JPH0744141B2 - Lighting optics - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to an illumination optical device for uniformly illuminating an object using a collimated light source such as a laser, and particularly to a semiconductor element such as an IC. The present invention relates to an illumination optical device suitable for an exposure apparatus for manufacturing a.

[Conventional technology]

2. Description of the Related Art Conventionally, as an illumination optical apparatus suitable for an exposure apparatus for manufacturing a semiconductor element such as an IC, an ellipsoidal mirror and one multi-source image formation are disclosed, for example, as disclosed in JP-A-56-81813. A device using an optical inflator as a means, and in order to further improve the uniformity of illumination, Japanese Patent Laid-Open No. 58-14770
As disclosed in Japanese Unexamined Patent Publication No. 8 (1994), there is known one using two optical inlators arranged in series. However, in these illumination optical devices, an ultrahigh pressure mercury lamp is used as a light source, and there is a drawback that light emission characteristics in a short wavelength region are insufficient and only a small amount of light can be obtained. For this reason, it has been proposed to use a laser as a high-power light source for short wavelengths, which replaces the ultra-high pressure mercury lamp.

[Problems to be solved by the invention]

However, as a light source of the illumination optical device as described above, a certain type of laser (for example, excimer laser, YA
When using a G laser, etc., the power of the laser is so strong that the lens itself may be destroyed, or ghost light may appear on the wafer due to reflection inside the lens.

Especially in an illumination optical system using an optical integrator consisting of a combination of biconvex positive lenses,
There was a high risk that the lens itself would be damaged due to the strong heat generated at the focal point. That is, when the optical integrator is an assembly of biconvex positive lenses and the rear focal point of each positive lens is configured to coincide with the exit side lens surface, the A condensing point will be formed. Therefore, when a high-power laser is used as the light source, the lens surface of the optical integrator may be destroyed.

Therefore, an object of the present invention is to solve these problems, even when using a light source having a very high light intensity such as a laser, there is no fear of destroying a light source element such as a lens, and the efficiency on an irradiated object is improved. An object of the present invention is to provide an illumination optical device which can obtain a good and uniform light intensity distribution.

[Means for solving problems]

The present invention, as shown in FIG. 1 showing the configuration of one embodiment,
A light source means 10 for supplying a substantially parallel light flux, a light source image forming means 1 for forming a plurality of light source images from the light flux supplied from the light source means, and a predetermined object plane by the light flux from the light source image forming means. In the illumination optical device having a condenser lens 3 for uniformly irradiating the light source, the light source image forming means is composed of an optical integrator composed of a plurality of lens elements arranged in parallel. And
Each lens element 101 of this optical integrator 1
Has a lens surface 101a having a positive refractive power on its incident side and a lens surface 101b having a positive refractive power on its exit side as well.
And the rear-side focal point F of each lens element is larger than that of the exit-side lens surface of each lens element. Each lens element is configured to be located rearward,
The light beams from the light source means are respectively condensed to form a light source image in the external space between each lens element and the condenser lens except the optical member.

[Action]

With the configuration of the present invention as described above, the substantially parallel light flux from the light source means 10 that enters the optical integrator 1 is
The optical integrator 1 is configured such that light is condensed by the converging action of the incident side lens surface of each lens element, but the rear focal point F of each lens element is located rearward of the exit side lens surface of each lens element. Therefore, the condensing point is located in the space behind the exit lens surface, and there is no risk of damaging each lens element due to the heat generated at the condensing point. Further, since the refracting power of the exit side lens surface is larger than that of the entrance side lens surface,
When the light source has a size, the function of the exit side lens surface as a field lens is sufficiently exerted, and it is possible to perform efficient illumination while preventing vignetting of illumination light at the subsequent condenser lens.

The configuration of individual lens elements of the optical integrator according to the present invention as described above will be described in detail with reference to the sectional optical path diagram of FIG.

