JP4696927B2 - Manufacturing method of microlens array - Google Patents

Description

The present invention relates to a microlens used for uniformly diffusing and condensing light emitted from a light source such as a halogen lamp, a cold cathode ray tube, or an LED incorporated in a liquid crystal display, or a light receiving element such as a CMOS or CCD. In particular, an image sensor represented by (2) and a condensing microlens formed on the image sensor have a high aperture ratio and can be individually adjusted in thickness and shape, even with a micro-pitch microlens. It relates to the method of manufacturing a microlens array microlenses are arranged.

In order to diffuse light from a light source in a liquid crystal display, etc., an organic film in which a coating film in which resin beads with a refractive index difference are dispersed in a transparent resin is formed, or a light diffusion plate in which fine irregularities are randomly formed Or, a lenticular lens or a prism sheet is incorporated.
These displays are used for a variety of purposes, such as use in portable devices and use on a face like a goggles type, and further miniaturization is progressing.

A light source used in such a small display is also reduced in size by using an LED or the like, and further downsizing of an optical functional element used accompanying this is demanded.
An optical functional element used for a small display LED is required to have a high light condensing property and a light diffusing property with a size of about several mm to 1 mm □.

  In these miniaturized optical function elements, it is difficult to incorporate a light diffusing plate, lenticular lens, or prism sheet in order to improve the light condensing property and light diffusing property. There is a need for optimization with lenses.

On the other hand, in the field of imaging devices, the region (opening as a photodiode) that contributes to photoelectric conversion of a light receiving device such as CMOS or CCD depends on the device size and the number of pixels, but is a pixel converted from the pixel pitch. It is limited to about 20 to 40% of the area, and the small opening leads to a decrease in sensitivity of the element.
In order to compensate for this, it is common to form a microlens on a light receiving element for light collection.

  In an image pickup device typified by a light receiving device such as a CMOS or CCD, pixel miniaturization is progressing as the number of pixels increases. The distance (pixel pitch) between each pixel of the image sensor is a direction in which 3 μm is cut and progressed to miniaturization of 2 μm or less.

Even in cameras for mobile phones, the number of pixels has been increased to 3 million pixels or 5 million pixels, and the microlenses arranged on the light receiving element are inevitably required to be miniaturized and increased in number of pixels. .
Usually, the microlens is hemispherical and is made of an organic resin, but the height of the lens is in the range of about 2 μm to 0.2 μm.

As a microlens formation technique, a technique using dry etching is disclosed in relatively detail (for example, see Patent Document 1).
Patent Document 1 discloses a technique for forming a lens into a hemispherical shape by using the thermal fluidity of a resin by thermal reflow, and forming an organic film such as PGMA or an OCD (SiO ₂ -based) inorganic film on the lens surface. Is also disclosed.

Further, it is disclosed in detail that the line width can be adjusted by transfer and processing by dry etching, and that CF ₄ or O ₂ gas is used as an etching gas for dry etching (for example, Patent Document 2). reference).
Hereinafter, a microlens formed by this dry etching technique is called a transfer lens, and this processing method is abbreviated as a transfer method.

  The transfer lens can reduce the layer structure including the color filter and the planarizing film on the photoelectric conversion element, and can increase the aperture ratio of the lens compared to the microlens manufactured by the thermal reflow method. The characteristic is that the characteristics can be improved.

In addition, a thermal reflow lens is formed with a photosensitive resin layer made of the same lens material on the underlying transparent resin layer, and this thermal reflow lens is used as a lens matrix, and the pattern of the lens matrix is dry-etched. A technique for forming a transfer lens by transferring to a transparent resin layer is disclosed (see, for example, Patent Document 3 and Patent Document 4).
Furthermore, a technique for reducing the gap between pixels using a photosensitive lens material is disclosed (for example, see Patent Document 5).

Hereinafter, a method for creating a transfer lens will be described with reference to FIGS. 22 (a) to 22 (e) and FIGS. 23 (f) to 23 (h).
First, the color filter 130 including the planarization layer 121 and the red filter 131R, the green filter 132G, and the blue filter 133B is formed on the semiconductor substrate 110 on which the photoelectric conversion element 111 is formed by a known method (FIG. 22A to FIG. 22). (See (c)).

Next, a transparent resin layer 141 for forming a transfer lens, an etching control layer 151, and a photosensitive resin layer 161 having thermal reflow properties are sequentially formed (see FIG. 22D).
As the photosensitive resin layer 161 having thermal reflow properties, generally, a positive photosensitive resin (usually a photosensitive phenol resin that is also used for a semiconductor resist) is used.
The etching control layer is preferably formed of a resin that has an etching rate slower than that of the lens matrix when dry etching described later.

  Next, a series of patterning processes such as pattern exposure and development are performed on the photosensitive resin layer 161 using a pattern exposure mask on which a predetermined pattern is formed, and a resist pattern 161a is formed at a predetermined position on the etching control layer 151. (See FIG. 22E).

  In the pattern exposure, a pattern exposure mask (usually referred to as a 5-fold reticle) in which a pattern having a size five times that of the microlens to be formed is used, and light having a wavelength of 365 nm is set as a main wavelength at the time of pattern exposure. In many cases, the pattern exposure is performed on the photosensitive resin layer by reducing the pattern on the mask to 1/5 with a stepper exposure apparatus.

FIG. 18 shows an example of design mask pattern dimensions used when forming microlenses with a pitch of 1.8 μm.
In the pattern exposure, the pattern exposure is performed with the stepper exposure apparatus being reduced to 1/5, so that the dimension on FIG. 18 is five times the pattern dimension on the five-times reticle mask.

  FIG. 19 shows a resist pattern formed by performing pattern exposure with exposure light having a wavelength of 365 nm on a photosensitive resin layer 161 made of a positive photosensitive phenol resin having thermal reflow using a reticle mask, and developing with an alkali solution. A schematic plan view of 161a is shown.

As shown in FIG. 19, the plan view shape of the resist pattern 161a obtained after development is a corner due to the influence of the resolution of the photosensitive resin layer 161 and the exposure wavelength (365 nm) even if the mask pattern is rectangular. The resist pattern has rounded corners.

