JPH0560901A - Infrared optical element and manufacturing method thereof - Google Patents

Abstract

PURPOSE:To obtain a lens or filter high in transmissivity in the infrared region by using a high purity polycrystal silicone. CONSTITUTION:An optical device such as a lens, a filter or a diffraction grating is made from the high purity polycrystal silicone obtained by passing a gaseous mixture of a high purity silicone compound and hydrogen on a heated base body at 900-1200 deg.C. In this case the silicone bar 32 prepared is set in the prescribed place in the reaction vessel 31 and is heated electrically to become 900 deg.C by a heating power source 33. Next, the high purity hydrogen and the high purity silicone compound, monosilane, are passed into the reaction vessel 31 and is allowed to react with each other for a prescribed time to obtain the polycrystal silicone. Next, the polycrystal silicone obtained in this way is machined in convex lens shape and is coated with zinc sulfide on the both side to use as the antireflection coating 12.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an infrared optical element that collects or transmits infrared light and a method for producing the same.

[0002]

2. Description of the Related Art In recent years, devices and measuring devices using infrared rays have been actively developed. Especially in the far infrared (5 μm to 15 μm
Development of the optical device (m) such as a pyroelectric infrared sensor is becoming active.

Particularly in a pyroelectric infrared sensor capable of measuring the position and temperature of the human body, the temperature of the human body (body temperature) is 3
Since it is around 00K, the infrared wavelength is 8 μm to 12 μm.
As a material that transmits this wavelength, relatively inexpensive single crystal silicon (Si), expensive but high-performance germanium (Ge), selenium zinc oxide (ZnSe), etc. are used for polishing and cutting. It has been used as a lens or filter by rubbing. (For example, Riichi Saeki et al., Mitsubishi Electric Technical Report vol.51 No.11, 1977, P.745.
~ P.748)

[0004]

SUMMARY OF THE INVENTION Silicon (Si) which has hitherto been used in inexpensive infrared lens systems and filter systems.
For C, a single crystal according to the CZ method (Chocolaski method) or the FZ method (floating method) has been mainly used. However, in the CZ method, since a single crystal is grown in a quartz crucible at a high temperature of 1400 ° C. or higher, mixing of oxygen from the quartz crucible cannot be avoided. Further, since the FZ method transforms polycrystalline silicon into a single crystal by high frequency heating in a high vacuum or in an inert gas, it contains less oxygen than the CZ method, but cannot completely eliminate oxygen. Therefore, the silicon produced by the conventional CZ method or FZ method contains a small amount of oxygen, and therefore has an infrared absorption band due to oxygen around 9 μm, which is inconvenient for human body temperature detection. Further, selenium zincate (ZnSe) and germanium (Ge) have a problem that they are expensive although they have little infrared absorption around 9 μm.

An object of the present invention is to solve the above problems and provide an inexpensive and high-performance infrared optical element.

[0006]

In order to achieve this object, the present invention uses a mixed gas of a high purity silicon compound and hydrogen as a gas.
An optical element such as a lens, a filter or a diffraction grating is formed by using a polycrystalline silicon having a purity of 99.999999999% or more obtained by flowing it onto a substrate heated to 00 ° C to 1200 ° C.

[0007]

According to the present invention, by using the above-mentioned high-purity polycrystalline silicon, a lens and a filter having a high transmittance in the infrared region, which cannot be obtained by using the conventional single-crystal silicon, can be obtained. It is a thing. This is because, as a method for obtaining polycrystalline silicon, a mixed gas of high-purity silicon compounds and hydrogen is used, and polycrystalline silicon is obtained by a thermal decomposition deposition method (CVD method) by hydrogen reduction. This is because there is no oxygen in the mixture. Therefore, a polycrystalline silicon lens or filter with almost no absorption in the 9 μm band can be obtained.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 is a cross-sectional view of an infrared lens produced by using polycrystalline silicon. Reference numeral 11 is a polycrystalline silicon lens processed into a lens shape, and 12 is an antireflection film. FIG. 2 is a sectional view of an infrared filter using polycrystalline silicon. Reference numeral 21 is a polycrystalline silicon filter processed into a planar shape, and 22 is an antireflection film. Further, FIG. 3 is a schematic view of a CVD apparatus for producing polycrystalline silicon. First,
A cylindrical silicon rod 32 having a diameter of 6 mm and a length of 600 mm is prepared, set at a predetermined position in the reaction vessel 31 as shown in FIG. 3, and electrically heated by a heating power source 33, and the silicon rod 32 is set to 900 To ℃. Then, the purity is set to 99.9999 in the reaction vessel 31 from the hydrogen cylinder 34 through the flowmeter 37.
% Hydrogen at a rate of 20 l / min and a purity of 99.9999 in the reaction vessel 31 from the silicon compound cylinder 35 through the flow meter 36.
% Silicon monosilane (SiH ₄ ) 10 l / min
It was made to flow and reacted for 16 hours to obtain polycrystalline silicon having a diameter of about 10 cm. Here, when the purity of this polycrystalline silicon was measured, it was 99.999999999%.

