JP2002116315A - Manufacturing method for micro optical element - Google Patents

Abstract

(57) [Summary] To obtain a fine optical element having high unevenness. SOLUTION: A thick resist film 3, which is a photosensitive resin, is applied on a surface of a substrate 1, and a gray scale mask 4 on which a predetermined pattern is drawn is brought into contact with the resist film 3 with an equal force. The first exposure is performed according to a predetermined pattern. Next, the gray scale mask 4 is replaced, the resist film 3 is brought into contact with the same force as before, and the second exposure is performed so as to form a pattern on the previous non-exposed portion. When development is performed after the multiple exposure process, a fine optical element having the sawtooth diffraction grating 6 is obtained.

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 fine optical element having an optical function element such as a diffractive optics, a microlens array or a hologram three-dimensional structure.

[0002]

2. Description of the Related Art Conventionally, diffractive optics,
A micro-optical element having a micro-optical function element such as a micro-lens array and a hologram three-dimensional structure is manufactured by repeating a photolithography process and an etching process, which are semiconductor manufacturing technologies.

[0003] The photolithography step is an exposure step of irradiating a resist-coated substrate with ultraviolet rays or the like through a mask to correctly pattern a pattern drawn on the mask at a predetermined position on the substrate. Developing a pattern formed in the form of a latent image on a resist on the substrate in the process to form a desired shape on the substrate.

[0004] The etching step refers to a step of similarly transferring the shape of a resist pattern formed in a photolithography step to a substrate using a wet or dry method or the like.

Therefore, in the case of manufacturing a fine optical element by a semiconductor manufacturing technique, a photolithography step is performed in which a resist is once again applied to a substrate having an uneven surface which has been subjected to a photolithography step and an etching step, and is then exposed and developed. The desired fine shape is formed by repeating the etching process.

However, in the production of a fine shape having a large uneven shape with large unevenness, in order to reduce the surface roughness, the conventional photolithography process and the etching process are repeated to form a resist on the unevenness on the substrate surface. Repeated application results in a failure to apply the resist uniformly on the substrate surface. Further, there is a problem that a shape error occurs due to ultraviolet scattering at the time of exposure due to unevenness of the substrate surface.

On the other hand, a gray substrate in which a pattern having a predetermined gradation is applied to a substrate coated with a photosensitive resin.
Exposure and development using a scale mask eliminates the need to overlay multiple photomasks for exposure,
A fine optical functional element can be formed on a substrate by one exposure.
Further, since superposition exposure is not required, a fine optical function element having no alignment error can be manufactured.

Further, by further anisotropically etching this substrate, an optical element whose shape is similarly transferred to various substrates made of, for example, glass or super steel can be manufactured.
Alternatively, a fine optical element whose shape has been transferred by raising an electroforming mold based on this substrate can also be manufactured.

The surface of the fine optical element manufactured in this way is smooth, but formed in a fine step shape. This is because there is a digital tone difference in the light absorption density applied to the gray scale mask, and there is a drawing size in which a pattern is drawn by an electron beam or a laser beam.

On the other hand, the desired characteristics of the photosensitive resin include not only high resolution but also a large latitude, that is, latitude, for correctly exposing to a wide gradation width of the gray scale mask. .

[0011]

However, in general, photosensitive resins cannot be properly exposed to a wide range of gradations of a gray scale mask, and the function of the gray scale mask cannot be fully utilized. . That is, when the thickness of the photosensitive resin is increased, the surface smoothness of the optical element that can be manufactured by one exposure is limited by a step difference obtained by dividing the thickness of the photosensitive resin by the latitude held by the photosensitive resin. Will be.

An object of the present invention is to provide a method of manufacturing a fine optical element having a large unevenness using a gray scale mask.

An object of the present invention is to provide a fine optical element having a desired shape and a smooth surface even if the thickness of the photosensitive resin is large, that is, the height of the unevenness of the fine optical element is increased. It is to provide a manufacturing method.

An object of the present invention is to provide a method of manufacturing a fine optical element having a small surface roughness and a variety of surface shapes, even if the photosensitive resin has a large thickness and has a large unevenness. .

An object of the present invention is to provide a fine optical element capable of enhancing the function by transferring the shape of the manufactured fine optical element to a substrate in a similar manner.