This is because when the pattern for a microlens shown in FIG. 18 is exposed using a stepper exposure apparatus, exposure light (exposure wavelength 356 nm) wraps around the pattern corner portion A, so that the pattern shape of the corner portion is accurate. This is because no image is formed on the photosensitive resin layer.
Moreover, the fact that the resolution of the photosensitive resin layer for forming the microlens is limited also causes the corner portion of the resin to be rounded.

  Next, the resist pattern 161a is subjected to heat treatment in the range of 150 ° C. to 250 ° C., and the resist pattern 161a is melted to form a lens matrix 161b (see FIG. 23F). In the lens matrix 161b, a convex lens (for example, a hemispherical cross section) is formed by surface tension generated on the surface of the resist pattern 161a upon melting.

  Next, by using the lens matrix 161b as a mask, the etching control layer 151 is etched by the dry etching described above, thereby forming the intermediate microlens 151a (see FIG. 23G).

  Here, the etching control layer 151 controls the fluidity of the lens matrix at the time of thermal reflow, and in addition to ensuring a round and smooth shape and dimensional stability, the intermediate lens height at the time of dry etching is adjusted as described above. It has the effect of adjusting and further reducing the gap between the intermediate lenses.

  Next, the desired microlens 141a can be formed by etching the transparent resin layer 141 by dry etching using the intermediate microlens 151a as an intermediate mask (see FIGS. 20 and 23H).

FIG. 20 shows a plan view shape of the microlens 141a obtained by the above-described thermal reflow method and transfer method.
As shown in FIG. 20, the gap 142 between the microlenses in the diagonal direction of the microlens 141a is large, and this gap 142 does not contribute to light collection and diffusion, so that the aperture ratio of the microlens is lowered. Become.

The difference between the shape of the microlens pattern in the design and the shape of the microlens actually obtained does not significantly affect the light condensing performance of the microlens at a pixel pitch of 3 μm, but at a pixel pitch of 2.5 μm The effect that the condensing property of the microlens begins to decline begins to appear.
Furthermore, when the pixel pitch is 2.2 μm or less, as shown in FIG. 20, the condensing performance is significantly reduced due to the decrease in the aperture ratio due to the increase in the gap 142 between the microlenses in the diagonal direction. .

FIG. 21 is a graph showing a change in effective aperture ratio between the thermal reflow lens formed by the thermal reflow method and the microlens formed by the dry etching method when the lens pitch is changed.
As described above, the thermal reflow lens is one that melts the resin by heat treatment and processes it into a convex lens shape by utilizing the surface tension of the resin at the time of melting, but is adjacent to the fluidization during thermal reflow. In order to prevent the lenses from sticking to each other, a gap of about 0.3 μm (a gap in the side direction of the lens having a rectangular shape in plan view) is required between the lenses.
As a result, the pixel pitch becomes finer and the effective aperture ratio rapidly decreases as shown in FIG.

Using a fluorocarbon-based gas as a gas for dry etching, and using a resin pattern that is hemispherical by heat reflow as a lens matrix, the transparent resin layer that is the base of the lens matrix is dry-etched to form a lens matrix The microlens obtained by shape transfer has a higher aperture ratio than the thermal reflow lens as shown in FIG. However, when the pixel pitch is 2.2 μm or less, the effective aperture ratio is less than 90% and is about 89%.
JP 60-53073 A JP-A-6-37058 Japanese Patent Laid-Open No. 6-112659 JP 2003-229550 A JP 2000-269474 A

  As described above, the microlens formation method for transferring the lens matrix to the transparent resin layer by dry etching as an intermediate mask is performed by using a photosensitive resin material having thermal reflow on the underlying transparent resin layer. In general, after forming a lens matrix by a procedure such as development and thermal reflow, the pattern of the lens matrix is transferred to a transparent resin layer as a base by dry etching to form a microlens.

  The present inventors have empirically confirmed that if the size of the microlens (the size of the microlens in plan view) is 3 to 4 times the wavelength of the light, it is effective for collecting and diffusing the light. ing. Therefore, for example, when the wavelength of green light is 550 nm, the size in plan view is 1.5 μm to 2.2 μm, and the curvature (or lens thickness) and inclination (in cross-sectional view) of the microlens. Optimum light collecting properties can be obtained by appropriately adjusting the shape of the slope portion.

  At the same time, the distance (lens gap) between the macro lenses in a plan view is reduced, that is, the gap between adjacent micro lenses is minimized, and the portion not covered by the micro lens (non-opening portion) is minimized. This is an important point for improving the aperture ratio of the micro lens and increasing the light utilization efficiency.

  As described above, imaging elements, LEDs, and the like are downsized, and microlenses as optical functional elements for condensing and diffusing are required to be formed on a substrate having a size of 1 mm to 2 mm □. For this purpose, it is desirable to form a microlens having a size close to 2 μm in an optimal shape in plan view.

  Note that the substrate constituting the imaging element has a substrate surface divided into a large number of pixel areas, and photoelectric conversion elements are arranged in the respective pixel areas. Since the pixel region has a rectangular shape in plan view partitioned in a lattice shape, the microlens formed on the pixel region is also formed in a substantially rectangular shape in plan view in order to increase the covering region and increase the aperture ratio.

  However, when the size of the microlens is in the vicinity of 2 μm, a microlens array in which a plurality of microlenses are formed in an array (matrix shape) has a high aperture ratio, and the gap in the diagonal direction of the microlens is filled. Relatively difficult.

This is because, in forming the microlens, since a fine pattern must be exposed, a high-precision stepper exposure apparatus used for semiconductor manufacturing with a pattern exposure wavelength of 365 nm (0.365 μm) is used. As a material for forming a microlens, for example, a photosensitive phenol resin is used as a resin having photosensitivity and heat reflow.

  For this reason, the exposure wavelength is 365 nm and the resolution of the photosensitive resin remaining after pattern exposure and development is combined, and gaps and gaps between microlenses (particularly, the planar view shape of the remaining resin is a square shape). In this case, it becomes difficult to fill the gap in the diagonal direction.

  According to the observations of the present inventors, when a positive photosensitive phenol resin used as a microlens material is patterned by a photolithography method, 0.2 μm to 0.3 μm formed on the pattern mask in an isolated single pattern. The width pattern can somehow be reproduced as a resin pattern.

