JP4400136B2 - Short arc type mercury vapor discharge lamp - Google Patents

Description

  The present invention relates to a short arc type metal mercury vapor discharge lamp, and more particularly to a short arc type mercury vapor discharge lamp used for ultraviolet irradiation with a wavelength of 365 nm.

  In a photolithography process (hereinafter referred to as an exposure process) for manufacturing a semiconductor, a short arc type mercury vapor discharge lamp is used as a light source, and ultraviolet light having a wavelength of 365 nm emitted from the lamp is used. In this exposure process, recently, a larger amount of ultraviolet rays has been required in order to increase the processing capacity per unit time. In order to meet this demand, the input to the lamp is increased, or xenon gas (Xe) is not used as a buffer gas, but krypton gas (Kr) or argon gas (Ar) is substituted, and several hundred thousand Pa is enclosed in terms of room temperature. In this way, the radiation efficiency is increased, and the amount of radiation with a wavelength of 365 nm from the lamp is increased.

  On the other hand, these rare gases naturally generate vacuum ultraviolet light such as resonance lines and excimer light under arc discharge, and the energy per one photon thereof is Xe <Kr <Ar <Ne (neon) <He (helium). ) In order. Now, under the vacuum ultraviolet light, when the temperature of the quartz glass of the bulb material becomes high, the quartz glass bulb is deteriorated. In order to prevent the deterioration of the quartz glass bulb, quartz glass containing OH groups is used. It can be seen that the temperature of the quartz glass bulb has a great influence on the deterioration rate of the quartz glass bulb.

In Patent Document 1, at least one rare gas of argon, krypton, and xenon is enclosed in an ultraviolet lamp corresponding to the short arc type mercury vapor discharge lamp of the present application in an amount of 0.1 × 10 ⁵ Pa or more in terms of 300K in terms of total pressure. A technique for defining the OH group concentration at a depth of 200 μm from the surface of the discharge vessel is disclosed.

Ultraviolet rays having a wavelength of 250 nm or less are also emitted from the arc discharge of the short arc type mercury vapor discharge lamp, and these lights cause damage to the optical components of the exposure apparatus and cause corrosion of the apparatus. In order to shield the ultraviolet light having a wavelength of 250 nm or less, the quartz glass bulb is often doped with titanium oxide (TiO ₂ ) as an ultraviolet absorber. For example, Patent Document 2 discloses a short arc type mercury vapor discharge lamp using a discharge tube manufactured from quartz glass doped with titanium oxide. Usually, the weight concentration of titanium oxide to be doped is 100 wtppm in terms of titanium (Ti). However, when such quartz glass doped with titanium oxide is used for the bulb, the degradation of the quartz glass bulb is accelerated. This is considered to be caused by the temperature rise of the glass due to ultraviolet absorption.

Further, as an influence on the temperature rise of the quartz glass bulb, there is heat radiation from the anode. The anode diameter is increased or decreased to lower the temperature at the tip of the anode and prevent the quartz glass bulb from becoming black. However, when the anode is enlarged, the temperature of the tip is lowered, but the temperature of the anode body portion is raised, resulting in an increase in the amount of heat radiation from the anode. This is considered to increase the infrared radiation absorbed by the quartz glass bulb, and as a result, cause the temperature of the quartz glass bulb to rise.
Japanese Patent No. 2891997 JP-A-8-96751

  The problem to be solved by the present invention is to remove radiation of ultraviolet rays having a wavelength of 250 nm or less, emit ultraviolet rays having a wavelength of 365 nm with high efficiency, and suppress deterioration of the quartz glass bulb, thereby maintaining a high irradiance maintenance rate. It is to provide a short arc type mercury lamp having a long lamp life.

We consider the mechanism that the relationship between the thermal radiation from the anode and the surface area of the quartz glass bulb affects the generation and suppression of bulb fogging. When considering the action of the anode, the anode temperature is kept constant at T ₀ for simplicity. The thermal radiation energy E from the anode surface is based on the Stefan-Boltzmann equation,
E = SεσT ₀ ⁴ Here, S is the surface area of the anode, ε is the emissivity, and σ is 5.67 × 10 ⁻⁸ W / m ² / K ⁴ in terms of Stefan-Boltzmann constant. From this equation, the radiant energy from the anode is proportional to its surface area. When the thermal radiation energy from the anode hits the quartz glass bulb, the ratio of the thermal radiation energy per unit surface area received by the quartz glass bulb is obtained by dividing by the surface area of the quartz glass bulb. If the emissivity of the anode surface increases, the radiation energy from the anode surface also increases. Therefore, the energy hitting the quartz glass bulb is also increased.

