JPH0226851B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field] The present invention relates to a method of manufacturing a micro Fresnel lens used in an optical system such as a pickup section of a compact disc player or a video disc player.

[Background technology]

In a micro Fresnel lens, by making the cross-sectional shape of the Fresnel zone serrated, the first-order diffraction efficiency of the lens can be greatly improved compared to the case of a rectangular cross-section.

Fig. 1 shows a cross section and a plan view of the entire micro Fresnel lens with a serrated cross section, and Fig.
Figures A to D show the formation process for one Fresnel zone. In Figure 1, 1 is a glass substrate, 2 is a transparent conductive film, and 3 is a resist layer. In Figure 1, a pattern has already been formed. This indicates the state in which the

The parallel incident light 4 is diffracted by the patterned resist layer 3, and the diffracted light 5 converges on a focal point 6. On the other hand, in FIG. 2, 7 is an electron beam,
8 to 12 indicate the regions of the resist layer 3 exposed by the electron beam 7, and 13 is a curve representing an ideal sawtooth cross-sectional shape, which was determined from the phase shift function.

Conventionally, to form a sawtooth cross section of a micro Fresnel lens, as shown in FIGS. 2A to 2D, a resist 3 is first applied on a glass substrate 1 with a transparent conductive film 2, and after the resist layer 3 is formed, an electron beam is applied. 1st on line 7
The layer is drawn (FIG. 2A). Next, the second layer is drawn, but at this time, the exposure area 9 of the second layer is
overlaps with the exposure area 8 of the first layer (FIG. 2B). Thereafter, drawing is repeated in the same manner from the third layer to the fifth layer to obtain multiple exposure areas 8 to 12 as shown in FIG. 2C, and development is performed as shown in FIG. Obtain a stepwise approximation. In FIG. 2, the number of times of multiple drawing is five, but even better approximation can be achieved by increasing this number of times. A similar Fresnel zone cross section can also be obtained by an exposure method using a multilayer photomask instead of electron beam lithography.

In a micro Fresnel lens, Fresnel zones as shown in Fig. 1 are formed according to the period determined by the phase shift function, and each zone has a second
It is configured to have an ideal sawtooth cross section as shown in Figure D. Here, the thickness of the patterned resist layer 3 is determined by the refractive index of the resist used therein and the wavelength of the incident light 4.

When parallel incident light 4 enters the resist layer 3 having the above-described shape from the glass substrate 1 side, the light is diffracted at each annular portion, and the diffracted light 5 converges on a focal point 6.

[Problems with background technology]

In a micro Fresnel lens, the period of the annular zone becomes shorter toward the outer periphery of the lens, so in the fine pattern portion near the outermost periphery, the annular zone width becomes an area of 1 μm or less. In the conventional micro Fresnel lens manufacturing method, since the layer forming the pattern is a resist layer, the fine pattern portion is affected by electron beam, far ultraviolet, or ultraviolet light scattering in the resist or by the proximity effect. The pattern shape deviates significantly from the designed shape. Furthermore, since the thickness of the resist layer is set to a certain value as described above, the thickness may not be set so that sufficient pattern resolution cannot be obtained depending on the refractive index of the resist and the wavelength of the incident light. There are times when you have to. On the other hand, since the shape of the sawtooth cross section varies considerably depending on the gamma value of the sensitivity curve of the resist, it becomes difficult to obtain a clear approximate cross section depending on the resist.

〔the purpose〕

This invention is intended to eliminate the above-mentioned deterioration in pattern accuracy that occurs near the outer periphery of the lens, and when patterning the lens, the resist pattern of each layer is transferred to another uniform layer. The purpose of the present invention is to provide a method for maintaining a uniform thickness from the center to the outer periphery and an appropriate cross-sectional shape, thereby obtaining a high-performance lens.

〔Example〕

3A to 3G show an embodiment of the present invention, and similarly to FIG. 2, they show a process in which a cross section of one Fresnel zone of a lens pattern is formed. In FIG. 3, 14 is a Si wafer substrate to which an oxide film 23 having a predetermined thickness is added, and 16 is a resist layer.

First, in FIG. 3A, a resist 16 is applied onto the Si wafer substrate 14, and in FIG. 3B, a pattern that is an inversion of the first layer of the annular pattern shown in FIG. 2 is applied to this resist layer 16 using an electron beam. 7. 17 is the electron beam irradiation area at this time, and after developing this, in FIG. 3C, the resist 16
Using as a mask, the substrate 14 is etched to a depth of about 1/5 of its thickness, and then the resist is removed and the resist 16 is applied again as shown in FIG. 3D, and an annular pattern is formed as shown in FIG. Draw the second-layer inverted pattern. At this time, the first layer and the second layer are aligned by the registration function of the drawing device. 18 is the electron beam irradiation area at this time. After developing this again, in Figure 3 F,
Using the resist pattern E in the same figure as a mask, the third
The substrate 14 is etched under the same conditions as in FIG.

By repeating the same operations as steps D to F for the third to fifth layers of the annular pattern, a pattern with a sawtooth cross section as shown in FIG. 3G is formed on the substrate 14. . 19 in G of the same figure
represents the ideal sawtooth cross section in this case.