However, since exposure light having a wavelength of 365 nm does not enter the mask pattern portion, it is difficult to reproduce the light shielding pattern having a width of 0.1 μm on the pattern mask as a resin pattern.
Similarly, even when the translucent pattern on the pattern mask is 0.1 μm wide, the pattern cannot be reproduced with the resin unless the photosensitive resin is subjected to excessive overexposure during pattern exposure.
For this reason, the single pattern having a width of 0.15 to 0.2 μm becomes a boundary region as to whether the pattern can be reproduced.

  An object of the present invention is to provide a method for manufacturing a microlens array having a high aperture ratio, high condensing property, and excellent light diffusibility, and to provide a microlens substrate excellent in condensing property and light diffusing property. There is to do.

In order to achieve the above object in the present invention, in claim 1, the etching rate is slower than the etching rate of the resin constituting the transparent resin layer and the lens matrix on the semiconductor substrate on which the photoelectric conversion elements are formed at a pitch of 2 μm or less. A step of forming an etching control layer having an etching rate, a step of forming a photosensitive resin layer having a thermal reflow property on the etching control layer, and a pattern for pattern exposure using a photomask on the photosensitive resin layer An exposure step, a step of performing a patterning process such as development to make the photosensitive resin layer a predetermined resist pattern, a step of thermally melting the resist pattern to form a hemispherical lens base, and a lens base Using the mask as a mask, dry etching is performed on the etching control layer to form an intermediate microlens. The method of manufacturing a microlens array and the micro lens shape of the lens mother die dry etching is performed on the transparent resin layer as a click is transferred to the transparent resin layer,
During the pattern exposure, a 1.5 μm rectangular main pattern for forming a microlens array is arranged in a matrix, and a pattern width of 0.15 to 0.2 μm is formed at four corners of the rectangular main pattern. A rectangular pattern having a pattern width of 0.2 μm is added to a portion where the corners of the main patterns adjacent to each other on the diagonal line are connected to each other and the rectangular main patterns intersect with each other. A method for producing a microlens array, comprising using a photomask capable of pattern-exposing a pattern in which a blank pattern is formed on a photosensitive resin layer.

According to a second aspect of the present invention , part of opposite sides of the rectangular main pattern is extracted with a shape correction pattern having a pattern width of 0.15 to 0.2 μm, and the cross-sectional shape becomes asymmetric. The microlens array manufacturing method according to claim 1 , wherein the microlens array is a microlens.

Hereinafter, embodiments of the present invention will be described.
The invention according to claim 1 includes a step of forming a photosensitive resin layer having thermal reflow properties on a substrate, a pattern exposure step of pattern exposure using a photomask on the photosensitive resin layer, and a patterning process such as development. Forming a resist pattern and a thermal reflow process for thermally melting the resist pattern to form a microlens array. In the method of manufacturing a microlens array, the microlens array is formed during the pattern exposure. Rectangular main patterns are arranged in a matrix, and shape correction patterns having a pattern width of 0.15 to 0.2 μm at the four corners of the rectangular main pattern are adjacent to the diagonal main pattern. Are added so as to connect the corners of each other, and the rectangular main pattern intersects with a rectangle. The Jo punching pattern is formed pattern is obtained to use a photomask capable of pattern exposure on the photosensitive resin layer.

FIG. 1 is a schematic diagram showing an example of a pattern layout of a mask pattern obtained by adding a shape correction pattern having a pattern width of 0.15 to 0.2 μm to four corners of a rectangular main pattern and removing the pattern. It is a top view. The dimensions shown in FIG. 1 are the dimensions of the pattern exposed to the photosensitive resin. When pattern exposure is performed using a 5-fold reticle, the dimensions on the 5-fold reticle are 5 times the dimensions of FIG. A pattern having is formed.
The mask pattern 10a is an example of a mask pattern used when pattern exposure is performed on a positive photosensitive resin layer, and includes four corners of a 1.5 μm square rectangular main pattern 11 serving as a light-shielding portion on the mask pattern. The pattern correction pattern 12a having a pattern width of 0.2 μm is added to the main pattern so that the main patterns are connected to each other, and the connection center portion where the shape correction patterns 12a intersect each other is a pattern of 0.15 to 0.2 μm. The pattern correction of the rectangular main pattern 11 is performed by removing the pattern with the shape correction pattern 13a having a width. It should be noted that a resist residue is likely to occur at a portion where the shape correction patterns 12a intersect with each other, and pattern defects are likely to occur. Therefore, in order to prevent unnecessary resist residue, a blank pattern is formed at the intersection (see FIG. 6).
Thus, by correcting the rectangular main pattern 11 with the shape correction pattern, the pattern reproducibility of the corner portion is improved even in the rectangular main pattern of 2.2 μm or less, and the roundness of the corner portion is reduced. Since the obtained microlens can be obtained, the lens aperture ratio of the microlens can be increased.

  FIG. 7 shows a case where patterns are added so that main patterns are connected to each other at four corners of a rectangular main pattern by a shape correction pattern having a pattern width of 0.15 to 0.2 μm. FIG. 3 is a schematic partial plan view showing an example of a pattern layout of a mask pattern obtained by extracting a part of the pattern with a shape correction pattern having a pattern width of 0.15 to 0.2 μm. Note that the dimensions shown in FIG. 7 are the dimensions of the pattern exposed to the photosensitive resin. When pattern exposure is performed using a 5-times reticle, the dimensions on the 5-times reticle are 5 times the dimensions of FIG. A pattern having is formed.

The mask pattern 10b is an example of a mask pattern used when pattern exposure is performed on a positive photosensitive resin layer, and a pattern width of 0.2 μm is formed at four corners of a rectangular main pattern 11 of 1.5 μm square. A pattern is added so as to connect the shape correction patterns 12a to be connected, and a pattern correction pattern 13a having a pattern width of 0.15 to 0.2 [mu] m is used to remove the pattern at the connecting central portion where the shape correction patterns 12a intersect each other. Further, a part of the side where the rectangular main patterns 11 face each other is extracted with a pattern 12b for shape correction having a pattern width of 0.2 μm, and the rectangular shape is formed so that the part where the pattern is removed becomes a recess. Pattern correction of the main pattern 11 is performed.
Thus, by correcting the pattern of the rectangular main pattern 11, the pattern reproducibility of the corner portion is improved even in the rectangular main pattern of 2.2 μm or less, and the lens aperture ratio of the microlens can be increased. And since the volume of the lens which reflows in the case of a heat flow can be adjusted with a recessed part, the cross-sectional shape and lens volume (thickness, curvature) of a microlens can be adjusted.

