JPS62109049A - Production of minute optical element - Google Patents

Abstract

PURPOSE:To obtain the titled element having an excellent optical characteristics by changing an accelerating voltage of an electron beam in a range of a low accelerating voltage so as to correspond to a shape of the titled element, thereby forming directly an image on the positive type electron beam resist, and by effecting a developing treatment, thereby changing the thickness of the electron beam resist film. CONSTITUTION:The positive type electron beam resist 12 is coated on a substrate 11, for example, in 1.3mum thickness, and an antistatic film 13 is vacuum- deposited on the resist 12 in 100Angstrom thickness. The image is formed directly on the positive type electron beam resist 12 by changing the accelerating voltage of the electron beam 14 in the range of the low accelerating voltage so as to correspond to the shape of the formed grating 12'. Thus, a depth of entering the electron beam 14 within the electron beam resist layer 12 becomes small, depending upon the accelerating voltage. Eve if a light exposure is somewhat excess, the thickness of the film after developing almost becomes constant.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a method for manufacturing micro optical elements. .

Conventional technology In recent years, thin-film micro optical elements such as micro Fresnel lenses and micro gratings have attracted attention as small, lightweight optical elements with various functions. Lithography is promising.

In addition, in order to achieve various light distributions and high efficiency, it is necessary to control the cross-sectional shape of the Fresnel lens or grating. For example, if the cross-sectional shape is made into a sawtooth shape with an appropriate film thickness, the diffraction efficiency will be approximately 160%. This high efficiency can be achieved.

As shown in FIG. 2, a conventional method for manufacturing a thin film micro-optical element using electron beam lithography involves first coating or depositing an electron beam resist 2 and an antistatic film 3 such as Au on a substrate 1. (a)), addition M of electron beam 4
By controlling the number of scans of the electron beam 4 while keeping the voltage constant, etching is performed directly on the resist 2 (Fig. 2(b)), and by etching and developing the antistatic film 3, a Fresnel with a sawtooth cross-sectional shape is formed. Lens or grating 2'
There is a method of manufacturing (Fig. 2(C)).

(Fujita et al.; “Blazed micro Fresnel lens fabricated by lightning beam lithography”, Journal of the Institute of Electronics and Communication Engineers (c),
J66-C, 1, PP, 85-91 (Sho 58-1)
) Problems to be Solved by the Invention In such conventional methods, the accelerating voltage is set to a high value, e.g.
Drawing is performed while keeping the voltage constant at 0kv or higher. At such high accelerating voltages, the electron beam passes through the coating and cysts and is mainly scattered by the substrate, causing the so-called proximity effect, and furthermore, the sensitivity characteristics of the resist must be accurately corrected to adjust the exposure dose. However, it was difficult to realize an ideal sawtooth shape, and a microscopic optical element with good optical properties could not be obtained. The present invention is intended to solve these problems, and an object of the present invention is to provide a thin-film micro-optical element with excellent optical properties.

Means for Solving the Problems In order to solve the above problems, Komei Koku changed the acceleration voltage of the electron beam in a low acceleration voltage range so as to correspond to the shape of the micro optical element, and created the positive electron beam. The film thickness of the electron beam resist is changed by directly writing on the resist and performing a current process.

Effect of the Invention The present invention uses the method described above to eliminate the harmful proximity effect caused by scattering of electron beams on the substrate, eliminates the need to correct the sensitivity characteristics of the resist, and easily provides optical characteristics with an ideal cross-sectional shape. EMBODIMENT OF THE INVENTION An embodiment of the present invention in which a micro optical element with good quality can be manufactured will now be described with reference to the drawings. FIG. 1 is a manufacturing process diagram of a grating according to an embodiment of the present invention. In FIG. 1, 11 is a substrate, 12 is a positive electron beam resist, and 13 is an antistatic film. In this embodiment, the substrate 11 was made of glass, the positive electron beam resist 12 was made of PMMA, and the antistatic film 13 was made of Hem. Any material may be used as the substrate 11 as long as it has excellent transmittance at the wavelength used by the grating. Also A
The U film is used only to prevent the electron beam 14 from being charged, and is not necessary if there is no concern about the electron beam 14 being charged, that is, if the substrate 11 or the resist 12 is conductive. Other metal thin films such as .

