JPH0822129A - Optical device for vacuum ultraviolet region - Google Patents

Abstract

PURPOSE:To prevent deposition of contaminants on optical elements or the surface of a sample and to efficiently obtain vacuum ultraviolet rays by replacing the inner gas of a chamber equipped with an optical system inside by inert gas containing no impurity gas. CONSTITUTION:This optical device is equipped with a chamber 29 which can be evacuated, an introducing route 31 and a discharging route 30 for inert gas attached to the outside of the chamber, and an optical system disposed inside of the chamber 29. The inside of the chamber is replaced by the inert gas from which impurity gas having absorption in a vacuum UV region is discharged or removed by adsorption to a specified proportion. As for the inert gas, argon is suitable because high purity argon is available at a rather low cost and gives small influences on the absorption lines in 100 to 220nm wavelength region. It is preferable that the partial pressure of carbon dioxide, oxygen, water vapor and carbon monoxide in the inert gas is <=1X10<-7>atm, <=2X10<-6>atm, <=5X10<-6>atm, and <=1X10<-5>atm, respectively. By this method, absorption of light in the transmitting passage is decreased to <=10% per 1m.

Description

Detailed Description of the Invention

[0001]

The present invention relates to photolithography, light C
An optical device such as a VD, a laser beam machine, or an optical measuring device represented by a spectrophotometer, particularly an optical device that has been required to be evacuated up to now, or a vacuum ultraviolet region (220 n).
(wavelength of m or less).

[0002]

2. Description of the Related Art Generally, light having a wavelength of 380 nm or less is invisible and is called ultraviolet light. Furthermore, the wavelength is 220
When it is less than nm, it cannot transmit light in the air. This is mainly due to absorption of light by oxygen in the air. Therefore, in the optical system in this wavelength range, it is necessary to keep the path vacuum in order to eliminate a factor that absorbs light such as oxygen from the light transmission path. Therefore, this wavelength range is called vacuum ultraviolet light, and its light is called vacuum ultraviolet light.

Vacuum ultraviolet light has a photon energy of about 6e.
Greater than V and highly active against substances. That is,
Since this energy region corresponds to the bond or molecular bond energy region between the atoms constituting the substance, light absorption occurs by irradiating the substance with vacuum ultraviolet light,
Photolysis changes the properties of substances and causes photochemical reactions.

Therefore, by measuring the physical properties such as absorption or reflection characteristics for vacuum ultraviolet light, the structural properties of the substance can be known. Further, the substance can be modified by irradiating it with vacuum ultraviolet light. For this reason, in recent years, this vacuum ultraviolet light has been used for measurement / measurement equipment, optical lithography,
It is used in optical devices in a wide range of fields such as photo CVD and laser processing machines.

In these optical devices, in order to use vacuum ultraviolet light efficiently, it is necessary to prevent the light amount from being attenuated as much as possible. Therefore, in the conventional device, an airtight chamber is provided, and an optical system such as a light source, a spectroscope, a mirror, and a lens is installed in the chamber to make the inside of the device a vacuum or continuously supply nitrogen gas to the chamber. Measurements were performed while pushing out gas such as internal air (hereinafter referred to as purge).

[0006]

SUMMARY OF THE INVENTION In such an optical device, a window material, a lens, which efficiently transmits vacuum ultraviolet light,
Prism, mirror, etc. are required. Quartz glass or a single crystal is used as a material for these optical elements for vacuum ultraviolet light. For example, absorption of these materials in the vacuum ultraviolet region,
A vacuum ultraviolet spectrophotometer is used to evaluate the reflective properties.

Conventionally, in this vacuum ultraviolet spectrophotometer, the inside of the chamber is evacuated for measurement. However, when the optical characteristics such as vacuum ultraviolet transmittance and reflectance of the material are measured with high accuracy by such a vacuum ultraviolet spectrophotometer, the cause of the vicinity of 200 nm is caused as shown in Fig. 2-c. Since unknown absorption occurs, the measurement could not be performed with sufficient accuracy.

Further, window materials, lenses used in the optical system,
Deterioration of the characteristics of optical elements such as a grating and a mirror occurs in a short period of time, resulting in an increase in stray light and a decrease in S / N ratio, which makes it impossible to perform measurement with sufficient accuracy. Further, even if the inside of the chamber is purged with nitrogen gas, absorption by impurity gases such as oxygen and water vapor contained in commercially available nitrogen gas cannot be ignored and becomes 185 nm.
The following was impossible to measure.

