JP7513823B1 - Exposure apparatus and exposure method - Google Patents

Abstract

[Problem] To provide an exposure apparatus and exposure method capable of shortening the time interval between the first exposure and the second exposure and realizing highly accurate stitched exposure. [Solution] The exposure apparatus is equipped with a mask stage 101 on which two masks 103a, 103b are mounted, and a wafer stage 102 on which a wafer 105 is mounted, and scans so that the scan direction of the wafer stage 102 when exposing the pattern of the first mask onto the wafer and the scan direction of the wafer stage 102 when exposing the pattern of the second mask onto the wafer are opposite to each other. [Selected Figure] Figure 1

Description

This disclosure relates to an exposure apparatus and exposure method used in EUV lithography (Extremely Ultraviolet Lithography) in the lithography process of semiconductor manufacturing.

In the semiconductor lithography process, ArF lithography, which uses an ArF excimer laser with an exposure wavelength of 193 nm as the exposure light source, uses an exposure device called an ArF exposure machine. Also, immersion lithography, which improves resolution by filling the space between the objective lens of the exposure machine and the wafer with water, uses an exposure device called an immersion exposure machine. These exposure machines are used in the mass production of most devices, including memory and logic. On the other hand, for the production of cutting-edge devices with particularly fine patterns, an exposure device called an EUV exposure machine with an exposure wavelength of 13.5 nm is used.

These exposure machines are sometimes called scanning exposure machines, or scanners for short, because the mask stage holding the mask and the wafer stage carrying the wafer are scanned in opposite directions at the moment of exposure. The scanner scans the mask and wafer while irradiating a narrow area (a narrow area in the width direction perpendicular to the scanning direction) of the pattern area on the mask (the area where the device pattern is drawn) with exposure light. In this way, the entire pattern area can be exposed. Note that the current mask magnification is 4x, so the pattern size on the mask surface is 4x the pattern size exposed on the wafer surface.

In addition, in future EUV lithography, in order to achieve even finer features, it is being considered to increase the NA (numerical aperture) of the projection optical system from the conventional 0.33 to 0.55. However, as the NA increases, the angular range of light that spreads from a point on the mask surface and the angular range of light that converges to a point on the wafer surface also become wider. This results in an increase in the amount of light that reduces the reflectance (which depends on the angle of incidence) on the mask surface. Therefore, in terms of the scanning direction in which the chief ray is tilted, the mask magnification is increased from 4x to 8x so that the angular range does not become wider. In other words, by increasing the magnification, the NA on the mask side becomes smaller and the angular range becomes narrower.

However, the width direction perpendicular to the scan direction is 4 times as before, so the mask magnification is 8x4 times, depending on the direction. As a result, when a normal 6-inch mask (a standard mask with a substrate size of a square with each side being 6 inches, hereafter referred to as a 6-inch mask) is used, the area exposed on the wafer is half the size of the conventional method (called full field), so it is called half field. Specifically, the maximum area of the pattern on the mask is 132 mm in the scan direction and 104 mm in the width direction, so on the wafer, in half field, it is 16.5 mm in the scan direction (33 mm in full field). However, in the width direction, both are 26 mm.

Therefore, when manufacturing a device larger than the half field (hereinafter referred to as a large device), two masks are required, and it is necessary to exchange the mask and perform exposure twice. The high NA type EUV exposure tool mentioned above is explained, for example, in the following non-patent document 1.

Jan Van Schoot, et. al., “High-NA EUV lithography exposure tool: program progress,” Proceedings of SPIE Vol. 11323, 1132307 (2020).

When exposing a large device that requires two masks with a high NA EUV exposure tool, a special exposure called stitching exposure is required at the joint between the half-field from the first mask and the half-field from the second mask, where the two masks overlap slightly.

In stitching exposure, two exposures using two masks must be performed with extremely high positional accuracy. Furthermore, when the resist is irradiated with exposure light, the chemical properties of the exposed area change rapidly over time, so it is desirable to shorten the time interval between the first and second exposures as much as possible and move quickly to the next process, PEB (Post Exposure Bake). However, in reality, only one side of the exposure using the first mask is performed on a large number of wafers, and then the second mask is switched to perform the other side of the exposure, which creates a problem of an extremely long time interval between the first and second exposures.

