JPH03225914A - exposure equipment - Google Patents

Abstract

PURPOSE:To obtain a clear image without being influenced by reflectance of a surface of a sensitive material on a wafer by providing a polarized light state converting means for converting linearly polarized light from a laser light source into circularly polarized light or unpolarized light and illuminating a mask with light which has passed through the polarized light state conversion means. CONSTITUTION:By providing Brewster windows 3, 5 to a light source 4 of an eximer or metallic vapor laser, linearly polarized light can be output without change with time and the reflectivity is always constant even if a semitransparent mirror 10 and reflecting mirrors 11, 16 are provided to the optical path of an aligner. Further by providing a lambda/4 plate or a polarized light eliminating plate 9, the linearly polarized light output from the laser light source 4 can be converted into circularly polarized light or unpolarized light so that the aligner is free from influence of a refractive index of a sensitive material.

Description

[Detailed description of the invention] [Industrial application field] The present invention relates to a semiconductor exposure apparatus.

[Conventional technology]

In recent years, semiconductor devices have become increasingly miniaturized, and the minimum line width of circuit patterns is about to reach the submicron range. For this reason, projection lenses with large numerical apertures have been developed for reduction projection type exposure equipment, but in order to further advance the miniaturization of semiconductor devices, it is necessary to further shorten the wavelength of exposure light. be. Therefore, the currently widely used g-line (436 nm) and i-line (365 nm) illumination lights from mercury lamps are expected to be a promising alternative to excimer laser light, which can provide light with even shorter wavelengths. This excimer laser light source can oscillate laser light of different wavelengths by changing the gas in the oscillation medium, but the media that provide stable and high output are xenon chloride (XeC1) (308 nm), krypton fluoride (
KrF) (248 nm) and argon fluoride (ArF)
(193 nm), and among these, krypton fluoride and argon fluoride, which have shorter wavelengths, are advantageous.

[Problem to be solved by the invention]

However, during development, it was discovered that the polarization state of excimer lasers changes over time. A reflecting mirror is also used in the illumination system of the exposure apparatus, and a change in the polarization state results in a change in reflectance, that is, a change in the amount of light corresponding to a change in the polarization state of the laser light source. This is important when trying to control a constant laser beam output by monitoring a part of the laser beam, and when trying to control the exposure amount on a wafer by controlling the laser beam output. This means that the correspondence between light output and exposure amount becomes sloppy.

Also, when a mask is illuminated with a linearly polarized light beam and a photosensitive substrate is exposed, the reflectance of the photosensitive material surface differs depending on the polarization direction (P-polarized light and S-polarized light), resulting in a difference in the line width of the projected pattern. .

The present invention has been made to solve these problems.

[Means to solve problems]

In order to solve the above problems, the present invention includes a light source 4 that illuminates a mask 18 on which a predetermined pattern is formed, and a fly-eye lens 12 that makes the light from the light source 4 substantially uniform on the mask 18. , in an exposure apparatus that exposes a pattern onto a wafer 20, the light source 4 includes an excimer or metal vapor laser light source equipped with Brewster windows 3 and 5 for outputting linearly polarized light; It is equipped with a λ/4 plate or a depolarization plate 9 that converts the linearly polarized light from 4 into circularly polarized light or non-polarized light.
Mask 18 with the light that has passed through the 4 plates or the depolarization plate 9.
It was decided to illuminate.

Further, the λ/4 plate or the depolarization plate 9 is provided in the optical path closer to the light source 4 than the fly-eye lens 12.

[For production]

According to the present invention, by providing the excimer or metal vapor laser light source 4 with the Brewster windows 3 and 5, linearly polarized light can be output without changing over time, and the semi-transmissive mirror 1
Even if the mirrors 11 and 11 and 16 are provided in the optical path of the exposure device, the reflectance is always constant.

Furthermore, by providing a λ/4 plate or a depolarization plate 9, the linearly polarized light output from the laser light source 4 can be converted into circularly polarized light or unpolarized light, which is not affected by the refractive index of the photosensitizer. There is no.

〔Example〕

FIG. 1 is a diagram showing the configuration of an exposure apparatus according to an embodiment of the present invention. The spontaneous oscillation bandwidth of the KrF excimer laser light source 4 is 300 pm, and the etalon 2 is provided to narrow this to 3 pm.

Although only the etalon 2 is shown here, it is also possible to narrow the band by using a grating and a prism. In that case, it is particularly effective because the polarization state is likely to change.

Further, the members 3 and 5 are Brewster windows, and since polarized light at a specific angle is substantially non-reflected, only the light of this polarized component is amplified by the reflecting mirror 1 and the semi-transmissive mirror 6. As a result, a nearly linearly polarized laser beam is transmitted to the semi-transmissive mirror 6.
The laser light source 4 outputs linearly polarized light.