An object of the present invention is to provide a fine optical element capable of enhancing its function by precisely replicating the shape of a manufactured fine optical element on various substrates.

[0017]

According to the first aspect of the present invention, there is provided a method for continuously exposing an exposure process using one or more gray scale masks having a pattern having a gradation. A fine optical function element formed on a substrate by multiple exposure performed by the method.

According to a second aspect of the present invention, the gray scale mask includes a pattern portion having a gradation and an opaque portion, and a non-exposed portion on the substrate by the opaque portion by the previous exposure, 2. The method for manufacturing a micro optical element according to claim 1, wherein exposure is performed by the pattern portion in a step.

According to a third aspect of the present invention, there is provided the method for manufacturing a fine optical element according to the first aspect, wherein the exposure amount is changed when performing the multiple exposure.

According to a fourth aspect of the present invention, in performing the multiple exposure, the gray scale scale providing an optical function is provided.
2. The method according to claim 1, wherein at least one or more alignment marks for mask alignment are formed on the substrate outside the main pattern area of the mask.

According to a fifth aspect of the present invention, there is provided a fine optical element manufactured by the manufacturing method according to any one of the first to fourth aspects.

According to a sixth aspect of the present invention, there is provided a method for manufacturing a fine optical element, wherein the fine optical element is similarly transferred to another substrate by etching.

According to a seventh aspect of the present invention, there is provided a method for manufacturing a fine optical element, wherein a transfer mold is formed by electroforming using the fine optical element according to any one of the fifth to sixth aspects.

According to an eighth aspect of the present invention, there is provided a method for manufacturing a fine optical element, comprising replica-molding the fine optical element manufactured in any one of the fifth to seventh aspects as a master mold. It is.

According to a ninth aspect of the present invention, there is provided a fine optical element produced by the method according to any one of the sixth to eighth aspects.

[0026]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described in detail based on the illustrated embodiment. FIG. 1 is a schematic diagram showing the fabrication of a micro-optical element according to the first embodiment. First, in FIG. 1A, a substrate 1 has a cleaned diameter of 100 mm and a thickness of 2 m.
m synthetic quartz substrate. An alignment mark portion 2 is formed outside the main pattern region on the substrate 1.

For example, a Cr film is formed on the surface of the substrate 1 by a normal film forming apparatus so that the film thickness becomes 100 nm. Thereafter, a resist is applied to the entire surface of the substrate 1 so as to cover the Cr film, and is exposed and developed by making contact with a mask provided with a predetermined alignment mark.

Next, leaving the alignment mark portion 2,
The exposed Cr film is removed by wet etching. Subsequently, the substrate 1 having the alignment mark 2 is obtained by removing the resist of the alignment mark 2 and washing again.

FIG. 3B shows a step of applying a thick resist film 3 as a photosensitive resin after the adhesion improving process by HMDS (hexamethyldisilazane) on the surface of the substrate 1 prepared in FIG. For example, a resist film 3 having a viscosity of 400 mPaS corresponding to g-line and i-line is applied on the surface of the substrate 1. This is using a spinner and rotating at 1000r
Under the condition of pm, a film thickness of 1
A resist film 3 having a thickness of 4.0 μm is formed to a uniform thickness. Next, the substrate 1 is directly placed on a hot plate to dry the resist film 3 for 3 minutes, and after drying, is cooled in a room for 20 minutes.

In (c), the substrate 1 prepared in (b) is placed on a stage of an exposure apparatus (not shown), and a gray scale mask 4 on which a predetermined gradation pattern is drawn is applied to the resist film 3. And the first exposure is performed. In this first exposure, the alignment mark portion 4a of the gray scale mask 4 is aligned with the gray scale mask 4 used in contact with the resist film 3 with reference to the alignment mark portion 2 on the surface of the substrate 1. The contact is made while finely adjusting the stage position using a microscope so as to match the mark portion 2. Thereafter, the entire surface of the substrate 1 is vertically irradiated with a first ultraviolet ray L1 mainly composed of g-rays with an irradiation amount of 78 mJ.