When an image pickup device such as a CMOS becomes finer (for example, a fine pixel of 2.2 μm or less, 1.8 μm, or 1.5 μm), the light receiving device is affected by the layout of transistor devices, aluminum wiring, and the like. The position of the photodiode is not the center of the pixel, but is shifted to the side direction or the diagonal corner direction.
At this time, the center position of the microlens is adjusted to the position of the light receiving element, and for example, the position adjustment and the delicate curvature adjustment are required in an amount of 0.1 μm to 0.3 μm.
By using a photomask having the pattern shown in FIG. 7, a technique capable of adjusting the position of a microlens and adjusting a delicate curvature is proposed.

The invention according to claim 3 includes a step of forming a transparent resin layer on a substrate, a step of forming a photosensitive resin layer having thermal reflow on the transparent resin layer, and a photomask on the photosensitive resin layer. A pattern exposure process for pattern exposure using the resist, a patterning process such as development to make the photosensitive resin layer a predetermined resist pattern, and the resist pattern is melted to form a hemispherical lens matrix And a step of dry etching the transparent resin layer using the lens matrix as a mask to transfer the shape of the lens matrix to the transparent resin layer to form a microlens. When
A rectangular main pattern for forming the microlens array is arranged in a matrix, and a shape correction pattern having a pattern width of 0.15 to 0.2 μm at the four corners of the rectangular main pattern is diagonal. A pattern in which a rectangular blank pattern is formed at a portion where the corners of the main pattern adjacent to each other are connected to each other and the rectangular main pattern intersects can be pattern-exposed on the photosensitive resin layer. A photomask is used.

FIG. 1 is a schematic diagram showing an example of a pattern layout of a mask pattern obtained by adding a shape correction pattern having a pattern width of 0.15 to 0.2 μm to four corners of a rectangular main pattern and removing the pattern. It is a top view. The dimensions shown in FIG. 1 are the dimensions of the pattern exposed to the photosensitive resin. When pattern exposure is performed using a 5-fold reticle, the dimensions on the 5-fold reticle are 5 times the dimensions of FIG. A pattern having is formed.
The mask pattern 10a is an example of a mask pattern used when pattern exposure is performed on a positive photosensitive resin layer, and a pattern width of 0.2 μm is formed at four corners of a rectangular main pattern 11 of 1.5 μm square. A pattern is added so as to connect the shape correction patterns 12a to be connected, and a pattern correction pattern 13a having a pattern width of 0.15 to 0.2 [mu] m is used to remove a pattern at the intersecting central portion of the shape correction patterns 12a. Yes.

By correcting the rectangular main pattern 11 in this manner, the pattern reproducibility of the resist pattern corner portion is improved even in a rectangular main pattern of 2.2 μm or less, and the roundness of the corner portion is reduced. Therefore, the lens aperture ratio of the microlens can be increased.
In particular, the lens aperture ratio of the microlens can be increased as compared with the thermal reflow microlens according to the first aspect.

  In FIG. 7, pattern correction patterns having a pattern width of 0.15 to 0.2 μm are added to the four corners of the rectangular main pattern, and a part of the rectangular main pattern is 0.15 to 0. It is a typical partial top view which shows one Example of the pattern layout of the mask pattern which extracted the pattern by the pattern for shape correction which has a pattern width of 2 micrometers. Note that the dimensions shown in FIG. 7 are the dimensions of the pattern exposed to the photosensitive resin. When pattern exposure is performed using a 5-times reticle, the dimensions on the 5-times reticle are 5 times the dimensions of FIG. A pattern having is formed.

The mask pattern 10b is an example of a mask pattern used when pattern exposure is performed on a positive photosensitive resin layer, and a pattern width of 0.2 μm is formed at four corners of a rectangular main pattern 11 of 1.5 μm square. A pattern is added so as to connect the shape correction patterns 12a having the shape correction pattern 12a, and a pattern correction pattern 13a having a pattern width of 0.15 to 0.2 [mu] m is used to remove the pattern at the intersecting central portion of the shape correction patterns 12a. Further, the rectangular main pattern 11 has a part of the opposite sides removed by a shape correction pattern 12b having a pattern width of 0.2 μm to form a concave portion, and pattern correction of the rectangular main pattern 11 is performed. .
Thus, by correcting the rectangular main pattern 11, the pattern reproducibility of the corner portion is improved even in the rectangular main pattern of 2.2 μm or less, and the lens aperture ratio of the microlens can be increased. In addition, the cross-sectional shape and lens volume (thickness, curvature) of the microlens can be adjusted.

  In the present invention, by using the mask pattern as described above and using dry etching together, the pattern reproducibility of the microlens corner is improved even in a fine pixel of 2 μm or less. Thereby, a lens aperture ratio can be raised (refer FIG. 16).

Hereinafter, a method for manufacturing a transfer type microlens array will be described.
FIGS. 14A to 14E and FIGS. 15F to 15H are schematic cross-sectional views showing an example of a method for manufacturing a transfer type microlens array.
First, the color filter 40 including the planarization layer 31, the red filter 41R, the green filter 42G, and the blue filter 43B is formed on the semiconductor substrate 20 on which the photoelectric conversion element 21 is formed by a known method (FIG. 14A to FIG. 14). (See (c)).

Next, a transparent resin layer 51 for forming a transfer lens, an etching control layer 61, and a photosensitive resin layer 71 having thermal reflow properties are formed (see FIG. 14D).
As the photosensitive resin layer 71 having heat reflow property, generally, a positive photosensitive resin (usually a photosensitive phenol resin also used for a semiconductor resist) is used, and a photosensitive phenol resin, a photosensitive phenol novolak resin, a photosensitive resin is used. A photosensitive polystyrene resin, a photosensitive acrylic resin, or the like can be used. What is necessary is just to have characteristics, such as thermal reflow property, photosensitivity, and alkali development (usually positive type). It is more desirable to have submicron high resolution.