Even if a mask stage capable of carrying two masks (hereafter referred to as a two-mask stage) could be used, the exposure area on the wafer when scanned in the same manner as in the past would be formed separately as half-field exposure area 106a and exposure area 106b on the wafer, as shown in FIG. 13, and would not be formed as one full field. FIG. 13 shows a side cross-sectional view of the two-mask stage 101 and the wafer stage 102, as well as a plan view of them from above. The areas near the boundaries in the scanning direction in the pattern areas 104a and 104b of the two masks 103a and 103b are indicated as A, B, C, and D, which correspond to the exposure area 106a on the wafer 105 and a, b, c, and d of the exposure area 106b.

The objective of this disclosure is to provide an exposure machine that can perform exposures with two masks in an extremely short time using a dual mask stage when exposing a large field device pattern.

To achieve the above goal, the exposure machine of the present invention is equipped with a mask stage that carries two masks and a wafer stage that carries a wafer, and scans the masks so that the scanning direction of the wafer stage when exposing the pattern of the first mask onto the wafer is opposite to the scanning direction of the wafer stage when exposing the pattern of the second mask onto the wafer. This makes it possible to join the exposure area where the pattern of the first mask is projected onto the wafer and the exposure area where the pattern of the second mask is projected onto the wafer.

According to the present disclosure, when performing pattern exposure on a large chip that requires two masks, exposure using each of the two masks can be performed in a short time, thereby achieving highly accurate stitched exposure.

1 is a schematic diagram showing an EUV exposure tool 100 according to a first embodiment. 2 is a schematic diagram showing an exposure state in the EUV exposure machine 100. FIG. 2 is a schematic diagram showing an exposure state in the EUV exposure machine 100. FIG. 2 is a schematic diagram showing an exposure state in the EUV exposure machine 100. FIG. 2 is a schematic diagram showing an exposure state in the EUV exposure machine 100. FIG. 2 is a schematic diagram showing an exposure state in the EUV exposure machine 100. FIG. 2 is a schematic diagram showing an exposure state in the EUV exposure machine 100. FIG. 2 is a schematic diagram showing an exposure state in the EUV exposure machine 100. FIG. 1 is a schematic diagram showing misalignment of two masks in an EUV exposure tool 100. FIG. 10 is a schematic diagram showing correction of the second exposure position in the EUV exposure tool 100. FIG. 10 is a schematic diagram showing correction of the second exposure position in the EUV exposure tool 100. FIG. 10 is a schematic diagram showing correction of the second exposure position in the EUV exposure tool 100. FIG. FIG. 1 is a schematic diagram showing an exposure state of a conventional high NA type EUV exposure tool.

First embodiment
Hereinafter, embodiments of the present invention will be described with reference to the drawings. A first embodiment of the present invention will be described with reference to Figs. 1 to 8. Fig. 1 is an explanatory diagram illustrating only a mask stage 101 and a wafer stage 102 of an EUV exposure machine 100. Figs. 2 to 8 are schematic diagrams for explaining the scanning operation of the mask stage 101 and the wafer stage 102. Here, for clarity of explanation, an XYZ three-dimensional orthogonal coordinate system will be used for explanation. Mask 103a
A plane parallel to the main surface of mask 103a, 103b is defined as the XY plane. A direction perpendicular to the main surfaces of masks 103a, 103b, i.e., the thickness direction of masks 103a, 103b, is defined as the Z direction. The X and Y directions are parallel to the edges of rectangular masks 103a, 103b.

In reality, there is a reduction projection optical system between the mask stage 101 and the wafer stage 102, but it is omitted here. The NA of the projection optical system is a high NA of 0.55. The EUV exposure machine 100 uses a two-mask stage 101 that can carry two masks (mask 103a and mask 103b). Mask 103a has a pattern area 104a in which an exposure pattern is formed. Mask 103a has a pattern area 104a in which an exposure pattern is formed.

