JP2566003B2 - Method for manufacturing infrared grid polarizer - Google Patents

Description

TECHNICAL FIELD The present invention relates to an infrared grid polarizer. Grid polarizers are often used in the infrared wavelength range where there is no suitable polarizing material.

(Prior Art) As shown in FIG. 2, a grid polarizer is one in which thin conductor wires are arranged in parallel in a grid pattern at a pitch equal to or less than the wavelength of the target light, and vibrates in a direction parallel to the conductor grid. The electric field component of the existing light is reflected by the grid polarizer, and the electric field component of the light vibrating in the direction perpendicular to the conductor grid has a property of transmitting through the grid polarizer. In the grid polarizer, the pitch distance d and the width a of the conductor grid affect the polarization characteristics. It is said that the smaller the pitch interval d is, the better the polarization characteristic is, and a / d is preferably 0.5 to 0.7. Therefore, the shorter the polarization wavelength is, the shorter the pitch of the conductor grid must be made.However, if it is made shorter, it becomes difficult to leave the gap between the conductors hollow by the conductor grid alone. , Forming a conductor grid.

However, in the conventional grid polarizer, as shown in FIG. 3, a photoresist layer is laminated on an appropriate substrate, a sinusoidal resist pattern is formed on the surface by a holographic exposure method, and a conductor is provided on the slope. It is produced by vapor deposition (a) or by making a replica of the blazed grating and vapor-depositing a conductor on the slope from the oblique direction (a). However, when the conductor is vapor-deposited on the slope, the vapor-deposition pattern shape becomes non-uniform and it is difficult to make the polarization characteristic constant. Further, when the conductor pattern is formed on the slope, the reason why the polarization characteristic is not good is that the light reflected by the conductor on the slope may enter the substrate from the slope on the opposite side. When a replica is used for the substrate, resin is usually used as the material of the replica.
However, since the resin is weak against heat and has a low transmittance for wavelengths in the infrared region, there is a problem that the performance as a polarizer in the infrared region is not good.

(Problems to be Solved by the Invention) An object of the present invention is to provide a method for manufacturing an infrared grid polarizer having good transmittance and polarization characteristics for light in the infrared region.

(Means for Solving the Problems) The present invention is to optically polish both surfaces of a heat-resistant substrate that absorbs little infrared light, and laminate an antireflection film on both surfaces of the substrate, and then reflect on the incident side. The upper surface of the prevention film is coated with Au and a photoresist, a resist pattern with a half-sine cross-section is formed on this photoresist by the holographic exposure method, Ar ion beam etching is performed using this resist pattern as a mask, and then the remaining resist is ashed. It is characterized by forming an Au lattice pattern consisting of high-density parallel filaments of rectangular cross section by removing.

(Operation) The grid polarizer is a thin linear conductor arranged in parallel, but since the conductor strip is held on the substrate,
Since there is no problem in terms of strength and the substrate uses a material having high transmittance for transmitting the measurement light, the substrate holding the conductor has high transmittance.

In the present invention, a high-density parallel line pattern of conductors (Au) is formed on a substrate by Ar ion beam etching, whereby a conductor pattern is formed on the substrate in parallel with the substrate surface. The reflected light does not re-enter the grid polarizer substrate from the opposite slope, and the polarization characteristics are improved. Further, the parallel line pattern of the conductor formed on the substrate can be formed clearly and with high density, and the polarization characteristic is improved also from this point.

In particular, in the infrared region, there are materials with high surface reflectance even if they have low absorption such as Si. By coating the substrate surface with an antireflection film, the transmittance of the target light of the substrate is It is also possible to obtain 100% transmittance in a narrow wavelength range, further improving the polarization characteristics.

(Embodiment) FIG. 1 shows a process drawing of an embodiment of the present invention. In FIG. 1, FIG. A shows the constituent layers of the grid substrate before the conductor grid 5 is processed.
Dielectric multilayer films ZnS, MgF ₂ are deposited on both sides of the Si substrate 1 (thickness 260 μm, outer diameter 50 mmφ) polished on both sides by vacuum deposition method,
Antireflection films 2 and 3 were formed. Next, the antireflection film 2 on the incident side
A Ni-Cr film (thickness 20Å) was vacuum-deposited as the conductor adhering film 4 on the upper surface of the in order to improve the adhesion with the conductor grid 5. An Au film (700 Å) to be the conductor grid 5 was vacuum-deposited on the upper surface of the adhesion film 4. Further, OFPR5000 as the photoresist 6 is spin-coated on the upper surface of the conductor grid 5 to a thickness of 2500 Å and baked in a fresh air oven at 90 ° C for 30 minutes to manufacture.

Next, two-beam interference fringes were printed on the photoresist 6 of the grid substrate manufactured as described above by the holographic exposure method. He-Cd laser (λ = 4416)
Å) is used to create a parallel light flux with a special filter and an off-axis parabolic mirror. The interference fringes to be printed were 2000 lines / mm so that the pitch interval was about 1/10 of the used wavelength.
Next, development was carried out so that the resist 6 had a sinusoidal half-wave cross section, that is, a / d of 0.5, as shown in FIG. The adjustment of the cross-sectional shape can be performed by adjusting the exposure time and the development time.

Next, using the photoresist pattern 6 as a mask
Ar ion beam etching is performed, and as shown in FIG.
Photoresist patterns 6 were patterned on the conductor grid 5 and the conductor adhering film 4 to form parallel grid patterns. The above etching was performed at an acceleration voltage of 500 eV and a gas pressure of 1.6 × 10 ⁻⁴ Torr. At this time, the etching rates of the resist 6 and the conductor grid 5 are about 1: 4.

Finally, the photoresist 6 used as the etching mask in the above is ashed and removed by O ₂ plasma by a barrel type plasma etching device, and finally washed to obtain a grid polarizer G as shown in FIG. I made it.

Further, in the above-mentioned embodiment, the antireflection film 2,
3 is coated to improve the transmittance in the measurement wavelength range, but if the substrate 2 is made of a material having a high transmittance, it is not necessary to coat the antireflection films 2 and 3.

(Effect of the invention) According to the present invention, since the parallel line pattern of Au is manufactured on the substrate by Ar ion beam etching, a high-density and clear parallel line pattern is manufactured as compared with the conventional vapor deposition method. Thus, an infrared grid polarizer having further improved polarization characteristics can be provided.

[Brief description of drawings]

FIG. 1 is a process drawing of an embodiment of the present invention, FIG. 2 is an operation explanatory view of a grid polarizer, and FIG. 3 is a perspective view of a conventional example. 1 ... Si substrate, 2,3 ... antireflection film, 4 ... conductor adhesion film, 5 ... conductor grid, 6 ... photoresist, G ...
… Grid polarizer.

Claims (1)

(57) [Claims] 1. A heat-resistant substrate that absorbs little infrared light is optically polished on both sides, an antireflection film is laminated on both sides of the substrate, and then Au or a photoresist is formed on the upper surface of the antireflection film on the incident side. Is coated on the photoresist by a holographic exposure method to form a sinusoidal half-wave cross-sectional resist pattern, Ar ion beam etching is performed using this resist pattern as a mask, and then the residual resist is removed by ashing to increase the rectangular cross-section height. A method for manufacturing an infrared grid polarizer, which comprises forming an Au lattice pattern composed of density parallel lines.