KR100204578B1 - Optical system of exposure apparatus - Google Patents

Abstract

BACKGROUND OF THE INVENTION 1. Field of the Invention [0002] The present invention relates to an optical system configured to focus a refracting power on a reflector to use a light source of a wide bandwidth.

The present invention, which is capable of reducing the number of lenses constituting the optical system and the thickness of all the lenses, includes a first lens group which is located at the rear end of the light source and is composed of four lenses, A second lens group, a second lens group, a second lens group, a second lens group, a second lens group, a second lens group, and a second lens group; And a third lens group consisting of five lenses corresponding to the surfaces.

Description

Optical system of exposure equipment

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical system of an exposure apparatus, and more particularly, to an optical system configured to use a wide-bandwidth light source by concentrating refractive power on a main reflecting mirror.

In the semiconductor manufacturing process, as the device density increases, miniaturization of the line width of a pattern constituting a circuit is required. In order to realize this, a stepper, which is an exposure equipment used in a semiconductor exposure process, . The function of the stepper for realizing the fine line width of the pattern is basically determined by the resolution of the optical system, and the resolution of the stepper optical system, that is, the resolution, is expressed by the following equation according to the wavelength of the light source and the numerical aperture of the optical system.

R = k ₁ ? / NA

Where R is the resolution, λ is the wavelength of the light source, NA is the numerical aperture of the optical system, and k ₁ is a constant.

Therefore, in order to form a finer pattern, it is necessary to use a light source of a shorter wavelength than the light source used in the conventional optical system, or further increase the numerical aperture of the optical system. Among these two methods, there are limitations in increasing the numerical aperture due to a problem in the process that the depth of focus becomes shallow and a problem in optical system such as aberration correction. For this reason, a method of shortening the wavelength of the light source is mainly adopted, and when an ultraviolet having a short wavelength is used as a light source, fused silica is the only optical material that can be practically used. However, since the absorption rate of molten quartz is also high, a loss of light due to high absorption is generated in a dioptric of the conventional concept at a wavelength of 193 nm or less, and thus the overall transmittance of the optical system is remarkably decreased and the practicality is halved .

To solve this problem, the thickness of fused quartz through which light passes is reduced by using a spherical lens or replacing some elements of the optical system with a reflector. In addition, as the size of a silicon substrate is increasing, a method of performing scanning without batch-wise exposure process has been attempted.

However, since a refracting optical system using only a lens or a part of an aspheric lens uses only fused quartz as an optical material, it is necessary to solve the problem caused by chromatic aberration only by the bandwidth of the excimer laser, There is no excimer laser with a narrow bandwidth.

SUMMARY OF THE INVENTION Accordingly, it is an object of the present invention to provide an optical system capable of reducing the number of lenses constituting the optical system and the thickness of the entire lenses.

The present invention for realizing the above-mentioned object is characterized by comprising a first lens group, which is located at a rear end of a light source and an object surface, and which is composed of four lenses, a second lens group which is located at a rear end of the first lens group, A wavelength plate and a main reflector positioned at the rear end of the polarization beam splitter, and an optical element positioned at the lower end of the wavelength plate and corresponding to an object surface to which light is irradiated, And a third lens group made of a lens.

FIG. 1 is an overall configuration diagram of an optical system according to the present invention; FIG.

2 is a detailed view of FIG. 1;

FIG. 3 is a graph showing the performance value (MTF: Modulation Transfer Function) of the optical system according to the spatial frequencies of the focus positions of the optical system shown in FIG.

FIG. 4 is a graph showing performance values of an optical crab according to the present invention at a spatial frequency of 2,000 cycles / mm; FIG.

DESCRIPTION OF THE REFERENCE NUMERALS

10: first lens group 20: second lens group

30: Third lens group 41: Polarizing light splitter

42: quarter wavelength plate 43: main reflector

50: wafer

Hereinafter, the present invention will be described in detail with reference to the accompanying drawings. 2 is a detailed view of FIG. 1, wherein the optical system of the present invention includes a first lens group 10, a second lens group 20, a polarization beam splitter 41, a polarized beam splitter, a wavelength plate 42, a main reflecting mirror 43, and a third lens group 30.

A light source R and an object surface 1 (hereinafter referred to as a mask used in a semiconductor exposure process) are located in front of the first lens group 10 and two prisms 41A, 41B are positioned. A quarter wave plate 42 and a spherical mirror 42 are disposed on the rear side of the polarization beam splitter 41 and a third lens group 30 and an object on which optical information is incident (Hereinafter referred to as a wafer which is an object of the exposure process) are respectively located.

On the other hand, the flat tube linear splitter 41 is formed by integrating the two prisms 41A and 41B, and the light beam splitting surface 41C, which is an area where the two prisms 41A and 41B are in contact with each other, . That is, the polarized light of the incident light source is transmitted through the light beam splitting surface 41C, but the light component perpendicular to the polarized light is reflected on the surface of the light beam splitting surface 41C. The polarized light of the light passing through the second lens group 20 is transmitted through the light beam splitting surface 41C of the polarization beam splitter 41 and irradiated onto the quarter wavelength plate 42, The polarized light (linearly polarized light) of the light is converted into circularly polarized light and irradiated to the main reflecting mirror 43. [ The light (circularly polarized light) reflected through the main reflecting mirror 43 again passes through the quarter-wave plate 42, and the circularly polarized light is changed to linearly polarized light. Therefore, the linearly polarized light is reflected 90 degrees without passing through the light beam splitting surface 41C and irradiated onto the third lens group 30. The information (information on the pattern formed on the surface of the mask 1) that has passed through the optical path is transferred to the surface of the wafer 50.