As a function of each lens element that constitutes the optical integrator, first, it is mentioned that the parallel light flux entering the incident surface is condensed on the exit side. Now, if the radius of curvature of the first surface of each lens element constituting the optical integrator is r ₁ , the radius of curvature of the second surface is r ₂ , the central thickness is d, the refractive index is n, and the focal length is f, then it becomes easy. From geometrical optics, the exit side back focus bf ₁ and the incident side back focus bf ₂ are Becomes

In the case of the present invention, the condensing point of each lens element of the optical integrator is exposed to the air to prevent the condensing on the exit surface. Therefore, in the formula (1), bf ₁ has a finite positive value ε. Means

In addition, the apex of the incident side lens surface of each lens element forming the optical integrator is configured so as to substantially coincide with the incident side focal point of the exit side lens surface of each lens element, so that the telecentric on the exit side of the optical integrator. Therefore, it is possible to prevent vignetting in the optical element such as a condenser lens following the optical integrator, and to improve the illumination efficiency with a small configuration. In this case, it is necessary that bf ₂ = 0 in the equation (2). Therefore, Is required. Therefore, in order to configure the optical integrator on the exit side in a telecentric manner, the absolute value of the radius of curvature needs to be | r ₁ |> | r ₂ |.

〔Example〕

 Hereinafter, the present invention will be described based on examples.

FIG. 1 is a development optical path diagram showing a schematic configuration of an embodiment in which the illumination optical device according to the present invention is used as an illumination device of a projection type exposure apparatus.

The collimated light beam supplied from the laser light source 11 as a light source is an optical integrator for forming a surface light source.
Under the action of 12, the light is condensed as a plurality of condensing points 12a on the surface A of the exit side space. Light fluxes from the plurality of condensing points 12a are converted into parallel light fluxes by a positive lens 13 as a collimator lens, and are incident on a main optical integrator 4 as a light source image forming means.

The main optical integrator 1 is composed of a plurality of lens elements arranged in parallel, and each lens element is
As shown in the perspective view of FIG. 3, a plurality of quadrangular rod-shaped elements 11 are bundled together, and both the incident surface 101a and the emission surface 101b of each rod-shaped element 101 are formed as convex lens surfaces. Then, the convex lens surface on the entrance surface 101a of each rod-shaped element 101 forms a focal point of the light flux at a position away from the exit surface of the rod-shaped element 101, and a light source image is formed at this point.

As described with reference to FIG. 2 described above, each of such lens elements has (i) a lens surface r ₁ having a positive refractive power on the entrance surface and a lens surface having a positive refractive power on the exit side as well. r ₂ and (ii) the refractive power of the exit side lens surface is larger than the refractive power of the entrance side lens surface (| r ₁ |> | r ₂ |), (iii) and the rear focal point F is It is configured to be located rearward of the exit-side lens surface of each lens element.

For this reason, the parallel light flux from the light source means 10 enters each lens element of the main optical integrator 1 and is formed for each lens element from one light source image in a space separated from its exit surface by ε = bf _1. It Therefore, a plurality of light source images, the number of which is equal to the number of lens elements forming the main optical integrator, are formed on the surface B separated by ε from the exit surface of the main optical integrator 1. The respective light source images formed here are substantially surface light source images formed by a plurality of condensing points by the surface light source forming optical integrator 12 in the light source means 10.

Light fluxes from a plurality of light source images formed on the surface B separated from the exit surface of the main optical integrator 1 in this manner pass through the output lens 2 and are converged by the condenser lens 3 to form a reticle as an illuminated object. Illuminate on R. Then, a predetermined pattern on the reticle R is transferred onto the wafer W by the projection objective lens L. Here, a plurality of light source images formed on the surface B of the exit side space of the main optical integrator 1 are re-imaged on the surface C corresponding to the entrance pupil La of the projection objective L by the condenser lens 3, so-called. Koehler illumination is achieved. Since the output lens 2 functions as a field lens, like the positive lens surfaces on the exit side of the main optical integrator 1, it is not always necessary and can be removed.

Next, the light source means 10 in the above embodiment will be described in detail.

As shown in the perspective view of FIG. 4A, the surface light source forming optical integrator 12 is configured by bundling a plurality of square rod-shaped elements 102, and the incident surface 1 of each rod-shaped element 102 is formed.
02a is formed on the convex lens surface. The convex lens surface on the entrance surface 102a of each rod-shaped element 102 forms a light condensing point on the surface A of the space apart from the exit surface 102b of the rod-shaped element 102. Then, the number of condensing points equal to the number of rod-shaped elements 102 forming the optical integrator for forming the surface light source are formed on the surface A, and the plurality of condensing points substantially form the surface A. A surface light source is formed. Therefore, the light source 11 and the optical integrator for forming the surface light source are
A surface light source forming member is constituted by 12 and.

