JPS6360442A - Illuminating optical system - Google Patents

Abstract

PURPOSE:To obtain a uniform light intensity distribution, and to execute an exposure being free from unevenness by providing a fly's eye lens having magnification corresponding to the light intensity distribution, in front of a diffusion plate. CONSTITUTION:The titled system is provided with a fly's eye lens 4 in front of a diffusion plate. That is to say, in an optical path where a laser light 2 having a Gaussian intensity distribution 1a from an excimer laser is projected as parallel rays to an observation surface 3, the fly's eye lens 4 is which element lenses 40-44 whose section is semicircular, respectively are arranged in the direction where the intensity distribution is uniform is provided so as to be orthogonal to the optical path. In such a state, as a relation in which each projected light of the observation surface 3 by plural respective lenses 40-44 is overlapped to each other, an arranged state of each element lens 40-44 and a distance to the observation surface 3 are determined, and also, in accordance with the intensity distribution in each part of the laser light 2, the enlargement magnification of each element lens 40-44 is varied. By these conditions, a projected light intensity composite value of the enter part becomes roughly uniform.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to an illumination optical system that irradiates laser light with a non-uniform intensity distribution as light with a uniform intensity distribution.

[Conventional technology]

In recent years, it has been proposed to use excimer laser light as light S when forming patterns of semiconductor integrated circuits.

However, the intensity distribution of the laser light emitted by an excimer laser is a uniform distribution on either the X or Y axis, which is perpendicular to the traveling direction, while the other has a Gaussian distribution. It becomes non-uniform, and the i
When used as a light source for forming a T-pattern, uneven exposure occurs, making it impossible to form high-quality patterns.

As a countermeasure for this, laser focus (Las@rF
Ocus) March 1982 issue, pages 42-44 (p@nn
Published by vel Publishing Company)
The method using a split prism described in , or Applied Optics (Appli@d Optlcm) Volume 19 2
No. 0, 1980, pp. 3545-3553 (0ptlc
A method of using an aspherical lens has been proposed, as described in the following publication (published by Al 8oo1, ty of Amerlea).

[Problem that the invention seeks to solve]

However, with the method of using a split prism, if there is even a slight deviation from the point of maximum utilization efficiency due to the adjustment status of the optical system, the uniformity of the intensity distribution and utilization efficiency will deteriorate rapidly. In addition, the method using an aspherical lens is extremely difficult and expensive to manufacture.

[Means for solving problems]

In order to solve this problem, the present invention provides a fly's eye lens in front of the diffuser plate.

[Effect]

Unconstrained intensity distribution - The rays have a uniform intensity distribution.

〔Example〕

FIG. 1 is a block diagram showing an embodiment of the present invention. In the figure, 1 is a laser beam with a Gaussian distribution on one side perpendicular to the traveling direction (the y direction) and a uniform distribution on the other side (the X direction), 4 is a fly's eye lens composed of a cylindrical lens, and 6 is a fly's eye lens. A frame for fixing the eye lens 4, T is a diffusion plate, 7a is a diffusion surface that functions to diffuse light in the diffusion plate 7, 8 is a positive lens, 9 is a collimation lens, 10
is a mask surface or a reticle surface, 11 is a laser beam emitted from one point of the diffusing surface 7a, 12&, 12b is an aperture, and 13
is an exciter. The diffuser plate 7 is installed so that the diffuser surface T& coincides with the position where the intensity distribution of the laser beam 1 becomes -like due to the fly's eye lens 4. The positive lens 8 is installed so that the position of its front focal point substantially coincides with the diffusion surface T& of the diffusion plate 7.

The collimation lens S is installed at a position such that its front focus substantially coincides with the back focus of the positive lens 8. Mask side 10
is installed so as to substantially coincide with the back focal plane of the condenser lens 3.

FIG. 2 is a perspective view of the fly's eye lens 4, in which each element lens 40 to 44 using a cylindrical lens with a semicircular cross section is formed by connecting them at the same pitch, and the central element lens 4
0 is set as the minimum magnification, and the element lenses 41, 43, 42, and 44 on both sides of this center have the same magnification, and the magnification increases as they are positioned laterally.

The tX3 diagram shows a side view seen from the y direction, (4) shows the configuration of the optical system, φ) shows the projected light intensity distribution on the observation surface, and in (2), the excimer which is omitted in the diagram is shown. Element lenses 40 to 44, each having a semicircular cross section, are arranged in the direction of non-uniform intensity distribution in the optical path in which laser light 2 having a Gaussian intensity distribution 1a from the laser is projected onto the observation surface 3 as parallel rays. A fly's eye lens 4 is provided perpendicularly to the optical path, and each of the element lenses 40 to 44 is arranged in such a manner that the respective projection lights on the observation surface 3 by the plurality of element lenses 40 to 44 overlap with each other.
44 and the distance from the observation surface 3, and also change the magnification of each element lens 40 to 44 according to the intensity distribution of the laser beam 2 in each part, and according to these conditions, As shown by the solid line in 0), the projected light intensity composite value at the center is #1 uniform.