  On the other hand, the quartz glass bulb member is doped with titanium (Ti) to shield light having a wavelength of 250 nm or less. The quartz glass doped with titanium is exposed to vacuum ultraviolet light from the arc while the lamp is on. And it is imagined that this vacuum ultraviolet light causes the degradation of quartz glass by breaking the titanium oxygen-silicon chain.

  Here, as the heat radiation energy from the anode increases and the temperature of the quartz glass bulb increases, naturally, this reaction rate is considered to increase at an accelerated rate. On the other hand, if an OH group is present as a component to suppress this fogging, it is presumed that it bonds to an unsaturated bond after the chain is broken to alleviate deterioration.

By the way, the present inventors have made various studies as factors affecting the temperature of the quartz glass bulb in the short arc mercury discharge lamp containing the rare gas described above, and titanium oxide (TiO ₂₎ doped into the quartz glass bulb. ), The size of the bulb, and the size of the anode are important factors, and the present invention has been completed by first finding that there is a correlation between them.

In a substantially spherical transparent quartz glass bulb doped with titanium oxide, an anode and a cathode are arranged facing each other, rare gas and mercury are enclosed, and the rare gas to be filled is krypton, argon, neon, or helium. At least one kind of rare gas is selected from the above, and the rare gas is sealed at 1 × 10 ⁵ Pa or more in terms of 25 ° C., and mercury is 0.2 mg / cm ³ to 7 mg / per unit volume of the valve internal volume. In a short arc type mercury vapor discharge lamp enclosed in the range of cm ³ , when the maximum diameter of the anode is D, the length thereof is L, and half of the maximum diameter of the substantially spherical bulb portion is R, 0.24 ≦ ( D × L) / R ² ≦ 1.34, and 5 ≦ N ≦ 60 when the average concentration of titanium oxide (titanium) in the thickness direction of the substantially spherical valve is N (wtppm). Characteristic And Toaku mercury vapor discharge lamp.

  In addition to the above, a short arc type mercury vapor discharge lamp is characterized in that the substantially spherical bulb contains OH groups at a concentration of 50 wtppm to 300 wtppm.

  The concentration of titanium referred to here is the weight ratio of titanium in the quartz glass and is expressed in wtppm. The measurement is performed by dissolving fluorescent X-rays or a sample in boiling acid and subjecting the solution to ICP analysis.

Here, (D × L) / R ² was introduced as a parameter representing the thermal effect of the thermal radiation from the anode surface on the bulb. The reason for adopting this parameter is as follows.
First, it can be seen that the amount of heat energy radiated from the anode surface is proportional to the surface area S from the equation of E = SεσT ₀ ⁴ described above. If the anode is considered to be approximately cylindrical with a diameter D (cm) and a length L (cm), and its surface area is represented by a side area, the side area is given by D × L × π. That is, S≈D × L × π. Part of the thermal energy radiated from this electrode is naturally received by the valve. Therefore, when the bulb is substantially spherical with a maximum radius R (cm), the surface area of the bulb is given by 4π × R ² . Now, the thermal energy from the anode surface received per unit area of the bulb is the energy radiated from the anode divided by the total surface area of the bulb, and calculated as S≈D × L × π,
D × L × π × ε × σ × T a ⁰ 4 / ^4π × ^{R 2.} That is, since it can be said that the valve is heat energy emission intensity E from the anode surface which receives per unit area is proportional to (D × L) / R ^2, was adopted as a parameter in the present invention (D × L) / R ² It is. Thermal energy flows to the valve by an amount corresponding to the area ratio, and contributes to the temperature rise of the valve. Therefore, when (D × L) / R ² becomes smaller, less energy is received per unit area of the heat energy from the electrode, and the influence on the temperature rise of the valve is less. Conversely, (D × L) / R ² When becomes larger, the energy received per unit area of the heat energy from the electrode becomes larger, and the influence on the rise of the valve temperature becomes larger.

Consider i-line (365 nm) radiation from a short arc mercury vapor discharge lamp. If the amount of mercury enclosed is less than 0.1 mg / cm ³ , the required i-line emission intensity cannot be obtained. ^{On the other hand, if} it exceeds 10 mg / cm ³ , the spectrum width of i-line is widened and the exposure resolution is lowered. In order to increase the luminous efficiency of the irradiance of i-line, any gas of Kr, Ar, Ne, He or a mixed gas thereof is used instead of Xe gas. The encapsulated amount necessary to increase the effect is that 1 × 10 ⁵ Pa or more of those mixed or single gas at 25 ° C. is required. If it is less than 1 atmosphere, a significant increase in luminous efficiency cannot be obtained. If it is higher than 8 × 10 ⁵ Pa, the spectrum width of the i-line will be too wide.

