JPS61137101A - Production of micro fresnel lens - Google Patents

Abstract

PURPOSE:To improve performance by forming a titled lens of layers each of which except a resist layer has a uniform film thickness thereby making uniform the film thickness from the center to the outside circumference of the lens and maintaining an adequate sectional shape. CONSTITUTION:The film thickness of the multi-layered films 20 formed by growing a silicon oxide film 15 on a silicon wafer 14, forming a nitride film layer 16 thereon and a silicon oxide film layer 17 thereon and forming successively a nitride film layer 18 and a silicon oxide film layer 19 is made equal to the design film thickness. The resist 21 is coated on such films 20 and after an annular pattern 22 of the 1st layer is drawn, the process from development of the resist layer 21 up to the removal of the resist after the etching of the layer 19 is executed. The resist 21 is then coated on the substrate and is positioned with the pattern of the 1st layer. The annular pattern 23 of the 2nd layer is drawn and the etching of the film 18 is executed after the developing process by which the resist is removed. The section approximate to the saw tooth-shaped staircase is obtd. to the films 20 by repeating the above- mentioned similar stage.

Description

[Detailed description of the invention] [Technical field] This invention u% optical disc player pick 79
The present invention relates to a method for manufacturing a Kill Micro Frele lens, since it is used in a lens system used in some parts or other optical equipment.

[Prior art]

In a micro Fresnel lens, by making the cross-sectional shape of the Fresnel zone 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.

Figure 1 (ω) shows a central sectional view and a plan view of a micro Fresnel lens with a sawtooth cross section, and Figure 2 (
A to (D) show the process of manufacturing the shape of one Fresnel zone that makes up the lens.

In FIG. 1, a resist layer 3 is placed on a glass substrate 1 through a transparent conductor tJIiJ2, and a flange ring pattern with a sawtooth cross section is formed on this resist layer 3. Parallel incident light 4 that has entered is diffracted at the Fresnel zone, and the diffracted light 5 converges on a focal point 6.

Conventionally, in order to manufacture a sawtooth cross section of a micro Fresnel lens as shown in Fig. 1, the manufacturing method shown in Fig. 2 A to To) was adopted, and First, a resist layer 3 is formed on a glass substrate 1 having a transparent conductive film 2, and a sawtooth cross section is formed with an electron beam 7 having an exposure amount corresponding to 115 of the electron beam sensitivity of the resist used. Draw the first layer ring pattern to
Continue in the same figure (BJ, overlaps with the ring pattern of the first layer,
In addition, a second layer of annular pattern having a width slightly narrower than that is drawn. After that, the same drawing is continuously repeated from the third layer to the fifth layer to obtain multiple exposure areas 8 to 12 as shown in FIG. In Figure 2, the number of times of multiple drawing is set to 5, but by increasing this number of times, it is possible to create a more approximate shape of the sawtooth cross section. Can be done.

The micro fresle lens forms concentric ring zones as shown in the 11th peak according to the radius determined by the phase shift function shown in Equation 11, and each ring zone has an ideal cross section of Fig. 2 0. 13, the thickness of the resist layer 3 forming this annular pattern is determined by the refractive index of the resist used and the wavelength of the incident light 4. It is calculated from equation (2).

f: Focal length (1) d-λ/△n d: film thickness, λ: wavelength.

△n: refractive index difference with air (2) Based on this design, from the back surface of the glass substrate 1, a ring pattern with a sawtooth cross section formed in the process shown in FIG. When parallel light 4 is made incident, the light is diffracted at each annular portion, and the diffracted light 5 converges on a focal point 6.

Due to the design of a micro Fresnel lens, the cycle of the annular zone becomes shorter toward the outer periphery of the lens, so depending on the specifications of the lens,
The annular width is in the submicron range. In the conventional manufacturing method of micro Fresnel lenses, the layer forming the pattern is a resist layer and multiple exposure is performed.
In the above-mentioned fine pattern part, due to electron beam scattering in the resist or proximity effect, the film thickness may decrease at the outer periphery, the pattern shape may deviate greatly from the designed shape, and the lens pattern film may be lifted. As mentioned above, since the resist is designed to have a certain value, depending on the refractive index of the resist and the wavelength of the incident light, it may not always be possible to process the resist under optimal conditions, and sensitivity and resolution may also be affected. Awakening. Therefore, it has been difficult to maintain a uniform film thickness from the center to the outer periphery of the lens and an ideal sawtooth cross section.

〔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 provides a method for maintaining a uniform film thickness from the center of the lens to the outer periphery and an appropriate cross-sectional shape. The purpose of this is to obtain a lens with higher performance.

[Example] Figures 3 (4) to (0) show an example of the present invention, and a cross section of one of the lens zones is produced in the same way as in Figure 2. The process is shown below.

In the figure, first, a silicon oxide film 15 is grown on a silicon wafer 14, and a nitride film layer 1 is grown on top of it.
6 is formed, and then a silicon oxide film layer 17 is formed again on top of this nitride film, and then a nitride film layer 18 . Then, a silicon oxide film layer 19 is sequentially formed.

The film thickness of the multilayer lN2O thus completed is made equal to the designed film thickness of the lens. After coating the resist 21 on this multilayer film 20, the third [kl
The annular pattern 22 of the first layer is drawn in (B), and the annular pattern 22 of the first layer is drawn in (C).
), after developing the resist layer 21, etching the uppermost silicon oxide film 19, and removing the resist, when etching the silicon oxide film 19,
The lower nitride film 18 serves as an etching stopper.