[0009]

As a result of intensive studies on these problems, the present inventors found that the operation of discharging gas from the chamber conversely contaminates the chamber and the optical system and measurement sample inside the chamber. Found the fact that was causing the problem. The pollutants referred to here are oil mist and fine particles that diffuse back from the oil rotary vacuum pump during vacuum exhaust, oil mist and fine particles adsorbed on the chamber inner wall surface, residual gas components, etc. To 200 nm as shown in Fig.2-c.
It was discovered that absorption was occurring in the vicinity.

Furthermore, these pollutants also adhere to the optical elements that make up the optical system, deteriorating the optical characteristics of the optical elements due to the photochemical reaction with vacuum ultraviolet light and the action of themselves, which shortens the life. I also understood that. Contaminants are reversibly desorbed to minute irregularities on the inner wall of the chamber,
It was also found that the material was easily vaporized by evacuation and was secondarily attached to the optical element. In addition, it was found that the trace amount of oxygen, water vapor, etc. remaining in the chamber also promoted the deterioration of the optical element. Similar phenomenon was confirmed not only in the vacuum ultraviolet spectrophotometer but also in all optical devices using vacuum ultraviolet light.

Therefore, in the present invention, in an optical device having a chamber capable of vacuum evacuation, an inert gas introduction path and an exhaust path provided outside the chamber, and an optical system provided inside the chamber, Is replaced by the inert gas removed by adsorbing or removing the impurity gas that has absorption in the vacuum ultraviolet region to a certain ratio or less, and contaminants may be added to the optical element or the sample surface constituting the optical system. Prevented from sticking 185n
The optical device is characterized in that vacuum ultraviolet light of m or less can be efficiently obtained.

[0012]

The feature of the present invention resides in that the above-mentioned problems are solved in the optical device in the vacuum ultraviolet region where vacuum has been indispensable until now, by substituting with an inert gas without making vacuum an essential condition. is there. The substitution in the present invention means filling with an introduced inert gas while keeping the chamber airtight or purging with an inert gas.

Since no vacuum is used in the present invention, it is possible to prevent contaminants generated during evacuation from adhering to the sample surface, the optical elements inside the chamber, and the inner wall surface of the chamber.
Further, it is possible to prevent the release of gas and contaminants from the inner wall surface of the chamber. In general, when the gas in the chamber is replaced with an inert gas, in order to perform the replacement efficiently, the chamber is once evacuated, and then the inert gas is introduced. In conventional vacuum evacuation as described above, oil mist and fine particles that diffuse back from the oil rotary vacuum pump, oil mist and fine particles that volatilize from the chamber inner wall, residual gas components, etc. adhere to the sample surface, Absorption around 200 nm like 2-c occurs. Cleaning of the inside of the chamber thus contaminated is generally performed by an operation called baking, but once the chamber is contaminated, it is extremely difficult to completely remove it. Therefore, when vacuum evacuation is also used, according to Japanese Patent Application No. 6-768878 “Optical device in the vacuum ultraviolet region in which contamination is prevented”, the contamination mixed in the chamber from the evacuation route during evacuation is used. It is necessary to use a means for eliminating the influence of substances, for example, the use of an oilless pump, or a cold trap or a filter of 200K or less installed in the vacuum exhaust path.

At this time, it is possible to share the inert gas introduction path and the vacuum exhaust path provided outside the chamber. So-called inert gas such as nitrogen, argon, helium, krypton or neon is suitable as the kind of the inert gas introduced in the present invention. Among these, high-purity products can be obtained at a relatively low price, and 100 to 220
Argon with the least influence of the intrinsic absorption line in the wavelength range of nm is most suitable. However, in the case of an inert gas, which is said to be a high-purity product on the market, although the amount of contained impurity gas may vary depending on the type of gas, the removal capacity is much larger than the amount of contained impurity gas. It can be treated equally regardless of species.

