JPS63118701A - Production of optical element - Google Patents

Abstract

PURPOSE:To improve optical characteristics by applying positive resist to the surface of a substrate, converging ion beams into the resist so as to make the beams correspond to the shape of an optical element while changing acceleration voltage to draw a picture and executing development processing to change the film thickness of the resist. CONSTITUTION:The positive resist 6 is applied to the glass substrate 1 and an electrification preventing film 3 is vacuum deposited on the surface of the resist 6. The acceleration voltage of ion beams 5 is periodically changed from a large value to a small value or a small value to a large value so as to correspond to the shape of a grating 20 with a fixed period to converge the ion beams 5 into the resist 6 and directly draw a picture. Finally, the film 3 is removed by etching and developed, so that resist is deeply peeled on the draw portion with a high ion beam acceleration voltage and the film thickness of the resist 6 can be changed to obtain the grating 20. Thus, an excellent sectional shape can be obtained with high reproducibility and the optical characteristics can be improved.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a method for manufacturing an optical element, and in particular provides a thin film micro optical element with excellent optical properties.

2. Description of the Related Art In recent years, thin film micro optical elements such as micro Fresnel lenses and micro gratings have attracted attention as optical elements that are small and lightweight and have various functions. In order to achieve various light distributions and high efficiency, it is necessary to control the cross-sectional shapes of Fresnel lenses and gratings. For example, if the cross-sectional shape is made into a sawtooth shape with an appropriate film thickness, a high diffraction efficiency of approximately 100 inches can be achieved.

As shown in FIG. 2, a conventional method for manufacturing a thin film micro-optical element involves first applying an electron beam resist 2 on a substrate 1.
An antistatic film 3 such as Au is coated or deposited, and as shown in b, the electron beam 4 is heated while the acceleration voltage of the electron beam 4 is constant.
The resist is exposed by drawing directly on the resist 2 by controlling the number of scans, etc., and then etching and development is performed on the antistatic membrane 3 as shown in C to form a 7-renel lens with a sawtooth cross-sectional shape and a grating. There was a method of manufacturing 2A. (Fujita et al.: “Blazed micro Fresnel lens fabricated by electron beam lithography.

Journal of the Institute of Electronics and Communication Engineers (') + 166- C* ' +
pp.

85-91 (Sho 5a-1)) Problems to be Solved by the Invention In such conventional methods, writing is performed using a low-mass electron beam, so that scattering within the resist and from the substrate causes so-called Proximity effects occur, and it is also necessary to accurately correct the sensitivity characteristics of the resist to adjust the exposure amount.
As shown in Figure C, grating sagging and surface irregularities are likely to occur, making it difficult to achieve an ideal sawtooth shape.In other words, an optical element with good optical properties could not be obtained.

The present invention has been made in view of these points, and an object of the present invention is to provide a thin film type optical element with excellent optical properties.

Means for Solving the Problems In order to solve the above-mentioned problems, the present invention uses an ion beam and manufactures it by changing the acceleration voltage.

Function: Since the present invention uses an ion beam with a heavier mass than an electron beam, scattering within the resist is less likely to occur.

Further, exposure control in the depth direction can be performed precisely by utilizing the fact that the penetration depth of ions changes depending on the accelerating voltage.

Embodiment FIG. 1 is a manufacturing process diagram of a grating according to an embodiment of the present invention. In the figure, 1 is a substrate, 6 is a positive resist, and 3 is an antistatic film. In this example, glass was used as the substrate 1, PMMA was used as the positive resist 6, and Au film was used as the antistatic film 3. However, the substrate 1 may be any material as long as it has excellent transmittance at the wavelength used by the grating. Furthermore, the Au film 3 is used only to prevent the ion beam 6 from being charged, and is not necessary when there is no concern about the ion beam 6 being charged, that is, when the substrate 1 or the resist 2 is conductive. No, A
Other metal thin films such as J may also be used.

Next, the manufacturing process will be explained. First, as shown in FIG. 1a, a positive resist 6, for example, 1
．． 3 μm coating, and on top of that, antistatic film 3 with a thickness of 10 μm, for example.
0 people vacuum evaporated. Next, the acceleration voltage of the ion beam 6 is periodically changed from a large value to a small value, or to a small value, so as to correspond to the shape of the grating 2' having a period of 5 μm, for example, which is manufactured as shown in FIG. to a large value, and was focused on the positive resist 6 and directly written. The present inventors have determined that the penetration depth of the ion beam 5 into the resist 6 layer is determined by the accelerating voltage of the ion beam 5.
It has been discovered that even if the exposure amount is exceeded, the film thickness after development remains almost constant. For example, as an ion beam, B
Using e, the accelerating voltage is large, 5oKV, 10
0KV, 150KV.

At 200 KV and above appropriate exposure, the film thicknesses of the resist 6 peeled off by development were O and S μm, respectively.

