JPH07280721A - Optical device in vacuum ultraviolet area prevented from pollution - Google Patents

Abstract

PURPOSE:To enable the high accuracy measurement of an optical characteristic in a vacuum ultraviolet area by providing means for eliminating the influence of pollutant intermixed from the outside of a chamber at the time of evacuation. CONSTITUTION:In the constitution of an optical device, an oilless vacuum pump is used to prevent the reverse diffusion of oil of an oil rotating vacuum pump 21. A cold lap is to be 200K or less to coagulate and catch pollutive components. Dust and particulates are eliminated by the filter of a filter insert part 25, and pollutant is efficiently eliminated by permutite or actuvated alumina in an adsorbent filled part 24. In a charged filter, scavenging can be performed effectively since particulates are fine and scarce and the quantity of charge is small. One or plural of these means are combined to evacuate while eliminating the influence of pollutant.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical device used in the vacuum ultraviolet region in which deterioration of optical characteristics due to the influence of a trace amount of contaminants is prevented.

[0002]

2. Description of the Related Art Light having a wavelength of 380 nm or less is invisible to the eyes and is called ultraviolet light. The wavelength becomes shorter and 2
When it is 20 nm or less, it cannot transmit light in the air. This is due to the absorption of light by oxygen in the air.
Therefore, in the optical system in this wavelength range, oxygen is excluded from the light path, so that the light path needs to be kept in vacuum. Therefore, this wavelength range is called the vacuum ultraviolet range.

In recent years, the field of application of vacuum ultraviolet light is expanding to measuring / measuring equipment, lithography technology, optical CVD, laser processing machines and the like. In these devices as well, in order to avoid the influence of absorption of vacuum ultraviolet light from the path of light, an airtight chamber with a vacuum inside is installed, and the inside of the light source, spectroscope, mirror, lens, window, etc. The system was installed.

[0004]

However, when the optical characteristics such as transmittance and reflectance in the vacuum ultraviolet region are measured with high accuracy by the apparatus having such a structure, absorption of unknown cause occurs at around 200 nm. , Could not be measured with sufficient accuracy. Further, as the optical characteristics of the optical system change with time, stray light and a decrease in S / N ratio due to deterioration of characteristics of optical elements such as a grating, a window and a mirror occur in a short period of time.

[0005]

As a result of intensive studies on these problems, the inventors found that the operation of exhausting the gas in the vacuum chamber conversely contaminates the chamber, the optical system inside the chamber, and the measurement sample. I found the fact that it was causing problems. The pollutants are minute back diffusion of oil in the oil rotary vacuum pump, fine particles, mist, gas components volatilized from the inner surface of the chamber, etc., which absorb light with a wavelength of around 200 nm and deteriorate accuracy, and further, optical elements. Adhered to and deteriorated the optical characteristics and shortened the life of the optical element.

In order to solve the above problems, therefore, in the present invention, an optical device having a chamber capable of vacuum evacuation, a vacuum evacuation path provided outside thereof, and an optical system provided inside the chamber. In the above, the optical device is provided with a means for eliminating the influence of contaminants mixed in the chamber from the vacuum exhaust path during vacuum exhaust.

[0007]

In the present invention, the provision of means for eliminating the influence of contaminants mixed from the outside of the chamber during evacuation makes it possible to prevent deterioration of measurement accuracy and deterioration of characteristics. The effect of preventing pollution is 100 nm or more 22
It is clearly visible below 0 nm. It ’s 170n
When m or less, the intensity of a light source such as a deuterium lamp decreases, and the effects of stray light and S / N ratio decrease due to contamination of optical elements such as gratings, windows, and mirrors become prominent. This is because the influence of oil absorption of pollution is great.

Reverse diffusion of oil in the oil rotary vacuum pump can be prevented by exhausting with an oilless vacuum pump. The oilless vacuum pump is a diaphragm pump, a cryopump, a dry pump, a turbo molecular pump, or the like. Even in a turbo molecular pump that is considered to be oil-free, the above-described contamination occurs even in a short time when rough evacuation by an oil rotary vacuum pump is performed as is generally done.

The degree of these contaminations cannot be adequately controlled by the ultimate vacuum displayed on the pressure gauge. In particular,
Once the inside of the chamber is contaminated, the influence of the contamination remains even if the vacuum degree is raised to a high level thereafter. When the oil rotary vacuum pump and the turbo molecular pump are combined due to cost constraints, it is necessary to devise the following effects of contaminants in the vacuum exhaust path and the chamber.

