JPS63211624A - Optical device for illumination - Google Patents

Abstract

PURPOSE:To facilitate high brightness illumination having simple structure and excellent uniformity by repeating the reflection of laser beams and forming a plurality of bundles of rays, generating optical path difference. CONSTITUTION:Beams from a coherent light source are inclined and projected, multiple reflection is generated between two mirror surfaces, emitting one part as transmitted beams by a partial reflecting mirror surface, and a plurality of luminous flux having predetermined optical path difference are generated. A mirror such as a multiple reflection mirror 2 is disposed so that a normal is tilted at theta=15 deg. in the incident direction of laser beams L, the incident position of laser beams at one end does not constitute a total reflection mirror surface, and the mirror 2 is antireflection-coated and an incident port I is shaped. On the other hand, the partial reflecting mirror surface on the other end side is also antireflection-coated locally, a transmitting port O is shaped, reflecting beams are reflected by reflecting mirror surfaces C, and branched into transmitted beams and reflected beams by partial reflecting mirror surfaces R again, and incoherent luminous flux is formed. Accordingly, luminous flux from a secondary light source does not interfere mutually on the surface of a body to be irradiated.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an illumination optical device, and in particular, to an illumination optical device when coherent light is used as an exposure light source for forming fine patterns. This invention relates to a structure that reduces the negative effects of interference.

[Prior art and its problems]

2. Description of the Related Art As semiconductor technology advances, semiconductor devices, including ultra-LSIs, are becoming more highly integrated. Since higher integration of semiconductor devices is achieved by miniaturizing elements, there is an increasing demand for fine and highly accurate pattern forming technology.

Usually, photolithography technology is used to form fine patterns.

In recent years, with the development of lasers such as excimer lasers that emit light at high output in the ultraviolet region, which is the wavelength used in photolithography, laser light has been attracting attention as a new light source for semiconductor exposure equipment.

Laser light generally has high brightness and directivity, so
When used as an exposure light source, it is extremely effective, but due to the strong coherence characteristic of laser light, speckles occur on the mask surface and image plane, which poses a problem that hinders improvement in resolution.

Therefore, in order to reduce speckles on the mask surface and image surface, a method (Japanese Patent Application Laid-Open No. 2003-120000) of using optical fibers to create an optical path difference equal to the coherence length, and then branching into multiple beams and recombining them. 6O-247643),
A method of providing an optical path difference equal to the coherence length using a step prism (Japanese Unexamined Patent Publication No. 61-169815), or a method of moving the light source image by changing the incident angle of the laser beam to the lens that forms the light source image. One type of scan mirror (solid state technology, summer 80's)
, 115-121), etc. have been proposed.

By the way, the laser beam of a conventional spontaneous oscillation excimer laser has a full width at half maximum of about 0.3 mm and a coherence distance of 200 μm.
Since the optical fiber or step prism is relatively short, the optical path difference caused by the optical fiber or step prism is small, so it is easy to manufacture the optical fiber or step prism.

However, when performing reduction projection exposure using a reduction lens made of only quartz lens material, a narrow band oscillation excimer laser must be used as a light source. In this case, the full width at half maximum is 0. Since the wavelength is about 05 nm and the coherence distance is about 12.5 m+s, manufacturing is difficult because the length difference between each optical fiber or each step of the step prism is about 12.5 m+s. be.

In addition, since the excimer laser is a pulsed laser, with one scan mirror type, interference cannot be eliminated unless exposure is performed with a number of pulses of 1000 or more, and the number of repetitions is 500H.
z requires an exposure time of 2 seconds or more, which poses a problem in that the throughput becomes extremely poor.

The present invention has been made in view of the above-mentioned circumstances, and when a plurality of secondary light sources are formed from a coherent light source, the structure is simple and the light beams from these secondary light sources do not interfere with each other on the surface of the object to be illuminated. An object of the present invention is to provide an illumination optical device that has the following features.

[Means for solving problems]

Therefore, in the present invention, in an illumination optical device including a coherent light source and a secondary light source forming member for forming a plurality of secondary light sources from a luminous flux supplied from the coherent light source, the coherent light source and the secondary light source forming member are provided. An optical path difference generating means consisting of a total reflection mirror and a partial reflection mirror arranged parallel to each other and facing each other is disposed between the part and the part,
The light from the coherent light source is incident from a laser beam entrance formed in a part of these total reflection mirrors or partial reflection mirrors at an angle to the normal direction of these reflection mirrors, and is repeatedly reflected to the partial reflection mirror. It is designed so that it can be ejected to the side.

[Effect]

That is, for example, as shown in FIG. 5, the principle of this repeating reflection mirror is such that a total reflection mirror surface C and a partial reflection mirror surface R are arranged parallel to each other and face each other so as to be separated by a distance d. , a laser beam entrance opening (2) with a width W is provided at one end of the total reflection mirror surface C, and a partial reflection mirror surface R
Consider the structure of a repeating reflection mirror in which a laser beam exit opening O with a width W is also provided at the other end. First, it is assumed that laser light is made to enter from the laser light entrance so as to form an angle θ with respect to the normal line of these reflecting mirror surfaces.