They were 0.8 μm, 1.0 μm, and 1.2 μm, and were almost determined by the accelerating voltage without depending on the exposure amount. In addition, since the ion beam 5 hardly passes through the substrate 1 side, the resist 6
The sensitivity has improved and the drawing time has become shorter.

In this embodiment, the acceleration voltage of the Be beam 6 is set to, for example, 1 KV at the peaks of the grating 20.

The valley part was set at 220KV, and the voltage was changed smoothly from IKV to 220KV to correspond to the shape of the grating 2'. Finally, when the antistatic film 3 is removed by etching and developed, as shown in FIG. The thickness of the grating 20 was obtained by changing the thickness of the grating 20.

The grating 2o is affected by scattering of the ion beam 5 within the resist 6 or scattering from the substrate 1. There was no influence of the so-called proximity effect, and a good sawtooth cross-sectional shape without droop or unevenness throughout the design was realized. Furthermore, since the penetration depth of the ion beam 6 is almost determined by the accelerating voltage regardless of the exposure amount, there is no need to accurately correct the sensitivity characteristics of the resistor 6 and adjust the exposure amount as in the conventional example. A good cross-sectional shape with good properties could be easily achieved. In other words, a grating 20 with good optical properties was obtained.

The film thickness of the resist 6 is d = 1.37xm in this example.
However, this means that the wavelength used for the grating 20 is H
Since the e-Ne laser has λ-0.63 and 287zm, and the refractive index of PMMA of resist 6 is n-1.6,
This is because the first-order diffraction efficiency is maximum when d=λ/(n-1)-1,3. The refractive index of positive resist is
Since it is approximately 1.6 to 1.7, it was found that the film thickness of the resist 6 may be d=2λ or less when trying to obtain high efficiency.

In this example, a case was explained in which Be was used as the ion, but similar effects could be obtained using other ions. At this time, the heavier the mass of the ion, the shallower the penetration depth, so it was necessary to appropriately set the accelerating voltage according to the mass of the ion. Also, considering that the accelerating voltage is 250 KV or less for practical use, Al with a mass of 27 is 25
The penetration depth was 0.871 m at 0 KV, and the S12+ of mass 28 had a penetration depth of 0.67 zm at 250 KV. Optical elements such as grating 20 use wavelength λ-0
, 4 to 1 μm, the maximum film thickness of the resist 6 must be about 2λ, that is, 0.8 μm to 271 m.

From the above experiments, we discovered that an optical element with particularly high efficiency can be realized by using ions with a mass of 27 or less.

In this example, the case where PMMA was used as the resist 6 was explained, but the same effect was obtained with other resists.

FIG. 2 shows an example of use of the grating 20 after completion of fabrication according to an embodiment of the present invention. This is an example in which when, for example, a He-Ne laser beam is incident as incident light 7 from the substrate 1 side, it is diffracted by the grating 2o and output as diffracted light 8 at a different angle from that of the incident light 7.

In this example, since a grating with a period of 5/JfH was fabricated, the output angle of the diffracted light 8 was approximately 7° with respect to the incident light 7. Moreover, since a good grating 2o with no droop could be produced in this example, the proportion of diffracted light was good, close to 100%. Further, the incident light 7 may be incident from the grating 20 side.

Furthermore, although this embodiment has described a grating with a sawtooth cross-sectional shape, similar effects can be obtained with methods of manufacturing other thin-film micro-optical elements such as gratings and Fresnel lenses with various cross-sectional shapes. Needless to say.

Effects of the Invention As described above, according to the present invention, the proximity effect of the beam is reduced, correction of the sensitivity characteristics of the resist is almost unnecessary, and it is possible to realize a good cross-sectional shape. This has the effect that a thin film micro-optical element can be realized.

[Brief explanation of the drawing]

FIGS. 1 and 2 are a manufacturing process diagram and a configuration diagram of a grating according to an embodiment of the present invention, respectively, and FIG. 3 is a manufacturing process diagram of a conventional grating. 1...Substrate, 20...Grating, 5...Ion beam, 6...Positive resist. Name of agent: Patent attorney Toshio Nakao and 1 other person/
--One substrate 3-Pre-charging film π---Grouting/-m-Substrate 7-Incoming light 8-@M element 2nd Figure π---Two gratings

Claims (5)

[Claims] (1) A positive resist is applied onto the substrate, an ion beam is focused and drawn on the resist while changing the acceleration voltage to correspond to the shape of the optical element, and development processing is performed to increase the film thickness of the resist. 1. A method for manufacturing an optical element, characterized by changing. (2) The method for manufacturing an optical element according to claim 1, wherein the mass of the ions is 27 or less. (3) The method for manufacturing an optical element according to claim 1, wherein the optical element is a Fresnel lens. (4) The method for manufacturing an optical element according to claim 1, wherein the optical element is a grating. (5) The method for manufacturing an optical element according to claim 1, wherein the thickness of the resist is twice or less the wavelength used by the optical element.