JPH0535688B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION "Field of Industrial Application" The present invention is applicable to quartz glass lenses used in laser stepper devices, mirrors and lenses used in high-output laser oscillation devices, etc. with a diameter of approximately 400 nm or less, preferably approximately 300 nm or less. The present invention relates to an optical quartz glass member used in a specific light wavelength range.

"Conventional technology" The integration of LSIs has been steadily increasing year by year, and with this, the ring graphing equipment that draws integrated circuit patterns is required to draw finer pattern widths. Step-and-repeat projection exposure equipment (stepper) is currently attracting attention as a phosphorography equipment that realizes drawing because it can provide a relatively high-intensity light source and high-performance projection lenses have been developed. There is.

However, the biggest drawback of the ring graphite system using such a stepper is that the exposure wavelength is large, and the resolution is limited by diffraction, but the solution to this problem is to increase the numerical aperture of the projection lens and shorten the wavelength. .

However, when increasing the numerical aperture of a projection lens, the depth of focus inevitably becomes shallower geometrically.
If currently used ultraviolet light in the G-line wavelength range (436 nm) is used as a light source, it will be extremely difficult to form a pattern width of 1 μm or less, which is required for the production of 4 Mbitt or 16 Mbitt DRAM, which is currently under development. It becomes difficult.

On the other hand, when using ultraviolet rays of 400 nm or less in order to shorten the wavelength, with ordinary optical glass, the light transmittance rapidly decreases and begins to be absorbed from around 365 nm, and the absorbed ultraviolet rays are absorbed by the lens. It increases the temperature and disrupts the focal position and other performance.

For this reason, it is necessary to select quartz glass as a projection lens material that does not absorb even in the ultraviolet region of 350 to 300 nm or less, but when lenses are manufactured using such quartz glass, aberration correction, especially chromatic aberration correction, is extremely difficult. It becomes difficult.

Therefore, in recent years, in order to use the quartz glass lens as a projection lens and eliminate the need for chromatic aberration correction,
A stepper device has been developed that combines a light source with a laser oscillator that can emit ultraviolet light in a specific wavelength range.

``Problems to be solved by the invention'' At present, as light sources used in such stepper devices,
In order to enable shorter wavelengths, KRF lasers with a wavelength of around 250 nm and ArF lasers with a wavelength of around 190 nm are attracting attention, but when using such short wavelength light sources in the far ultraviolet region, Even if a quartz glass lens, for example, is used as a projection lens, the following problems still occur.

In other words, when using a light source in the short wavelength range as described above, even if the lens is manufactured using quartz glass, the light transmittance will decrease due to the presence of impurities mixed inside, and the lens will be damaged due to light absorption. Due to the rise in internal temperature, the focus position is slightly distorted, and 0.8
It becomes extremely difficult to form fine patterns of ~0.5 μm or less.

In addition, in the stepper device described above, in order to realize even finer patterns, the numerical aperture is increased in addition to the shortening of the wavelength, and the collimated light source is moved in a direction perpendicular to the optical axis using a scan mirror. However, with existing quartz glass, when trying to form a light image at a position off the optical axis, in-plane distortion occurs, making it even more difficult to form the fine pattern. It is becoming.

In view of such prior art, the present invention is intended to be used in quartz glass members for stepper lenses and other specific light wavelength regions, which makes it possible to form fine patterns of 0.8 to 0.5 μm or less without causing the above-mentioned thermal distortion or in-plane distortion. The purpose of the present invention is to provide a quartz glass member for optical use.

“Means for Solving the Problems” In order to achieve the technical problems, the present invention
In optical quartz glass members used in specific wavelength ranges such as laser light sources of 400 nm or less, preferably 300 nm or less, synthetic quartz glass is used as the starting material, and striae are not observed from any of the three coordinate directions. Furthermore, substantially no fluorescence is generated by irradiation with a low-pressure mercury lamp having a wavelength of 254 nm, and the refractive index difference △n is 5×10 ^-6 at least in the area through which light is transmitted.
We propose an optical quartz glass member characterized by the following homogeneity.

Such a glass member is obtained by performing striae removal treatment on a synthetic quartz glass base material obtained by hydrolyzing and melting a high-purity silicon compound in an oxyhydrogen flame, and then subjecting it to heat treatment. I can do things.

Here, striae refers to growth fringes with different refractive index distributions that occur when crystal or synthetic quartz glass is melted, grown, and solidified, and such striae can be easily observed using, for example, an interferometer or a strain tester. I can do things.

In addition, no fluorescence occurs when irradiated with a low-pressure mercury lamp for at least 10 minutes in a dark room.
This means that no fluorescence is visually observed.

