JP2639514B2 - Laser lithography equipment - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a laser lithography apparatus, and more particularly to a quartz glass lens for an optical system such as a projection lens or a mirror of a laser oscillated from a specific light wavelength region of about 400 nm or less, preferably about 300 nm or less. The present invention relates to a laser stepper device using the same.

[0002]

2. Description of the Related Art Conventionally, high integration of LSI has been steadily progressing year by year, and a lithography apparatus for writing an integrated circuit pattern has been required to draw a finer pattern width.
A step-and-repeat type projection exposure apparatus is currently used as a lithography apparatus that realizes such fine pattern width drawing in that a relatively high-luminance light source is obtained and a high-performance projection lens is being developed. (Stepper)
Is attracting attention.

The biggest drawback of a lithographic apparatus using such a stepper is that the exposure wavelength is large and the resolution is limited by diffraction, but the solution is to increase the numerical aperture and shorten the wavelength of the projection lens. No.

[0004]

However, when the numerical aperture of the projection lens is increased, the depth of focus inevitably becomes geometrically shallow, and the currently used g-ray wavelength range (436n
In the case where the ultraviolet light of m) is used as a light source, it is extremely difficult to form a pattern width of 1 μm or less, which is required for manufacturing a 4Mbitt or 16Mbitt DRAM which is currently being eagerly developed.

On the other hand, when ultraviolet light of 400 nm or less is used to shorten the wavelength, the wavelength used in ordinary optical glass is
The light transmittance suddenly drops from around 365 nm and starts absorbing,
The absorbed ultraviolet rays increase the lens temperature, and degrade the focal position and other performances.

For this reason, it is necessary to select quartz glass as a projection lens material which does not absorb light even in the ultraviolet region of 350 to 300 nm or less. A stepper device was manufactured by incorporating a lens formed using such quartz glass. If
Aberration correction, especially chromatic aberration correction, becomes extremely difficult.

Therefore, in recent years, a stepper device has been developed in which a light source is combined with a laser oscillator capable of oscillating ultraviolet light in a specific wavelength range in order to eliminate the need for chromatic aberration correction while using the quartz glass lens as a projection lens.

At present, as a light source used in such a stepper device, in order to make it possible to shorten the wavelength, a light source having a wavelength of about 250 nm is used.
rF lasers, and furthermore, ArF lasers with a wavelength of around 190 nm, have attracted attention.However, when such a short-wavelength light source in the deep ultraviolet region is used, even if a quartz glass lens is used as the projection lens, the following still applies. Problems. That is, when the light source in the short wavelength region as described above is used, even if the projection lens is manufactured using quartz glass, the light transmittance is reduced due to the presence of impurities and the like mixed therein, and the light absorption is caused by the light absorption. The focus position was slightly out of order due to the rise of the lens internal temperature,
It becomes extremely difficult to form a fine pattern of 0.5 μm or less.

In the above-mentioned stepper apparatus, in order to realize a further fine patterning, the numerical aperture is increased in conjunction with the shortening of the wavelength, or a collimated light source is orthogonal to the optical axis by a scan mirror. In the projection lens using existing quartz glass, in-plane distortion occurs when trying to form an optical image at a position shifted from the optical axis, It is more difficult to form the fine pattern.

The present invention has been made in view of the above-mentioned prior art, and does not cause thermal distortion or in-plane distortion in the projection lens, and particularly, in the range of 0.8 to 0.5.
It is an object of the present invention to provide a stepper or other laser lithography apparatus capable of forming a fine pattern of μm or less.

[0011]

According to the present invention, there is provided a laser oscillator which oscillates an ultraviolet laser beam having a specific wavelength range of 400 nm or less as a light source, a striae which is not recognized from any of three coordinate directions, and which is 254 nm. without substantially generating fluorescence by irradiation of a low-pressure mercury lamp having a wavelength of, a lens made of a synthetic quartz glass member having a refractive index difference △ n has a 5 × 10 ^-6 or less of homogeneity in yet areas through which light passes Other optical systems, while transmitting or reflecting the laser light by the optical system, 0.8 reticle on a Si substrate via a reticle.
A laser stepper device and other lithography devices characterized in that an integrated circuit pattern having a pattern width of μm or less can be drawn.

In this case, the optical system is formed by using a quartz glass ingot obtained by hydrolyzing and melting a high-purity silicon compound containing no impurity element such as a metal element by a direct flame method as a starting material. It is preferable to use a quartz glass material.

[0013] Stria refers to growth fringes having different refractive index distributions generated when a quartz crystal or a synthetic quartz glass is melt-grown and solidified. Such striae can be easily measured by, for example, an interferometer or a strain tester. Can be observed. In addition, it is said that no fluorescent light is generated substantially by using a low-pressure mercury lamp in a dark room at least.
This means that no fluorescence is observed visually when irradiated for about 10 minutes.

[0014]

According to the present invention, the light transmittance of, for example, a projection lens constituting the optical system is ensured at a high level to the extent that fluorescence is not generated by irradiation with a low-pressure mercury lamp. The rise in internal temperature due to the light absorption of the light source used can be suppressed to a very small extent, and even if the internal temperature rises slightly, striae is removed from any of the three coordinate directions. Distortion is less likely to occur, so that the focal position and other performances can be maintained within a specified accuracy range.