Here, since the laser light source is used, the light flux from the light source 11 is almost completely collimated, and it is considered that the individual condensing points formed on the surface A have substantially no size. For this reason, the exit side of the rod-shaped element 102 forming the optical integrator 12 for forming the surface light source does not require a lens action such as a so-called field lens. Therefore, the emission surface 102b of the rod-shaped element 102 is formed flat here. However, it is possible to give some lens action.

Then, the collimator lens is provided by the positive lens 14 which is arranged away from the surface A in order to avoid strong converging positions of a plurality of converging points by the surface light source forming optical integrator 12.
Regarding the system including 13 and the incident surface 101a of the main optical integrator 1, the A surface where a plurality of condensing points are formed and the B surface in the exit side space of the main optical integrator 1 are configured to be conjugate. Therefore, on the surface B in the emission side space of the main optical integrator 1, the rod-shaped element forming the optical integrator 12 for forming the surface light source is formed.
The number of condensing points corresponding to the product of the number of 102 and the number of rod-shaped elements 101 constituting the main optical integrator 1 is formed, and a uniform substantially surface light source is formed on this surface B.

The focal length of the positive lens 14 arranged on the exit side of the surface light source forming optical integrator 12 is substantially equal to the distance between the positive lens 14 and the incident surface of the main optical integrator 1. The focal point of the collimator lens 13 on the light source side substantially coincides with the A surface on which the plurality of condensing points are formed, and the light flux from the A surface is converted into a parallel light flux.

In addition, in the present embodiment, the first aperture stop S ₁ having a variable aperture is provided on the surface A of the exit side space of the surface light source forming optical integrator 12, and the inside of the exit side space of the main optical integrator 1 is provided. The second aperture stop S ₂ having a variable aperture is also provided on the surface B of FIG. This first aperture stop
By changing the aperture of S ₁ , it is possible to control the amount of light reaching the irradiated object while keeping the σ value constant, and by changing the aperture of the second aperture stop S ₂ , it is possible to control the σ value. The σ value is defined as the value of the ratio of the NA of the illumination optical system to the NA (numerical aperture) of the projection objective lens, and the balance between the resolution and the contrast of the projection objective lens can be adjusted by this value. Such a combination of the _two aperture stops S ₁ and S ₂ makes it possible to control the light amount and the σ value independently, and to change the light amount supplied from the light source and the projection pattern on the reticle R. Depending on the fineness of the resist, the characteristics of the resist applied on the wafer, etc.
It is possible to realize the optimum lighting condition.

Incidentally, it goes without saying that the light source 11 in the above-described embodiment includes a beam shaping optical system and a beam expander optical system for forming the laser beam into a beam shape having a substantially isotropic predetermined width. . Further, the present invention is not limited to the case where the light beam from the light source is constantly radiated onto the object surface such as the reticle R as in the above-mentioned embodiment.
As disclosed in Japanese Patent Laid-Open No. 226317 and Japanese Patent Laid-Open No. 61-212816, the present invention can be applied as it is to an illuminating device configured to scan a beam on an object plane.

FIG. 5 is an optical configuration diagram of the second embodiment according to the present invention,
By making the beam scan on the object plane, it is possible to eliminate illumination unevenness such as a speckle pattern due to the coherence of laser light. In FIG. 5, members having substantially the same functions as those of the members shown in FIG. 1 are designated by the same reference numerals.

The laser light flux supplied from the light source 11 is angularly scanned by the rotating mirror 30, and is incident on the afocal converter 40 including two positive lenses 41 and 42. The parallel light flux emitted from the afocal converter 40 is incident on the optical integrator 1 including a plurality of lens elements as shown in FIGS. 2 and 3.