Next, the obtained polycrystalline silicon is processed into a convex lens shape having a radius of curvature of 100 mm, and zinc sulfide (ZnS) is used as the antireflection film 12 on both sides of 2.25 μm.
As a result of coating, an infrared lens having a focal point of 9 μm was measured, and good condensing characteristics and light intensity were obtained.

The polycrystalline silicon is 6 mm in diameter from the center.
A disk with a diameter of 7 mmφ and a thickness of 4 mm is cut out from the part except the part, and both sides of this disk have the maximum surface roughness (Rmax).
However, a mirror surface processing was performed so as to have a thickness of 0.02 μm, and zinc sulfide (ZnS) was coated on both surfaces as an antireflection film 22 by a vacuum deposition method to a thickness of 2.25 μm to obtain a filter. Then, the infrared transmittance (transmittance at a wavelength of 9 μm) of the polycrystalline silicon coated with ZnS was measured 90
%Met. The results are shown in Material No. 1 of (Table 1).

In the following, the results of the polycrystalline silicon, the purity of the silicon and the infrared transmittance when the kind of the raw material gas at the time of making the filter, the kind of the deposition gas and the deposition conditions are changed by the same method (Table 1), Material No. 2
~ 4. In addition, Material Nos. 5 to 8 in (Table 1) are comparative examples other than the present invention.

[0013]

[Table 1]

As can be seen from (Table 1), the high-purity polycrystalline silicon produced by the CVD method has a better infrared transmittance than the single-crystal silicon obtained by the conventional method, and an excellent infrared optical element can be obtained. ..

[0015]

As is apparent from the above description, the infrared optical element using the polycrystalline silicon by the CVD method of the present invention is
Ge, ZnS, which has higher performance than the infrared optical element using the single crystal silicon by the CZ method or the FZ method, which has been conventionally used.
It is cheaper than the infrared optical element using the e crystal.

[Brief description of drawings]

FIG. 1 is a sectional view of an infrared lens according to an embodiment of the present invention.

FIG. 2 is a sectional view of the infrared filter of the same embodiment.

FIG. 3 is a CVD for producing the polycrystalline silicon of the same embodiment.
Device schematic

[Explanation of symbols]

 11 Polycrystalline Silicon Lens 12, 22 Antireflection Film (ZnS) 21 Polycrystalline Silicon Filter 31 Reaction Vessel 32 Silicon Bar 33 Heating Power Source 34 Hydrogen Cylinder 35 Silicon Compound Cylinder 36, 37 Flowmeter

Claims (3)

[Claims] 1. An infrared optical element in which a polycrystalline silicon having a purity of 99.999999999% or more, which is formed by a CVD method (chemical vapor deposition method), is processed into a lens shape or a filter shape. 2. A mixed gas of a silicon compound and hydrogen is heated to 900 ° C.
A method for producing an infrared optical element, characterized by processing an infrared optical lens by processing polycrystalline silicon obtained by pouring it onto a substrate heated to ˜1200 ° C. into a lens shape. 3. The silicon compound is monosilane (SiH ₄ ),
The method for manufacturing an infrared optical element according to claim 2, wherein the method is any one of trichlorosilane (SiHCl ₃ ), dichlorosilane (SiHCl ₂ ), and silicon tetrachloride (SiCl ₄ ).