JP2915385B1 - Short arc mercury lamp - Google Patents

Abstract

A short arc mercury lamp that has high luminous efficiency and suppresses bright spot movement near the tip of a cathode, suppresses flicker of irradiance, and enhances arc stability in response to a demand for an increase in the amount of radiation of a light source. To provide. SOLUTION: In a short arc type mercury lamp in which mercury and a rare gas are sealed, the rare gas is at least Ar and K
r, and the mixed gas filling pressure of Ar and Kr is 1.0 to
8.0 atm, and the current density at the tip of the cathode is 10 to 3
It is a short arc mercury lamp of 12 A / mm ² . Further, the lamp is turned on with the anode facing upward.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a short arc type mercury lamp having high light-collecting efficiency and high light stability used in a semiconductor exposure apparatus.

[0002]

2. Description of the Related Art In recent years, a short arc type mercury lamp which emits ultraviolet light having a center wavelength of 365 nm (hereinafter referred to as i-line) has been used for an exposure step in a semiconductor manufacturing process. The degree of integration of semiconductor integrated circuits is increasing year by year, and accordingly, the demand for the resolution at the time of exposure is also increasing. Further, due to the increase in the diameter of the wafer, the exposure area is increased, or the amount of ultraviolet light emitted from the light source is required to be increased by a modified illumination technique used for achieving high resolution.

[0003] Furthermore, huge capital investment is required to make a semiconductor manufacturing line, and in order to recover the funds,
It is also required to increase the throughput, which is an index indicating the output per unit time of the product, and therefore, the exposure light source is required to have higher luminous efficiency and light collection efficiency.

Conventionally, in a short arc type mercury lamp,
Xe is usually enclosed as a buffer gas in order to improve the starting characteristics of the lamp and to keep the gas and the arc tube warm. It has also been proposed to enclose a rare gas other than Xe at a pressure of less than 10 atm as disclosed in, for example, JP-A-54-086979. However, these rare gases are often sealed as a starting gas for facilitating the start of discharge, and the difference in i-line output characteristics between these gas types is not sufficiently known.

[0005] In a commercially available short arc type mercury lamp for semiconductor exposure, A is a rare gas other than Xe.
r and Kr are hardly used, and even if they are used, 1.
There is only one that is sealed from less than 0 atm to a sufficient number of atm.

As a result of diligent research by the present inventors, it has been found that in a lamp in which Xe is sealed as a buffer gas, if Xe is sealed at 8.0 atm or more, the i-line spectrum width radiated from the lamp is broadened and the resolution of exposure is reduced. Was.

[0007] In a lamp in which Ar or Kr is sealed as a buffer gas, the arc moves sharply near the tip of the cathode as the lamp current increases, and the luminance fluctuates greatly. I also found it to cause.

[0008]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a short arc mercury lamp having a high luminous efficiency, which meets the demand for increasing the radiation amount of a light source as described above, and to provide a cathode tip. The object is to suppress the movement of the bright spot in the vicinity, suppress the flicker of the irradiance, and increase the arc stability.

[0009]

Means for Solving the Problems In order to solve the above problems, as in the invention according to claim 1, a cathode and an anode are arranged in an arc tube so as to face each other, and mercury and a rare gas are disposed in the arc tube. In the short arc type mercury lamp in which is sealed, at least Ar and Kr are sealed, and the total sealing pressure of the Ar and Kr at room temperature is 1.0 to 8.0 atm. Assuming that the maximum cross-sectional area of the cathode from the extreme end of the cathode to the length of 0.5 mm on the cathode body side is S (mm ² ) and the supply current to the lamp is I (A), 10 ≦ I / A short arc type mercury lamp, wherein S (A / mm ² ) ≦ 234 .

Alternatively, there is provided a short arc type mercury lamp according to claim 1, which is vertically lit with the anode positioned upward.

FIG. 5 is a schematic diagram showing the shape of the arc discharge at the tip of the cathode. The state where the arc spreads between the cathode 2 and the anode 3 is shown. As described above, the maximum cross-sectional area of the cathode between the front end of the cathode 2 and the length of 0.5 mm on the side of the cathode body is specified. However, in a short arc type mercury lamp, the arc region 5 generated between the electrodes is usually As shown in FIG. 5, the arc is seen from the tip of the cathode to the body, and the area where the arc covers the cathode 2 is the area between the front end of the cathode 2 and a length of about 0.5 mm on the cathode body side. . This is the cathode tip discharge region 4. Therefore, the tip of the cathode functioning effectively at the time of discharge is 0.5 0.5 from the tip to the cathode body.
mm, the maximum cross-sectional area of the cathode in this range is regarded as the effective tip cross-sectional area of the cathode, and the diameter of the maximum cross-section is defined as the effective tip diameter of the cathode.