In (d), the gray scale mask 4 is removed, and following the exposure in (c), a new gray scale mask 5 is contacted to the resist film 3 with an equal force as in (c). Then, multiple exposure for performing the second exposure is performed. The gray color used in the second exposure
The scale mask 5 finely adjusts the stage position with a microscope in the same manner as the gray scale mask 4 described above, and the gray scale is adjusted with reference to the alignment mark portion 2 on the substrate 1 surface.
The alignment mask 5a of the scale mask 5 is aligned and contacted, and the entire surface of the substrate 1 is vertically irradiated with 312 mJ of ultraviolet light L2 mainly composed of g-line, which is different from the first exposure amount of ultraviolet light L1.

After such a multiple exposure step, the film is immersed in a commercially available developer, for example, for 5 minutes and 30 seconds, and is immersed in ultrapure water for 40 minutes.
The substrate is washed for two seconds to remove pure water attached to the substrate 1.

In (e), multiple exposure steps (c) and (d)
3 shows a cross-sectional view of the substrate 1 developed after the above process, and a fine optical element having a sawtooth diffraction grating 6 formed by patterns 4b and 5b of gray scale masks 4 and 5 is formed. After development, an alignment mark portion 7 is also formed on, for example, the alignment mark portion 2 other than the main pattern providing an optical function.

The patterns of the gray scale masks 4 and 5 used in the first and second exposures are line pattern portions 4b and 5b having digital gradation.
And solid portions 4c and 5c formed of light-impermeable portions. The transmission gradation of the solid portions 4c and 5c is set so that the transmittance of ultraviolet rays is reduced to such an extent that the resist film 3 is not exposed to light during exposure. Gray
The scale masks 4 and 5 are patterned so that the arrangement of the line pattern portions 4b and 5b and the solid portions 4c and 5c is switched. That is, the line pattern unit 4
b and the solid portion 5c overlap, and the solid portion 4c and the line pattern portion 5b overlap.

An alignment mark 2 on the surface of the substrate 1;
Although the alignment marks 4a and 5a of the gray scale masks 4 and 5 are different, there is no problem even if the alignment marks 4a and 5a of the gray scale masks 4 and 5 are the same. In the present embodiment, different alignment mark portions 4a, 5a are used, respectively.
The transmittance of the alignment mark portions 4a, 5a is set to a transmission gradation level that is not sensitive to ultraviolet rays, similarly to the solid portions 4c, 5c.

The width of each of the line pattern portions 4b and 5b and the solid portions 4c and 5c is 20 μm. Further, the transmission gradation of the line pattern portions 4b and 5b is changed so that the width of 20 μm is divided into 100 and the transmittance changes in gradation every line width of 0.2 μm.

The resist film 3 used in this embodiment is sensitive to the transmission gradation width of this 100 division range as shown in FIG. 2, and the gradation and the development amount of the resist film 3 show a proportional relationship. ing. The transmission gradation width of each of the gray scale masks 4 and 5 has a performance indicating a gradation change divided by 100, but the resist film 3 used in the present embodiment has a performance of 10 gradations.
Beyond the 0 division range, it becomes almost flat, does not show the ability to expose linearly to high transmission gradations, and the relationship between transmission gradation and transmittance shows that the transmission ratio increases as the number of transmission gradations increases. There is a relationship that the rate decreases.

When the fine pattern shape of the fine optical element thus formed was measured by a three-dimensional shape measuring device, a sawtooth diffraction grating 6 having a height of 14 μm and consisting of line patterns was formed at a period of 40 μm. The width of each step corresponds to the line width of the gray scale masks 4 and 5.
At 2 μm, the step is 0.07 μm.

The alignment mark 7 has the same pattern as the gray scale masks 4 and 5 and is formed at a height of 7 μm. A Ni electroforming mold is raised on the basis of the produced fine optical element, and the produced electroforming mold transfers the original shape of the diffraction grating 6. Next, when the fine optical element is formed on the optical glass surface by transfer using a replica using the above-described electroforming mold to form a fine optical element, the manufactured fine optical element also has the same shape as the diffraction grating 6, and The effect can be obtained.

In the method of manufacturing a fine optical element according to the present embodiment, the latitude of the photosensitive resin is gray.
Even if it does not support the entire gradation width of the scale mask, there is no shape defect or shape error, and the surface is rough even for fine shapes with high irregularities, that is, the surface is smooth without widening the steps of each step. Can be Further, in this embodiment, the exposure is performed twice, but it is also possible to manufacture by performing the exposure more times.

