JPH03212611A - Light quantity controller - Google Patents

Abstract

PURPOSE:To allow the control of the irradiation light quantity to a surface to be irradiated with high accuracy over a long period of time even if a high-output laser is used as a light source by disposing a parallel plane plate having a pair of light passage surfaces in the optical path between the light source and the surface to be irradiated and controlling the incident light quantity of the surface to be irradiated. CONSTITUTION:The parallel plane plate 13 disposed in the optical path between the light source 10 and the surface 14 to be irradiated consists of quartz, fluorite, etc., which do not substantially absorb the luminous flux of the short wavelength from the light source 10. The light transmission surface thereof is formed in the original state of a black material which is not formed with a coating film, etc. The parallel plane plate 13 is turned in the luminous flux by a driving means 11 in accordance with the output signal from a detecting means 17 disposed near the surface 14 to be irradiated is turned in the luminous flux to an adequately set an incident angle theta, by which a part of the irradiation light quantity is reflected and the transmitted light quantity is controlled to control the irradiation light quantity to be made incident on the surface 14 to be irradiated. The parallel plane plate 13 has no absorption and since the materials to absorb light are not formed at all on both surfaces, the long-term durability as the optical element is maintained.

Description

Detailed Description of the Invention (Industrial Application Field) The present invention relates to a light amount control device that controls the amount of light irradiated onto an irradiated surface when the irradiated surface is irradiated with a luminous flux emitted from a light source. , for example, relates to a light amount control device that precisely controls the amount of light irradiated to an irradiated surface such as a mask or reticle when the irradiated surface is irradiated with high energy or ultraviolet light beam in semiconductor manufacturing equipment, etc. be.

(Prior art) Conventionally, for example, in projectors, etc., the amount of light irradiated onto the film surface is controlled by using NDs with various transmittances in the optical path.
(Neutral Density) This is done by placing a filter. ND filters are generally constructed so that a desired transmittance can be obtained by depositing a metal film such as Cr or a dielectric multilayer film on the surface of a glass substrate, or by mixing a dye into the substrate itself.

In addition, by rotating a so-called wedge ND filter, which has optical properties similar to ND filters and whose transmittance changes continuously in the circumferential direction, in the optical path, a desired transmittance can be obtained with a single filter, and the irradiated surface can be A variety of devices have been proposed that control the amount of light emitted. A similar method is also used in which a polarizing plate is used to achieve the same effect when the light beam is polarized.

In addition, for example, in semiconductor manufacturing equipment, the quality of the pattern transferred onto the wafer surface is greatly influenced by the performance of the illumination device, such as fluctuations in the amount of light irradiated on the irradiated surface.

For this reason, the present applicant has developed a light amount control device that controls the amount of irradiated light on the irradiated surface to a predetermined value, which is particularly suitable for exposure equipment for semiconductor manufacturing, for example, in Japanese Patent Laid-Open No. 62-187815 and Japanese Patent Laid-Open No. This is proposed in Japanese Patent No. 63-193130.

The light amount control devices proposed in these publications place interference filters and deflection elements in the optical path, and control the amount of light irradiated onto the irradiated surface by detecting the amount of light reflected or deflected by these optical elements. ing.

(Problems to be Solved by the Invention) Methods of applying a vapor-deposited film on the substrate surface or impregnating the substrate itself with dye to absorb light flux and change the transmittance can be used, for example, for vapor-deposited films, as well as metal films and dielectric films. Body membranes with a high refractive index also have some degree of absorption, especially in the ultraviolet region.

If the light beam targeted for this absorption is a high-energy light beam in the ultraviolet region, such as from an excimer laser, the deposited film or substrate will be altered by light absorption, its optical properties will change, and the irradiated surface will A problem arises in that highly accurate control of the amount of irradiation light becomes difficult.

Further, regarding polarizing plates, there is a problem in that the only ones that can be used in the ultraviolet region are crystal prisms that are expensive and have a limited size.

The present invention is made of a material that absorbs the irradiated light beam at an appropriate position in the optical path from the light source to the irradiated surface only to the extent that it does not have an adverse effect on the irradiated light beam, that is, it does not substantially absorb it, and its optical properties do not change. An object of the present invention is to provide a light amount control device that controls the amount of light irradiated onto a surface to be irradiated with high precision by arranging optical members.