Next, in Figure 3 (C), coat the resist) 21 on the board again, perform registration (alignment) with the first layer pattern in Figure 3 (G), and then apply the second layer of copper. After 23 minutes of the theoretical pattern is drawn and developed, the nitride film 18 is etched and the resist is removed to obtain the cross-sectional shape shown in FIG. When etching the nitride film 18, the underlying silicon oxide film 17 serves as an etching stopper.

By repeating the same steps as shown in FIG. 0 and below, it is possible to obtain a cross-section of the multilayer film 20 that resembles a step-like sawtooth shape as shown in FIG. 3 (G). 24 represents the ideal sawtooth cross section in this case. Figures 4(A) to (C) show that a photopolymer ( This figure shows the process of obtaining the final micro Fresnel lens using photocurable resin.

In FIG. 4, the photopolymer 25 is dropped onto the multilayer film 20 on the silicon wafer substrate 14 obtained in FIGS. After the glass substrate 26 is placed over the dropped photopolymer 25 so that the 7 otobolima spreads over the entire lens pattern, the photopolymer 25 is cured into the 7 otobolymer by UV irradiation light 27 from the glass substrate side.Next, after curing The silicon wafer substrate is peeled off from the photopolymer adhered to the glass substrate.
) to obtain a micro Fresnel lens.

In this invention, the layer that forms the sawtooth pattern is a mold for obtaining the final microfleful lens, and as shown in Figure 7.23, 21 resists and a multilayer film 20 are processed. Furthermore, what is used as a micro-flare lens is a replica molded from the processed multilayer film 20 by 7 Otobolima, and the design of the lens is based on the photo. This is done taking into account the refractive index of the polymer. Therefore, the annular radius is determined from equation (1) as in the case of the prior art, but the V foot of the film thickness is determined from equation (2) using the refractive index of the photopolymer. Then, the lens obtained in this way is used as bait (Fig. 4C).
), based on FIG. 1 and ITA's 11th work, the present invention converges light by diffraction at the annular portion for parallel incident light from the back surface of the glass substrate. The following embodiments may be considered outside the range.

(1) In the embodiment shown in Fig. 3, direct drawing with an electron beam is used to form a pattern on the resist 21, but a multilayer photomask or reticle is used to form a pattern on the resist 21. (2) In the embodiment shown in FIG. 3, a silicon oxide film and a nitride film are alternately laminated in order to form the multilayer film 20. A multilayer structure can also be formed by combining a nitride film and a metal film.

(3) In the embodiment shown in FIG. 3, the multilayer film 20 is formed of two types of films, a silicon oxide film and a nitride film, but three or more types of etched films such as an oxide film, a nitride film, and a metal film are used. (4) In the example shown in FIG. Although a silicon wafer is used as the substrate, it is also possible to use a metal plate other than silicon or a glass plate as the substrate.

(5) ±1 In the example, a vT lens is obtained by photopolymerizing the serrated annular pattern formed on the substrate, but this method is not limited to the photopolymer method, and may be made by injection method, etc. [Effect] As described above, in the present invention, the micro Fresnel lens pattern is formed in a layer other than the resist layer with a uniform thickness. With this method, it is only necessary to form an annular pattern for one layer, and the pattern can be processed under the optimum conditions for that resist. Also, unlike conventional methods, it is not necessary to give multiple exposures to the resist, so it is possible to process the pattern in the resist. The scattering of the drawn electron beam and the influence of the proximity effect can be minimized, and the film thickness is reduced at the fine pattern part on the outer periphery of the lens, as seen in the resist layer turn. No more crumbling.

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 lens pattern, and the cost of manufacturing can be reduced.

[Brief explanation of the drawing]

Figure 11: Cross-sectional view and plan view of a micro Fresnel lens with a serrated cross section, Figures 2 through (c)
31 to 0) are cross-sectional views showing the steps of manufacturing a serrated ring pattern according to the conventional method, and 31 to 0) are sectional views showing the steps of manufacturing a serrated ring pattern according to an embodiment of the present invention. Cross-sectional view % Figure 4 (4), (B), (C5 is a diagram showing the cross-sectional view of the process order of manufacturing a duplicate lens from the pattern master of 3rd □□□, 14... Non-silicon A 15...Silicon oxide film 16...Nitride film 17...Silicon oxide film 18...Nitride film 19...Silicon oxide film 20...Multilayer film 21...Resist 22...Electron Line exposure area 23...Electron beam exposure area 24...Ideal sawtooth cross section Patent applicant Pioneer Corporation (I-7 Figure 1 (A) Figure 2 Wa'18 1986-1371tll (5) No. Figure 3 (A) (F) (C)

Claims (3)

[Claims] (1) A step of forming a multilayer film by alternately stacking a predetermined number of layers of two or more types of films that can be formed on a substrate and that do not allow the other to be etched under the conditions that one is etched, and the final layer of the multilayer film. Pattern-etching the upper layer to form a first-layer ring pattern of the micro Fresnel lens, and pattern-etching a second layer of the multilayer film to overlap the ring-zone pattern of the first layer and have a ring-zone width. forming a first layer ring pattern with a smaller ring width, and sequentially pattern-etching the third or more layers of the multilayer film to sequentially form a third or higher layer ring pattern with a stepwise smaller ring width. and obtaining a replica of the patterned multilayer film, the method comprising the steps of: obtaining a replica of the patterned multilayer film, wherein the cross section of the annular pattern of each layer has a sawtooth-like approximate surface. (2) The manufacturing method according to claim 1, wherein the substrate is silicon, metal, or glass. (3) The manufacturing method according to claim 1 or 2, wherein the multilayer film is a film of three or more types in which the layer immediately below is not etched when one layer is pattern-etched.