When Ar and Kr are used as the buffer gas, these gases have a higher heat transfer coefficient than the Xe gas, so that the temperature of the gas around the arc rapidly decreases, and therefore, it is considered that the arc contracts. Can be That is, due to this arc contraction, the radiance is higher than that of a lamp using Xe as a buffer gas, and the lamp becomes closer to a point light source. Therefore, it is considered that the light collection efficiency of the light collecting mirror is increased, and as a result, the irradiance on the reticle surface is increased.

It is considered that an arc which has been self-contracted by a magnetic field generated by an electric current in the vicinity of the cathode tends to spread rapidly due to light atoms, causing arc instability. Then, as the current density decreases, the self-magnetic field decreases, the degree of self-shrinkage of the arc also decreases, and the arc is considered to move in a stable direction.

[0014]

Next, the present invention will be described with reference to the drawings. FIG. 1 is a sectional view of an embodiment of the short arc type mercury lamp of the present invention. A cathode 2 and an anode 3 are arranged opposite to each other in an arc tube 1 made of quartz, and the respective electrodes are connected to a sealing portion 6 via internal lead members 12 and 13.
7 are connected to the foil portions 8 and 9 respectively. External lead members 10 and 11 are connected to the foil portions 8 and 9, respectively.

<Example 1> A specific experimental example of the present invention will be described. In a substantially spherical quartz arc tube 1 having an outer diameter of about 55 mm, an anode 3 made of tungsten and having a diameter of 20 mm and a cathode 2 made of tungsten containing about 2 wt% of thorium oxide and having an effective tip diameter of 1.0 mm are placed between the electrodes. The lamps were placed facing each other at 4.0 mm, and 4.5 mg / cc of mercury was enclosed per unit volume in the lamp. The lamp was turned on by a constant power supply at an input of about 2100 W, and was in a posture with the cathode facing upward. FIG. 2 shows a sectional view of the cathode shape.

A lamp in which Xe was sealed at 2 atm at room temperature was manufactured and used as a reference lamp A for evaluating the present invention. Except for the filling gas, all specifications were the same, and five types of lamps (BF) filled with a mixed gas of Ar and Kr were produced. further,
Two types of lamps (GH) in which Xe was added to Ar and Kr were produced.

The i-line irradiance of the lamp was measured by the optical system shown in FIG. That is, the light emitted from the lamp 14 passes through the elliptical mirror 15 and the first plane reflecting mirror 16, reaches the collimating lens 17, the band-pass filter 18 having a center wavelength of 365 nm and a bandwidth of 10 nm, and the integrator lens 1
9, the light is reflected by the second plane reflecting mirror 21, passes through the condenser lens 22, and reaches the reticle surface 23. Then, a silicon photodiode detector 24 was arranged on the reticle surface 23. The position of the detector 24 was always fixed, and each lamp was turned on to measure the irradiance of the i-line. FIG. 4 shows the results.

Here, the measurement error of the irradiance of light is generally said to be 1 to 2%, and if it exceeds 4%, the throughput in the exposure step of the semiconductor manufacturing process is clearly improved. Accordingly, when the relative i-line irradiance increased by 4% or more compared to the reference lamp A, it was considered that the effect of the mixed gas of the Ar gas and the Kr gas was effective.

At room temperature, Ar1.5atm and Kr1.5at
m and Xe at 2.0 at
Comparing with lamp A in which only m is enclosed, when lamp D is mounted on an exposure machine and used, i
The UV irradiance of the line was increased about 10% over lamp A. However, in the lamp E sealed in the arc tube at a sealed pressure of a mixed gas of Ar5 atm and Kr5 atm of 10 atm at room temperature, the i-line irradiance increased by 18%, but the spectral width of the i-line was widened and the resolution in exposure was lowered. .
As described above, in the experiment using the lamp fixture, it was found that the relative i-line irradiance on the reticle surface was effectively improved when a mixed gas of Ar and Kr was sealed at 1 to 8 atm at room temperature.

Further, the charging pressure of the mixed gas of Ar and Kr is 1.
If the value is from 0 to 8.0 atm, it is shown that the same effect is obtained. Note that the irradiance of the i-line increases with the increase of the sealing pressure of Xe up to about three times the sealing pressure of the mixed gas of Ar and Kr.
The line irradiance showed a decrease. Therefore, in the mixed gas of Ar, Kr and Xe, the total sealing pressure of Ar and Kr is 1.0 to 8.0 atm, and the sealing pressure of Xe is Ar
And Kr are preferably three times or less the total sealing pressure.

<Embodiment 2> Next, an experiment on arc stability will be described. The amount of mercury charged was 4.5 mg / cc, and the amount of rare gas charged was Ar with the same type of lamp manufactured as a prototype in Example 1.
Lamps MP having 1.5 atm, Kr 1.5 atm, and Xe 0.5 atm with different effective tip diameters of the cathode were prototyped. A constant current power supply was used for lamp lighting.

The measuring method is as follows. Silicon photodiode detector 2 on reticle surface 24 shown in FIG.
4, the maximum value of the output signal is MA,
With the minimum value as MI, the evaluation of arc stability is 2 (MA
−MI) / (MA + MI) × 100%. Normal,
It is said that when the arc stability is up to 5%, unevenness in exposure does not occur during exposure printing. The result is shown in FIG.
7 is shown in FIG. From this result, the cathode tip current density I / S, which is the ratio of the current supplied to the lamp to the effective tip area of the cathode, is 10 to 234 (A /
It was found that the range of mm ² ) was an appropriate condition for arc stability.

Using the lamp M, the lamp N, and the reference lamp A, which are the lamps having the strongest arc stability among the lamps produced in Example 2, the anode was turned on and the arc stability was measured. A constant power source was used as the power source.

From the results shown in FIG. 8, it can be seen that when the lamps M and N in which Ar is filled are turned on with their anodes facing upward, the arc stability is significantly improved. The arc became unstable when the lighting posture was inclined by about 35% or more from the normal direction with respect to the ground. Generally, it is considered that a short arc mercury lamp, which is lit with the anode turned down, raises the coldest point temperature at the lower part of the arc tube and is useful for preventing unvaporized mercury during lighting. However, by applying a heat insulating film or the like on the cathode side of the outer wall of the arc tube, the lighting can be performed with the anode facing upward. As shown here, in the lamps M and N in which Ar and Kr are sealed, the variation in the irradiance of the reticle surface when the lamp is lit with the anode facing upward is 1/3 of that when the lamp is lit with the anode facing down. It was found to be reduced to 1/4.

[0025]

As described in detail above, the short-circuit
In rare-earth mercury lamps, the amount of rare gas enclosed is small.
Both are Ar and Kr, and the total encapsulation of this Ar and Kr
The pressure is 1.0 to 8 atm, the lamp current (I) and the cathode
Ratio I / S to the effective tip area (S) of the234
(A / mm^Two) Can increase the luminous efficiency.
Irradiance of i-line can be increased and arc stability
The degree can be increased. And the increase in the radiation amount of the light source
Providing high-efficiency discharge lamps that meet demands
be able to.

Further, in the short arc type mercury lamp, when the anode is turned on with the anode positioned upward, the fluctuation of the cathode luminescent spot can be suppressed, and the arc stability can be increased.

[Brief description of the drawings]

FIG. 1 is a sectional view of one embodiment of a short arc type mercury lamp of the present invention.

FIG. 2 shows a sectional view of a cathode shape.

FIG. 3 shows the relative i of the short arc mercury lamp of the present invention.
The schematic diagram of the optical system which measured the line intensity is shown.

FIG. 4 shows irradiance by a lamp in which a mixed gas of Ar and Kr is sealed.

FIG. 5 shows a schematic view of the shape of an arc discharge at the tip of an electrode.

FIG. 6 shows experimental results regarding arc stability.

FIG. 7 is a diagram showing a relationship between arc stability and cathode tip current density.

FIG. 8 shows a lighting posture and arc stability.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Arc tube 2 Cathode 3 Anode 4 Cathode tip discharge area 5 Arc area 6 Sealing part 7 Sealing part 8 Foil part 9 Foil part 10 External lead member 11 External lead member 12 Internal lead member 13 Internal lead member 14 Lamp 15 Elliptical mirror Reference Signs List 16 first plane reflecting mirror 17 collimating lens 18 band-pass filter 19 integrator lens 20 aperture 21 second plane reflecting mirror 22 condensing lens 23 reticle surface 24 silicon photodiode detector 25 monitor 26 power supply

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-8-77967 (JP, A) JP-A-2-304857 (JP, A) JP-B-62-2428 (JP, B2) (58) Field (Int.Cl. ⁶ , DB name) H01J 61/88 H01J 61/16 H01J 61/86

Claims (2)

(57) [Claims] 1. A short arc type mercury lamp in which a cathode and an anode are arranged opposite to each other in an arc tube, and mercury and a rare gas are sealed in the arc tube. And the sealing pressure at room temperature of the total of Ar and Kr is 1.0 to 8.
0 atm.
The maximum cross-sectional area of the cathode over a length of 5 mm is S (m
m ² ) and the current supplied to the lamp is I (A), where 10 ≦ I / S (A / mm ² ) ≦ 234 . 2. The short arc type mercury lamp according to claim 1, wherein the lamp is vertically lit with the anode positioned upward.