Here, the afocal converter 40 enlarges or reduces the width of the laser rear side from the light source 11 at a desired magnification, and the afocal converter 40 causes the turning mirror 30 and the incident surface of the optical integrator 1 to be separated from each other. It is almost conjugate. Therefore, as the rotating mirror 30 rotates,
The angle of the parallel light flux incident on the incident surface of the optical integrator 1 continuously changes in a desired range, and a plurality of condensing points formed on the surface D in the exit side space of the optical integrator 1 are within this surface. Move continuously. At this time, one condensing point continuously moves on the surface D of the exit side space of one lens element that constitutes the optical integrator 1, and scans the exit side space on the surface D corresponding to the lens element. . In this way, a substantial surface light source is formed on the D surface in the exit side space of the optical integrator 1. The luminous flux from the substantial surface light source is guided by the condenser lens 3 onto the reticle R as an irradiated object, and the reticle R surface is uniformly illuminated in a predetermined time by the luminous fluxes from a plurality of condensing points. To be done. Then, a desired pattern on the reticle R is transferred onto the wafer surface by a projection objective lens (not shown).

Even in a configuration in which the incident angle to the optical integrator is variously changed by such beam scanning, and as a result, the laser speckle generated on the wafer surface is reduced, the exit surface of the optical integrator is configured by the configuration of the optical integrator according to the present invention. The risk of causing physical damage to the can be reduced.

Although each of the above embodiments is an illumination optical device of a projection type exposure apparatus, the present invention is not limited to this, and is effective as an illumination optical device of various exposure apparatuses. Also,
The configuration shown is a developed optical path diagram for the sake of clarity.In an actual device, it is desirable that a reflecting member is provided in a desired casting and the optical path is bent to make the entire device compact. Needless to say.

〔The invention's effect〕

As described above, according to the present invention, the formation position of the multiple light source images by the light source image forming means having a high light intensity is set as a space outside the multiple light source image forming means to avoid light collection inside the element or on the surface. Even if a light source with a very high light intensity such as a laser is used, there is no risk of destroying optical elements such as lenses. Then, an illumination optical device that can efficiently obtain a uniform light intensity distribution on the illuminated object is realized.

[Brief description of drawings]

FIG. 1 is a developed optical path diagram showing a schematic configuration of a first embodiment according to the present invention, FIG. 2 is a sectional optical path diagram showing an action of a rod-shaped element which constitutes a main optical integrator, and FIG. 3 is a perspective view illustrating its shape. FIG. 4A is a perspective view showing the shape of a rod-shaped element constituting an optical integrator for forming a surface light source used in the light source means, FIG. 4B is a sectional optical path diagram showing its action, and FIG. It is an optical-path figure which shows schematic structure of 2nd Example. [Description of Symbols of Main Parts] 1 ... Optical integrator (light source image forming means) 3 ... Condenser lens 10 ... Light source means 11 ... Light source 12 ... Surface light source forming optical integrator (surface light source forming member) R, W ... Irradiated object L: Projection objective lens

Claims (6)

[Claims] 1. A light source means for supplying a substantially parallel light flux, a light source image forming means for forming a plurality of light source images from the light flux supplied from the light source means, and a predetermined light flux from the light source forming means. In an illumination optical device having a condenser lens for uniformly illuminating an object surface, the light source image forming means is composed of an optical integrator composed of a plurality of lens elements arranged in parallel, and each lens element of the optical integrator is The entrance surface has a lens surface having a positive refracting power and the exit surface also has a lens surface having a positive refracting power, and the refracting power of the exit side lens surface of each lens element is the refraction of the entrance side lens surface. And a rear focal point of each lens element is located rearward of an exit side lens surface of each lens element,
Each of the lens elements collects a light beam from the light source means and forms a light source image in an external space other than an optical member between the lens element and the condenser lens. Illumination optical device. 2. The apex of the incident side lens surface of each lens element constituting the optical integrator is configured to substantially coincide with the incident side focal point of the exit side lens surface of each lens element. Claim 1 to
The illumination optical device according to the item. 3. The light source means has a member forming a substantially surface light source and a positive lens component for converting a light beam from the substantially surface light source formed by the member into a substantially parallel light beam. The illumination optical device according to claim 2. 4. A member forming the substantially surface light source includes a light source which emits a substantially collimated light beam, and another optical integrator which is disposed in the collimated light beam and forms a large number of condensing points. The illumination optical device according to claim 3, further comprising: 5. An optical integrator constituting a member for forming the substantially surface light source has a positive lens surface on the incident side and an exit surface located on the incident light side of a focal point on the exit light side of the positive lens surface. The illumination optical device according to claim 4, characterized in that it has. 6. The illumination optical apparatus according to claim 2, wherein the optical means has a scanning member for changing the angle of the parallel light flux incident on the optical integrator.