At this time, the laser light entering from the laser beam entrance hits the region R1 of the partial reflection mirror, and part of it is emitted as transmitted light T1, and the rest is reflected by the region R1 and hits the region C1 of the total reflection mirror surface. .

The light hitting this region C1 is totally reflected and illuminates the region R2 of the partially reflecting mirror. A part of the light irradiating this region R2 is emitted as transmitted light T2, and the rest is reflected by the region R2, and irradiates the region C2 of the total reflection mirror.

When transmission and reflection are repeated n times in this manner, all the light that finally hits the laser beam exit O is emitted as transmitted light Tn, and a luminous flux consisting of n rays with optical path differences between each other. can occur.

Here, if the angle formed by the incident laser beam with respect to the normal direction of the repeating reflection mirror is θ, the interval between the total reflection mirror surface C and the partial reflection mirror surface is d, and the refractive index of the medium between the mirrors is n, then X m 2 n d cos θ (1
) For details on the coherence length, please refer to Max Horn and Emil Wolff's ``Principles of Optics''.
If the center wavelength of the light beam supplied from a coherent light source is λ and the wavelength width is Δλ, then the coherence length is -λ2/Δλ... ... (
2) is given by

Therefore, by designing the repeating reflection mirror so that X>, it is possible to obtain light beams that do not interfere with each other.

〔Example〕

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

As shown in FIG. 1, this illumination optical device has a full width at half maximum of 0.
A narrow band oscillation excimer laser light source 1 that outputs a coherent laser beam of 005na+, a repeating reflection mirror 2 that generates a beam of light with an optical path difference from the laser beam, and a plurality of secondary light sources 3 near the exit surface. It is composed of an integrator (fly's eye lens) 4 to form the reticle, and a condenser lens 5 to condense the light from the secondary light source, so that the surface of the reticle 6 is irradiated with laser light.

As shown in a partially enlarged view in FIG. 2, this repeating reflection mirror 2 has a refractive index of n-1, a thickness of d=
It is made by coating both sides of a 4.5 mm quartz substrate 2S with a total reflection mirror surface 2C and a partial reflection mirror surface 2R, respectively, and the normal to the direction of incidence of laser light is θ-1.
5@ It is arranged so as to be inclined, and the laser beam incident position at one end does not constitute a total reflection mirror surface, but is coated with an antireflection coating to form an entrance port I. On the other hand, a portion of the partially reflecting mirror surface on the other end side is also coated with an anti-reflection coating to form a transmission aperture O, and like the above-mentioned repeating mirror, only one portion of the light hits the partially reflecting mirror surface R. The light is branched into transmitted light and reflected light, the reflected light is further reflected by the reflective mirror surface C, and is again branched into transmitted light and reflected light by the partially reflective mirror surface R...thus, the optical path difference 2 n d cos θ
The light beam is configured to continue to be reflected repeatedly while causing the light beam to form a non-wavelength light beam.

The full width at half maximum of the narrowband oscillation excimer laser used here is 0.
．． The length is 005n-, and the coherence distance is 12°511I1
It is about 1.

On the other hand, the optical path difference caused by the repeating reflection mirror is 2 n d cos θ −2X1. 5083
8X4. 5mII

Therefore, when this illumination optical device is used for exposure in photolithography, it is possible to form extremely precise fine patterns without speckles.

Furthermore, the repeating reflection mirror used here has a simple structure, is inexpensive, and is easy to manufacture.

Furthermore, this repeating reflection mirror has a light utilization efficiency of 100
%, and compared to the conventional method using an optical fiber as the optical path difference generating means, the light utilization efficiency is significantly increased.

Further, it is possible to easily generate a light beam having an infinite number of optical path differences.

In addition, since it is possible to perform exposure without interference with a lower number of pulses than in the conventional single scan mirror type, exposure time can be reduced and throughput can be improved.

In addition, in the embodiment, the reflectance of the partial reflection mirror was set to be constant over the entire surface, but in reality, each mirror region R1
...The intensity of the transmitted light from Rn is somewhat non-uniform.

Therefore, it is possible to make the intensity uniform by changing the reflection of the partial reflection mirror for each region.

That is, in FIG. 5, the partial reflection mirror R is R1...
- Suppose that it is divided into Rn regions and divided into n luminous fluxes, and when the incident light intensity is 1, the intensity of transmitted light from each region T 1-
T n is T 1 m T 2- T 3 ・= −−T
The relationship n-1/n should be satisfied. Each area R1・
...If the reflectance at Rn is expressed as R1...Rn,
TI-(1-R1) T2- (1-R1-TI)(1-R2)-(1-R1
-1/n) (1-R2) Tk-(1-ni/n) (1-Rk) Tn-(1-n/n) (1-Rn) Each area is set so that the above n formulas are satisfied. Reflectance R1...R
By determining n, it becomes possible to irradiate light with uniform light intensity over the entire surface.