Each optical member of the present optical system for forming the optical condensation as described above will be described in detail as follows.

A. Light source (R)

In the present invention, an ArF excimer laser having a wavelength of 193 nm is used as the light source (R). The light emitted from the light source R passes through the mask 1 having the pattern formed thereon and then the light is split into light beams of the first and second lens groups 10 and 20 and the polarization beam splitter 41 The light reflected by the main reflecting mirror 43 passes through the surface 41C and the wavelength plate 42 and is reflected by the main reflecting mirror 43. The light reflected by the main reflecting mirror 43 passes through the third lens group 30 and is emitted to the wafer 50, Information (a pattern formed on the mask) is transferred onto the surface of the wafer 50.

B. First, second and third lens groups 10, 20 and 30,

The optical system used in the present invention is a catadioptric system having a reduction magnification of 1/4 and numerical aperture (NA) of 0.5, and has an image size of ø24 mm and an exposure area of 22 × 5 mm ² as a scan type.

The first lens group 10 located on the rear surface of the mask 1 is composed of four lenses 11, 12, 13 and 14 and is used for aberration correction. The third lens group 30 disposed under the polarization beam splitter 41 is composed of four lenses 21, 22, 23, and 24, and performs aberration correction and focusing. Aberration correction is performed in the process of transmitting light, and an image of a pattern finally formed on the mask 1 is formed on the surface of the wafer 50. [

C. The polarization beam splitter 41 and the light beam splitting surface 41C,

As described above, the two prisms 41A and 41B constituting the polarization beam splitter 41 are arranged in a state in which the light beam splitting surface 41C is tilted by 45 degrees with respect to the optical axis, It is coated to enable splitting. That is, the polarized light of the incident light source is transmitted through the light beam splitting surface 41C while the light component perpendicular to the polarized light is reflected on the surface of the light beam splitting surface 41C. Therefore, the polarized light of the light that has passed through the second lens group 20 is transmitted through the light beam splitting surface 41C of the polarization beam splitter 41 and irradiated to the quarter-wave plate 42.

D. The 1/4 wavelength flat plate 42 and the main reflecting mirror 43,

The light transmitted through the light beam splitting surface 41C of the polarization beam splitter 41 is transmitted through the wave plate 42 and the linearly polarized light of light is converted into circularly polarized light and irradiated to the main reflecting mirror 43. [ The circularly polarized light reflected through the main reflecting mirror 43 again has the quarter-wave plate 42, and the circularly polarized light is converted into linearly polarized light. Therefore, the linearly polarized light is reflected 90 degrees without passing through the light beam splitting surface 41C, and is irradiated to the third lens group 30 to transfer the information (information on the pattern formed on the mask surface) to the surface of the wafer 50. [

2 shows a state in which the quarter wavelength plate 42 and the main reflecting mirror 43 are disposed at the back of the polarization beam splitter 41. However, the lens groups 10, 20 and 30 are arranged on the same axis The quarter-wave plate and the main reflecting mirrors 42 and 43 may be positioned above the polarization beam splitter 41 in order to arrange the surface of the wafer 50 perpendicular to the optical axis.

The characteristics of the respective optical members constituting the optical system of the present invention are shown in the following Table.

FIG. 3 is a graph showing the MTF (Modulation Transfer Function) of the optical system according to spatial frequencies at the focal position of the optical system shown in FIG. 2. The center field (0.0 field) of the object up to a spatial frequency of 3,000 cycles / (Tangential) and sagittal (sagittal) performance values for the first, second, and third clocks, 0.5, 0.8, 0.9, and 1.0 field of the clock, respectively. It can be seen that it has a high resolution to balance.

FIG. 4 is a graph showing the performance values of the optical system according to the present invention at a spatial frequency of 2,000 cycles / mm. The performance values of the optical system for the spatial frequency of 2,000 cycles / , 0.5, 0.8, and 0.9, respectively. The graph shows the focal range as a performance value for a spatial frequency of 2,000 cycles / mm.

In the present invention as described above, it can be seen that the first lens group and the second lens group are used for aberration correction and condensation, and the main reflector determines the structure of the optical system, so that most of the refractive power is concentrated. It is possible to use a wide bandwidth light source. Also, by thinning the lenses of the first, second, and third lens groups, the entire optical system and the high transmittance can be obtained, and uniform high resolution can be obtained at all the viewing angles, so that a wide focal length range can be expected.

Claims (4)

An optical system of an exposure apparatus, comprising: a first lens group which is located at a rear end of a light source and an object plane and which includes four lenses; a second lens group which is located at a rear end of the first lens group and is composed of four lenses; 2, and a wavelength plate and a main reflecting mirror positioned at the rear end of the polarization beam splitter, and a light guide plate disposed at the lower end of the wavelength plate and corresponding to an object surface to which light is irradiated, And a third lens group made up of a long lens. The prism of claim 1, wherein the two prisms constituting the polarization beam splitter are arranged so that the light beam splitting surface, which is the area to be contacted, is tilted by 45 degrees with respect to the optical axis, And the light component perpendicular to the polarized light is reflected. The optical system according to claim 1, wherein the surface curvature radius, the refractive index, the thickness, and the distance from the front lens of each of the first lens group, the second lens group, and the third lens group are as follows. The optical system according to claim 1, wherein the main reflector has an oval radius of -329.0 mm and an interval from the wavelength plate is 8.5542 mm.