That is, as shown by the dotted line of ω), the respective projected light intensities 50 to 54 by the respective element lenses 40 to 44 are non-uniform, but by adding these, a complementary composite value is obtained. 60 is obtained, and the central part of this has a uniform intensity distribution.

The process of converting a laser beam with an uneven intensity distribution into a laser beam with an uneven intensity distribution using a fly's eye lens is as follows. For example, the vertical direction of the y-axis perpendicular to the traveling direction is assumed to be the y-axis, and only that direction has a Gaussian distribution as shown in the intensity distribution 1a in FIG. 3.

The light intensity factor 1 for each part of the laser beam 2 having the intensity distribution 11 is given by the following equation, where σ is the standard deviation of the Gaussian distribution and X is the distance from the center O.

I l= *xp (−X σ') −−−−−−−
-----------(1) Also, each element lens 40 to 44
The center coordinate position of xn (n=o, 1.2...
), and in this example, the center coordinate position of the element lens 40 is Xs, the center coordinate position of the element lens 41.43 is respectively XI, X-1, and the center coordinate position of the element lens 42.44 is each X! , X-* and K, each element lens 4
The magnification factor from 0 to 44 is Kn (n = Oll, 2...
Similarly, the element lens 40 is expressed by K, the element lenses 41 and 43 are expressed by Kl and K-S, and the element lenses 42 and 44 are expressed by Km and K-1. If the width of each element lens 40 to 44 is 2R, on the observation surface 3, the relationship is -1 for K1= and one snow for Kl=, so that it is enlarged and projected to 2R1) Kn. Therefore, each intensity distribution 50 to 54 in FIG. 1(B) is
Each intensity distribution is In (n=0, l, 2...
), and similarly to the above, the element lens 40 is the Ioqg element lens 41, the 43 element lens is II,
I-t, the element lens 42.44 is Il, I-
If υ is denoted by s, it is given by the following equation.

・−１・・・・・・・・・・・・−(2) Therefore, the composite value 600 intensity distribution is expressed by the following equation.

■=ΣIn ・・・・・・・・・−−
--------(3) Note that the change in magnification of each element lens 40 to 440 may be determined by the following formula.

KH=to6+r・In+・・・・・・・・・
・・・・・・・・・・・・・・・ (4) Calculate the intensity distribution 60 using equations 1 to 3 and set the intensity ■ of X=O to 100%, and when the intensity I becomes 99% or 101% Find the value Xm of X, and define the laser light utilization efficiency l as follows.

FIG. 4 shows the relationship between Ko, η, and Xm/σ in the case of R/σ=0.1, using r in equation (4) as a parameter. The dimensions (width x height) of the laser beam generated from the excimer laser are, for example, 30n x 20m1II.
I, and the height that has a Gaussian distribution is generally smaller. From FIG. 4, if the value of .sigma. is selected so that Xm/σ is 1.5 to 2, the laser beam can have a substantially square dimension. In this case, if a fly's eye lens with r=0 or 2 is used, the utilization efficiency η is about a factor of 64, and the value of η is approximately constant regardless of KO. That is, it is possible to adjust the excimer laser, the illumination optical system, etc. with plenty of time.

From these facts, by using a fly's eye lens, the direction with Gaussian distribution is
The laser beam 1 is spread out by the laser beam 1 and irradiates the diffusion surface T of the diffusion plate 1 with the other directions unchanged. Therefore, on the diffusing surface T&, the intensity distribution of the laser light is approximately -like, and the shape of the light irradiation area is approximately square. Diffusion surface 7a
Although the light emitted from the diffusion surface 7a is scattered light, the intensity of the light emitted from each point of the diffusion surface 7a is approximately constant.

As shown in FIG. 1, the laser beam 11 emitted from one point on the diffusing surface Ta travels so as to be focused on one point on the mask surface 10, and the mask surface 10 is illuminated with light of -like intensity. When the diffusion surface T1 is considered as a light source, the method of illuminating the mask surface 10 is a critical illumination method. The diaphragm 12& is configured to extract only a region where the intensity distribution of the laser beam is approximately --like, thereby preventing unnecessary light from being scattered within the optical lens barrel. Aperture D12b
is for changing the collimation half angle α.

Here, since the light irradiating the diffusing surface 7a is a laser beam and has a high coherence, interference fringes are formed on the diffusing surface T&. Therefore, if the position of the fly's eye lens 4 is changed by the vibrator 13 every time pulsed laser light is generated from the excimer laser, the adverse effects of exposure unevenness due to interference fringes generated on the diffusion surface 7m can be prevented. Further, when the coherence range is high, speckles occur, but the influence of these speckles can be prevented by constantly changing the position of the fly's eye lens 4.

