KR20020014299A - Reticle having blazed grating for correcting source shift - Google Patents

Abstract

PURPOSE: Provided is a reticle with a blaze lattice placed for correcting lighting system variance which varies blaze lattice pitch in corresponding to each location within a slit as angle error so that it corrects the angle error of source. CONSTITUTION: In the reticle which consists of a first side to form chrome pattern and a second side to form a diffraction lattice to adjust light system variance, the reticle with the blaze lattice placed for correcting lighting system variance is characterized by forming the blaze lattice(81, 82, 83) in a corresponding place within a scanner slit as each different condition such as various pitches for respective place to correct lighting system variance on reticle(80) glass side.

Description

Reticle having blazed grating for correcting source shift}

TECHNICAL FIELD The present invention relates to a reticle used in a lithography process, which is one of the manufacturing processes of a semiconductor manufacturing apparatus, and more particularly, to a reticle used to form a pattern on a wafer in an exposure apparatus such as a scanner.

With advances in semiconductor technology, high speed and high integration of semiconductor devices are in progress. In connection with this, the necessity of pattern refinement is gradually increasing, and refinement | miniaturization and high precision are calculated | required also in the size of a pattern. As the size of the pattern decreases, the specification of CD (critical dimension) uniformity also decreases proportionally, and efforts are being made to review and newly discover factors that were previously insignificant in the lithography process.

In recent years, the field of research on the effect of the aberration present in the illumination system on the CD uniformity has attracted attention. Among them, from the recent research on the measurement of the source shift and the effects of the illumination shift on the exposure result, there is an illumination shift in the actual exposure system, which causes a pattern abnormality in the defocused state. It is known that it causes and inhibits uniformity. In order to measure the illumination system displacement, a grating pinhole mask in which a grating pattern is formed in a pinhole is used to form a source image pattern by zero-order light and first-order light. do. For images with primary light, the grating pitch can be adjusted so that it overlaps the NA (numerical aperture) boundary of the projection lens. Observing how the left and right primary light images overlap the NA boundary will confirm the displacement of the illumination system. Can be. When the illumination system displacement is present, since the intensity and the optical path of the left and right primary light are different, it may cause pattern deformation and pattern movement.

On the other hand, in order to form a pattern on a wafer with an exposure apparatus such as a scanner, a reticle on which a disc pattern is drawn is required. The reticle according to the prior art is formed with a chrome pattern on one side, the other side of the reticle is made of a flat glass surface. When using the reticle according to the prior art having such a configuration, it is not possible to adjust the amount of light, direction, etc. of the light incident from the illumination system by itself. Therefore, the reticle according to the prior art is vulnerable to illumination system displacement or light quantity change on the surface thereof, so that the influence of the reticle is transferred as it is on the wafer.

An object of the present invention is to overcome the problems according to the prior art, to provide a reticle having a configuration that can correct the illumination system displacement in the exposure apparatus.

1 is a view showing a part of a typical reticle in which the grating pinhole is formed.

2 is a conceptual diagram illustrating a method of measuring an illumination system displacement in an exposure apparatus.

3 is a graph evaluating the effect of the illumination system displacement on the actual process margin.

4 is a cross-sectional view showing the main part configuration of the reticle according to a preferred embodiment of the present invention.

FIG. 5 is a diagram showing a source image formed by first-order diffraction light and zero-order diffraction light when there is an illumination system displacement at the same position of the projection lens.

6 is a cross-sectional view illustrating a grating pattern formed in the grating pinhole of the reticle.

FIG. 7 illustrates an example in which the illumination system displacement in the scanner slit is different from one position to another.

FIG. 8 is a cross-sectional view of a blaze grating for correcting illumination system displacement on a reticle glass surface according to the present invention at various pitches according to respective positions corresponding to respective positions in the scanner slit.

FIG. 9 illustrates a corrected source image formed for each position of a scanner slit after correcting illumination system displacement by applying the blaze grating shown in FIG. 8.

10A through 10F are cross-sectional views illustrating a method of manufacturing a reticle according to a preferred embodiment of the present invention in order of process.

<Explanation of symbols for the main parts of the drawings>

30: glass substrate, 30a: first surface, 30b: second surface, 32: diffraction grating, 80: reticle, 81, 82, 83, blaze grating.

In order to achieve the above object, the reticle according to the present invention comprises a first surface on which a chromium pattern is formed, and a second surface on which an opposite side of the first surface is formed, and a diffraction grating for adjusting illumination system displacement is formed. Include.

The diffraction grating may be configured in the form of a blaze grating having a triangular profile or a square profile.

In addition, the blaze grating may be formed at various pitches according to the amount of source displacement.

According to the present invention, a reticle capable of correcting the angle error of the source by varying the pitch of the blaze grating corresponding to each position in the slit according to the angle error of the source that varies for each position in the scanner slit.

