JP4439326B2 - Method for forming microlens, solid-state imaging device including microlens, and liquid crystal display device - Google Patents

Description

  The present invention relates to a method of forming a microlens, and a solid-state imaging device and a liquid crystal display device including the microlens.

  The microlens used in the solid-state imaging device and the liquid crystal display device uses a photosensitive photoresist as a microlens material, which is formed into a flat plate shape on a substrate and is photolithography processed into a rectangle with a desired line width, and then the rectangular pattern Is processed into a lens shape having a predetermined radius of curvature by thermal reflow. (Patent Document 1)

FIG. 3 shows a configuration disclosed in Patent Document 1. 1 is a semiconductor substrate, 2 is a photoelectric conversion region, 3 is a transfer electrode for transferring charges generated in the photoelectric conversion region 2, 4 is a charge transfer unit, and 5 is An interlayer insulating film, 6 is a light-shielding film, 7 is a transparent flattening film formed of a resin having a high optical transmittance in order to suppress the step between the photoelectric conversion region 2 and the transfer electrode 3 to a certain value or less, 9 A microlens for efficiently collecting incident light on the photoelectric conversion region 2 is shown.
Japanese Patent No. 2945440

  With the recent miniaturization of pixels, the area of the photoelectric conversion region 2 continues to be reduced. In order to obtain sufficient condensing even for a smaller photoelectric conversion region, it is essential to increase the refractive index of the microlens 9. In addition, it is effective to add a metal oxide to the microlens material in order to increase the refractive index of the microlens 9.

  In the conventional processing of the microlens 9, patterning is made into a rectangular shape through a mask on a positive type photosensitive resin of phenol borac or polystyrene, and this is processed into a lens shape by thermal reflow. In this case, for example, a high refractive index resist material having a weak reflow property containing a metal oxide such as titanium oxide could not obtain a lens shape having a desired radius of curvature without being sufficiently melted by heat. .

  Thus, when the microlens does not have a lens shape having a desired radius of curvature, there is a problem that the light incident on the solid-state imaging device is not sufficiently condensed on the photoelectric conversion region 2 and the sensitivity is deteriorated.

  The present invention creates a lens shape having a desired radius of curvature even for a metal oxide-containing microlens material for the purpose of increasing the refractive index of the microlens, thereby obtaining a high light condensing rate for a fine pixel. It is an object to provide a highly sensitive solid-state imaging device.

The microlens formation method of the present invention includes a step of forming a microlens material layer in a flat plate shape on a substrate, a step of exposing the microlens material layer formed in a flat plate shape by defocus, and developing and patterning Characterized by comprising the steps of:
The microlens forming method of the present invention is characterized by further comprising a reflow step after the patterning step. Furthermore, the microlens formation method of the present invention is characterized in that the microlens material layer is a high refractive index lens material. In particular, the high refractive index lens material includes a metal oxide. Titanium oxide is preferable as the metal oxide.
The microlens forming method of the present invention is characterized in that the substrate is a solid-state imaging device. The microlens forming method of the present invention is characterized in that the substrate is a liquid crystal display device.

  The solid-state imaging device of the present invention is characterized in that the microlens formed by the above method is provided so as to focus on the photoelectric conversion region formed on the semiconductor substrate. The liquid crystal display device of the present invention is characterized in that the microlens formed by the above method is provided so as to focus on the pixel region.

In the microlens according to the present invention, a microlens material layer is formed in a flat plate shape on a substrate, and this is exposed with defocus, developed, and patterned. Can be formed in the shape of a microlens having a radius of curvature of 2 mm, and a high light collection rate can be obtained. Moreover, the lens shape can be shaped by reflowing as necessary. Alternatively, it includes a step of exposing the microlens material layer by defocusing, a step of developing, and a step of reflowing. The desired curvature radius can be obtained by combining the curvature formation by the sex.
In addition, the solid-state imaging device of the present invention is a solid-state imaging device with a finer photoelectric conversion region because the microlens made of a high refractive index lens material is disposed so as to focus on the photoelectric conversion region formed on the semiconductor substrate. Even in such a case, a high light collection rate can be obtained, and a high output can be obtained. The liquid crystal display device can focus light on the picture element region, increase efficiency, and increase luminance.

  In the present invention, a conventionally known material can be used as the lens material, but the present invention is effective when applied to a high refractive index resist material which is not easily melted by heat. For example, it is possible to use a positive resist layer mainly composed of a polyimide-based polymer having a weak reflow property and containing a metal oxide such as titanium oxide. In the case of the present invention, the exposure is performed by shifting the focal position at the time of exposure, so that the light intensity distribution is strong in the central part and weak in the peripheral part, and is formed in a circular or elliptical shape. Is formed into a microlens having a desired curvature

  Hereinafter, the macro lens of the present invention can be applied to a solid-state imaging device and a liquid crystal display device. Here, the configuration of the micro lens will be described in detail by taking a CCD as an example. FIG. 1 is a sectional view when the microlens of the present invention is formed on a CCD, and FIG. 2 is a manufacturing process diagram for forming the microlens on the CCD. 1 and 2 show only two and a half of the microlenses and the CCD, but in reality, a large number of microlenses and CCDs are arrayed vertically and horizontally. 1 and 2, 1 is a semiconductor substrate, 2 is a photoelectric conversion region, 3 is a transfer electrode for transferring charges generated in the photoelectric conversion region 2, and 4 is a charge transfer portion, which is formed by the photoelectric conversion region 2 and the transfer electrode 3. The charge transfer portions 4 are alternately formed on the semiconductor substrate 1. 5 is an interlayer insulating film, 6 is a light-shielding film, 7 is a transparent flattening film formed of a resin having a high optical transmittance in order to keep the step between the photoelectric conversion region 2 and the transfer charge portion 3 below a certain value. Examples of materials that can be used include acrylic resin, urethane resin, polyimide resin, epoxy resin, alkyd resin, phenolic resin, silicone resin, polyester resin and other transparent polymer resins, BPSG (Boron Phosphide Silicate Glass), PSG ( Examples thereof include inorganic compounds such as Phosphide Silicate Glass) and SiN (Silicon Nitride).

