JPS6144628A - Preparation of fresnel microlens - Google Patents

Abstract

PURPOSE:To obtain a stamper for a Fresnel microlens with high accuracy, by repeating a process wherein an annular band pattern is transferred to the resist layer applied to a substrate before the substrate is etched selectively. CONSTITUTION:Resist 16 is applied to a Si-wafer substrate provided with an oxide film 23 (stage A) and a first annular band pattern is transferred to the resist layer 16 and electron beam is allowed to irradiate a part 17 through said pattern (stage B). After the resist layer 16 is developed, the resist 16 is used as a mask to etch the film 23 (stage C) and, subsequently, the resist 16 is removed and the resist 16 is again applied to the entire surface of the film 23 (stage D). Electron beam is allowed to irradiate a part 18 through a second annular band pattern (stage E) and, after the resist 6 is removed, said part 18 is etched (stage F). These stages are repeated (stage G) to obtain a stamper having a shape near to an ideal saw-toothed cross-sectional area 19. This stamper is used as a mold to mold a resin 20 and a Fresnel microlens is obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field] The present invention relates to a method of manufacturing a micro Fresnel lens used in optical systems such as pickup sections of impact disc players and video disc players.

[Background technology]

In a micro Fresnel lens, by making the cross-sectional shape of the seven Fresnel zones into a sawtooth shape, the first-order diffraction efficiency of the lens can be significantly improved compared to the case where the cross-section is rectangular.

Fig. 1 shows a cross section and a plan view of the entire micro Fresnel lens with a sawtooth cross section, and Fig. 2 η) to a:
In Fig. 1, 1 is a glass substrate, 2 is a transparent conductive film, and 3 is a resist layer. In Fig. 1, a pattern has already been formed. It shows the state of being formed.

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, the second
In the figure, 7 is an electron beam, and 8 to 12 are electron beams 7.
9 shows the area of the resist layer 3 exposed by 9, and 13 is a curve representing the sawtooth shape of the ideal cross section, which was obtained from the phase shift function.

Conventionally, in order to form a sawtooth cross section of a micro Fresnel lens, as shown in FIG.
After forming the first layer, the electron beam 7 is used to draw the first layer (the second layer is drawn).
(A>) Next, the second layer is drawn, but at this time, the exposure area 9 of the second layer overlaps the exposure area 8 of the first layer (Figure 2).

From the third layer to the fifth layer, drawing is repeated in the same way, @
A step approximation of the ideal cross section 13 is obtained by obtaining 51-' and i4@exposed area 8 to 12 as shown in FIG. In Figure @2, the number of multiple drawings is set to five, but by increasing this number, even better approximation can be achieved. In addition to electron beam lithography, a similar 7-Less annular cross section can also be obtained by an exposure method using a multilayer photomask.

In a micro Fresnel lens, Fresnel zones as shown in Fig. 1 are formed according to the period t determined by the phase shift function, and each ring zone is constructed as shown in Fig. 2 with an ideal sawtooth cross section. Ru.

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 WI3 having the following shape from the glass substrate 191, 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 lpm or less. In the conventional micro Fresnel lens manufacturing method, since the layer forming the pattern is a resist layer, the pattern shape is changed in the fine pattern portion by electron beam, far ultraviolet, or ultraviolet light scattering in the resist or by proximity effect. It deviates greatly from the shape that was designed.

Furthermore, since the film thickness of the resist layer is set to a constant value for iC as described above, the film thickness must be set so that sufficient pattern resolution may not be obtained depending on the refractive index of the resist and the wavelength of the incident light. If so, it may be bad. On the other hand, the shape of the sawtooth cross section varies greatly depending on the gamma value of the sensitivity curve of the resist, making it difficult to obtain a clean approximate cross section depending on the resist.

〔the purpose〕

This invention is intended to eliminate the deterioration in pattern accuracy that occurs near the outer periphery of the lens as described above, and when patterning the lens, by transferring the resist pattern of each layer to another uniform layer, the center 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〕

The third muff to Q show an embodiment of the present invention, and show the process in which a cross-section of one Fresnel zone of the lens pattern is formed in the same manner as in FIG. In FIG. 3, 14 is a glass substrate, and 16 is a resist layer.

First, in FIG. 3 (roll), a resist 16 is applied on the glass substrate 14, and in FIG.
A pattern obtained by inverting the first layer of the annular pattern in FIG. 2 is drawn with an electron beam 7.