  Next, pattern exposure is performed on the photosensitive resin layer through a photomask. At this time, the photosensitive resin layer 71 is pattern-exposed to the pattern shown in FIG. 1 and developed with a developer such as organic alkali to form a resist pattern 71a at a predetermined position on the etching control layer 151 (FIG. 14 (e)).

  In pattern exposure, a pattern exposure mask (usually referred to as a 5 × reticle) in which a pattern having a size five times that of the microlens to be formed is used, and light having a wavelength of 365 nm is set as a main wavelength at the time of pattern exposure. In many cases, the photosensitive resin layer is subjected to pattern exposure after being reduced to 1/5 with a stepper exposure apparatus. At this time, a pattern having a size five times that of FIG. 1 is formed on the five times reticle.

Next, the resist pattern 71a is subjected to heat treatment in the range of 150 ° C. to 250 ° C., and the resist pattern 71a is subjected to thermal reflow (fluidization of the resist pattern 71a) to form the lens matrix 71b (FIG. 15 ( f)).
The lens matrix 71b forms a convex lens (for example, a hemispherical cross section) due to surface tension generated on the surface of the resist pattern 71a during melting.

  Next, by using a dry etching apparatus, the etching control layer 61 is etched using the lens master 71b as an intermediate mask, thereby forming an intermediate microlens 61a (see FIG. 15G).

  Here, in the invention according to claim 5, the etching control layer 61 is formed between the transparent resin layer 51 and the photosensitive resin layer 71. By making the etching rate of the etching control layer slower than the etching rate of the lens master, the lens diameter of the lens master 71b is made larger to reduce the “narrow gap” between the microlenses, and at the time of etching and after etching Roughness of the surface of the lens 51a is suppressed.

In order to suppress the roughness of the microlens surface, the resin is preferably a resin in which many benzene rings are introduced into the resin skeleton used in the etching control layer 61 and the transparent resin layer 51.
Or even if the ultraviolet absorber etc. which have a benzene ring are added, the effect which suppresses surface roughness is acquired.
The resin that can be used for the etching control layer 61 may be a thermosetting resin or a photosensitive resin that can be developed with an alkali.

For this dry etching, a fluorocarbon-based gas is used, but a single gas such as CF ₄ , C ₂ F ₆ , C ₃ F ₈ , C ₄ F ₈ or a mixed gas thereof is preferable.
In particular, when a gas having a high carbon ratio with a carbon atom / fluoro atom ratio is used, the intermediate microlens 61a shown in FIG. This is because CFx is easily formed on the side walls of the lens master 71b and the intermediate microlens 61a during dry etching, and the lens shape can be increased.
The lens matrix pattern becomes larger, resulting in a smaller gap between the lenses and a “narrow gap” effect.

Based on the lens mother die before shape transfer processing, a special micro-lens aspheric or asymmetrically processed by dry etching, the number of F atoms, such as _{C 2 F 6, C 3 F} 8, C 4 F 8 On the other hand, it is preferable to use a fluorocarbon-based gas having a large number of C atoms.
Further, a chlorofluorocarbon gas partially containing hydrogen atoms may be introduced.

  Next, a desired microlens 51a is formed by dry etching the transparent resin layer 51 using the intermediate microlens 61a as an intermediate mask in a dry etching apparatus, and the color filter 40 and the microlens 51a are formed on the semiconductor substrate 20. Can be obtained (see FIG. 15 (h) and FIG. 16).

The “narrow gap” is difficult to advance when the gap between the lenses becomes small. Since the “narrow gap” effect is reduced when the distance between the lenses is reduced to zero gap, the etching rate is reduced to CF _{4 in} the dry etching process in which the shape of the intermediate microlens 61a having the zero gap is transferred to the transparent resin layer 51. It is desirable to switch to a gas with a quicker gas.

On the contrary, the transparent resin layer 51 on which the microlenses 51a are formed has a wide resin selection range. A fluorine-containing acrylic resin in which a fluorine group is introduced into a resin skeleton or a silicon-containing acrylic resin into which silicon is introduced can be used for the purpose of low reflectivity required for a microlens for an image sensor such as a reduction in S / N ratio.
When a high refractive index is required, an acrylic resin into which a halogen group is introduced such as polyimide resin or sulfur, or an inorganic material such as SiN (silicon nitride) also falls within the selection range.
In addition to the materials described above, a heat-resistant acrylic resin can be used for applications where heat resistance is important.
It is possible to adjust the thickness (curvature) of the microlens by using a lens base photosensitive resin, an etching control layer, and a transparent resin with different etching rates.

The microlens substrate formed by the method of manufacturing a microlens array according to the present invention has a lens curvature and refractive index required as an optical element on a semiconductor substrate (silicon wafer) on which photoelectric conversion elements called CMOS and CCD are formed. -A microlens array whose shape can be adjusted can be formed.
In this case, the size of the micro lens may be 2.2 μm pitch, but may be formed with a size larger than 2.2 μm if necessary.

  In the invention according to claim 8, the microlens substrate manufactured by the method of manufacturing a microlens array according to any one of claims 1 to 7 is a corner of the main pattern 11 having a rectangular shape of 1.5 μm square. Since the pattern exposure is performed using a photomask in which a mask pattern to which a shape correction pattern 12a having a pattern width of 0.2 μm is connected is arranged on the microlens array. The microlens area can be secured 90% or more of the array pixel area of the photoelectric conversion element.

  In the invention according to claim 9, the microlens substrate manufactured by the method for manufacturing a microlens array according to any one of claims 1 to 7 is 1.5 μm square as a photomask used for pattern exposure. A pattern is added so as to connect a shape correction pattern 12a having a pattern width of 0.2 μm to the corner of the rectangular main pattern 11, and a part of the rectangular main pattern is 0.15 to 0.2 μm. Since pattern exposure is performed using a photomask in which a mask pattern extracted with a shape correction pattern having a pattern width of 1 is arranged, the shape of the microlens of the microlens array can be partially changed.