The beam from the laser light source 4 is shaped into a parallel beam with a desired cross-sectional shape by a lens system 7.8 such as a cylindrical lens and a beam expander, and is converted from linearly polarized light to circularly polarized light by a λ/4 plate 9.

Here, a part of the laser beam is split by the semi-transmissive mirror 10 and focused onto the photoelectric conversion element 24 via the condensing lens 23 . The photoelectric conversion element 24 generates a voltage proportional to the output (peak of pulsed light emission) of the excimer laser light source 4. The output voltage of the photoelectric conversion element 24 is the same as that of the excimer laser light source 4.
The power source 25 controls the voltage applied to the discharge electrode in the laser chamber so that the output voltage of the photoelectric conversion element 24 becomes a predetermined value.

On the other hand, the laser beam that is converted into circularly polarized light by the λ/4 plate 9 and transmitted through the semi-transmissive mirror 10 is reflected by the reflecting mirror 11 and enters the fly-eye lens 12.

Laser light from each element lens of the fly-eye lens 12 is superimposed on a reticle blind 14 as an illumination field stop via a lens system 13 as a condenser lens into a --like intensity distribution. The beam passing through the blind 14 is reflected by a reflecting mirror 16 via a lens system 15, and illuminates a reticle 18 with a uniform illuminance distribution via a condenser lens 17. wafer 20
It is projected onto and exposed to light. In the above configuration, the fly
The exit surface (secondary light source) of the eye lens 12 and the projection lens 1
The reticle blind 12 is conjugate with the pupil (entrance pupil) plane Ep of the lens system 15.9. The condenser lens 17 makes it conjugate with the reticle 18.

Incidentally, one of the important specifications of an exposure apparatus is the unevenness of illuminance on the wafer 20. Measurement of illuminance unevenness will be explained based on FIG. 2. A light receiving element 22 is provided on a wafer stage 21, and the wafer stage 21 is moved so that the light receiving element 22 scans the entire exposure area, and an interferometer 27 reads the position coordinates. At the same time, the excimer laser light source 4 is caused to oscillate with a constant output (constant discharge voltage), and the output P1 of the light receiving element 22 is outputted, and the output P of the excimer laser light source 4 is outputted by the photoelectric detection element 24. It also detects. The outputs P+ and Po are held at their peak values in peak hold circuits 28 and 29, respectively,
It is input to the divider 30. In the divider 30, P, /PG
The result is stored in the memory 31 in correspondence with the position coordinates determined by the interferometer 27, and displayed on the display unit 32.

Furthermore, since it is not possible to directly measure the exposure amount while exposing the pattern onto the wafer 20, the output P0 of the photoelectric conversion element 24 is used for measurement. Photoelectric conversion element 24
The output P0 of the light receiving element 22 and the output P1 of the light receiving element 22 are the ratio P
+/P o is predetermined and P at a given exposure amount. The value of is also determined accordingly. Therefore, the first
In the figure, the output P of the photoelectric conversion element 24 during exposure. The controller 26 measures P. The laser power supply 25 is set to a predetermined value.
The exposure amount is controlled by controlling the . However, wafer 2
When exposing with multiple pulses per shot on 0, output P for each pulse. By integrating, the total exposure amount per shot is made constant.

In the above configuration, the same effect can be obtained even if the λ/4 plate 9 is provided between the semi-transmissive mirror 10 and the reflecting mirror 11 or between the reflecting mirror 11 and the fly-eye lens 12. However, in order to reduce unnecessary interference fringes that occur when the multiple secondary light sources of the fly-eye lens 12 are superimposed on the reticle blind 14 by the lens system 13, a reflecting mirror is used for each pulse of the laser beam. 11 is rotated by minute angles to vibrate n/2 periods with multiple pulses of laser light for exposure, a λ/4 plate 9 is placed between the reflector 1 and the fly eye lens 12. cannot be set. Further, in these cases, the laser light irradiated onto the semi-transmissive mirror 10 remains linearly polarized light.

The same effect can also be obtained by replacing the λ/4 plate 9 with a depolarizing plate made of crystalline quartz, but in this case, the laser light that passes through the depolarizing plate is not circularly polarized but unpolarized. be.

In addition, similar effects can be obtained when a metal vapor laser such as a copper vapor laser or its harmonics is used instead of the excimer laser as the light source 4.

Next, a modification according to the embodiment of the present invention will be explained based on FIGS. 3 and 4.

FIG. 3 shows lens systems 7 and 8 in the configuration shown in FIG.
The polarizer 33 is irradiated with the shaped laser beam. This polarizer 33 is arranged so that its entrance plane is perpendicular to the optical axis of the laser beam and is rotatable. As a result, if the angle between the polarization plane and the direction of the polarization plane of the polarizer 33 is θ, the light amount transmittance of the laser light passing through the polarizer is COS
It can be expressed as θ, and can be changed continuously by rotating the polarizer.