FIG. 4 shows the process of obtaining the final micro Fresnel lens made of photopolymer using the Si wafer substrate produced as described above as a standby, which is called the 2P method. In FIG. 4, 20 is a photopolymer (photocurable resin), 21 is a glass substrate, and 22 is a photopolymer 2.
This is irradiation light for curing 0. In FIG. 4A, the photopolymer 20 is dropped onto the patterned Si wafer substrate 14, and in B, the glass substrate 21 is placed over the photopolymer 20.
When the lens pattern has spread over the entire lens pattern, the photopolymer 20 is exposed to the irradiation light 22 to be cured, and then the Si wafer substrate 14 is peeled off from the glass substrate 21 to which the photopolymer 20 is adhered, and the photopolymer 20 is cured as shown in FIG. Obtain a micro Fresnel lens.

In FIG. 3, the ideal sawtooth cross section 19 is approximated in stages by five exposure, development, and etching steps, but even better approximation can be achieved by increasing this number of times.

In this invention, since the layer forming the pattern serves as a master for ultimately obtaining a micro Fresnel lens, the thickness of the sawtooth cross section is determined from the refractive index of the photopolymer 20. Further, the period of the annular zone is calculated from the phase shift function as in the conventional case. What is actually used is a copy made using the layer designed as described above as a stamper, and its function is the same as in the conventional case.

The embodiments of the present invention are as follows.

(1) In Figure 3, direct electron beam writing is used to form the annular pattern, but the pattern may also be formed using ultraviolet rays, deep ultraviolet rays, or X-ray exposure using a multilayer photomask. .

(2) In the embodiment shown in Figure 3, an oxide film layer grown on a Si wafer is used as the layer to be etched.
Any film that can be etched, such as a nitride film or PSG, can be used, and is not limited to an oxide film. Furthermore, the substrate is not limited to a Si wafer as long as it is a substrate on which the above film can be provided to a predetermined thickness. Furthermore, although the pattern is formed on the coating layer by providing it on the substrate, the pattern may be formed by directly etching the substrate as long as the substrate can be etched, such as a glass substrate or a metal substrate.

(3) In the above embodiment, the layer to be etched or the substrate to be etched is used as a stamper to make a copy, but the cross section shown in FIG. It is also possible to manufacture a stamper using a conventional technique such as casting, and to make a replica from the stamper, and the same effect as in the above embodiment can be obtained.

(4) In the above embodiment, the case of forming a sawtooth cross section was explained, but this method may also be used to form a micro Fresnel lens pattern with a rectangular cross section, and in that case, the patterning is done in one layer. Only . FIGS. 5A to 5C show an example of this, and in FIG. 5A, the Si wafer substrate 14 is
A resist layer 16 is coated and formed thereon, and the resist is patterned as shown in FIG. B. After the Si wafer substrate 14 is etched using the patterned resist layer 16 as a mask as shown in FIG. Obtain a stamper for duplication. Note that all of the above embodiments can also be applied to a rectangular cross-section lens.

(5) In the above example, a copy is made using the 2P method from the substrate on which the micro Fresnel lens pattern is formed, but this copy production method is not limited to the 2P method, and may also be made using a copying technique such as the injection method. Good too.

〔effect〕

As described above, in the present invention, since the micro Fresnel lens pattern is formed using a layer other than the resist layer with a uniform thickness, the resist layer simply forms a Fresnel ring pattern for one layer. Compared to applying multiple exposures to the resist layer at once, the effects of scattering and proximity effects in the resist can be minimized, and the effects of resist-specific film thickness and resolution problems can be minimized. A uniform and highly accurate pattern can be obtained over the entire surface of the lens without limitations such as problems with the gamma value of the sensitivity curve.

On the other hand, since the pattern forming layer is used as it is as a stamper for duplication, a large number of duplicate lenses can be manufactured from one master pattern, and cost reduction is also possible.

[Brief explanation of drawings]

Figure 1 is a front sectional view and plan view of a micro Fresnel lens with a sawtooth cross section, Figures 2 A to D
FIGS. 3A to 3G are cross-sectional views of sawtooth Fresnel zones according to the prior art in the order of the pattern formation process, FIGS. Figures 5A to 5C are cross-sectional views showing the steps of manufacturing a duplicate lens from the pattern master shown in Figure 3, and Figures 5A to C are the steps of forming a pattern of a micro Fresnel lens with a rectangular cross section as another embodiment of the present invention. FIG. 1, 21...Glass substrate, 2...Transparent conductive film,
3, 16...Resist layer, 4...Parallel incident light, 5
...Diffracted light, 6...Focal point, 7...Electron beam, 8,
9, 10, 11, 12, 17, 18... Electron beam irradiation area, 13, 19... Ideal sawtooth cross section, 20...
Photopolymer, 22...Irradiation light.

Claims (1)

[Claims] 1. After applying a resist onto a substrate, transferring a first annular pattern having micro Fresnel lens annular zones to the resist, selectively etching the substrate, and removing this resist, A resist is again applied onto the substrate, and a second annular pattern having micro Fresnel lens annular zones is aligned with the first annular pattern, and then transferred onto the resist, followed by selective etching and resist removal operations. and then repeating the above operation a predetermined number of times to form an approximate sawtooth cross section on the substrate, from which a stamper is obtained and replicated. Method. 2. The manufacturing method according to claim 1, wherein the substrate is made of glass or metal. 3. The manufacturing method according to claim 1 or 2, wherein the pattern transfer to the resist is performed using a photomask having the annular pattern. 4. The manufacturing method according to claim 1 or 2, wherein the pattern transfer to the resist is performed by direct writing with an electron beam.