(Means for Solving the Problems) The light amount control device of the present invention includes a pair of light passing surfaces that are not coated with a coating film that does not substantially absorb the light flux between the light source and the irradiated surface. Place a parallel plane plate with
It is characterized in that the amount of light incident on the irradiated surface is controlled via the parallel plane plate.

In this Ikemizu invention, the parallel plane plate is rotated by a driving means to change the relative angle of incidence of the light beam onto the parallel plane plate, thereby changing the amount of transmitted light passing therethrough and irradiating the irradiated surface. Controls the amount of light.

(Embodiment) FIG. 1 is a schematic block diagram of an embodiment in which the present invention is applied to a projection exposure apparatus for semiconductor manufacturing. In the figure, lO is a light source, for example, a KrF excimer laser (
wavelength 248.4nm), the fourth harmonic of YAG laser, etc. (
It consists of a laser that emits a high-output beam in the ultraviolet region (wavelength: 265 nm).

12 is an illumination optical system for illuminating an irradiated surface 14 such as a reticle or a mask.

A parallel plane plate 13 is made of a material such as quartz or fluorite that absorbs short-wavelength light from the light source 10 only to the extent that it does not have an adverse effect, that is, does not substantially absorb it. The light transmitting surface of the parallel plane plate 13 is made of a raw material without any coating film or the like applied thereto. You can place it anywhere.

Furthermore, the row face plate 13 is rotatably controlled by the driving means 11 in the optical path, so that the incident angle θ of the light beam l can be arbitrarily set, and thereby the amount of transmitted light can be arbitrarily controlled. has been done.

Reference numeral 15 denotes a projection optical system that projects circuit patterns and the like on the reticle surface, which is the irradiated surface 14, onto the wafer 16 surface.

Reference numeral 17 denotes a detection means, which is disposed near the irradiated surface 14 and detects the amount of light irradiated onto the irradiated surface 14.

Note that the driving means 11 rotates the parallel plane plate 13 in the light beam based on the output signal from the detecting means 17.

In this embodiment, when the light beam from the light source 10 is irradiated onto the irradiated surface 14 through the illumination optical system 12, a part of the amount of irradiated light is reduced by appropriately setting the inclination of the parallel plane plate 13 arranged in the optical path. The amount of light that is reflected and transmitted is controlled, thereby controlling the amount of irradiation light that enters the irradiated surface 14.

In particular, based on the output signal from the detection means 17, the driving means 1
8, the amount of transmitted light can be arbitrarily controlled by rotating the parallel plane plate 11 and changing the incident angle θ.

For example, as shown in FIG. 2, when a light beam l is incident on a plane-parallel plate 13 made of a material with a refractive index n=1.5 at an incident angle θ, the transmittance of P-polarized light and S-polarized light per surface is 3. The result will be as shown in the figure.

Note that when the luminous flux is not polarized, it becomes the average value of the transmittance of P-polarized light and S-polarized light (the curve shown by the dotted line).

In the example shown in FIG. 2, the parallel plane plate 13 has two surfaces, a front surface and a back surface, so the actual transmittance is the square of the value shown in FIG. 3.

In this embodiment, the parallel planes 1i13 do not substantially absorb light, and both surfaces are not coated with any light-absorbing substance such as a vapor deposited film, so they are used initially as optical elements to control the amount of transmitted light. It has good long-term durability and takes values as shown in FIG. 3 over a long period of time, thereby making it possible to achieve a light amount control device that can accurately control the amount of transmitted light.

In this embodiment, if there is no need to change the amount of transmitted light, the driving means 11 may not be used and the incident angle θ of the light beam onto the parallel plane plate 13 may be fixed.

Generally, as shown in FIG. 2, when a light beam l is incident on a parallel plane plate 13 having a thickness t at an incident angle θ, an optical axis shift of ΔX occurs in the transmitted light beam. At this time, the optical axis deviation ΔX is 0. For example, n = 1.5.0270 degrees, tl 0 mm
When ΔX=6.65 mm. Furthermore, when the light beam l is an imaging light beam, it becomes a cause of optical axis deviation and comatic aberration.