  If the titanium concentration is less than 5 wtppm, the transmittance of ultraviolet rays of 250 nm or less increases, and a large amount of ultraviolet rays are transmitted. For this reason, the ultraviolet light shielding effect is not observed, and the optical apparatus is inconvenienced by ultraviolet irradiation. Further, when the titanium concentration exceeds 60 wtppm, the deterioration of the quartz glass bulb is accelerated.

In an approximately spherical transparent quartz glass bulb doped with titanium oxide, the anode and the cathode are arranged facing each other, rare gas and mercury are enclosed, and the rare gas to be enclosed is krypton, argon, neon, helium. at least one kind of noble gas is selected from among, those rare gas is sealed 1 × 10 5 ^Pa or more at 25 ° C. terms, 10 mg / cm ³ mercury from unit volume per 0.2 mg / cm ³ of bulb volume In the lamp in which the maximum diameter of the anode is D (cm), the length is L (cm), and half of the maximum diameter of the bulb substantially spherical portion is R (cm), 0.24 ≦ (D × L) / R ² ≦ 1.34, short arc mercury vapor discharge in which 5 ≦ N ≦ 60, where N (wtppm) is the average titanium concentration in the thickness direction of the substantially spherical valve By using a lamp, the wavelength is 250 nm. Provides a short arc type mercury lamp with high irradiance maintenance rate and long lamp life by removing the ultraviolet radiation below, emitting ultraviolet light with a wavelength of 365 nm with high efficiency, and suppressing the deterioration of the quartz glass bulb can do.

  Further, by including OH groups having a concentration of 50 wtppm to 300 wtppm in the quartz glass bulb, it is possible to provide a short arc type mercury vapor discharge lamp having a higher lamp irradiance and a longer lamp life.

A schematic configuration of the short arc type mercury vapor discharge lamp of the present invention is shown in FIG.
A short arc type mercury vapor discharge lamp 10 has a substantially spherical transparent quartz glass bulb 1 doped with titanium oxide, an anode 2 and a cathode 3 facing each other, and a rare gas and mercury are enclosed, As the rare gas to be filled, at least one kind of rare gas is selected from krypton, argon, neon, or helium, and those rare gases are sealed at 1 × 10 ⁵ Pa or more in terms of 25 ° C., and mercury is contained in the valve volume. per unit volume 0.2 mg / cm ³ from 10 mg / cm ³ of is sealed. Symbol 4 is a sealing part, and symbol 5 is a base. FIG. 2 shows parameters of each part of the short arc type mercury vapor discharge lamp 10. The length R (cm) half of the maximum diameter of the bulb bulb portion of the quartz glass bulb 1, the maximum diameter D (cm) of the anode 2, and the total length L (cm) of the anode 2.

In order to confirm the effect of the present invention, the following evaluation experiment was performed.
Short arc type mercury vapor discharge lamp with parameters of length R (cm) half of the maximum diameter of bulb bulb of quartz glass bulb 1, maximum diameter D (cm) of anode 2, and total length L (cm) of anode 2 11 were produced. The (D × L) / R ² value for each parameter is summarized in the table of FIG.

The lamps having the lamp numbers A1 to A11 were filled with 5 mg / cm ³ mercury per unit volume of the bulb internal volume and argon (Ar) equivalent to 3 × 10 ⁵ Pa at room temperature. When the lamp was turned on, the lamp was lit so that the power consumption of the lamp was 5 kW. A constant power source was used as the power source.

Now, with respect to the lamps of lamp numbers A1 to A11, quartz glass having an OH group concentration of less than 10 ppm, the titanium doping amount is expressed as n (wtppm), and (D × L) / R ² and white cloudiness of the bulb ( The relationship between occurrence of white turbidity was investigated. The cloudiness of the valve was confirmed visually. The results are shown in the table of FIG.

From this evaluation experiment 1, an anode and a cathode are arranged opposite to each other in a substantially spherical transparent quartz glass bulb doped with titanium oxide, and argon and mercury are enclosed. Argon is 1 × 10 in terms of 25 ° C. encapsulated ⁵ Pa or more, in lamps mercury is 10 mg / cm ³ from unit volume per 0.2 mg / cm ³ of bulb volume enclosed, the maximum diameter of the anode D (cm), the length L (cm ), Where R (cm) is a half of the maximum diameter of the substantially spherical bulb portion, 0.24 ≦ (D × L) / R ² ≦ 1.34, and in the thickness direction of the substantially spherical valve When the average concentration of titanium is N (wtppm), if 5 ≦ N ≦ 60, a short arc type mercury vapor discharge lamp having a low lamp turbidity, a high irradiance maintenance rate, and a long lamp life is obtained. I found out that I could do it.