The purity of the inert gas needs to be as high as possible in order to prevent absorption of vacuum ultraviolet light in the region of 100 nm to 220 nm affected by the impurity gas. For example, in the wavelength region of 185 nm or less, it has hitherto been said that evacuation of the chamber is essential. Even if it is nitrogen gas or commercially available high-purity nitrogen gas, for example, since the oxygen partial pressure in the cylinder is about 1 × 10 ⁻⁴ atm,
Nitrogen purging is essentially 185 nm to 2 even in the vacuum ultraviolet region.
Only effective at 20 nm.

Therefore, it is important to set the partial pressure of the impurity gas component as follows. The partial pressure of carbon dioxide is 1 × 10 ⁻⁷ atm or less, the partial pressure of oxygen is 2 × 10 ⁻⁶ atm or less, the partial pressure of water vapor is 5 × 10 ⁻⁶ atm or less, and the partial pressure of carbon monoxide is 1 × 10. ^-5 atm or less As a result, the absorption of light through the passage is 10% per 1 m.
It can be suppressed to a level below (absorption coefficient 0.001 cm ^-1 or less), and can be used as an inert gas for optical devices in the vacuum ultraviolet region. Further, when a long optical path length is required, it can be achieved by further lowering the partial pressure of the impurity gas component. This relationship can be calculated from the absorption coefficient of gas. In order to suppress the absorption of light in the optical path, it is desirable that the partial pressure of the impurity gas contained in the gas introduced into the chamber satisfies all of the above conditions, but it may depend on the wavelength range used and the accuracy of use of the optical device. It is possible just by satisfying

Various methods are conceivable for monitoring the partial pressure of the gas, but in the present invention, stabilized zirconia is used for oxygen and carbon monoxide, and alkali ions such as β-alumina and NASICON are used for carbon dioxide. This is done by using a conductive solid electrolyte. Also,
The water vapor can be known by measuring the dew point of the introduced inert gas using a crystal oscillator. The partial pressure of these impurity gases is measured at a site immediately after the impurity gas is removed from the introduced gas and immediately before the introduction into the chamber.

In the present invention, in order to discharge and remove the above-mentioned impurity gas from the commercially available inert gas, the following discharge and removal means are provided in the inert gas introduction path. As a method of discharging oxygen molecules in an inert gas, a method of removing other substances by combustion, a method of forcibly excluding only oxygen molecules in the gas, a method of interrupting the flow of oxygen molecules in the gas, etc. Various methods are possible. The most effective method among them is a method of forcibly eliminating only oxygen molecules in the gas. Specifically, for example, stabilized zirconia _{(CaO-ZrO 2, Y 2} 0 3 -ZrO 2, ThO 2 -Z
rO ₂ etc.) is used to remove only oxygen molecules. Stabilized zirconia has the property of becoming an oxygen ion conductor (oxygen ion transport number becomes almost 1) at high temperature (700 ° C or higher), and the potential difference can be obtained by making a difference in oxygen concentration through the stabilized zirconia. As a result, it will function as an oxygen concentration battery (oxygen sensor). By forcibly applying the opposite potential to this potential,
The pump plays a role of discharging oxygen molecules from the lower oxygen concentration to the higher oxygen concentration. By using this property, a trace amount of oxygen in the inert gas can be efficiently removed. By this method, the oxygen partial pressure in a commercially available inert gas can be made 1 × 10 ⁻¹⁰ atm or less, so that the influence of oxygen absorption loss on vacuum ultraviolet light can be eliminated.

Next, there are steam and carbon dioxide, and synthetic zeolite or activated alumina is a substance which selectively and efficiently adsorbs them. Therefore, by inserting these into the inert gas introduction path, it is possible to remove water vapor and carbon dioxide from the inert gas to be replaced. Since carbon monoxide can be converted to carbon dioxide by oxidation, it can be similarly removed by the above method.

The specific role of each part is as follows. (1) A combustible gas such as methane or carbon monoxide is reacted with oxygen in a furnace at 700 ° C. (2) Oxygen pump made of stabilized zirconia removes residual oxygen that did not react in (1). (3) Using synthetic zeolite or activated alumina, water vapor and carbon dioxide generated as a result of the combustion reaction in (1) or contained as an impurity gas in the inert gas are removed.

