JPH02166783A - Homogenizer for excimer laser - Google Patents

Abstract

PURPOSE:To make intensity distribution uniform by providing incident beam dividing means, means for so processing the divided first beam that an optical image is reverse at right and left sides and upper and lower sides, and means for superposing part of an output beam on a second beam. CONSTITUTION:A beam splitter 11 is disposed obliquely at 45 degrees with respect to an optical axis on the optical path 12 of an excimer laser. When a laser beam 16 is incident, part 17 is reflected perpendicularly, the remaining beam 18 is passed as it is to be incident into a right angle prism 13, reflected at an input side and deflected at 180 degrees. An emitting beam 18a from the right angle prism 13 is next incident to a roof prism 15 so that the image is reversed to be deflected at 90 degrees at upper and lower sides and at right and left sides, and an emitting beam 18b is incident in a direction perpendicular to the laser beam 16 from the rear face with respect to the beam splitter 11. Part 18c is reflected, and superposed on the reflected beam 17 reflected by the beam splitter 11.

Description

Detailed Description of the Invention (Field of Industrial Application) The present invention relates to a light source for an exposure device using an excimer laser;
The present invention relates to light sources for various processing devices such as annealing and optical CVD devices. More particularly, the invention relates to a homogenizer for homogenizing the intensity of the beam generated by such a light source.

(Prior art and problems to be solved) In excimer lasers used in exposure equipment such as lithography and processing equipment such as annealing or optical CVD,
Uniformity of light intensity within the irradiation area is required. In order to obtain this uniformity, illumination optical systems that generally include a combination of an inch grater and a condenser lens are widely used.

FIG. 2 shows the beam pattern of the excimer laser and the light intensity distribution in the orthogonal axial direction in this pattern. As can be seen from the figure, the distribution of light intensity in the beam cross section 1 of the excimer laser is not uniform, and there are fine irregularities and inclinations, and the excimer laser cannot be used as a light source as it is.

FIG. 3 shows an example of an optical system used to homogenize this beam. As described above, this optical system includes an inch grater 2, into which a beam shaped into an appropriate beam shape is incident. The divided beams that have passed through this inch grater 2 hit respective image points, and the diverging light from there is collected by a condenser lens 3, and a uniform beam area is formed at the focal point position 4. Ru.

(Problem to be Solved by the Invention) However, in the beam homogenizing means as described above, when the incident beam originally has a light intensity distribution in a certain direction, the light intensity distribution obtained by passing through the condenser lens is The non-uniformity remains in the beam as well. In addition, when using an optical system that uses such inch grater and condenser lenses,
It has the disadvantage that the intensity loss is relatively large, and the intensity uniformity position is limited to the focal position of the condenser lens.
In areas other than this uniform position, the light beam is spread out as a whole, which is inconvenient in handling.

On the other hand, excimer lasers have many transverse modes in the beam plane, but the number of transverse modes changes depending on the structure of the resonator and the degree of band narrowing by the wavelength selection element inside the resonator, and the degree of coherence changes. changes. In particular, when used as an exposure light source, it is necessary to suppress this coherence as much as possible in order to eliminate speckle noise. Speckle noise can be reduced by increasing the number of exposure shots when the light sources are coherent, or by forming multiple light sources using a beam steering mechanism, or alternatively.
It can be removed by rotating the inch grater. However, increasing or decreasing the number of exposure shots has a correlation with the sensitivity characteristics of the resist used, making it impractical.
A beam steering mechanism or an inch grater rotation mechanism is undesirable because it increases the size and complexity of the illumination optical system of the exposure apparatus.

In view of the above problems, it is an object of the present invention to eliminate the non-uniformity of the intensity distribution in a certain direction that exists in a beam, which cannot be removed by the method of making the intensity distribution uniform using an inch grater and a condenser lens. The object of the present invention is to realize an excimer laser light source device that can be used as an excimer laser and has low coherence.

(Means for Solving the Problems) In order to achieve the above object, the excimer laser homogenizer of the present invention includes a dividing means for dividing an incident beam into a first beam and a second beam, and a dividing means for dividing an incident beam into a first beam and a second beam. means for processing the first beam so that its optical image is reversed horizontally and vertically; and at least a portion of the output beam from the means is superimposed on the second beam split by the splitting means. The invention is characterized in that it is equipped with a superimposing means for combining.