As a comparative example, a sawtooth-shaped period of 40 μm of the fine optical element is obtained from a line pattern obtained by dividing the resist by 100, which is the division number of the gradation width in which the resist linearly responds to the transmission gradation of the gray scale mask. Of the fine pattern obtained by one exposure using a three-dimensional shape measuring instrument, using a mask having a radiation dose of 156 mJ, and a height of 14
A μm saw-toothed grating was formed at a period of 40 μm.

However, the width of each step is 0.4 μm, which is larger than 0.2 μm corresponding to the line width of the gray scale mask.
m, and the level difference is 0.14 μm. The alignment mark portion is determined by the transmission gradation used for the gray scale mask as in the embodiment, and is the same as that in the first embodiment, and is formed to have a height of 14 μm. However, as compared with the first embodiment,
A fine optical element having a rough surface was formed, and the desired diffraction effect was not obtained.

As a second embodiment, a resist film having a viscosity of 100 mPaS is applied to the substrate 1 used in the first embodiment on the surface of the substrate 1 by using a spinner so that the film thickness becomes uniform. A resist film having a thickness of 2.1 μm is formed by application under the condition of a rotation speed of 3000 rpm. Next, the resist film is dried on a hot plate heated to 120 ° C. for 5 minutes.

Subsequently, the irradiation amount for the first exposure was 45.5 m.
Ultraviolet light mainly composed of g-line of J, irradiation amount 182m for the second exposure
A multiple exposure process is performed using a gray scale mask in the same manner as in the first embodiment, using ultraviolet rays mainly composed of i-line of J,
Thereafter, by penetrating, for example, 2 minutes and 30 seconds into a developing solution designated by the resist and developing, a fine shape is formed as in the first embodiment.

In this way, it is possible to obtain a sawtooth-shaped fine diffraction grating having a pitch of 40 μm and a height of 2.1 μm without any shape defect or shape error. Further, the obtained diffraction grating has a step of 0.01 μm with respect to a mask line width of 0.2 μm.

Next, the substrate is placed in a normal parallel plate type high frequency plasma etching apparatus and etched. At this time, the same amount of the CHF ₃ reaction gas and the inert Ar gas were mixed in the etching gas, and the gas pressure was 2.66P.
4 hours 12 minutes at an output of 100 W in the atmosphere of a.
Perform etching.

Thereafter, on the surface of the substrate 1 taken out of the etching apparatus, a fine sawtooth-shaped diffraction grating having a pitch of 40 μm and a height of 14 μm is formed. This corresponds to 0.2 μm, and the level difference is 0.07 μm. In addition, the resist film is entirely etched, and a fine diffraction grating showing a desired diffraction effect is formed in which a fine shape is similarly transferred to the synthetic quartz substrate of the substrate 1.

When the replica is molded and transferred onto another optical glass using the micro optical element composed of this synthetic quartz substrate as a mold, the shape of the micro diffraction grating formed and transferred is the same as that of the mold. A fine optical element exhibiting the effect can be obtained.

According to the second embodiment, even if the latitude of the photosensitive resin used does not correspond to the entire gradation width of the gray scale mask as in the first embodiment, A fine optical element having a smooth surface can be manufactured without a surface defect, that is, without widening a step of each step with respect to a fine shape having high irregularities without a shape defect or a shape error.

In the second embodiment, the etching is performed after the second exposure, whereas as a comparative example, the etching is performed after the first exposure, and then the second exposure is performed. A mask composed of a line pattern obtained by dividing the sawtooth-shaped period of the micro-optical element by 40 μm by 100, which is the division number of the gradation width at which the resist film linearly responds to the transmission gradation of the gray scale mask, ie, the mask line 0.4μ width
The first gray color whose transmission gradation is changed by m
Scale mask and its transmission gradation is relatively 0.2μ
2 with the second gray scale mask shifted by m
Use the first and second exposures.
A fine shape was formed as an alignment mark portion intersecting the second time so that the non-transmissive portion did not overlap.

In the first photolithography step, a resist having a viscosity of 10 mPaS
The coating was uniformly applied to the substrate at 00 rpm to form a resist film having a thickness of 1.05 μm. In the first exposure, the first exposure
UV irradiation using a gray scale mask of 2
Exposure was at 3 mJ.