The linearly polarized laser light whose light intensity is controlled by the polarizer 33 is
The light is irradiated onto the λ/4 plate 9 and converted into circularly polarized light. In this case, since the direction of the polarization plane is changed by the polarizer 33, the λ/4 plate must also be rotated in accordance with the direction of the polarization plane.

Further, FIG. 4 shows that in the configuration shown in FIG. 1, the laser beam shaped by the lens systems 7 and 8 is irradiated onto a λ/2 plate 34 arranged rotatably with respect to the optical axis of the laser beam. This λ
By rotating the /2 plate 34, the plane of polarization can be rotated without changing the amount of laser light. Further, if the angle between the polarization plane of the laser beam and the optical axis of the λ/2 plate 34 is θ, then the rotation angle of the polarization plane of the laser beam that has passed through the λ/2 plate 34 can be expressed as 2θ.

Now, the linearly polarized light that has passed through the λ/2 plate 34 is irradiated onto a fixed polarizer 33, where the amount of light is controlled. In other words, when the polarization plane rotated by 2θ by the λ/2 plate 34 passes through the polarizer 33, the amount of laser light becomes cos 2
It passes through with a transmittance expressed by θ. Furthermore, by rotating the λ/2 plate 34, the amount of transmitted laser light changes continuously.

11 The linearly polarized laser light that has passed through the polarizer 33 is converted into circularly polarized light by the λ/4 plate 9. In this case, even if the plane of polarization is rotated by rotating the λ/2 plate 34, the polarizer 33
Since the polarization plane of the laser beam is specified in the direction of the polarization plane of the polarizer 33 by passing through the λ/4 plate 9, there is no need to rotate the λ/4 plate 9.

As described above, if the configuration shown in FIG. 3 and FIG. Since the laser light irradiated onto the laser beam 11 becomes circularly polarized light, it does not affect the resolution of the pattern on the wafer. Also, among the above configurations, λ/4
The same effect can be obtained by replacing plate 9 with a depolarizing plate, but in the case of a depolarizing plate, if the settings are appropriate, the third
Even in the configuration shown in the figure, there is no need to rotate it like a λ/4 plate.

As described above, although the projection optical system is used in this embodiment, it goes without saying that the present invention can also be applied to an exposure apparatus such as a proximity method that does not use a projection optical system.

〔Effect of the invention〕

-12= As described above, according to the present invention, since the Brewster window is provided in the excimer laser light source or the metal vapor laser light source, temporal changes in the polarization state are eliminated, and a reflecting mirror is provided in the optical path of the exposure device. Also, it is possible to always obtain a constant reflectance, that is, a constant amount of light depending on the output of the laser light source. For this reason,
Effects such as measurement of illuminance unevenness and control of exposure amount can be obtained accurately.

Further, by using laser light converted from linearly polarized light to circularly polarized light or non-polarized light as exposure light, clear resolution can be obtained without being affected by the reflectance of the surface of the photosensitive material on the wafer.

[Brief explanation of drawings]

FIG. 1 is a diagram showing the configuration of an exposure apparatus according to an embodiment of the present invention, FIG. 2 is a block diagram showing measurement of illuminance unevenness of the exposure apparatus according to an embodiment of the present invention, and FIGS. 3 and 4 are FIG. 2 is a diagram illustrating a modification of the configuration of an exposure apparatus according to an embodiment of the present invention. [Explanation of symbols of main parts] ■...Reflector, 2...Etalon, 3, 5...Brewster window, 4...Laser light source, 6. lO...Semi-transparent mirror, 9...λ/4 plate or depolarization plate, 22-
... Light receiving element, 24... Photoelectric conversion element, 25... Laser power source, 33... Polarizer, 34... λ/2 plate.

Claims (2)

[Claims] (1) An illumination means for illuminating a mask on which a predetermined pattern is formed, and an illuminance distribution uniformization means for making the light from the illumination means substantially uniform on the mask, and the pattern is applied to a photosensitive substrate. In an exposure apparatus that performs exposure, the illumination means includes an excimer or metal vapor laser light source equipped with a Brewster window for outputting linearly polarized light, and converts the linearly polarized light from the laser light source into circularly polarized light or non-polarized light. An exposure apparatus comprising a polarization state converting means for converting the polarization state, and illuminating the mask with light that has passed through the polarization state converting means. (2) The exposure apparatus according to claim 1, wherein the polarization state converting means includes a wavelength plate or a depolarization plate provided in an optical path closer to the light source than the illuminance distribution uniformizing means.