Next, a preferred embodiment of the present invention will be described in detail with reference to the accompanying drawings.

In order to measure the illumination system displacement due to the non-telecentricity of the condenser lens, a conventional reticle 10 or a grating pinhole mask, in which a grating pinhole 11 is formed, is typically used as shown in FIG. 1. do. In order to measure the illumination system displacement, a grating 12 is formed inside the grating pinhole 11, and the pitch of the grating 12 is set such that the diffracted beam of the primary light reaches the NA boundary region of the projection lens. .

FIG. 2 is a conceptual diagram illustrating a method of measuring illumination system displacement in an exposure apparatus, wherein the zero-order light and the first-order light of a beam diffracted by the reticle 10 when there is an illumination system displacement at a source 21 of the illumination system. The imaging image on the same position 22 and the wafer 23 is shown. In order to measure the illumination system displacement, a source image pattern is formed on the wafer 23 to measure the degree of overlap with the NA boundary region of the same position 22, and through this degree of overlap, the center of the source image is moved to the same position (22). Measure how far from the center it is. At this time, the reticle 10 is placed on the mask stage of the exposure apparatus so that the upper surface on which the pattern is formed is exposed, and the wafer 23 coated with the conventional photoresist material is exposed through the reticle 10. Each diffraction beam is generated by the grating 12 pattern of the reticle 10. The non-uniformity of the shape and the light intensity of the source 21 is transferred by the zero-order light passing through the grating pinhole 11 linearly. The first diffraction beam is irradiated to the boundary portion of the same position 22. The illumination system displacement is measured from the shape of these diffraction beams.

When the illumination system displacement as described above exists, the image shift amount varies depending on the pattern period. Thus, for example, in the case of a pattern composed of two or more periods, such as in an active region pattern, image distortion occurs in the non-focal plane. Also, the amount of illumination system displacement may vary depending on the position within the exposure area. In this case, the CD uniformity of the pattern is affected.

3 is an evaluation of the effect of the illumination system displacement on the actual process margin, when the 0.20 μm line and space pattern is exposed using an annular type illumination system, when there is no displacement, It is a figure which shows the result of simulating a process window change with respect to these illumination system displacements, when it is divided into the case where the displacement amount is 0.1 (sigma) and the displacement amount is 0.2 (sigma). From the results of FIG. 3, it was confirmed that the optimum focus, depth of focus, and light intensity change as the amount of displacement increases, thereby predicting that pattern uniformity may decrease as the amount of displacement increases.

4 is a cross-sectional view showing the main part configuration of the reticle according to a preferred embodiment of the present invention. The reticle according to the present invention includes a plurality of diffraction gratings 32 for correcting the illumination system displacement on the second surface 30b, which is the opposite surface of the first surface 30a on which the chrome pattern on the glass substrate 30 is formed. Is formed. The diffraction gratings 32 may be formed to have various pitches according to the amount of illumination system displacement. The diffraction grating 32 may be configured in the form of a blazed grating having a triangular profile or a square profile. When the diffraction grating 32 is configured in the form of a blaze grating having a triangular profile, the diffraction grating 32 may be formed to have an appropriate range of machining angles γ depending on the amount of displacement of the illumination system.

The amount of illumination system displacement per position in the slit can be measured by the method described above with reference to FIGS. 1 and 2. Such illumination system displacement may soon be understood as the incident light source with an error at an angle that is not perpendicular to the reticle plane. Therefore, the illumination system displacement can be converted into an angle error amount that can be physically corrected.

5 and 6 are diagrams for explaining a process of converting an illumination system displacement into an amount that can be corrected by the diffraction grating 32 by developing a relationship between the illumination system displacement and an angle error, and FIG. 5 is a projection lens. FIG. 6 shows source images 42 and 43 formed by first-order diffraction light and zero-order diffraction light, respectively, when an illumination system displacement exists at the same position 41 of FIG. It is sectional drawing which shows the state in which the grating pattern 51 was formed in the grating pinhole.

In FIG. 5, the distance P between the center of the source image 42 formed by the first-order diffraction light and the center of the source image 43 formed by the zero-order diffraction light is given by Equation 1 according to Bragg's law. .

P * sin (θ) = nλ

In Equation 1, n is an integer. Therefore, the distance P between the center of the source image 42 formed by the first-order diffraction light and the center of the source image 43 formed by the zero-order diffraction light can correspond to the angle amount θ. In FIG. 5, it is assumed that the vector amount of the distance between the center of the source image 43 formed by the zeroth order diffracted light and the center of the same position 41 is r .

In FIG. 6, when the period of the grating pattern 51 on the reticle 50 is p , the angle error φ corresponding to the displacement of the illumination system in the horizontal direction may be represented by Equation 2.

