JP2001085657A - Method for manufacturing solid-state image pick up element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for stably manufacture a micro-lens having a high aperture coefficient providing an interval between micro-lenses on a solid-state image pick up element of 0.2 to 0.3 μm without any fusion of micro- lenses. SOLUTION: After a photosensitive resin as the material of micro-lens is coated, exposed and developed, the ultraviolet ray including far ultraviolet region is irradiated for temporary hardening of the edge portion at the external circumference of photosensitive resin, and thereafter the resin is heated for formation through dissolution, deformation and hardening. Moreover, the wavelength of the ultraviolet ray including the far ultraviolet region used is 200 to 365 nm, and the dose is 50 to 100 mJ/cm2 at the wavelength of 254 nm per film thickness of lens material of 1 μm.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a solid-state imaging device having a focusing microlens.

[0002]

2. Description of the Related Art As shown in FIG. 4, for example, a solid-state imaging device such as a CCD (Charge Coupled Device) includes a photoelectric conversion unit including a plurality of rectangular light receiving elements 2 embedded in a substrate 1 such as silicon. It is composed of two regions of a signal readout circuit portion such as an electrode layer 3 connected from the light receiving element 2, and a lower smoothing layer 4 made of a transparent material and a gap between the light receiving elements 2 are formed on these two layers. Light-shielding layer 5 provided on the site,
In addition, a device corresponding to a color image has a configuration in which red, green, and blue color filter layers 6 are formed.

Here, the signal readout circuit section is an insensitive area to the incident light component. Therefore, conventionally, the light component incident on the insensitive area is condensed on the photoelectric conversion unit to achieve high sensitivity of the imaging device, and as one of effective means that does not deteriorate other devices, the solid-state imaging device is used. A microlens array integrated with an imaging element has been proposed, in which a transparent convex lens-shaped microlens array is arranged on the substrate, and an incident light component reaching a signal readout circuit, which is an insensitive area, is focused on a photoelectric conversion unit. ing.

[0004] As a method of forming a micro lens,
In general, a heat flow method is used in which a pattern is formed from a heat-softening material, and the pattern is formed by heating and melting, deforming, and curing.
The method of forming a microlens by a heat flow method is as follows. A photosensitive resin serving as a lens material is applied to a thickness of 0.5 to 5 μm, and after exposure and development, an ultrahigh pressure mercury lamp or the like has a wavelength of 365 nm.
Is irradiated with ultraviolet light called an i-line centered at the center, and then deformed by heating and dissolving to cure into a hemispherical convex lens shape. The ultraviolet light used here has a wavelength suitable for decomposing the photosensitive agent in the photosensitive resin of the lens material and improving the light transmittance.

[0005]

In recent years, CCDs have been developed for higher resolution and smaller size, as represented by digital camera applications. With the increase in resolution, the pixel size is reduced, the light receiving area of the image sensor is reduced, and the problem of inevitably lowering the light sensitivity occurs.

As one method for solving this problem, the aperture ratio of a micro lens formed on each pixel may be increased to improve the light sensitivity. In other words, the distance between adjacent microlenses may be reduced.

[0007] At present, 2 is adopted for digital cameras and the like.
The pitch of the microlenses of the one million pixel CCD is about 5 μm, and the interval between the microlenses to be formed is 0.2 to 0.3, which is necessary for avoiding the above-described decrease in light sensitivity.
μm.

However, in the above-described microlens formed by the conventional heat flow method, as shown in FIG.
There is a heat flow amount (deformation expansion amount) of 0.2 μm on one side of the pattern during heating and melting. Since this flow amount is large, even if an attempt is made to form the microlens at an interval of 0.2 to 0.3 μm, the adjacent microlenses may adhere to each other due to the variation in the amount of heat flow. It is difficult to form independent microlenses at intervals.

Therefore, an object of the present invention is to provide a microlens having a high aperture ratio in which the distance between the microlenses on the solid-state imaging device is 0.2 to 0.3 μm, without causing adhesion between the microlenses. It is to provide a method that can be manufactured.

[0010]

The present inventors have made intensive studies and found that the distance between microlenses was 0.2 to 0.3 μm.
A method of forming a microlens by a heat flow method that can stably form a microlens having a high aperture ratio of m without adhesion between the microlenses was found.