In this way, the impurity gas component that absorbs vacuum ultraviolet light can be removed. As a filter, a method using a polytetrafluoroethylene laminated microfiltration membrane capable of capturing particles of about 0.01 μm is effective for removing fine particles from the inert gas introduction path. However, considering the pressure resistance of the filter, the pressure loss of the exhaust system and the maintenance, it is desirable to use a charging filter in the exhaust path. In particular, if a honeycomb-shaped or mesh-shaped electrode is used, oil mist as well as fine particles such as dust can be effectively captured without these problems.

Hereinafter, the present invention will be described in more detail by way of examples, but the present invention is not limited to these.

[0023]

EXAMPLES The conventional and the vacuum ultraviolet spectrophotometers of the present invention were used to compare and measure the transmittances from 100 nm to 240 nm.
FIG. 1 shows a schematic view of an optical device according to the present invention. The measurement of the vacuum ultraviolet region transmittance was performed as follows using the single beam method. (1) Inject vacuum ultraviolet light from a deuterium lamp as a light source into a spectroscope (2) Irradiate the sample with dispersed vacuum ultraviolet light (3) Convert the transmitted light into visible light with a scintillator (sodium salicylate) (4) The transmitted light intensity was converted into an electric signal by a photomultiplier tube. The electric signal was subjected to arithmetic processing using the following formula 1 to obtain a vacuum ultraviolet region transmittance. T = I / I ₀ = (1−R) ² · exp (−a · t) Equation 1 Here, T: transmittance I, I ₀ : transmission and incident intensity R: light with respect to sample surface Reflectance at normal incidence a: Sample absorption coefficient t: Sample thickness At this time, in order to perform highly accurate measurement, the incident light intensity (REF measurement) is measured by the transmitted light intensity (SAMPLE measurement). ) Before and after. The incident light intensity was measured twice
This is because the drift amount of the light source is corrected by averaging.

A synthetic quartz glass produced by a flame hydrolysis method which does not have absorption due to impurities and structural defects was used as a measurement sample in the vacuum ultraviolet region, and the measurement conditions shown in Table 1 were used.

[0025]

[Table 1]

No. For No. 1, the vacuum was evacuated by a combination of an ordinary oil rotary vacuum pump and a turbo molecular pump, and the degree of vacuum in the chamber was set to about 10 ⁻⁵ Torr and measured. The measurement result of the vacuum ultraviolet transmittance is 2 as shown in Fig. 2-c.
Absorption due to contaminants occurred near 00 nm. Further, when the measurement was continued by such a method, deterioration of the optical element was caused and stray light increased.

No. In No. 2, the argon gas supplied from the cylinder was measured as it was introduced and purged into the chamber. The partial pressure of carbon dioxide in this case is 1
× 10 ^-5 atm, oxygen partial pressure 1 × 10 ^-4 atm, water vapor partial pressure 10 ^-5 atm, carbon monoxide partial pressure 1 × 10 ^-4
It was atm. In this case, 200n as shown in Figure 2-b.
Absorption by contaminants near m was not observed, but the intensity of incident light and transmitted light could not be obtained due to absorption of impurity gas such as oxygen contained in argon gas, and measurement at 185 nm or less could not be performed.

No. No. 3, the argon gas supplied from the cylinder was passed through an oxygen pump heated to 700 ° C or higher,
Furthermore, the measurement was performed while introducing and purging the gas in the chamber using the gas that passed through the synthetic zeolite. At this time, the partial pressure of carbon dioxide in the argon gas is 1 × 10 ^-8 at
m, oxygen partial pressure is 1 × 10 ^-17 atm, water vapor partial pressure is 1
× 10 ^-6 atm, carbon monoxide partial pressure is 1 × 10 ^-7 atm
Met.

In this case, as shown in FIG. 2-a, absorption by contaminants in the vicinity of 200 nm did not occur, and there was no problem in measurement at 185 nm or less. No. For No. 4, after vacuum evacuation was performed by a combination of a normal rotary pump and a turbo molecular pump, the argon gas supplied from the cylinder was introduced into the chamber as it was, and after replacement, measurement was performed.