By setting the cold trap to 200 K or less, the polluting components can be aggregated and captured. The filter can remove dust and particles. Synthetic zeolite or activated alumina can remove pollutants efficiently. Further, in the charging filter, since the particles are fine particles and the charge amount is small and the number of particles is small, the particles can be effectively collected.

By combining one or more of these means, it is possible to evacuate while eliminating the influence of contaminants.

[0012]

EXAMPLES The present invention will be described in more detail below with reference to examples, but the present invention is not limited thereto.

[0013]

Example 1 FIG. 4 shows a schematic diagram of an optical system used in the present invention. Table 1 shows the conditions at the time of measurement. Table 1
Nos. 1 to 5 are measured by using the optical system according to the present invention, and No. 6 is conventionally performed as a comparative example.
It is measured by using an optical system having a combination of an oil rotary vacuum pump and a turbo molecular pump. As the sample, synthetic quartz glass manufactured by the flame hydrolysis method was used.

The result of No. 6 measured using the conventional optical device is shown in FIG. 1-a. An abnormal drop in the transmittance curve is seen near 200 nm. Further, at 160 nm or less, the apparent transmittance curve rises due to contamination of the optical element. The synthetic quartz glass used as a sample here has no absorption at 200 nm and does not transmit at 160 nm or less. On the other hand, the result shown in FIG. 1-b is obtained by using the oil-free pump instead of the conventional method, which is 200 nm compared with the case where the conventional optical device is used.
The generation of non-essential absorption bands in the silica glass near nm was suppressed, and very good transmittance measurement results were obtained. Also,
The transmittance at 160 nm or less showed a normal value of almost 0%.

Further, even in the combination of the conventional oil rotary vacuum pump and the turbo molecular pump, when a cold trap is used as in Nos. 2 to 5 and a filter is used,
The same results as in FIG. 1-b were obtained depending on the conditions in both cases of using an adsorbent and applying a voltage, and the effect was confirmed.

[0016]

[Table 1]

[0017]

Example 2 When fluorite was evaluated under the same conditions as in Example 1, the same results as in the case of quartz glass were obtained. An example of this result is shown in FIG.

[0018]

According to the present invention, it is possible to obtain a highly accurate optical system which is free from the influence of various contaminants caused by vacuuming and which prevents deterioration of the characteristics of the optical system in the vacuum ultraviolet region. By using this optical system, it became possible to measure the optical characteristics in the vacuum ultraviolet region with high accuracy.

[Brief description of drawings]

FIG. 1 is a schematic view of an optical device used in the present invention.

FIG. 2 is an example of a measurement result based on Example 1.

FIG. 3 is an example of a measurement result based on Example 2.

[Explanation of symbols]

21 ... Oil rotary vacuum pump 22 ... Turbo molecular pump 2
3 ... Electrode application part 24 ... Adsorbent filling part 25 ... Filter insertion part 26 ... Cold trap 29 ... Chamber and spectroscope 31 ... Gas introduction port 32 ... Leak port 33
… Lamp 34… Lens 35… Grating 36
… Slit 37… Sample 38… Detector

Claims (7)

[Claims] 1. An optical device having a chamber capable of vacuum evacuation, a vacuum evacuation path provided outside the chamber, and an optical system provided inside the chamber. An optical device provided with means for eliminating the influence of contaminants mixed in. 2. The optical device according to claim 1, wherein a usable wavelength region of the optical system is 100 nm or more and 220 nm or less. 3. The optical device according to claim 1, wherein the means for eliminating the influence of the contaminant is vacuum exhaust by an oilless vacuum pump. 4. The optical device according to claim 1, wherein the means for eliminating the influence of the contaminant is a cold trap of 200 K or less installed in the vacuum exhaust path. 5. The optical device according to claim 1, wherein the means for eliminating the influence of the contaminant is a filter installed in a vacuum exhaust path. 6. The optical device according to claim 1, wherein the means for eliminating the influence of the pollutant is synthetic zeolite or activated alumina installed in a chamber or in a vacuum exhaust path. apparatus. 7. The optical device according to claim 1, wherein the means for eliminating the influence of the contaminant is a charging filter installed in the chamber or in the vacuum exhaust path.