Pattern areas 104a and 104b on masks 103a and 103b are 132 mm in the scanning direction (horizontal direction in the figure). Masks 103a and 103b are placed on mask stage 101 so that they are spaced apart in the X direction. For example, the gap between pattern area 104a of mask 103a and pattern area 104b of mask 103b is g.

As in FIG. 13, the ends of the pattern area in the scanning direction are A and B in mask 103a, and C and D in mask 103b. That is, the end on the -X side of pattern area 104a is A, and the end on the +X side is B. The end on the -X side of pattern area 104b is C, and the end on the +X side is D. The distance from B to C is g. As in FIG. 13, the positions on wafer 105 where A to D should be exposed are also shown as a to d.

In the EUV exposure machine 100 of this embodiment, unlike the two separate exposure areas 106a, 106b on the wafer shown in the lower part of Figure 13, which is an explanatory diagram of a case where the present invention is not applied, the exposure areas 106a and 106b are formed as one closely-contacted full field. The details of this mechanism will be explained using Figures 2 to 8.

Illumination light IL from the light source is reflected by the masks 103a and 103b and enters the wafer 105. The illumination light IL is EUV light with an exposure wavelength of 13.5 nm. As shown in FIG. 2, the mask stage 101 scans leftward (-X direction), and the wafer stage 102 scans rightward (+X direction). In other words, the mask stage 101 and the wafer stage 102 move in opposite directions. The illumination light IL is irradiated onto the left end A of the pattern area 104a of the mask 103a on the mask stage 101, and exposure begins (the dotted line shows the principal ray CR of the illumination light IL, and in reality, the angle of incidence with respect to the wafer 105 is 6 degrees). As a result, the right end a of the exposure area 106a is formed on the wafer 105 on the wafer stage 102. Note that although a to d are to be exposed on the wafer 105, they are shown by dotted lines because they have not yet been exposed. In Figures 2 to 8, unexposed areas on the wafer 105 are shown with dotted lines, and exposed areas are shown with solid lines.

Next, as shown in FIG. 3, when the right edge B of pattern area 104a of mask 103a is illuminated by scanning, exposure of exposure area 106a ends (on wafer 105, exposed areas from a to b are indicated by solid lines). Immediately after this, pattern area 104b of mask 103b on mask stage 101 crosses the chief ray CR of illumination light IL, but scanning continues without illumination at this time. In other words, as shown in FIG. 4, mask stage 101 and wafer stage 102 only perform scanning without illumination light L1 illuminating masks 103a and 103b. For example, by stopping the light source or blocking the light with a shutter or the like, it is possible to perform only scanning without exposure to illumination light IL.

Next, as shown in FIG. 5, when the chief ray CR of the illumination light IL passes d on the wafer 105 (i.e., passes the entire full field to be exposed) and reaches a distance L from d on the wafer, the wafer stage 102 starts to invert. At this stage, the area between c and d on the wafer 105 is not exposed, and is therefore shown by a dotted line. The wafer stage 102 is moving in the -X direction. The mask stage 101 is also moving in the -X direction. The value of L is approximated by the following equation (1) as a function of the distance shown as g in FIG. 1 (the distance between pattern area 104a and pattern area 104b). For example, if g is 40 mm, L is 5 mm.

2L = g/4 ... (1)

Next, immediately after the chief ray CR of the illumination light IL passes D of the mask 103b on the mask stage 101, the mask stage 101 starts to invert (Figure 6). This causes the mask stage 101 to move in the +X direction. Immediately after that, the chief ray CR of the illumination light IL reaches D of the mask 103b again, and exposure of the exposure area 106b begins (Figure 7). In other words, the illumination light IL is reflected by the mask 103b and enters the wafer 105. In synchronization with the inversion of the mask stage 101, the illumination light IL is irradiated onto the mask 103b. Then, the exposure of the exposure area 106b ends when the chief ray CR of the illumination light IL reaches C of the mask 103b (Figure 8).