  For lamp numbers A6 and A11, since the bulb diameter was too large, the temperature in the bulb did not rise, mercury was not evaporated, arc instability was caused, and intense illuminance fluctuations were caused. Further, the UV light shielding effect was confirmed by measuring the spectral irradiance with a spectrophotometer to determine whether or not ultraviolet rays having a wavelength of 250 nm or less were emitted from the bulb.

In this evaluation experiment 1, although argon was used as a rare gas, at least one kind of rare gas was selected from argon, krypton, neon, and helium, and the rare gas was converted to 25 ° C. If it is sealed at 1 × 10 ⁵ Pa or more, in addition to obtaining high radiation efficiency of i-line, the influence of thermal radiation from the anode on the bulb is the same, so it is assumed that the same effect is exhibited Is done.

  On the other hand, even with lamp numbers A4, A5, A7, A9, and A10, the lamp is turned on for about 500 hours to about 900 hours, and white cloudiness (white turbidity) has started to occur in the lamp. In order to improve the occurrence of the cloudiness, lamps with lamp number A4 were selected from these lamps as representatives, and only four OH groups (A4a, A4a, A4b, A4c, and A4d) were made as prototypes and their cloudiness generation time was investigated.

  Here, the quartz glass bulb was first mixed with water vapor and sealed, and then left in a high-temperature furnace maintained at 1100 ° C. for a long time, so that a large amount of OH groups were doped in the quartz glass bulb. . Next, while evacuating the inside of the quartz glass bulb, the bulb is exposed to a high temperature atmosphere of about 1100 ° C., and the OH group concentration in the quartz glass bulb is controlled by the exposure time to control the four glass bulbs. Lamps (A4a, A4b, A4c, A4d) were manufactured.

  The results of these lamps using a quartz glass bulb in which the OH group concentration is controlled are shown in the table of FIG. 4. As the OH group concentration becomes higher, the time when white turbidity occurs is 1000 hours, 1300 hours, 1700 hours. It became late. That is, it was found that when the OH group concentrations were 50 wtppm, 120 wtppm, and 300 wtppm, the time until the occurrence of white turbidity was 1000 hours or more, and the occurrence of white turbidity in the valve could be suppressed. However, at 1000 wtppm, the blackening of the inner surface of the bulb progressed rapidly, resulting in a rapid decrease in irradiance in 200 hours. This blackening is thought to be due to the fact that the OH groups in the bulb were released into the lamp as water during the lighting time, reacted with the electrode, tungsten was evaporated, and the evaporated substance adhered to the bulb.

  From this evaluation experiment 2, it has been found that the turbidity of the bulb can be prevented from occurring for 1000 hours or more by including the OH group at a concentration of 50 wtppm to 300 wtppm in the quartz glass bulb.

1 shows the overall configuration of a short arc type mercury vapor discharge lamp according to the present invention. The parameter of each part of the short arc type mercury vapor discharge lamp concerning the present invention is shown. The evaluation experiment result of this invention is represented. The evaluation experiment result of this invention is represented.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Quartz glass bulb 2 Cathode 3 Anode 4 Sealing part 5 Base 10 Short arc type mercury vapor discharge lamp

Claims (2)

In a substantially spherical transparent quartz glass bulb doped with titanium oxide, an anode and a cathode are arranged facing each other, rare gas and mercury are enclosed, and the rare gas to be filled is krypton, argon, neon, or helium. At least one kind of rare gas is selected from the above, and the rare gas is sealed at 1 × 10 ⁵ Pa or more in terms of 25 ° C., and mercury is 0.2 mg / cm ³ to 10 mg / cm per unit volume of the valve internal volume. ^In the short arc type mercury vapor discharge lamp enclosed in the range of ³ ,
When the maximum diameter of the anode is D (cm), its length is L (cm), and half of the maximum diameter of the bulb substantially spherical portion is R (cm),
0.24 ≦ (D × L) / R ² ≦ 1.34
A short arc mercury vapor discharge lamp, wherein 5 ≦ N ≦ 60, where N (wtppm) is the average concentration of titanium in the thickness direction of the substantially spherical bulb. 2. The short arc type mercury vapor discharge lamp according to claim 1, wherein the substantially spherical bulb contains an OH group having a concentration of 50 wtppm to 300 wtppm.

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