FIG. 5 shows a second embodiment, in which the light that has passed through the aperture of the diaphragm 121 is focused on one point on the mask surface 10, so that the mask surface 10 is illuminated with a laser beam of -like intensity. Diffusion surface 7
When m is regarded as a light source, the method of illuminating the mask surface 10 is the Kohler illumination method. It is used to change the aperture p12mil and the collimation half angle α.

FIG. 6 shows a third embodiment, in which a positive lens 15 is provided in front of the diffuser plate T, and the positive lens 15 forms an image of the observation surface 3 onto the diffuser surface T&. In this configuration, the size of the area where the light intensity distribution is negative on the diffusing surface T& can be adjusted by adjusting the focal length of the positive lens 15, etc., so the degree of freedom in designing the entire illumination optical system is increased. Although not shown in FIG. 6, the influence of interference fringes and speckles can be removed by constantly changing the position of the fly's eye lens 4 or positive lens 15 as in the example of FIG.

FIG. 7 shows a fourth embodiment, in which the Koehler illumination method is applied to the one shown in FIG. 6. FIG. 8 shows a fifth embodiment in which the front focal point of the fly's eye lens 4 is arranged so that the focal point of the central lens of the fly's eye lens 4 substantially coincides with the front focal point of the positive lens 15, and the diffusing surface T
The focal lengths of the fly's eye lens 4 and the positive lens 15 are determined so that the intensity distribution of light at & is approximately equal.

In this way, the laser beam will be incident on the diffuser plate T approximately perpendicularly, unlike the laser beam incident on the diffuser plate 7 obliquely in FIGS. 1 and 5 to 7. Therefore, the direction of light scattered by the diffusing surface 7a is approximately equal to -fc compared to other surfaces. Furthermore, if the positive lens 15 in FIG. 8 is a cylindrical positive lens, the light can be scattered even more uniformly.

FIG. 9 shows another embodiment, in which 16&, 16b are positive lenses, 1T is an optical integrator, and 18 is a mirror. By configuring the illumination optical system using an optical integrator in this way, it is possible to further improve the uniformity of light on the mask surface and the light collection efficiency.

The above embodiments have shown the case where the light source is a laser beam whose light intensity distribution in the y-axis direction is Gaussian, but the light source is a laser beam whose light intensity distribution in the X-axis direction is also Gaussian. In this case, two fly's eye lenses may be used and arranged so as to be perpendicular to each other. Although the exciter is not shown in Figures 7 to 9, the effects of interference fringes and specs can be seen by changing the positions of the fly's eye lens, lenses, diffuser plate, etc. in the same way as in the example up to Figure K6. Removing is the same as in the previous example. At this time, the range of position change may be within ±10 μm, and the direction of position change may be perpendicular to the optical axis, parallel to it, or a combination of these directions.

Furthermore, if the laser oscillation is continuous, the positions of the fly's eye lens, lens, diffuser plate, etc. may be changed during the laser beam irradiation time. Even if the intensity distribution of the fly's eye lens is other than the glass type, the magnification of the fly's eye lens may be set according to the intensity distribution. Also,
The diffuser plate may also be rotated around the optical axis during vibration.

〔Effect of the invention〕

As explained above, this invention has the effect that a fly's eye lens having a magnification corresponding to the light intensity distribution is provided in front of the diffuser plate, so that a uniform light intensity distribution can be obtained and even exposure can be performed. has.

[Brief explanation of the drawing]

Fig. 1 is a configuration diagram showing an embodiment of the present invention, Fig. 2 is a perspective view of a fly's eye lens, Fig. 3 is a diagram illustrating the state in which uniform light is obtained by the fly's eye lens, and Fig. 4 The figure is a graph showing the characteristics obtained by the fly's eye lens, and FIGS. 5 to 9 are configuration diagrams showing other embodiments. 1.2,11...Bankenshi/-f light, 1a...Intensity distribution of fist laser light, 3...Observation surface, 4...φ-Fly's eye lens, 7...Diffusion plate , 7a... Diffusion surface, 8.15, 1γ... Positive lens, 9... Collimation lens, 10... Mask surface, 12 &, 1
2b-...diaphragm υ, 13...bonding exciter.

Claims (1)

[Claims] In an illumination optical system that irradiates laser light with an uneven intensity distribution in at least one of two directions orthogonal to the direction of travel through a diffuser plate, a plurality of element lenses are directed in the direction where the intensity distribution is uneven in the optical path. An array of fly's eye lenses is provided in front of the diffuser plate, orthogonal to the optical path, and the magnification of the element lenses changes according to the light intensity at each part of the laser beam, and each element lens projects light onto the observation plane. An illumination optical system characterized in that the illumination optical system overlaps and is arranged in a relationship such that the combined values thereof are substantially uniform.