  Next, a manufacturing process for forming a microlens on a solid-state imaging device will be described with reference to FIGS. First, as in the prior art, the photoelectric conversion region 2 and the charge transfer portion 4 are formed on the surface of the semiconductor substrate 1, and the transfer electrode 3, the interlayer insulating film 5, the light shielding film 6, and the transparent planarizing layer 7 are formed on the semiconductor substrate 1. Form.

  Next, a photosensitive agent that contains a metal oxide such as titanium oxide on the transparent planarizing film layer 7 and can suppress light absorption in the visible light wavelength region by bleaching by irradiation with ultraviolet rays or the like, Further, a positive resist layer 8 mainly composed of a polyimide-based polymer having thermoplasticity is formed by spin coating or the like (FIG. 2A). As the positive resist layer 8, other than titanium oxide, other than metal oxide, other than polyimide, a layer capable of increasing the refractive index can be used. Moreover, what is necessary in order to form microlenses, such as a hardening | curing agent, may be contained.

  Thereafter, the positive resist layer 8 is patterned by exposure and development by a photolithography technique using a mask (not shown) so that each photoelectric conversion region 2 is focused on the microlens. At this time, a desired focus offset value is set using the autofocus function of the exposure machine, and the focus position during exposure is set to be shifted. By shifting the focal position at the time of exposure, the light intensity distribution does not match the shape of the mask, and the light is also exposed to the portion of the positive resist layer 8 that is normally masked. The subsequent pattern is not the same as the mask shape, and the cross section of the pattern shape of the positive resist layer 8 is not rectangular, but is formed in a circle or ellipse, and the peripheral portion of the mask pattern is weakly exposed. Is formed into a microlens having a desired curvature (FIG. 2B). The distance by which the focal position is shifted during exposure is determined by the material, thickness, light wavelength, intensity, exposure time, type of developer, development time, etc. of the positive resist layer 8, and from the best focus of the exposure machine. The offset amount is set to an optimum value in view of the finished lens shape. The reason why the resist pattern is irradiated with light such as ultraviolet rays (for example, 350 to 450 nm) is to decolorize the photosensitive agent contained in the patterned positive resist layer 8 and enhance the transmittance. . In addition to i-line, exposure may be performed using a KrF line material, and the intensity of light at the time of exposure is about 300 mJ / cm 2.

  Next, the patterned positive resist layer 8 is heated and thermally deformed to form a pseudo hemispherical microlens 9. (FIG. 2 (c)) The heating temperature at this time is optimized from the balance of the critical value of the thermal melting of the polymer, the crosslinking start temperature of the thermosetting agent, the temperature dependence of the refractive index of the microlens 9, and the like. For example, it is set to 300 ° C. This heating step does not necessarily need to be thermally deformed, and if a microlens shape can be obtained by defocusing, it is only necessary to shape the lens shape. Alternatively, the distribution of each process may be determined by confirming the shape of each process so that a desired radius of curvature of the microlens can be obtained by combining lens formation by defocusing and deformation by heating. Finally, a transparent layer 10 such as an acrylic resin is formed on the microlens 9 as necessary.

A photoelectric conversion region 2 and a charge transfer portion 4 are formed on the surface of the semiconductor substrate 1, and a transfer electrode 3, an interlayer insulating film 5, a light shielding film 6, and a transparent planarizing layer 7 are formed on the semiconductor substrate 1. A polyimide positive resist layer 8 containing titanium oxide, a bleaching photosensitive agent, and a thermosetting agent is formed thereon, and a mask is aligned with the lens position, and exposure is performed with defocus. The exposure wavelength at this time was 365 nm and the intensity was 300 mJ / cm ² . Thereafter, heat treatment is performed to obtain a microlens.

It is sectional drawing of the solid-state image sensor of one Example of this invention. It is a manufacturing-process figure of the solid-state image sensor to microlens formation. It is process sectional drawing of the solid-state image sensor in which the conventional microlens was formed.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Semiconductor substrate 2 Photoelectric conversion area | region 3 Transfer electrode 4 Charge transfer part 5 Interlayer insulation film 6 Light-shielding film 7 Transparent planarization film 8 Positive type resist layer 9 Micro lens

Claims (7)

Forming a microlens material layer in a flat plate shape on a substrate;
Exposing the microlens material layer formed in the flat plate shape by defocusing;
Ri Do and a step of patterning developed to,
The method for forming a microlens, wherein the microlens material layer comprises a positive resist layer mainly composed of a thermoplastic polymer containing a metal oxide . The method of forming a microlens according to claim 1, further comprising a step of reflowing after the patterning step. Forming a microlens according to claim 1 or 2, wherein the metal oxide is titanium oxide. Forming a microlens according to any one of claims 1 to 3, wherein the substrate is a solid-state imaging device. Forming a microlens according to any one of claims 1 to 3, wherein the substrate is a liquid crystal display device. A solid-state imaging device, characterized in that claim a microlens formed by the formation method of any one of the microlens of claim 1 to 3, provided so as to focus on the photoelectric conversion region formed in a semiconductor substrate. The liquid crystal display device, characterized in that a microlens formed by the formation method of any one of the microlenses of claims 1 to 3, provided so as to focus on the pixel area.

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