"Effects of the Invention" The present invention has achieved a high level of light transmittance to the extent that no fluorescence is generated when irradiated with a low-pressure mercury lamp, thereby minimizing the increase in internal temperature caused by the light absorption of the light source used in the specific wavelength range. In addition to being able to hold it down, even if the internal temperature rises slightly,
Since striae are removed from any of the three coordinate directions, there is less risk of thermal distortion, and as a result, the focal point position and other various performances can be maintained within specified tolerances.

Further, according to the present invention, in order to have a homogeneity of refractive index difference Δn of 5×10 ^-6 or less at least in the area where the light is incident, the collimated light source is moved in a direction perpendicular to the optical axis by a scan mirror. There is no risk of in-plane distortion occurring even when attempting to form a light image by substantially enlarging the light source image.

Furthermore, projection lenses for steppers are generally formed with curved convex or concave lenses, so if striae exists in any of the three coordinate directions, the refractive index and density will differ between the striae and other parts. Therefore, a minute wave phenomenon occurs during precision polishing, causing problems in terms of surface smoothness and uniformity of wall thickness, which also affects variations in refractive index and other various performances. However, in the present invention, since striae are removed from any of the three coordinate directions, the above problem is solved.

Therefore, by using the projection lens for a stepper manufactured according to the present invention, when an integrated circuit pattern is drawn using a laser that oscillates light in a specific wavelength range in the short-wavelength deep ultraviolet region as a light source, the light generated within the projection lens. Since thermal strain and surface strain are removed, fine integrated circuit patterns can be drawn.

The present invention can also be used as a material for a deflection mirror or lens member of an oscillation device that outputs a laser beam in a specific optical wavelength region of about 300 nm or less, other than the stepper projection lens described above.

"Embodiments" Hereinafter, preferred embodiments of the present invention will be described in detail by way of example with reference to the drawings. However, the dimensions, materials, shapes, relative positions, etc. of the components described in this example are as follows, unless otherwise specified.
This is not intended to limit the scope of the invention, but is merely an illustrative example.

First, the manufacturing procedure of the optical quartz glass member according to the present invention will be explained based on FIG.

After producing a quartz glass ingot 1 by hydrolyzing and melting high-purity silicon tetrachloride that does not contain impurity elements such as metal elements in an oxyhydrogen flame by a direct flame method, the ingot 1 is heated to a temperature above its softening point. The heating and cooling operations are repeated, and the direction of softening due to its own weight is changed each time it is heated to remove internal striae. That is, by repeating this operation, striae in the three coordinate directions of the quartz glass lump are removed.

Next, the quartz glass block from which the striae have been removed in this way is heated at a temperature of around 1000°C to obtain a quartz glass block 2 from which distortion has been removed, and this is cut into a size according to the dimensions of the quartz glass block for optical use. A glass member 3 is manufactured.

This quartz glass member 3 is
Irradiated with a 250nm KrF laser and a low-pressure mercury lamp with a corresponding wavelength of 254nm for 10 minutes, no fluorescence was visually observed, and when the refractive index difference △n was examined using a two-beam interference refractometer, the result was 2.5×10 It was confirmed that the homogeneity was ^-6 .

An integrated circuit pattern having a pattern width of 0.5 μm or less could be obtained by incorporating a stepper projection lens made from a quartz glass member having such physical properties into a conventionally known stepper device shown in FIG. 2 and drawing the image.

In the figure, 10 is a KrF excimer laser that oscillates a laser beam, 11 is a deflection mirror, 12 is an illumination optical system, 13 is a 10x reticle, 14 is a projection lens according to the present invention, 15 is a quartz window, and 16 is a It is a Si substrate.

Therefore, according to this embodiment, the effects of the present invention can be smoothly achieved.

[Brief explanation of the drawing]

Fig. 1 is a schematic diagram showing the manufacturing procedure of an optical quartz glass member according to an embodiment of the present invention, and Fig. 2 shows a stepper device incorporating a projection lens manufactured using such an optical quartz glass member. It is a schematic diagram.

Claims (1)

[Claims] 1. In an optical quartz glass member used in a specific wavelength range of approximately 400 nm or less, a high purity silicon compound is hydrolyzed in an oxyhydrogen flame,
Synthetic quartz glass obtained by melting was used as the starting material, no striae was observed from any of the three coordinate directions, and no fluorescence was substantially generated when irradiated with a low-pressure mercury lamp having a wavelength of 254 nm. Furthermore, there is a refractive index difference Δn at least in the area through which light is transmitted.
A quartz glass member for optical use, characterized by having a homogeneity of 5×10 ^-6 or less.