Therefore, in the present invention, when the occurrence of optical axis deviation or coma aberration is particularly harmful, two parallel plane plates 13a and 13b are used as shown in FIG. It is preferable to arrange the respective inclinations so that their respective inclinations can be adjusted so that the angles of incidence are within the same range, the absolute value of the incident angle θ is the same, and the direction of incidence is opposite (the direction of inclination is opposite).

According to this, there is no optical axis deviation ΔX, and the occurrence of coma aberration can be prevented.

Generally, the transmittance when a light beam is incident on a certain surface is different for P-polarized light and S-polarized light, as shown in Figure 3, so if the light beam l is polarized, the amount of transmitted light for both polarizations is different. is changing. Furthermore, when the light beam is a condensed imaging light beam, astigmatism occurs.

In the present invention, in order to eliminate changes in transmittance due to polarized light and the effects of astigmatism, two parallel plane plates 13c and 13d are used as shown in FIG. It is best to arrange it so that

This is preferable because the P-polarized light and the S-polarized light are reversed by the plane-parallel plates 13c and 13d, and there is no difference in the amount of light between the two polarized lights, and the occurrence of astigmatism is also eliminated.

In this Ikemizu invention, two systems shown in FIG. 4 are used, and all the parallel plane plates have approximately the same thickness, and as shown in FIG. If the incident planes B of the light beams 13c and 13d are configured to be perpendicular to each other, a light amount control device can be achieved that solves various problems such as optical axis deviation, changes in the amount of transmitted light due to polarization characteristics, coma aberration, and astigmatism. be able to. In order to preserve polarization characteristics and eliminate astigmatism, at least the parallel plane plate 13a should have the same thickness as either one of the parallel plane plates 13c or 13d, and the parallel plane plate 13b should have the same thickness as the other one. Just configure it.

(Effects of the Invention) According to the present invention, a plane parallel plate having the above-mentioned optical properties is arranged in the optical path between the light source and the surface to be irradiated, and by controlling the amount of transmitted light, a light source such as an excimer laser or the like can be used. Even if a high-output laser is used, it is possible to achieve a light amount-side mv device that can control the amount of light irradiated onto the irradiated surface with high precision over a long period of time.

[Brief explanation of drawings]

FIG. 1 is a schematic block diagram of an embodiment of the present invention, FIG. 2 is an explanatory diagram of a part of FIG. 1, FIG. 3 is an explanatory diagram of the transmittance of P-polarized light and S-polarized light, and FIGS. Each figure is an explanatory diagram of a part of another embodiment of the present invention. In the figure, 1 is a light beam, 10 is a light source, 11 is a driving means, 12 is an illumination optical system, 13.13a to 13d are parallel seven-sided plates, and 14
15 is a projection optical system, 16 is a wafer, and 17 is a detection means.

Claims (5)

[Claims] (1) A parallel plane plate having a pair of light passing surfaces without a coating film that does not substantially absorb the light flux is arranged in the light flux between the light source and the irradiated surface, and the light beam is passed through the parallel plane plate. A light amount control device characterized by controlling the amount of light incident on an irradiated surface. (2) The light amount control device according to claim 1, wherein the parallel plane plate is rotated by a driving means within the light beam to vary the incident angle of the light beam onto the parallel plane plate. (3) The two parallel plane plates are arranged so that the incident planes of the light beams are the same plane, and the absolute values of the incident angles are substantially equal and the directions of incidence are opposite.
The light amount control device described. (4) The light amount control device according to claim 1 or 2, wherein the two parallel plane plates are arranged so that the incident angles to the two parallel plane plates are substantially the same and the incident planes are perpendicular to each other. (5) When arranging four parallel plane plates in the light beam, two
The two parallel plane plates are arranged so that the incident plane of the luminous flux is the same plane A and the directions of incidence are opposite to each other, and the other two parallel plane plates are arranged so that the incident plane of the luminous flux is the same plane B that is perpendicular to the plane A. 3. The light amount control device according to claim 1, wherein the light amount control device is arranged so that the directions thereof are opposite to each other.