In order to correct the calculated angular error using the blaze grating, the machining angle γ given by the width and depth of the blaze grating must be given. 4 shows the definition of the machining angle γ. Since the machining angle γ must be able to correct the source angle error in a given region, it can be calculated from the conditions that should be refracted in the vertical direction from the glass surface constituting the reticle 10. When the refractive index of air at 248 nm, the exposure wavelength at room temperature, and the refractive index of glass are n _o and n _q , respectively, the lattice processing angle γ that can correct the angle error φ of the source is given by Equation (3).

Since the machining angle γ varies depending on the distribution of angular errors in the exposure area, the γ (x, y) function depending on the coordinates of the glass surface can be calculated.

FIG. 7 illustrates an example in which the illumination system displacement in the scanner slit 71 is different from one position to another. When there is an illumination system displacement in the scanner slit 71, various patterns of source images 72, 73, and 74 are formed on the wafer when the grating pinhole is used. Here, the illumination system displacement was arbitrarily set. Based on the shift amount measured in FIG. 7, blaze gratings 81, 82, and 83 are formed on the glass surface of the reticle 80 corresponding to each position in the scanner slit 71. The results are shown in FIG. In FIG. 8, blaze gratings 81, 82, and 83 for correcting the illumination system displacement on the reticle glass surface are formed under different conditions, that is, various pitches, according to respective positions corresponding to respective positions in the scanner slit 71. In FIG. . The structure of the blaze grating corresponding to the amount of illumination system displacement in each source image 72, 73, 74 is as shown by "81", "82" and "83", respectively. FIG. 9 illustrates corrected source images 92, 93, and 94 formed by positions of the scanner slits 71 after correcting illumination system displacement by applying the blaze gratings 81, 82, and 83 shown in FIG. 8. Indicates.

Next, a method of forming a blaze grating satisfying the given gamma on the glass substrate 100 constituting the reticle will be described with reference to FIGS. 10A to 10F. In this example, a method of manufacturing a reticle in which a blaze grating having a rectangular profile is formed will be described.

Referring to FIG. 10A, a first etching region 102 is formed on a second surface 120 of the glass substrate 100 having the first surface 110 on which the chrome pattern 112 is formed, which is the opposite surface of the first surface 110. ) To form a first photoresist pattern 122.

Referring to FIG. 10B, a first step lowered by the first depth d1 from the second surface 120 by etching the first etching region 102 by using the first photoresist pattern 122 as an etching mask. A portion 102a is formed and the first photoresist pattern 122 is removed.

Referring to FIG. 10C, a second photoresist pattern 132 exposing the second etching region 104 is formed on the second surface 120 on which the first stepped portion 102a is formed.

Referring to FIG. 10D, a second step lowered by the second depth d2 from the second surface 120 by etching the second etching region 104 using the second photoresist pattern 132 as an etching mask. A portion 104a is formed and the second photoresist pattern 132 is removed.

Referring to FIG. 10E, a third photoresist pattern 142 exposing a third etching region 106 on the second surface 120 on which the first stepped portion 102a and the second stepped portion 104a are formed. To form.

Referring to FIG. 10F, a third step lowered by the third depth d3 from the second surface 120 by etching the third etching region 106 using the third photoresist pattern 142 as an etching mask. A portion 106a is formed and the third photoresist pattern 142 is removed. Thereby, the cross-sectional structure in which the blaze grating is formed on the glass substrate 100 which comprises a reticle is obtained.

Since the depth of each lattice grating formed by the etching amount of the glass substrate 100, that is, the first, second and third stepped portions 102a, 104a and 106a is fixed, in order to change γ for a given depth Should give a change in pitch between the grids. The angle error of the source may be corrected by varying the lattice pitch corresponding to each position in the slit according to the angle error of the source that varies for each position in the scanner slit.

In the reticle according to the present invention, a blaze grating is formed on the side opposite to the first surface on which the chrome pattern is formed in order to correct the illumination system displacement in an exposure apparatus such as a scanner. The blaze grating may have various structures and pitches according to the amount of displacement of the illumination system. Accordingly, the angle error of the source may be corrected by varying the blaze lattice pitch corresponding to each position in the slit according to the angle error of the source that varies for each position in the scanner slit.

The present invention has been described in detail with reference to preferred embodiments, but the present invention is not limited to the above embodiments, and various modifications can be made by those skilled in the art within the scope of the technical idea of the present invention. Do.

Claims (3)

A first surface on which a chrome pattern is formed, And a second surface constituting a surface opposite to the first surface, and having a diffraction grating for adjusting illumination system displacement. The reticle of claim 1, wherein the diffraction grating is configured in the form of a blaze grating having a triangular profile or a square profile. The reticle of claim 2, wherein the blaze grating is formed at various pitches according to a source displacement amount.