KR960006824B1 - Adjuster of stepper - Google Patents

Abstract

Light interception and transmission regions of the diaphragm are in a grid repeated to convert the light transmitted through fly eye lens into diffracted light. The size of the grid is several mm. Using the stepper, the resolution of the lens can be enhanced by about 15%, even if the NA value of the lens is low.

Description

Stepper aperture

1 is a block diagram of a stepper.

2 is a plan view showing the aperture shape of a conventional stepper.

3 is a plan view showing a lattice stop shape according to the present invention.

4 is a diagram showing gray light generated through the lattice aperture.

5 (a) and (b) show that the incident light and the vertically incident light pass through the mask and the transparent lens.

* Explanation of symbols for main parts of the drawings

1: disc mirror 2: mercury lamp

3: reflector 4: fly-eye lens

5: aperture 6: reflector

7: condenser lens 8: mask

9: transparent lens 10: wafer

The present invention relates to a stepper aperture which is an exposure apparatus used to form a pattern in a semiconductor manufacturing process.

In the photolithography process technology, exposure technology for improving the resolution has been continuously developed in the direction of increasing the NA (Numerical Aperture) of the lens and reducing the wavelength (λ) of the exposure light. Therefore, the relation can be expressed by the following Rayleigh equation.

Conventionally, the exposure technique uses a stepper as an exposure apparatus. Referring to FIG. 1, the configuration and operation of the stepper will be described below.

Visible light emitted from the mercury lamp (2) is reflected by the original mirror (1) and the reflector (3), and then connected, and then a bundle of optical fibers or quartz rods is used to transmit light having a specific wavelength by the filter and improve uniformity. The circular diaphragm 5 is installed at the focal position of the fly's eye lens 4 in order to block the diffracted light around the adjacent vicinity after passing through the fly's eye lens 4 composed of The light transmitted through the diaphragm 5 is focused on the condenser lens 7 by the reflector 6, transmitted through the mask 8 to the transparent lens 9, and irradiates the transmitted light beam on the wafer 10 in parallel. . At this time, the diffraction light having harmonic components is generated by the lattice pattern present on the mask, of which at least zero order light, +1 order light and -1 order light are focused through the incident pupil of the projection lens, Spatial image shape transfer is possible. At this time, the 0th order light affects the light intensity, and the ± 1st order light determines the light contrast, enabling image formation, and the image fidelity of the mask pattern on the wafer so that a large number of harmonic components such as ± 2nd order and ± 3rd order can be focused. Is improved.

Based on the optical axis, the diffraction angle of ± 1st order And increases with increasing exposure wavelength and decreasing grating pattern size P on the mask.

Therefore, very large lens NA needs to be manufactured to simultaneously focus the 0th order light and the ± 1th order light that have passed through the small pattern size.

In addition to increasing the NA sharply reducing the focus margin, there are also various technical limitations in manufacturing, so the practical lens NA has been reported to be about 0.60 for the G and I lines, and about 0.50 for the DUV stepper lens.

The conventional aperture formation is as shown in FIG. Conventionally, the circular structure (a) is mainly used, but the structure of the diaphragm that blocks the central portion through which light passes and transmits the edge portion is improved as shown in (b), (c), and (d). The problem arises in the uniformity distribution of light.

Therefore, in order to solve the problem of the uniformity distribution of light, the stepper aperture is formed into a lattice diaphragm shape in consideration of the size and shape of the fly's eye lens to obtain uniform light intensity and high light intensity. The purpose is to provide an aperture of a stepper to obtain a.

Hereinafter, the present invention will be described in detail.

3 shows the manufacture of a stepper stop by a lattice stop according to the present invention. When passing through the lattice aperture, diffraction light having a myriad of harmonic components is generated as shown in FIG.

FIG. 5 (a) shows light focused through the transparent lens 9 when ± 1st diffraction light enters the mask 8 inclinedly, and ± 1st diffraction light on the mask pattern is obliquely incident In this case, the diffracted light plays the role of zero-order light based on the mask upper surface. When the inclined incident ± 1 order light is defined as 0 order light, the ± 1 order light and 0 order light generated when the mask is transmitted are focused on the incident pupil of the transparent lens separately according to the incident direction. Shape transfer is possible. At this time, the original zero-order light passing through the lattice aperture affects the light intensity when passing through the mask pattern, but does not help to improve the image contrast. As the light uses only two light beams, 0th and + 1st, or 0th and -2nd, when the incidence of light is inclined, the lens has a small NA value, so that the diffraction light can be focused and the resolution is improved. For the resolved pattern, a small NA lens is actually used, thereby improving the focus margin.

As shown in FIG. 5B, in the conventional vertical incidence method, an angle with respect to the ± first-order diffracted light generated when the mask 8 is transmitted is given as sin θ = λ / P around the optical axis. Where sin θ is the angle of the first order diffracted light, λ is the wavelength of the incident light, and P is the pitch size of the mask image pattern.

That is, as the pattern size P on the mask is smaller, the angle of the diffracted light increases. Therefore, in the conventional exposure method which enables image formation transfer by focusing the zero-order light and the ± 1-order light simultaneously, a larger high NA lens is required as the pattern size on the mask to be formed is reduced.

The manufacturing method of the iris is possible by placing a light shielding agent such as chromium (Cr) on a substrate of quartz (Qz), CaF ₂ , LiF ₂ and the like having a high transmittance of irradiated light. It is possible by forming a hole to be made.

The shape of the region through which light transmits may be any shape, such as a circle, a hexagon, a hexagon, and an oval. Depending on the size of the pattern to be resolved and the characteristics of the process, the distance between each other and the size of the light transmitting hole may be optimized. Uniformity of light intensity distribution can be improved by setting the light shielding and transmission region in a lattice shape, and the angle of ± 1st order diffracted light can be adjusted by adjusting the grating size, so that the incident angle according to the pattern size on the mask can be freely adjusted.

According to the present invention, since the image formation can be transmitted using only two lights by inclined incidence instead of the conventional vertical incidence method, the resolution having a low NA value is improved by 15% or more compared with the conventional method. Therefore, the process capability of the exposure apparatus can be extended by the oblique incidence method, and the process improvement effect of the same trend as the phase inversion mask can be expected by using the classical mask.

Claims (2)

The stopper of the stepper, the step of the stepper, characterized in that the light transmitted through the fly-eye lens is formed in a lattice shape of the light blocking and the transmission region is repeated so that the diffracted light is formed. According to claim 1, wherein the lattice is a stepper aperture, characterized in that formed in a few mm size.