In this case, as shown in FIG. 2D, absorption by contaminants occurred near 200 nm, and in addition, measurement at 185 nm or less could not be performed. No. No. 5 was equipped with a filter and a pollution preventive means by synthetic zeolite in the exhaust path, and was evacuated by an oil-free pump. The same operation as in 3 was performed. At this time, the partial pressure of carbon dioxide in the argon gas is 1 × 10 ⁻⁸ atm, the partial pressure of oxygen is 1 × 10 ⁻¹⁷ atm, and the partial pressure of water vapor is 1 × 10 ⁻⁶ a.
tm, the partial pressure of carbon monoxide was 1 × 10 ⁻⁷ atm.

In this case, replacement with argon gas was carried out promptly, and no contamination by vacuum exhaust was observed. The result is also No. It was equivalent to 3.

[0032]

As described above, according to the present invention, it is possible to prevent deterioration of the characteristics of an optical device used in the vacuum ultraviolet region and to use it stably without being affected by various pollutants. By using this optical device, a highly accurate optical device without a decrease in the amount of vacuum ultraviolet light was obtained.

[Brief description of drawings]

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

FIG. 2 is a measurement result by a vacuum ultraviolet spectrophotometer shown in the example.

FIG. 3 is an enlarged view of a range of 170 to 220 nm in FIG.

[Explanation of symbols]

 21 ... Oil rotary vacuum pump 22 ... Turbo molecular pump 23 ... Electrode application part 24 ... Adsorbent filling part 25 ... Filter insertion part 26 ... Cold trap 27 ... Oxygen pump 28 ... Heating furnace 29 ... Chamber and spectroscope 30 ... Gas outlet 31 ... Gas inlet 32 ... Leakage 33 ... Lamp 34 ... Lens 35 ... Grating 36 ... Slit 37 ... Sample 38 ... Detector

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Office reference number FI technical display location H01L 21/205

Claims (13)

[Claims] 1. An optical device used in a vacuum ultraviolet region having a chamber, an inert gas introduction path and an exhaust path provided outside the chamber, and an optical system provided inside the chamber, wherein the inside of the chamber contains impurities. An optical device which is replaced by an inert gas containing no gas. 2. An optical device used in the vacuum ultraviolet region, which comprises a chamber, an inert gas introduction path and an exhaust path provided outside the chamber, and an optical system provided inside the chamber, and is inert inside the chamber. The partial pressure of carbon dioxide in the inert gas when substituting with gas is 1 × 10 ⁻⁷ at
An optical device characterized by being m or less. 3. An optical device used in a vacuum ultraviolet region having a chamber, an inert gas introduction path and an exhaust path provided outside the chamber, and an optical system provided inside the chamber, wherein the inside of the chamber is inert. An optical device having an oxygen partial pressure in the inert gas of 2 × 10 ⁻⁶ atm or less when the gas is replaced. 4. An optical device used in a vacuum ultraviolet region having a chamber, an inert gas introduction path and an exhaust path provided outside the chamber, and an optical system provided inside the chamber, wherein the inside of the chamber is inert. An optical device characterized in that the partial pressure of water vapor in the inert gas when substituting with gas is 5 × 10 ⁻⁶ atm or less. 5. An optical device used in a vacuum ultraviolet region having a chamber, an inert gas introduction path and an exhaust path provided outside the chamber, and an optical system provided inside the chamber, wherein the inside of the chamber is inert. The partial pressure of carbon monoxide in the inert gas when replacing with gas is 1 × 10 ⁻⁵ at
An optical device characterized by being m or less. 6. The optical device according to claim 1, wherein a wavelength range used by the optical system is 100 nm or more and 220 nm or less. 7. An optical device according to claim 1, wherein the inert gas is argon. 8. The optical device according to claim 1, wherein means for discharging and removing an impurity gas is provided in the inert gas introduction path. 9. An optical device, wherein a stabilized zirconia oxygen pump is used as the means for discharging the impurity gas according to claim 8. 10. An optical device, characterized in that synthetic zeolite or activated alumina is used for the means for removing the impurity gas according to claim 8. 11. The optical device according to claim 1, wherein a stabilized zirconia oxygen pump is installed in the inert gas introduction path, and synthetic zeolite or activated alumina is installed between the oxygen pump and the chamber. An optical device characterized by. 12. The optical device according to claim 1, wherein a means for removing contaminants is provided in the inert gas introduction path. 13. An optical device, wherein a charging filter is used as the means for removing contaminants according to claim 12.