens layer FIG. 3 shows the light transmittance of the microlens layer before and after light irradiation. Microlens material: RU-1600P FIG. 4 shows the light transmittance of the microlens layer before and after light irradiation. Microlens material: TSMR-V3 FIG. 5 shows the light transmittance of the microlens layer before and after light irradiation. Microlens material: AZ-2400 FIG. 6 shows the light transmittance of the microlens layer before and after light irradiation. Micro lens material: OFPR-800

──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Jun Tanaka 292 Yoshida-cho, Totsuka-ku, Yokohama-shi, Kanagawa Prefecture Inside Hitachi, Ltd.Production Technology Laboratory (72) Inventor Toshio Nakano 3300 Hayano, Mobara-shi, Chiba Pref. Within the Mobara Factory (72) Inventor Akiya Izumi 3300 Hayano, Mobara City, Chiba Prefecture Inside the Mobara Factory, Hitachi Co., Ltd. (72) Inventor ▲ Taka ▼ Shi 3681 Hayano, Mobara City, Chiba Prefecture Hitachi Device Engineering Co., Ltd. (56) References JP-A-60-38989 (JP, A) JP-A-60-53073 (JP, A) JP-A-61-208276 (JP, A) JP-A-62-293239 (JP, A) Tokuhyo Hei 3-505655 (JP, A) Toru Hara and Masahiro Kashiwagi, Ed., “Handbook of Materials for Semiconductor Process Materials”, Science Forum, April 25, 1983, P. . 274-275 (58) Fields surveyed (Int. Cl. ⁶ , DB name) H01L 27/14

Claims (2)

(57) [Claims] 1. A light receiving unit formed on a semiconductor substrate for performing photoelectric conversion, a scanning unit for extracting an electric signal generated by the light receiving unit, a passivation film for protecting the light receiving unit and the scanning unit, and a color filter layer. A solid-state imaging device having a microlens provided with a lens fixing layer on the solid-state imaging device made of, and provided with a convex lens made of a photoresist pattern on the lens fixing layer, wherein the photoresist material is irradiated with light. Bleach efficiently,
A solid-state imaging device with a microlens, comprising a 1 μm-thick organic silicon-based positive resist having a light transmittance at a wavelength of 400 nm or more after light irradiation of 95% or more at a wavelength of 1 μm. 2. A light receiving unit for performing photoelectric conversion on a semiconductor substrate,
And a scanning unit for extracting an electric signal generated by the light receiving unit, and a lens fixed on a solid-state imaging device on which a passivation film for protecting the light receiving unit and the scanning unit and a color filter layer are formed. Providing a layer, forming a photoresist pattern on the lens fixing layer, exposing the entire photoresist pattern, heat treatment,
A method of manufacturing a solid-state imaging device with microlenses, further comprising forming convex lenses by light etching using oxygen plasma.