Subsequently, after the first exposure, the resist was developed for 90 seconds using a developing solution specified for the resist, and further placed on a hot plate heated to 120 ° C. for 2 minutes to dry the resist. After cooling, the substrate was placed in a high-frequency plasma dry etching apparatus, and etching was performed for 2 hours and 10 minutes under the same conditions as in the second embodiment to transfer a fine shape similarly.

Thereafter, on the surface of the substrate taken out of the etching apparatus, a saw-toothed grid having a height of 7 μm was formed to a thickness of 40 μm.
Each step was formed with a period, the step width of each step was 0.4 μm, and the step difference was 0.07 μm.

Next, the resist film remaining around the main pattern portion is immersed in a stripping solution, stripped, washed and dried. The resist was applied several times to form a resist having a thickness of 1.05 μm from the upper part of the saw-toothed lattice substrate. However, the application state of the resist film was different from the first application, and a wavy undulation was generated.

Subsequently, the second gray scale mask was brought into contact with the resist film while being aligned with the alignment mark portion, and was irradiated with ultraviolet rays having a dose of 91 mJ for exposure. After the exposure, development was carried out for 8 minutes and 20 seconds using a developer designated by the resist. Next, the resist was dried by placing it on a hot plate heated to 120 ° C. for 4 minutes, and after cooling, the substrate was placed in a high-frequency plasma dry etching apparatus, and etched under the same conditions as the previous time for 2 hours and 10 minutes. Was similarly transferred.

When the obtained fine pattern shape was measured by a three-dimensional shape measuring instrument, a saw-toothed grating having a height of less than about 14 μm was formed at a period of 40 μm. In addition, the width of each step was approximately 0.2 μm, and the level difference was 0.07 μm. However, a shape defect portion whose shape was disordered was also recognized. In addition, the alignment mark part
Since they were arranged so as to intersect at the first time, their height was 7 μm.

A replica was formed on an optical glass as a mold using the fine shape produced in this way. However, the diffraction effect of the fine optical element was inferior to that obtained in the second embodiment, and the desired effect was obtained. No properties could be obtained.

[0058]

As described above, according to the method for manufacturing a fine optical element according to the present invention, the height of the unevenness of the optical element is increased by performing multiple exposures continuously using a gray scale mask. Even so, the surface property is not restricted by the step difference obtained by dividing the thickness by the latitude specific to the photosensitive resin.

[Brief description of the drawings]

FIG. 1 is a schematic diagram illustrating the production of a micro optical element according to a first embodiment.

FIG. 2 is an explanatory diagram of a relationship between a gray scale of a gray scale mask and a resist development amount.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Substrate 2, 7 Alignment mark part 3 Resist film 4, 5 Gray scale mask 6 Sawtooth diffraction grating

Claims (9)

[Claims] 1. A fine optical function element is formed on a substrate by multiple exposure in which an exposure step is continuously performed using one or a plurality of gray scale masks having a pattern having a gradation. A method for manufacturing a fine optical element. 2. The gray scale mask comprises a pattern portion having a gradation and an opaque portion, and is exposed to a non-exposed portion on the substrate by the opaque portion in a previous process and to the pattern portion in a subsequent process. Claim 1.
3. The method for producing a micro optical element according to 1. 3. The method according to claim 1, wherein an exposure amount is changed when performing the multiple exposure. 4. The method according to claim 1, wherein at the time of performing the multiple exposure, at least one alignment mark for mask alignment is formed on the substrate outside a main pattern area of the gray scale mask providing an optical function. The method for manufacturing a micro optical element according to claim 1. 5. A micro-optical element manufactured by the manufacturing method according to claim 1. 6. A method for manufacturing a micro optical element, wherein the micro optical element according to claim 5 is similarly transferred to another substrate by etching. 7. The method according to claim 5, wherein
A method for manufacturing a fine optical element, wherein a transfer mold is formed by electroforming. 8. A method for manufacturing a micro-optical element, comprising replica-molding the micro-optical element manufactured in any one of claims 5 to 7 as a matrix. 9. A micro-optical element produced by the manufacturing method according to claim 6. Description: