JP2915368B2 - Short arc mercury lamp - Google Patents

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 mercury lamp, there has been proposed a method of increasing the radiance of the arc by reducing the diameter of the tip of the cathode in order to increase the light collection efficiency. Similarly, it has been proposed to increase radiance by enclosing Ar or Kr as a buffer gas at a pressure of several atmospheres. However, there was no other way to improve the radiance.

It is already known that the radiance is high and the light collection efficiency of the light collecting mirror increases as the light source becomes closer to a linear light source or a point light source. Further, in recent years, with the development of the exposure technique for a large-sized work, the lamp as a light source has been more strictly required to stabilize the irradiance maintenance rate on the reticle surface.

[0006]

An object of the present invention is to provide a short arc type mercury lamp having a high radiance and a high irradiance maintenance rate in response to a demand for an increase in the amount of radiation of a light source as described above. It is to provide.

[0007]

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. Is enclosed in a short arc type mercury lamp, the anode cross-sectional area at a position of 2 mm in the tube axis direction from the tip of the anode is S (mm ² ), and the lamp current is I (A). 0.917 ≦ [(I / 10) ² /
S] ^0.5 ≦ 1.27 (A / mm) is satisfied, and further, tungsten powder is applied to the anode surface from the anode tip region to the anode body, excluding at least the width of 2 mm in the tube axis direction from the anode front end. A short arc type mercury lamp in which a sintered layer is formed.

[0008]

[0009]

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

A specific experimental example of the present invention will be described. An anode having a diameter of 15 mmφ, a tip cone angle of 90 °, an effective tip diameter of 9.0 mm, and a tungsten containing about 2 wt% of thorium oxide is placed in a substantially spherical quartz glass arc tube having an outer diameter of about 55 mm. A cathode having an effective tip diameter of 1.0 mm is disposed to face each other with a distance between the electrodes of 4.0 mm, and mercury is transferred to the arc tube at a rate of 4.5 per unit volume.
A lamp containing mg / cc and containing Xe at 2 atm at room temperature was manufactured, and the lamp was designated as lamp A1 as a reference lamp for evaluating the present invention.

In the present application, the effective tip diameter of each of the cathode and anode means a maximum diameter in a region of an electrode (effective tip region) which is covered with an arc during discharge and functions effectively. In the case of the anode, the diameter is 2 mm from the front end of the anode in the tube axis direction. In the case of the cathode, the maximum diameter is 0.5 mm in the tube axis direction from the front end of the cathode. There are various types of anode shapes, and external views of typical anode shapes are shown in FIGS. 3 (a), 3 (b) and 3 (c), and show the effective anode tip region in each anode shape. FIG. 4 shows the anode effective tip region 4 and the arc image 26.
The positional relationship of is shown.

With the exception of the anode effective tip diameter, the specifications were the same as those of the reference lamp A1. As shown in Table 1, seven types of lamps having different anode effective tip diameters were produced. The lamp was turned on with a constant power source at a power of about 1500 W with the cathode facing up.

[0013]

[Table 1] Prototype lamp used in the experiment

The light collection efficiency of the lamp was measured by the optical system shown in FIG. That is, the light emitted from the discharge lamp 14 passes through the spheroid mirror 15 and the plane reflecting mirror 16, reaches the collimating lens 17, the bandpass filter 18 having a central wavelength of 365 nm and a bandwidth of 10 nm, and the integrator lens 19.
, Is reflected by the plane reflecting mirror 21, passes through the condensing lens 22, and reaches the reticle surface 23. Then, the silicon photodiode detector 23 is placed on the reticle surface 23.
Was placed. The position of the detector 24 was always fixed, and each lamp was turned on to measure the irradiance of the i-line. Lamp A1
Table 2 shows the measurement results of the i-line irradiance from the lamps A2 to A8. Set the i-line irradiance of the reference lamp A1 to 1
, The i-line irradiance of each lamp is represented by a relative value. The voltage was 23.1 V, the current (I) was 65 A, and the same conditions were used for each lamp.

[0015]

[Table 2] Anode effective tip diameter and relative i-line irradiance

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. From this, it was considered that there was an effect when the relative i-line irradiance increased by 4% or more compared to the reference lamp A1. For example, if the anode effective tip diameter is 6.2
mm and the anode effective tip diameter is 9.0 mm.
When compared with the reference lamp A1 described above, when the lamp A6 is mounted on an exposure apparatus and used, the ultraviolet irradiance of i-line on the reticle surface is increased by about 11% as compared with the lamp A1. An increase in the irradiance thus means an increase in the radiance of the lamp. FIG. 7 shows the relationship in Table 2.

Further, in the lamp A8 having a smaller anode effective tip diameter, the i-line ultraviolet irradiance on the reticle surface in the initial stage of lighting increased by about 14% compared with the lamp A1, but the anode tip melted in about 100 hours after lighting. Deformation resulted in significant bulb blackening. Therefore, the lamps of A3 to A7 can be used practically, and the lamp of A8 cannot be used because the irradiance maintenance rate is poor. FIG. 5 shows A1 and A5, A6, A7,
9 shows irradiance maintenance rate curves of five types of lamps A8.

As described above, in the experiment using the lamp fixture, the relationship between the lamp current (I) and the anode sectional area (S) at the position of the anode effective tip diameter is 0.917 ≦ [(I / 10)
² / S] ^0.5 ≤ 1.27 (A / mm)
It was found that reticle surface illuminance was effectively improved.

<Embodiment 2> Lamp A tested in Embodiment 1
1, A5, A6, A7, A8, and six types of lamps having the same shape specifications, and at least the anode tip region excluding a width of 2 mm in the anode axial direction from the anode tip. The i-line irradiance maintenance ratio after lighting for 750 hours on five lamps having a sintered layer of tungsten powder formed on the anode surface over the part was examined. The results are shown in Table 3. The lamps on which the sintered layer of the tungsten powder was formed were designated as lamps B1, B5, B6, B7 and B8.

[0020]

Table 3 Relative i-ray irradiance maintenance ratio of lamps with and without a sintered layer of tungsten powder formed on the anode

The sintering of tungsten powder on the anode surface
It went as follows. Tungsten powder having an average particle size of 5 μm was mixed with butyl acetate and nitrocellulose, mixed well, and then applied to the anode with a brush or the like. The coated area is the anode surface from the anode tip area to the anode body excluding the width of 2 mm in the anode axis direction from the tip of the anode. And about 2
A sintering treatment was performed in a vacuum high-temperature furnace at 000 ° C. for about 2 hours. The thickness of the tungsten powder sintered layer is not particularly limited, but is, for example, about 1 to 10 μm.

From the results in Table 3, it can be seen that sintering tungsten powder on the anode surface improves the irradiance maintenance rate while maintaining high radiance as compared to a lamp having an anode that does not form sintered tungsten. I understand. FIGS. 5 and 6 show the relative i-line irradiance maintenance rates of the lamp shown in Table 3 in which the sintered layer of tungsten powder was not formed on the anode and the lamp in which the sintered layer was formed.

[0023]

As described above, the short arc type mercury lamp of the present invention has an anode sectional area of S (mm ² ) and a lamp current of I (A) at a position 2 mm in the tube axis direction from the tip of the anode. ), I and S are 0.917 ≦ [(I / 1
0) ² / S] ^0.5 ≦ 1.27 (A / mm) By setting the value in a range satisfying the relational expression, the illuminance on the reticle surface is effectively improved.

Further, 2 m from the tip of the anode to the anode axis direction
By sintering tungsten powder on the anode surface from the anode tip region to the anode body except for the width of m, the irradiance maintenance ratio is improved while maintaining high radiance.

[Brief description of the drawings]

FIG. 1 shows an external view of a short arc type mercury lamp according to an embodiment of the present invention.

FIG. 2 is a schematic view of an optical system for measuring the relative i-line intensity of the short arc type mercury lamp of the present invention.

FIG. 3 shows an external view of a typical anode shape of the short arc type mercury lamp of the present invention.

FIG. 4 shows the positional relationship between the anode effective tip region and the arc image of the short arc type mercury lamp of the present invention.

FIG. 5 shows the relationship between the reticle surface irradiance maintenance ratio of each prototype lamp having a different effective anode tip diameter according to the present invention.

FIG. 6 is a reticle surface irradiance maintenance ratio of a trial lamp in which a sintered layer of tungsten powder is formed on the anode surface from the anode tip region to the anode body in each of the trial lamps according to the present invention having different anode effective tip diameters. Shows the relationship.

FIG. 7 shows the reticle surface illuminance with respect to the square root of 1/10 of the current value per anode cross-sectional area at the position of the anode effective tip diameter in each of the prototype lamps having different anode effective tip diameters according to the present invention. The relationship of the increase rate is shown.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Arc tube 2 Cathode 3 Anode 4 Anode effective tip area 5 Area for forming sintered layer of tungsten powder 6 Sealing section 7 Sealing section 8 Foil section 9 Foil section 10 External lead member 11 External lead member 12 Internal lead member 13 Inside Lead member 14 Discharge lamp 15 Elliptical mirror 16 First plane reflecting mirror 17 Collimate lens 18 Band pass filter 19 Integrator lens 20 Aperture 21 Second plane reflecting mirror 22 Condensed lens 23 Reticle surface 24 Silicon photodiode detector 25 Monitor 26 Arc image

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-9-115479 (JP, A) JP-A-3-274648 (JP, A) JP-A-2-304857 (JP, A) 127025 (JP, U) (58) Field surveyed (Int. Cl. ⁶ , DB name) H01J 61/073 H01J 61/86 H01J 61/88

Claims (1)

(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. Where S (mm ² ) is the cross-sectional area of the anode and I (A) is the lamp current at the position
And S are 0.917 ≦ [(I / 10) ² / S] ^0.5 ≦ 1.2
7 (A / mm), and a sintered layer of tungsten powder is formed on the anode surface from the anode tip region to the anode body, excluding at least a width of 2 mm in the tube axis direction from the tip of the anode. A short arc type mercury lamp characterized by being formed.