In addition, in the embodiment, the repeating reflection mirror is formed on the quartz substrate 2S.
A total reflection mirror surface and a partial reflection mirror surface were formed on both sides of the substrate, but the substrate is not limited to a quartz substrate. Other materials may be used as long as the thickness is taken into consideration according to the refractive index, and two mirrors are arranged facing each other at a predetermined interval, that is, an air gap is formed. It is also effective. For example, if laser light with the same full width at half maximum as in the example is made to enter from the same direction, the refractive index is n-1, so by substituting it into equation (1), the air gap d' is 2d' cos 15''< 12
．． 5 d'> 6.47 m+s.

Furthermore, as shown in FIG. 3, by combining two repeating reflection mirrors, the first repeating reflection mirror 20 and the second repeating reflection mirror 30, a light beam consisting of incoherent light rays is generated in a lattice pattern. You can do it like this.

That is, the first repeating reflection mirror 20 generates a light beam in the vertical direction, the second repeating reflection mirror 30 generates a light beam in the horizontal direction, and the light beams can be generated in a lattice pattern.

In addition, as shown in FIG. 4, there is an entrance to the partial reflection mirror 2R'! Also effective is a repeating reflection mirror in which an exit opening O is formed and the laser beam is incident from the partial reflection mirror side and is repeatedly reflected.

〔Effect of the invention〕

As described above, according to the illumination optical device of the present invention, a total reflection mirror surface and a partial reflection mirror surface are separated by a predetermined distance by using an optical path difference as a means for generating an optical path difference while using a coherent light source of laser light. The two mirrors are placed facing each other, and one of the two mirrors is provided with a light entrance, and one of the two mirrors is arranged on the optical path at an angle with respect to the direction of light incidence. Light reflects repeatedly,
Since multiple beams of light are formed while creating an optical path difference, it is possible to perform high-intensity illumination with a simple structure and extremely excellent uniformity, and when used for exposure in photolithography, the throughput is reduced. Since it is possible to use light with a shorter wavelength (laser), it is possible to obtain a fine pattern with extremely high precision.

[Brief explanation of the drawing]

FIG. 1 is an explanatory diagram of an illumination optical device according to an embodiment of the present invention, and FIG.
The figure shows a repeating reflection mirror used in the same device, FIGS. 3 and 4 show modified examples of the repeating reflection mirror, and FIG. 5 is a diagram illustrating the principle of the repeating reflection mirror of the present invention. C... Total reflection mirror surface, R... Partial reflection mirror, L... Laser light, 1... Excimer laser light source, 2... Repeated reflection mirror, 2S... Quartz substrate, 2C... ... Total reflection mirror surface, 2R, 2R' ... Partial reflection mirror surface, 3 ... Secondary light source, 4 ... Integrator, 5 ... Condenser lens, 6 ... Reticle, 20 ... First repeating reflection mirror, 30...Second repeating reflection mirror, ■.
... Inlet port, 0... Input port. Figure 1 S Figure 2 Procedure? ■Authentic (spontaneous) April 1, 1986 2, Name of the invention Illumination optical device 3, Relationship to the famous case for amendment Patent applicant (123) Komatsu Ltd. 4, Agent (104) Tokyo 6th floor, Ginza Daisaku Building, 2-11-2 Ginza, Chuo-ku, Tokyo Tel: 03-545-3508 (Representative) 5
, Detailed Description of the Invention column and Brief Description of Drawings column 6 of the object of the amendment ” is corrected. (2) Correct "X>" in the second line of page 8 to "X>l". (3) Correct "optical path difference" on the 19th line of page 13 to "optical path difference." (4) On page 14, line 11, "Can be done. 4゜Drawing section" should be corrected to "Can be done." (5) "Simple explanation" in the second line of the same page is corrected to "4. Brief explanation of the drawings."

Claims (2)

[Claims] (1) A coherent light source, a secondary light source forming member for forming a plurality of secondary light sources from a luminous flux supplied from the coherent light source, and a secondary light source forming member interposed between the coherent light source and the secondary light source forming member. An illumination optical device comprising an optical path difference generating means, wherein the optical path difference generating means has a total reflection mirror surface and a partial reflection mirror surface arranged facing each other so as to be parallel to each other and spaced apart by a predetermined interval. a mirror surface, the light from the coherent light source is incident at an angle to an entrance provided at one end of one of the two mirror surfaces, and is transmitted as transmitted light on the partially reflecting mirror surface. What is claimed is: 1. An illumination optical device characterized in that it is configured to cause a plurality of light beams having a predetermined optical path difference by repeatedly reflecting between two mirror surfaces while emitting a portion of the light beams. (2) The partially reflecting mirror surface is configured to be divided into a plurality of regions, and the reflectance of each region is successively changed stepwise.
) The illumination optical device described in item 1.