As described above, during exposure of the exposure area 106a (from a to b) on the wafer 105, the wafer stage 102 scans in the +X direction, but during exposure of the exposure area 106b (from d to c), the wafer stage 102 scans in the -X direction. In other words, the scanning direction of the wafer stage 102 is opposite when exposing the exposure area 106a and when exposing the exposure area 106b. Also, the scanning direction of the mask stage 101 is opposite when exposing the exposure area 106a and when exposing the exposure area 106b. As a result, the exposure area 106a and the exposure area 106b are joined, and the full-field exposure is completed. This method makes it possible to shorten the time interval between the first exposure and the second exposure, thereby realizing highly accurate stitching exposure.

Next, the fine adjustment of the position of the exposure area 106b in the EUV exposure machine 100 will be described with reference to FIGS. 9 to 12. In the EUV exposure machine 100, two masks, 103a and 103b, are held by the mask stage 101. For this reason, as shown in FIG. 9, there is a possibility that the masks 103a and 103b may be misaligned in the Y direction. In other words, there is a possibility that a slight shift (width direction misalignment) occurs in the width direction (Y direction) between the pattern area 104a of the mask 103a and the pattern area 104b of the mask 103b at a level that cannot be detected by the naked eye. However, when the masks 103a and 103b are held by the mask stage 101, it becomes difficult to mechanically fine-tune the mask 103b so that this shift can be reduced to zero. Note that FIG. 9 shows a state in which the masks 103a and 103b are significantly misaligned for ease of understanding.

As shown in FIG. 10, the EUV exposure machine 100 can shift and fine-tune in the width direction (Y direction) when the mask stage 101 is inverted, which is performed after the exposure of the exposure area 106a is completed and before the exposure of the exposure area 106b is started. More specifically, the mask stage 101 can be moved in the Y direction after the exposure of the exposure area 106a in FIG. 3 is completed and before the exposure of the exposure area 106b in FIG. 7 is started. By moving the wafer stage 102 in the Y direction, the positional misalignment between the mask 103a and the mask 103b can be cancelled out and exposure can be performed. The mask stage 101 may be moved in the Y direction instead of the wafer stage 102.

When this shift is performed when there is no misalignment between pattern area 104a of mask 103a and pattern area 104b of mask 103b, exposure area 106b will be misaligned in the width direction relative to exposure area 106a, as shown in Figure 11 or Figure 12. On the other hand, when pattern area 104a and pattern area 104b are misaligned in the width direction, this shift allows fine adjustment so that the positions match. Therefore, when the mask stage 101 is inverted, the position of the mask stage 101 can be finely adjusted according to the amount of misalignment between pattern area 104a and pattern area 104b in the width direction.

The above describes an embodiment of the present invention, but the present invention includes appropriate modifications that do not impair its objects and advantages, and is not limited to the above embodiment.

100 EUV exposure machine 101 mask stage 102 wafer stage 103a, 103b mask 104a, 104b pattern area 105 wafer 106a, 106b exposure area IL illumination light CR chief ray

Claims (4)

A mask stage that can hold two masks;
a wafer stage on which a wafer is mounted;
An exposure apparatus that scans such that the scanning direction of the wafer stage when exposing the pattern of a first mask onto the wafer and the scanning direction of the wafer stage when exposing the pattern of a second mask onto the wafer are opposite to each other. The exposure apparatus according to claim 1, characterized in that, after pattern exposure of the first mask, the wafer stage moves in a direction perpendicular to the scanning direction when the stage is inverted before starting pattern exposure of the second mask. The exposure apparatus according to claim 1 or 2, characterized in that the NA of the projection optical system that projects the mask pattern onto the wafer is 0.55 or more. An exposure method using an exposure apparatus equipped with a mask stage capable of mounting two masks, comprising the steps of:
When exposing a pattern of a first mask onto a wafer, the wafer stage is scanned in a first direction;
an exposure method in which, when exposing a pattern of a second mask onto the wafer, the wafer stage is scanned in a second direction opposite to the first direction;

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