In a preferred embodiment of the invention, an excimer laser
Each of the above means is constructed by arranging a beam splitter and a combination prism on the optical path of the laser, thereby obtaining an excimer laser beam having the required characteristics. To explain in more detail with reference to FIG.
Place it at an angle. This beam splitter 11
A right angle prism 13 is arranged on the rear side. This right-angle prism 13 is arranged so that the incident side surface 13a of the orthogonal reflecting surfaces is line-symmetrical with respect to the beam splitter 11 with respect to a line segment 14 orthogonal to the optical path 12. It is. On the other hand, a roof prism 15 is arranged at a position facing the other exit side surface 13b of the right angle prism I3. The reflective surface 15a of this roof prism 15 is located at the right angle prism 13 with respect to the above-mentioned line segment 14.
They are arranged in a line-symmetrical relationship with the reflecting surface 13b of the rectangular prism 13, and are arranged in a line-symmetrical relationship with the beam splitter 11 with respect to the center line 13c of the right-angle prism 13.

(Operation) The operation of the present invention will be explained using the preferred embodiment shown in FIG. 1 as an example. First, when the laser beam 16 is incident on the beam splitter 11, a portion 17 thereof is reflected at right angles, and the remaining beam 18 is transmitted as is. The transmitted beam 18 enters the rectangular prism 13, is reflected by the reflection surface 13a on the input side and the reflection surface 13b on the exit side, and is deflected by 180 degrees. The emitted beam 18a from the right-angle prism 13 then enters the roof prism 15, and is deflected by 90 degrees so that its image is turned upside down and reversed left and right. The emitted light 18b thus deflected enters the beam splitter 11 from the rear surface in a direction perpendicular to the laser beam 16.

A portion 18c of this incident beam 18b is reflected and follows an optical path similar to beam 18 described above. However, the remaining beam 18d that has passed through this beam splitter 11 is superimposed on the reflected beam 17 that has been reflected by this beam splitter 11. In this way, the reflected beam of the beam splitter 11 is a superposition of the immediately reflected reflected beam 17 incident thereon and the beam 18b transmitted therethrough and then passed through the right angle prism and the roof prism. As a result, non-uniformity in the intensity distribution in one direction that exists within the beam is eliminated and coherence is suppressed.

(Example) In the configuration shown in FIG. 1, the beam splitter 11 is set at 45 degrees of incidence and the reflectance is 30%,
An anti-reflection coating was applied to the entrance surface of the roof prism 15, and the exit surface of the roof prism 15 was bonded to the entrance surface of the roof prism 15 by optical contact.

Furthermore, the exit surface of this roof prism 15 was coated with an antireflection film. When the optical system with this configuration was used, it was confirmed that the uniformity of the light intensity distribution in the obtained beam was improved and the coherence was reduced.

(Effects of the Invention) As explained above, a part of the excimer laser beam is made into a state in which the image is inverted horizontally and vertically, and the beam processed in this way is superimposed on the original beam to form the beam. I'm trying to form it. Therefore, according to the present invention, the light intensity distribution within the obtained beam can be made uniform, and coherence can also be suppressed.

[Brief explanation of the drawing]

Fig. 1 is a configuration diagram showing an apparatus according to an embodiment of the present invention, and Figs. 2 (A) to (C) are diagrams for explaining the light intensity distribution in each axial direction in the beam cross section of a typical excimer laser. A beam cross-sectional view and a graph showing a light intensity distribution, and FIG. 3 are a configuration diagram showing a conventional illumination optical system. Explanation of symbols in Figure 1 11...Beam splitter 13...Right angle prism 15...Roof prism

Claims (1)

[Claims] A splitting means is arranged on the optical path of the excimer laser and splits the incident beam into first and second beams, and the first beam split by the splitting means is arranged so that its optical image is reversed horizontally and vertically. 1. An excimer laser homogenizer comprising: means for deflecting the beam, and superposing means for superimposing at least a part of the output beam from the means on a second beam split by the splitting means.