In the invention according to claim 10, the microlens substrate produced by the method for producing a microlens array according to any one of claims 1 to 7 is 1.5 μm square as a photomask used for pattern exposure. A pattern is added so as to connect a shape correction pattern 12a having a pattern width of 0.2 μm to the corner of the rectangular main pattern 11, and a part of the rectangular main pattern is 0.15 to 0.2 μm. Since pattern exposure is performed using a photomask in which a mask pattern extracted with a shape correction pattern having a pattern width of 1 is arranged, the microlens of the microlens array can be configured by a microlens having an asymmetric cross section.

  First, after the planarization layer 31 is formed on the semiconductor substrate 20 on which the photoelectric conversion element 21 is formed by a spin coating method, the color filter 40 including the red filter 41R, the green filter 42G, and the blue filter 43B is formed by a known photolithography method. (See FIGS. 14A to 14C).

  Next, a 0.8 μm-thick transparent resin layer 51 made of an acrylic resin containing a benzotriazole-based UV absorber at a solid ratio of 5%, a 0.8 μm-thick etching control layer 61 made of a novolac resin, and a heat reflow property A photosensitive resin layer 71 having a thickness of 0.4 μm made of the photosensitive phenol resin was sequentially formed (see FIG. 14D).

Next, the photosensitive resin layer 71 was pattern-exposed with a stepper using a 5 × reticle. When the 5 × reticle is reduced to 1/5, shape correction patterns 12a having a width of 0.2 μm are added to four corners of a 1.5 μm rectangular pattern shown in FIG. A pattern 10a is formed by removing the pattern at the center of the connection where the lines intersect with a pattern 13a for shape correction having a pattern width of 0.2 μm.
Next, development processing was performed with a developer such as organic alkali to form a resist pattern 71a at a predetermined position on the etching control layer 151 (see FIG. 14E).
FIG. 2 shows an electron micrograph of the resist pattern 71a.

Next, the resist pattern 71a was heat-treated with a hot plate heated to 200 ° C., and the resist pattern 71a was subjected to a heat reflow process to form a hemispherical lens master 71b (see FIG. 15F).
FIG. 3 shows an electron micrograph of the lens master 71b.

  Next, an intermediate microlens 61a was formed by etching the etching control layer 61 using the lens master 71b as an intermediate mask with a dry etching apparatus (see FIG. 15G).

Next, the transparent resin layer 51 is dry-etched with a dry etching apparatus using the intermediate microlens 61 a as an intermediate mask to form a microlens 51 a having a height of 0.4 μm, and the color filter 40 is formed on the semiconductor substrate 20. In addition, the microlens substrate 100a on which the microlenses 51a were formed could be manufactured (see FIG. 15H).
FIG. 4 shows an electron micrograph of the microlens 51a, and FIG. 5 shows an enlarged cross-sectional photograph of the microlens 51a.
As can be seen from the electron micrograph of FIG. 4, by adding the 0.2 μm width shape correction pattern 12 a to the four corners, the roundness of the corner portion of the microlens is reduced and the aperture ratio is increased. It was confirmed.
The aperture ratio of the microlens 51a was about 94%.

In the second embodiment, the manufacturing process is the same as that of the first embodiment except that the semiconductor substrate and the photomask are different. Therefore, the manufacturing process will be described with reference to FIGS.
First, the semiconductor substrate 20a having the photoelectric conversion element 21 displaced in the side direction from the center of the pixel.
A color filter 40 composed of the planarizing layer 31, the red filter 41R, the green filter 42G, and the blue filter 43B was formed on the top in the same manner as in Example 1 (see FIGS. 14A to 14C).

  Next, a 0.8 μm-thick transparent resin layer 51 made of an acrylic resin containing a benzotriazole-based UV absorber at a solid ratio of 5%, a 0.8 μm-thick etching control layer 61 made of a novolac resin, and a heat reflow property A photosensitive resin layer 71 having a thickness of 0.5 μm made of the photosensitive phenol resin was sequentially formed (see FIG. 14D).

Next, the photosensitive resin layer 71 was pattern-exposed with a stepper using a 5 × reticle. When the 5 × reticle is reduced to 1/5, a shape correction pattern 12a having a width of 0.2 μm is added to four corners of a 1.5 μm rectangular pattern shown in FIG. A part of opposite sides of the pattern is extracted by a shape correction pattern 13b having a pattern width of 0.2 μm, and a shape correction having a pattern width of 0.2 μm is formed at a connecting central portion where the shape correction patterns 12a intersect. A pattern 10b that has been removed from the pattern 13a for use is arranged.
Next, development processing was performed with a developer such as organic alkali to form a resist pattern 72a at a predetermined position on the etching control layer 151 (see FIG. 14E).
FIG. 8 shows an electron micrograph of the resist pattern 72a.

Next, the resist pattern 72a was heat-treated with a hot plate heated to 200 ° C., and the resist pattern 72a was subjected to heat reflow treatment to form a hemispherical lens matrix 72b (see FIG. 15F).
FIG. 9 shows an electron micrograph of the lens matrix 72b.

Next, an intermediate microlens 62a was formed by etching the etching control layer 61 using the lens mother block 72b as an intermediate mask with a dry etching apparatus introduced with a fluorocarbon-based gas C ₃ F ₈ (FIG. 15G). reference).

Next, in a dry etching apparatus introduced with a fluorocarbon gas CF ₄ , the transparent resin layer 51 is dry-etched using the intermediate microlens 62a as an intermediate mask to form a cross-sectional asymmetric microlens 52a on the semiconductor substrate 20a. A microlens substrate 100b on which the color filter 40 and the asymmetrical microlens 52a were formed could be manufactured (see FIG. 17A).
FIG. 10 shows an electron micrograph of the microlens 52a, and FIG. 11 shows an enlarged cross-sectional photograph of the microlens 52a.

  As can be seen from the electron micrograph of the resist pattern 72a in FIG. 8, pattern correction patterns having a width of 0.2 μm are added to the four corners, and a part of the opposite sides of the rectangular main pattern is 0.2 μm. By removing the pattern with the shape correction pattern 13b having the pattern width of 1, the portion where the pattern is removed with the shape correction pattern 12b is recessed.

As can be seen from the cross-sectional enlarged photograph of FIG. 11, the microlens is processed into an asymmetric rounded shape as a whole.
In addition, it was confirmed that the height peak of the microlens 52a was shifted by about 0.2 μm from the center on the side opposite to the portion where the pattern was removed by the shape correction pattern 13b.
The aperture ratio of the microlens 52a was about 92%.