That is, the invention according to claim 1 provides a method for manufacturing a solid-state imaging device having a microlens,
When forming a microlens on the upper layer of each element, after applying, exposing and developing a photosensitive resin as a material, far ultraviolet (Dee
(p-UV) region, and then heat to dissolve
A method for manufacturing a solid-state imaging device, characterized by being formed by deformation and hardening.

Further, the present inventors consider that the wavelength of the far ultraviolet light for temporarily curing the edge portion of the outer periphery of the microlens is 2
It has been found that 00 to 300 nm is suitable. Further, the wavelength of the ultraviolet light for decomposing the red colored photosensitive agent in the photosensitive resin of the lens material and improving the light transmittance of the photosensitive resin is 365 nm.

In other words, the invention according to claim 2 is characterized in that the wavelength of the ultraviolet light including the far ultraviolet region used in forming the microlens is 200 to 365 nm, and the manufacturing of the solid-state imaging device according to claim 1 is performed. Is the way.

Further, the irradiation amount of the ultraviolet light including the far ultraviolet region is
The wavelength 2 per 1 μm of the thickness of the photosensitive resin used as the lens material
If the wavelength is less than 50 mJ / cm ^{2 at} 54 nm, the edge portion of the outer periphery of the microlens cannot be temporarily cured, and if the irradiation amount is 100 mJ / cm ² or more at the same wavelength, not only the edge portion of the outer periphery of the microlens but also the central portion of the microlens can be temporarily cured. It has been found that the composition hardens and a hemispherical microlens cannot be obtained by subsequent heating, resulting in a trapezoidal shape.

That is, the invention according to claim 3 is characterized in that the irradiation amount of the ultraviolet light including the far ultraviolet region used at the time of forming the microlens has a wavelength of 254 nm per 1 μm of the film thickness of the lens material.
^{2. The} method according to claim 1, wherein m is 50 to 100 mJ / cm ² .

According to the above method, the distance between the microlenses provided on the solid-state imaging device is 0.2 to 0.3 μm.
The microlens having a high aperture ratio of m can be formed stably without adhesion between the microlenses.

[0017]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be described with reference to the following examples and comparisons with comparative examples.

<Embodiment> FIG. 1 schematically shows a manufacturing process of a solid-state imaging device formed on a semiconductor substrate. The semiconductor substrate A includes a photodiode section including the light receiving element 2 shown in the figure, a charge transfer section,
In addition, a semiconductor element such as a transfer electrode and a vertical register portion including a vertical register portion is formed by the same method as the conventional method, and a lower smoothing layer 4, a light shielding layer 5, a color filter 6,
Further, an overcoat layer 7 for smoothing the surface was laminated by a conventional method.

A photosensitive resist "MFR380H" manufactured by JSR Co., Ltd. is spin-coated on the semiconductor substrate A on which the above-described semiconductor elements, color filters, etc. are formed, at a rotation speed of 1800 min- ^1. ° C
Baking for 3 minutes on a hot plate with a film thickness of 1.25
μm (see FIG. 1A).

After exposing the semiconductor substrate A with an i-line stepper manufactured by Nikon Corporation, an alkali developer N
After performing spin development for 30 to 40 seconds using MD-W (manufactured by Tokyo Ohka Kogyo Co., Ltd.) and rinsing with pure water,
Spin drying was performed. At this time, the interval between the microlens patterns was 0.45 μm, and the film thickness was 1.2.
μm (see FIG. 1 (b)).

Further, the amount of ultraviolet radiation having a wavelength of 254 nm of 60 mJ / c using ultraviolet light including a deep ultraviolet region, for example, a far ultraviolet lamp UXM-501MA manufactured by Ushio Inc.
Irradiation with ultraviolet light was performed until the volume reached m ² .

Thereafter, the semiconductor substrate A was heated for 3 minutes using a hot plate at 100 ° C., and then heated for 6 minutes on a hot plate at 180 ° C. to perform melting, deformation and hardening, as shown in FIG. A microlens 8 having such a pitch of 5 μm, an interval between microlenses of 0.25 μm, and a film thickness of 1.5 μm was completed (see FIG. 1C). The amount of heat flow at this time was 0.1 μm on one side of the pattern as shown in FIG.
m.

As shown in FIG. 5, in the semiconductor substrate of this embodiment, there was no appearance irregularity due to adhesion of the microlenses, and good external appearance characteristics were obtained.

