JPS58193545A - Photomask - Google Patents

Abstract

PURPOSE:To measure the shape and distortion distribution of a projected image by providing numbers of the 1st patterns and the 2nd pattern in a photomask and exposing those two kinds of pattern in an overlapping state. CONSTITUTION:Numbers of patterns 16 whose overlap error is measured in combination with a pattern 17 at the center part of the photomask 15 are arranged at intervals (l) at a circumferential part which is distance (m) away from the pattern 17. The patterns of this photomask 15 are projected temporarily on a wafer 7 to form a pattern 8; and an X.Y stage 6 on which the wafer 7 is mounted is moved by m/10 in a direction (x) and by nl/10 (n; number of patterns from the center of a side to the farthest pattern) in a direction (y) to cover the pattern group 16 on the mask 15 and then exposure is carried out to form a pattern 19. At this time, projected images of measured patterns 16a in the pattern 18 are set overlapping with the projected image of the pattern 17 in the center of the pattern 19 and the overlap error is measured.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides a photomask that is capable of measuring the shape of a projected image, including reduction ratio eye difference, rotation, distortion, etc., in a photomask used in a reduction projection exposure apparatus that forms a pattern through a lens. It is related to.

In a reduction projection fog light device, it is necessary to accurately know the shape of the image that is projected, including distortion, from the viewpoint of examining the resolution line width accuracy and overlay accuracy.

Conventionally, to measure the image shape or image distortion of a reduction projection exposure device, a photomask (hereinafter referred to as a reticle) on which the original image pattern shown in Fig. 1 is drawn is illuminated with an illumination system l as shown in Fig. This was done by arranging the patterns 8 on the wafer 7 through the lens 3 and measuring the extent to which the peripheral areas of adjacent patterns overlapped each other. When the patterns 9a, 9b, toa, and lOb on the reticle 2-1 overlap, the alignment error can be measured. Therefore, when trapezoidal distortion occurs in the projected image as shown in FIG. 3, the image distortion can be calculated from the non-uniformity of the degree of overlap between adjacent pattern peripheries.

However, as shown in Figure 4, when the left and right sides of the projected image have distortions such that the top and bottom sides are shifted parallel to each other, the above method has the disadvantage that it is not possible to obtain an accurate image shape. Ta.

Therefore, an object of the present invention is to provide a photomask that eliminates the -F defect and allows accurate determination of the shape of a projected image.

In order to achieve -Objective F-, the present invention uses a reduction projection light device to synthesize a projected image of a large number of patterns arranged around or inside the reticle and a specific pattern on the reticle, A medium photomask (reticle) is constructed so that the image shape is measured using a mirror surface mounted on an X/Y stage as a reference.

Hereinafter, the present invention will be explained in detail with reference to Examples.

FIG. 5 shows an embodiment in which the present invention is applied to a reticle for measuring the image shape of a 1/10 reduction projection exposure apparatus. There is a pattern 17 in the center of the reticle 15,
At the periphery of the reticle 150 at a distance m from the center, a large number of patterns 16, which can be used to measure overlay errors by combining with the pattern I7, are arranged at intervals t.

First, the pattern of the reticle 15 is once projected onto the wafer 7 to form a pattern 18 shown in FIG. next,
The X-Y stage 6 on which the wafer 7 is placed is moved m/m in the X direction.
10, nz/l in the X direction.

(n indicates the number of patterns from the center of the side to the outermost pattern.) After the pattern group 16 on the reticle 15 is covered by moving the pattern group 16, exposure is performed to form the pattern 19. At this time, the projected image of the measurement pattern 16a included in the pattern 18 and the projected image of the pattern 17 located at the center of the bar p-:/19 overlap, and the overlay error can be measured.

While moving the position It of the X-Y stage 6 by Kt/10 in the y direction, exposure is repeated (2n+t) times to form pattern 1.
Pattern 19 is arranged on the right side of 8. A pattern 19 is formed all over the periphery of the pattern 18 in a similar manner. The X-Y stage 6 is mounted on the 92
Accurate positioning is performed by the laser length measuring device 4 using the axis mirror 50 surface as a reference.

Although the projection position of the pattern 16 included in the range of the pattern 18 changes due to the image distortion of the reduction lens 3, the pattern 19
The projection positions of the pattern 17 located at the center of the pattern 17 are arranged depending only on the flatness of the two-axis mirror 5. Generally, the flatness of the biaxial mirror 5 is 0.06
This amount, which is considered to be less than μm (λ/10), can be ignored when measuring the amount of image distortion. Therefore, if there is no distortion in the shape of the image, the overlay error that can be read from the projected images of patterns 16 and 17 will be zero, but if there is image distortion, an overlay error will occur, and by measuring that error, the shape of the image can be determined. can be determined accurately.