In the third embodiment, the manufacturing process is the same as that of the first embodiment except that the semiconductor substrate and the photomask are different. Therefore, the manufacturing process will be described with reference to FIGS.
First, as shown in FIG. 17B, the planarization layer 31 and the red filter 41 </ b> R are formed on the semiconductor substrate 20 a having the photoelectric conversion element 21 shifted in the diagonal direction from the center of the pixel by the same method as in the first embodiment. A color filter 40 composed of a green filter 42G and a blue filter 43B was formed (see FIGS. 14A to 14C).

  Next, a 0.8 μm-thick transparent resin layer 51 made of an acrylic resin containing a benzotriazole-based UV absorber at a solid ratio of 5%, a 0.8 μm-thick etching control layer 61 made of a novolac resin, and a heat reflow property A photosensitive resin layer 71 having a thickness of 0.4 μm made of the photosensitive phenol resin was sequentially formed (see FIG. 14D).

Next, the photosensitive resin layer 71 was pattern-exposed with a stepper using a 5 × reticle. When the magnification is reduced to 1/5, the 5 × reticle is added with a 0.2 μm-wide shape correction pattern 12a at three corners of a 1.5 μm rectangular pattern shown in FIG. One corner of the rectangular main pattern is extracted with a shape correction pattern 13c having a pattern width of 0.2 μm, and further, a shape correction having a pattern width of 0.2 μm is made at the connecting central portion where the shape correction patterns 12a intersect. A pattern 10c that has been removed from the pattern 13a for use is arranged.
Next, development processing was performed with a developer such as organic alkali to form a resist pattern 73a at a predetermined position on the etching control layer 151 (see FIG. 14E).

Next, the resist pattern 73a was heat-treated with a hot plate heated to 200 ° C., and the resist pattern 73a was subjected to a heat reflow process to form a hemispherical lens matrix 73b (see FIG. 15F).
Here, the lens matrix formed using the mask pattern 10c can adjust the volume of the lens that is melted and reflowed by heat by removing the pattern with the shape correction pattern 12c, so that the lens height (lens curvature) can be adjusted. You can adjust it.

Next, an intermediate microlens 63a is formed by etching the etching control layer 61 using the lens matrix 73b as an intermediate mask with a dry etching apparatus into which a fluorocarbon gas C ₃ F ₈ is introduced (FIG. 15G). reference).

Next, by dry etching apparatus was introduced fluorocarbon gas CF _4, the intermediate microlens 63a as an intermediate mask, by dry-etching the transparent resin layer 51, to form an asymmetric microlens 53a, on a semiconductor substrate 20a A microlens substrate 100c on which the color filter 40 and the asymmetric microlens 53a were formed was able to be manufactured (see FIG. 17A).
Here, an asymmetric macro lens having a gentle curve at one corner of the micro lens could be processed.

  First, the color filter 40 including the planarization layer 31, the red filter 41R, the green filter 42G, and the blue filter 43B is formed on the semiconductor substrate 20 on which the photoelectric conversion element 21 is formed by a known method (FIG. 14A to FIG. 14A). (See (c)).

  Next, a 0.8 μm-thick transparent resin layer 51 made of an acrylic resin containing a benzotriazole-based UV absorber at a solid ratio of 5%, a 0.8 μm-thick etching control layer 61 made of a novolac resin, and a heat reflow property A photosensitive resin layer 71 having a thickness of 0.4 μm made of the photosensitive phenol resin was sequentially formed (see FIG. 14D).

Next, the photosensitive resin layer 71 was pattern-exposed with a stepper using a 5 × reticle. When the magnification is reduced to 1/5, the 5 × reticle is provided with a 0.2 μm-wide shape correction pattern 12a at four corners of a 1.5 μm rectangular pattern shown in FIG. A portion of the rectangular main pattern is extracted with the shape correction patterns 13d and 13e having a pattern width of 0.2 μm, and the connecting central portion where the shape correction patterns 12a intersect each other has a pattern width of 0.2 μm. A pattern 10d that has been removed from the shape correction pattern 13a is disposed.
Next, development processing was performed with a developer such as an organic alkali to form a resist pattern 74a at a predetermined position on the etching control layer 151 (see FIG. 14E).

Next, the resist pattern 74a was heat-treated with a hot plate heated to 200 ° C., and the resist pattern 74a was subjected to heat reflow treatment to form a hemispherical lens matrix 74b (see FIG. 15F).
Here, in the lens matrix formed by using the mask pattern 10d, a part of a 1.5 μm rectangular main pattern is removed by pattern correction patterns 13d and 13e having a pattern width of 0.2 μm. Therefore, the thermal reflow lens is thin as a whole.

Next, an intermediate microlens 64a was formed by etching the etching control layer 61 using the lens master 74b as an intermediate mask with a dry etching apparatus into which a fluorocarbon-based gas C ₃ F ₈ was introduced (FIG. 15G). reference).

Next, in a dry etching apparatus into which a fluorocarbon gas CF ₄ is introduced, the microlens 54 a is formed by dry etching the transparent resin layer 51 using the intermediate microlens 64 a as an intermediate mask, and a color is formed on the semiconductor substrate 20. A microlens substrate 100d on which the filter 40 and the microlens 54a were formed could be manufactured (see FIG. 15H).
Here, the microlens 54a was able to produce a microlens having a central portion lower than the microlens 51a produced in Example 1 by about 0.1 μm.
The aperture ratio of the microlens 54a was about 93%.

As described above, according to the method for manufacturing a microlens array of the present invention, a photomask in which a pattern correction pattern is added or a mask pattern in which a part of the mask pattern is removed by the shape correction pattern is used. By performing pattern exposure, it is possible to provide a microlens substrate with optimized light collection and scattering effects.
In the image pickup device, light collection can be optimized even in a fine pixel having a pitch of 2 μm or less regardless of the position of the light receiving device, and microlenses having different shapes and thicknesses are arranged according to the optical conditions of the image pickup device chip. As a result, it is possible to eliminate the difference in condensing properties between the center and the end of the chip, which has been a problem in the past.
Further, since the refractive index difference of the color filters of each color such as red, green and blue is corrected, the thickness of each lens formed corresponding to the red, green and blue filters can be adjusted.