Further, in the projection lens according to the present invention, since the refractive index difference Δn has a homogeneity of 5 × 10 ⁻⁶ or less in at least the area where light is incident, the collimated laser light source is adjusted to the optical axis by the scan mirror. Even if the light source image is moved in the orthogonal direction to substantially enlarge the light source image to form an optical image, there is no possibility that in-plane distortion will occur.

Furthermore, since the projection lens is generally formed of a curved convex or concave lens, if stria exists in any one of the three coordinate directions, the refractive index and the density of the stria and the other portions are reduced. Because of the difference, a fine waving phenomenon occurs during precision polishing, causing problems in terms of surface smoothness and uniformity of wall thickness,
Again, it affects the refractive index variation and other performances. However, in the projection lens of the present invention, since the stria is removed from any of the three coordinate directions, the above problem is solved.

Therefore, according to the present invention, an integrated circuit pattern is formed by using a lithographic apparatus which combines a laser light source oscillating from the oscillator and oscillating a specific wavelength band light in a short ultraviolet ray region and a projection lens having the above-mentioned configuration. Is drawn, thermal distortion and surface distortion generated in the projection lens are removed, so that a fine integrated circuit pattern can be drawn. In particular, the line width of a pattern image formed on a photoresist on a wafer is reduced. Since the thickness can be set to 0.8 μm or less, DRAM of 4 Mbitt or 16 Mbitt can be easily manufactured.

[0018]

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a block diagram showing an embodiment of the present invention; However, unless otherwise specified, the dimensions, materials, shapes, relative arrangements, and the like of the components described in this embodiment are not intended to limit the scope of the present invention, but are merely illustrative examples. Not just. First, a procedure for manufacturing an optical quartz glass member for manufacturing a projection lens, a mirror, and the like used in the present invention will be described with reference to FIG. High-purity silicon tetrachloride that does not contain impurity elements such as metal elements is hydrolyzed and melted in an oxyhydrogen flame by a direct flame method to produce a quartz glass ingot 1, which is then heated to a temperature above its softening point. The cooling operation is repeated, and the direction of softening due to its own weight is changed for each heating to remove internal striae. That is, by repeating this operation, striae of the quartz glass block in the three coordinate directions are removed.

Next, the quartz glass block from which the stria is removed in this manner is heated at a temperature of about 1000 ° C. to obtain a quartz glass block 2 from which the distortion is removed, and this is cut into a size corresponding to the dimensions. The optical quartz glass member 3 is manufactured. This quartz glass member 3 has a wavelength of 250 nm and a wavelength of 254 nm corresponding to a KrF laser in a dark room.
Irradiated with a low-pressure mercury lamp having a wavelength of 10 minutes, but no fluorescence was observed visually, and when the refractive index difference Δn was examined using a two-beam interference refractometer, it was found that the homogeneity was 2.5 × 10 ^-6 The thing was confirmed.

Next, a projection lens and a mirror to be incorporated into the stepper according to the embodiment of the present invention are manufactured from the quartz glass member having such physical properties, and then assembled into the stepper device shown in FIG.

In this figure, reference numeral 10 denotes Kr for oscillating laser light.
F excimer laser oscillator, 11 is a turning mirror, 12 is an illumination optical system, 13 is a 10-fold reticle, 14 is a projection lens made of the quartz glass member, 15 is a quartz window, and 16 is a Si substrate.

According to this embodiment, the KrF laser light oscillated from the KrF laser oscillator 10 is transmitted to the turning mirror 1
1 and 11, the light is incident on the pattern surface on the reticle 4 via the illumination optical system 12, and a pattern image obtained by the incidence is formed on the Si substrate 16 via the projection lens 14 to draw a line width. As a result, an integrated circuit pattern having a pattern width of 0.5 μm or less was obtained.

[0023]

As described above, according to the present invention, no thermal distortion or in-plane distortion occurs in the projection lens,
A stepper or other laser lithography apparatus capable of forming a fine pattern of 0.5 μm or less can be obtained.

[Brief description of the drawings]

FIG. 1 is a schematic view showing a stepper device according to an embodiment of the present invention.

FIG. 2 is a schematic view showing a manufacturing procedure of an optical quartz glass member to be a material for manufacturing a projection lens incorporated in the stepper device.

[Explanation of symbols]

 10 KrF excimer laser oscillator 14 Projection lens 16 Si substrate

Claims (2)

(57) [Claims] 1. A KrF laser having a wavelength of about 250 nm as a light source.
Or a laser oscillator that emits ArF laser light having a wavelength of about 190 nm , and substantially emits fluorescence when irradiated by a low-pressure mercury lamp having a wavelength of 254 nm without striae in any of the three coordinate directions. No, and the refractive index difference Δn is 2.5 × 10
^A lens made of a synthetic quartz glass material having a homogeneity of ^-6 or less, and a laser beam transmitted or reflected by the optical system while passing or reflecting the laser light on a Si substrate via a reticle; A laser lithography apparatus characterized in that an integrated circuit pattern having a pattern width can be drawn. 2. The optical system according to claim 1, wherein the high-purity silicon compound is
2. The laser lithography apparatus according to claim 1, wherein the synthetic lithographic glass material is formed using a quartz glass ingot obtained by hydrolysis and melting as in a direct flame method as a starting material.