For example, the overlay error measurement pattern can measure minute dimensional differences, and may be an application of a combination of main scale and width scale used in known calipers.

In FIG. 5, if the spacing t of the patterns 16 is made small and the patterns 16 are arranged closely, the shape of the monk can be determined more accurately. Conversely, if the value of t is set large and the pattern 16 is placed, for example, only at the four corners of the reticle 15, the amount of distortion at that position can be measured. Furthermore, by appropriately arranging the pattern 16 not only on the periphery of the reticle 15 but also on the inside, it is also possible to measure the distortion distribution of the entire projected image.

Now, in the first embodiment described above, the stop position error of the X-Y stage 6 is included as an error factor during image shape measurement. Therefore, in the second embodiment described below, the shape measurement error caused by the stop position error of the X-Y stage 6 is corrected to more accurately determine the image shape. That is, in the center of the reticle 15, instead of the IT pattern 17 shown in FIG. 5, a pattern group consisting of three butters 20a, 20b, and 20c arranged at a distance t as shown in FIG. 7 is provided. Ta.

Here, patterns 20b and 20C are combined with pattern 16 and pattern 20a! ! The error can be measured accordingly.

The pattern of this reticle 15 is once projected onto the wafer 7 as shown in FIG. 2, and the pattern 23 shown in FIG.
form. In the figure, pattern 21 is a projected image of second pattern 16 for measuring alignment error. Next, using the same means as in the first embodiment, the pattern 24 is formed by repeating exposure while moving the X-Y stage 6 by a fixed distance of t/10. At this time, the patterns 20a, 20b, and 20C set in the center of the reticle 15 are projected to form patterns 22m, 22b, and 22C, and as shown in FIG. 8, the X-Y stage 6 is set in the X direction. In the case of one-step feeding, the combination of the pattern 21 and the pattern 22b makes it possible to measure the shape of a monk in exactly the same way as in the first embodiment. Similarly, when forming patterns 24 one after another, the patterns 22 and 2 included in the pattern 24 to be formed next are
2C, the mutual positional relationship of the patterns 24 can be measured from this. When the X-Y stage 6 is fed by a fixed distance in the X direction, the image shape from patterns 21 and 22C becomes patterns 22a and 22b! IIX-Y stage 6
It is possible to measure the interrelationship of the stopping positions of the By correcting the relative positional relationship of the pattern 24 to the measured monk shape, that is, the error in the stop position of the XY stage 6, the shape of the projected image can be obtained more accurately. It is also possible to measure the distortion distribution of the projected image in exactly the same way as in the first embodiment.

As described above, according to the photomask (reticle) according to the present invention, the shape or distortion distribution of a projected image formed on a wafer through a projection lens can be accurately measured with one surface of a two-axis mirror as a reference.

[Brief explanation of drawings]

Figure 1 is a schematic diagram of a conventional reticle for measuring image distortion, Figure 2 is a schematic diagram of a reduction projection optical device, Figure 3 is a diagram showing conventional image distortion measurement, and Figure 4 is a diagram showing that measurements cannot be made using the conventional method. 5 is a schematic diagram of a photomask (reticle) according to the present invention; FIG. 6 is a diagram illustrating image distortion measurement using a photomask according to the present invention; FIG. 7 is a diagram showing 1 Mon distortion and a stage. A schematic diagram of the first pattern of a photomask (reticle) according to the second embodiment, in which the positional error of It is a diagram. 2... Reticle, 3... Projection lens, 4... Laser length measuring device, 5... 2-axis mirror, 6... XφY stage, 7... Wafer, 9a, 9b, toa, lQb
- Overlapping eye difference measurement pattern, 15... Reticle with new pattern arrangement, 16, 17, 20a. 20b, 20C...Patterns for measuring overlay error. Agent: Patent attorney Toshiyuki Hakata. 10th,. 'v) 5 Figure 1 Figure 2 Figure 7 Continued from page 1 0 Inventor Riei Kurosaki 1-280 Higashi Koigakubo, Kokubunji City, Hitachi, Ltd. Central Research Laboratory 0 Inventor Sumio Hosaka 1-280 Higashi Koigakubo, Kokubunji City Inside Hitachi, Ltd. Central Research Laboratory

Claims (1)

[Claims] ! , in a photomask used in a reduction projection exposure device,
A large number of first patterns are provided in the periphery or inside of the projected area in the photomask, and at least one second pattern is provided that can measure the overlay error by combining with the first pattern. . A photomask characterized in that the shape or distortion distribution of a projected image is measured by exposing the second pattern over the first pattern.