Next, the manufacturing process will be explained. First, for example, 1.3 μl' of positive electron beam resist 12 is applied onto the substrate 11.
dl cloth, and the antistatic film 13 was vacuum-deposited thereon by, for example, 100 people (FIG. 1(a)). Next, the applied voltage of the electron beam 14 was varied in a low acceleration voltage range so as to correspond to the shape of the grating 12' to be manufactured, and writing was performed directly on the positive electron beam resist 12 (Fig. 1(b)). . The present inventors found that in a low accelerating voltage range, the penetration depth of the electron beam 14 into the 12 layers of the electron beam resist is small depending on the accelerating voltage, and even if the exposure dose exceeds the It was found that the film thickness was almost constant. for example,
The magnitude of acceleration voltage is 10KV, 5KV, 2KV, I
rtA peeled off by development when the exposure was above the proper level with KV.
Thickness is 1.2 μm, 0.45 μtg, 0.22
μrg was almost constant at 0.11 μ■. Further, since the electron beam 14 does not pass through the substrate 11 side, the sensitivity of the resist 12 is improved and the drawing time is shortened.

In this example, the acceleration voltage of the electron beam 14 was smoothly changed from 10 to 0.1 KV. Finally, the antistatic film 13 is etched and removed, and developed to change the film thickness of the resist 12, and the grating 12'
was obtained (Fig. 1(C)). The grating 12' is
Affected by scattering of the electron beam 14 from the substrate 11,
A good cross-sectional shape as designed was achieved without the influence of the so-called proximity effect. Furthermore, since the penetration depth of the electron beam is determined by the accelerating voltage and not by the exposure amount in the low applied Jili voltage range, there is no need to accurately correct the sensitivity characteristics of the resist 12 and adjust the exposure amount as in the conventional example. , it was possible to easily realize a good cross-sectional shape with good reproducibility. As a result, a grating 12' with good optical properties was obtained.

The film thickness of the resist 12 was set to d = 1.3 μl in this example, but this is because the wavelength used by the grating 12' is He
- Since λ of the No laser is 0.6328 μrg and the refractive index of PMMA of the resist 12 is n = 1.5,
The first-order diffraction efficiency is d-λ/(n-1) = 1.3μt
This is because it is maximum when . Since the refractive index of the positive electron beam resist 12 is about 1.5 to 1.7, if high efficiency is to be obtained, the film thickness of the resist 12 is d=2λ
I found that the following is fine.

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.

According to the present invention, the proximity effect of the electron beam is reduced, correction of the sensitivity characteristics of the resist is almost unnecessary, a good cross-sectional shape can be realized, and a thin film microoptical device with good optical properties can be used. This has the effect of turning the element blue.

[Brief explanation of drawings]

FIG. 1 is a manufacturing process diagram of a grating according to an embodiment of the present invention, and FIG. 2 is a manufacturing process diagram of a conventional grating. 11...Substrate, 12...Positive electron beam resist, 12'...Grating, 14...Electron beam agent Yoshihiro Morimoto Figure 1 Figure 2

Claims (1)

[Claims] 1. Applying a positive electron beam resist on the substrate, changing the acceleration voltage of the electron beam in a low acceleration voltage range so as to correspond to the shape of the micro optical element, and applying the positive electron beam resist to the substrate. A method for manufacturing a micro-optical element, characterized in that the film thickness of the electron beam resist is changed by performing direct drawing and development treatment on a beam resist. 2. The method of manufacturing a micro-optical element according to claim 1, wherein the acceleration voltage of the electron beam is 10 kV or less. 3. The method for manufacturing a micro optical element according to claim 1, wherein the micro optical element is a Fresnel lens. 4. The method for manufacturing a micro optical element according to claim 1, wherein the micro optical cable is a grating. 5. The method for manufacturing a micro-optical element according to claim 1, wherein the film thickness of the positive electron beam resist is set to be less than twice the wavelength used by the micro-optical element.