In the example described above, the microlens array is formed on the semiconductor substrate having the photoelectric conversion element, but the embodiment of the present invention is not limited to this.
For example, a microlens substrate in which a microlens array is formed on a glass substrate by the above-described method can uniformly collect and diffuse light.
Therefore, a high-quality display device can be obtained by incorporating such a microlens substrate into a light source such as an LED.

FIG. 6 is a schematic partial plan view showing an example of a pattern layout of a mask pattern in which a shape correction pattern having a pattern width of 0.15 to 0.2 μm is added to four corners of a rectangular main pattern. It is explanatory drawing which shows the electron micrograph of the resist pattern 71a. It is explanatory drawing which shows the electron micrograph of the lens mother die 71b. It is explanatory drawing which shows the electron micrograph of the micro lens 51a. It is explanatory drawing which shows the electron micrograph of the cross-sectional structure of the micro lens 51a. It is explanatory drawing which shows the shape correction pattern 13a arrange | positioned in the connection center part to which the pattern 12a for shape correction was added. A pattern for shape correction having a pattern width of 0.15 to 0.2 μm is added to four corners of the rectangular main pattern, and a part of the rectangular main pattern is a pattern of 0.15 to 0.2 μm. It is a typical partial top view which shows one Example of the pattern layout of the mask pattern extracted by the pattern for shape correction which has a width | variety. It is explanatory drawing which shows the electron micrograph of the resist pattern 72a. It is explanatory drawing which shows the electron micrograph of the lens mother mold 72b. It is explanatory drawing which shows the electron micrograph of the micro lens 52a. It is explanatory drawing which shows the electron micrograph of the cross-sectional structure of the micro lens 52a. A shape correction pattern 12a having a width of 0.2 μm is added to three corners of a 1.5 μm rectangular pattern, and one corner of a 1.5 μm rectangular main pattern has a pattern width of 0.2 μm. It is a typical fragmentary top view which shows one Example of the pattern layout of the mask pattern by which the mask pattern 10c extracted by the pattern 12c is arrange | positioned. A shape correction pattern 12a having a width of 0.2 μm is added to four corners of a 1.5 μm rectangular pattern, and a portion of the 1.5 μm rectangular main pattern is corrected to have a pattern width of 0.2 μm. It is a typical fragmentary top view which shows one Example of the pattern layout of the mask pattern by which the mask pattern 10d from which the pattern was removed by the patterns 12d for use and 12e was arrange | positioned. (A)-(e) is typical structure sectional drawing which shows a part of manufacturing process of the manufacturing method of the transfer-type microlens array. (F)-(h) is typical structure sectional drawing which shows a part of manufacturing process of the manufacturing method of the transcription | transfer type microlens array. It is a model fragmentary top view which shows the planar view shape of the micro lens 51a produced with the manufacturing method of the micro lens array of a transfer system. (A) is a schematic fragmentary sectional view which shows one Example of the microlens board | substrate of this invention. (B) is a schematic plan view which shows an example of the arrangement state of the photoelectric conversion element shifted in the diagonal direction from the center of the pixel. It is a model partial top view which shows an example of the design mask pattern dimension used when forming a micro lens of a 1.8 micrometer pitch. It is a model fragmentary top view which shows the planar view shape of the resist pattern 161a. It is a model fragmentary top view which shows the planar view shape of the micro lens 141a. It is explanatory drawing which shows the change of the effective aperture ratio of the micro lens formed by the thermal reflow method when the pixel pitch is changed, and the micro lens formed by the dry etching method. (A)-(e) is typical structure sectional drawing which shows a part of manufacturing process of the manufacturing method of the transfer-type microlens array. (F)-(h) is typical structure sectional drawing which shows a part of manufacturing process of the manufacturing method of the transcription | transfer type microlens array.

Explanation of symbols

10a, 10b, 10c, 10d ... Mask pattern 11 ... Rectangular main patterns 12a, 13a, 13b, 13c, 13d ... Shape correction patterns 20, 20a, 110 ... Semiconductor substrates 21, 111 ... Photoelectric conversion Elements 31, 121 ... Flattening layer 40 ... Color filters 41R, 131R ... Red filters 42G, 132G ... Green filters 43B, 133B ... Blue filters 51, 141 ... Transparent resin layers 51a, 52a, 53a, 54a , 141a... Microlens 61, 151... Etching control layer 61a, 62a, 63a, 64a, 151a... Intermediate lens 71, 161. , 72b, 73b, 74b, 161b... 0b, 100c, 100d ...... micro-lens substrate

Claims (2)

Forming an etching control layer having a lower etching rate than the etching rate of the resin forming the transparent resin layer and the lens mother die on a semiconductor substrate in which the photoelectric conversion element is formed in 2μm pitch below the etching control layer Forming a photosensitive resin layer having thermal reflow properties on the substrate, pattern exposure step of pattern exposure using a photomask on the photosensitive resin layer, and patterning treatment such as development to form the photosensitive resin layer. A step of forming the resist pattern, a step of thermally melting the resist pattern to form a hemispherical lens matrix, and performing dry etching on the etching control layer using the lens matrix as a mask to form an intermediate microlens, Thereafter, the lens base type dry etching is performed on the transparent resin layer an intermediate microlens as a mask The method of manufacturing a microlens array and the micro lens Jo is transferred to the transparent resin layer,
During the pattern exposure, a 1.5 μm rectangular main pattern for forming a microlens array is arranged in a matrix, and a pattern width of 0.15 to 0.2 μm is formed at four corners of the rectangular main pattern. A rectangular pattern having a pattern width of 0.2 μm is added to a portion where the corners of the main patterns adjacent to each other on the diagonal line are connected to each other and the rectangular main patterns intersect with each other. A method for producing a microlens array, comprising using a photomask capable of pattern-exposing a pattern in which a blank pattern is formed on a photosensitive resin layer. A part of opposite sides of the rectangular main pattern is extracted with a pattern for pattern correction having a pattern width of 0.15 to 0.2 μm, and the microlens has an asymmetric cross-sectional shape. The method of manufacturing a microlens array according to claim 1 .