17 is the electron beam irradiation area at this time, and after developing this, as shown in FIG.
Thereafter, the resist is removed, and a resist 16 is applied again as shown in FIG. 3(2), and a second layer inversion pattern of the annular pattern is drawn as shown in FIG. 3(2). 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 fishing, the same figure (to)
Using the resist pattern as a mask, the substrate 14 is etched under the same conditions as in Fig. 3C>.

By repeating the same operations as the steps from 1 to 2 for the 3rd to 5th layers of the annular pattern, the substrate 14 has a serrated cross section as shown in FIG. 3G. Form a hatan. In Figure G), reference numeral 19 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 S1 Unihachi substrate prepared as described above as a stamper.
It is called the p-method. @ In Figure 4, 20 is 7 otobolima (photocurable resin)], 21 is a glass substrate, 22
is the irradiation light for curing the photopolymer 20t. 7 Otobolima 20 is dropped onto the patterned glass substrate 14 using the fourth muff, and 7 Otovolima 20 is dropped with [F]).
A glass substrate 21 is placed on top of the photopolymer 2o, and the 7 otobo polymer 2o is spread over the entire lens pattern.
The glass substrate 14 is peeled off from the glass substrate 21 to which the otopolymer 20 is adhered, to obtain a micro Fresnel lens as shown in FIG. 5(5).

In FIG. 3, the ideal sawtooth cross section 19 is approximated as a step by performing the exposure, development, etching process five times, but a better approximation can be achieved by increasing the number of times.

In this invention, since the layer forming the pattern serves as a mask for ultimately obtaining a micro Fresnel lens, the thickness of the sawtooth cross section is determined from the refractive index of the photopolymer 20. The period of the annular zone t is calculated from the phase shift function as in the conventional case. The actual operation is performed by optical replication using the layer designed as described above as a stamper, and its operation is the same as in the conventional case.

The embodiments of the present invention are as follows.

(1) In FIG. 3, direct writing with an electron beam 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 7-oto-mask.

(2) In the embodiment shown in FIG. 3, the layer to be etched is St
Although it uses an oxide film layer grown on the wafer, nitride J
2. Any film that can be etched such as
The substrate is also not limited to the S1 wafer.

(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.
Using this as a master, a stamper can be manufactured by a conventional technique such as Nii casting, and a copy can be made 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, patterning is performed in one layer. Only the 5th
Figures (G) to (G) to (G) show one example of this, in which a resist (R16) is coated and formed on the glass substrate 14 in Figure (2), and the resist is patterned in Figure (F). C
) After etching the glass substrate 14 using the resist pattern 16 as a mask, the resist 14 is etched.
6 is removed to 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 embodiment, a copy is made by the ZP method from the substrate on which the micro Fresnel lens pattern is formed, but this copy production method is not limited to the ZP method, and a copying technique such as the injection method may be used. .

〔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 is used to simply form a Fresnel zone 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 problems of film thickness and resolution inherent to V-sist 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 mask pattern, and costs can be reduced.

[Brief explanation of drawings]

FIG. 1 is a front sectional view and a plan view of a nine-microphone Fresnel lens with a serrated cross section, and FIGS. 3 (2) to 3 are cross-sectional views of the process of forming a pattern with a sawtooth cross section according to an embodiment of the present invention in S order, and 4th muff to Ω are the process order of manufacturing a duplicate lens from the pattern master in FIG. 3. FIGS. 5A and 5B are cross-sectional views of a pattern forming process of a micro Fresnel lens having a rectangular cross section as another embodiment of the present invention. 1.21...Glass substrate 2...Transparent conductive film 3,16...Resist layer 4
...Parallel incident light 5...Diffracted light 6...Focus
7...Electron beam8.9,10,11,12,
17.18...Electron beam irradiation area 13.19...Ideal sawtooth cross section 20...Photopolymer 22...Irradiation light

Claims (4)

[Claims] (1) A resist is applied onto the substrate, a first ring pattern having micro Fresnel lens rings is transferred to the resist, selective etching is performed on the substrate, and after removing this resist, the first ring pattern having the micro Fresnel lens ring is transferred onto the substrate. After applying a resist and aligning a second annular pattern having micro Fresnel lens annular zones with the first annular pattern, the resist is transferred to the resist, selective etching and resist removal are performed, and the following steps are performed. . A method for manufacturing a micro Fresnel lens, characterized in that by repeating the above operation a predetermined number of times, an approximate sawtooth cross section is formed on the substrate, and a stamper is obtained from this to be replicated. (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 drawing with an electron beam.