<Comparative Example> First, similarly to the above embodiment,
Semiconductor substrate A was prepared by a conventional method. The semiconductor substrate A
In the same manner as in the above example, a photosensitive resist “MFR380H” manufactured by JSR Co., Ltd. was applied by spin coating at a rotation speed of 1800 min- ¹ and baked on a hot plate at 100 ° C. for 3 minutes to form a film. It was formed to a thickness of 1.25 μm.

After exposing the semiconductor substrate A with an i-line stepper manufactured by Nikon Corporation, an alkali developer N
After performing spin development for 30 to 40 seconds using MD-W (manufactured by Tokyo Ohka Kogyo Co., Ltd.) and rinsing with pure water,
Spin drying was performed. At this time, the distance between the microlens patterns was 0.65 μm, and the film thickness was 1.2.
μm.

Further, ultraviolet irradiation was performed using an ultra-high pressure mercury lamp which emits ultraviolet light containing almost no deep ultraviolet region. At this time, the amount of ultraviolet irradiation is 300 mJ / c at a wavelength of 365 nm.
m ² .

Thereafter, the semiconductor substrate A was heated on a hot plate at 100 ° C. for 3 minutes, and then heated on a hot plate at 180 ° C. for 6 minutes to perform melting, deformation and hardening, as shown in FIG. A microlens 8 having a pitch of 5 μm, an interval between microlenses of 0.25 μm, and a film thickness of 1.5 μm was completed. The amount of heat flow at this time was 0.2 μm on one side of the pattern as shown in FIG.

As shown in FIG. 6, in the semiconductor substrate of this comparative example, unevenness in appearance due to adhesion of microlenses was partially generated in the semiconductor substrate, and did not satisfy good appearance characteristics. .

In this comparative example, as a method of reducing the amount of heat flow in order to prevent adhesion of the microlenses, there is a method of lowering the temperature during the heat flow. However, when the heat flow was performed at a low heat flow temperature in this comparative example, the amount of heat flow at the time of forming the microlenses was reduced, and adhesion of the microlenses could be prevented. When viewed, the shape was not a hemispherical shape but a trapezoidal shape, and a microlens with a good shape could not be obtained.

[0030]

According to the method for manufacturing a solid-state imaging device of the present invention, the distance between microlenses for compensating for the decrease in light sensitivity due to the decrease in the pixel size and the light receiving area accompanying the increase in the resolution of the solid-state imaging device is reduced. In this case, the wavelength of the ultraviolet light used in the temporary curing of the edge portion of the photosensitive resin outer periphery before the lens shape processing of the photosensitive resin by heating at the time of forming the microlens includes 200 to 300 nm, so that the microlenses can be formed. Can be formed into a stable shape without causing adhesion.

[0031]

[Brief description of the drawings]

FIG. 1 is an explanatory diagram showing a manufacturing process of a solid-state imaging device having a microlens by a heat flow method.

FIG. 2 is an explanatory view schematically showing a microlens according to an embodiment of the present invention.

FIG. 3 is an explanatory view schematically showing a microlens of a comparative example.

FIG. 4 is a cross-sectional view illustrating an example of a configuration of a solid-state imaging device.

FIG. 5 is an electron micrograph showing a cross section of a microlens according to an example of the present invention.

FIG. 6 is an electron micrograph showing a cross section of a microlens of a comparative example.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Silicon base 2 Light receiving element 3 Electrode layer 4 Lower smoothing layer 5 Light shielding layer 6 Color filter 7 Overcoat layer 8 Micro lens

Claims (3)

[Claims] In a method of manufacturing a solid-state image pickup device having a microlens, when forming a microlens on an upper layer of each device, a photosensitive resin as a material is applied, exposed and developed, and then an ultraviolet light including a far ultraviolet region is included. A method for producing a solid-state imaging device, comprising irradiating light, and subsequently heating to dissolve, deform, and cure the solid-state imaging device. 2. The method for manufacturing a solid-state imaging device according to claim 1, wherein a wavelength of ultraviolet light including a far ultraviolet region used in forming the microlens is 200 to 365 nm. 3. An irradiation amount of ultraviolet light including a far ultraviolet region used for forming a microlens is 50 to 100 mJ / cm ^{2 at} a wavelength of 254 nm per 1 μm of film thickness of a lens material.
The method for manufacturing a solid-state imaging device according to claim 1, wherein