JPH0770583B2 - Wafer alignment method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Outline] In wafer alignment in which a disk-shaped wafer having a facet on a part of its outer periphery is placed on a rotatable table and rotated to align the facet with a predetermined direction. , When the mounted wafer comes near the alignment position, the outer peripheral side surface of the wafer is irradiated with a light flux so that the irradiation position comes to the facet, the reflected light is detected from two directions, and the difference in the light amount By obtaining the stop position of the rotation,
This is intended to improve the alignment accuracy.

[Industrial application field]

The present invention relates to a wafer alignment method in which a disk-shaped wafer having a facet on a part of its outer circumference is placed on a rotatable table and rotated to align the facet with a predetermined direction.

In the exposure of the photolithography technique used for manufacturing semiconductor devices and the like, since the alignment of the wafer is necessary, the alignment is often performed before the exposure.

In addition, it is desired that this alignment should improve the alignment accuracy as the exposure pattern becomes finer.

[Conventional technology]

FIG. 4 is a plan view showing an example of a conventional method of the above alignment.

In the figure, the wafer W to be aligned is
It has a disk shape having a facet F whose outer peripheral side surface is a flat surface on a part of the outer periphery, and is mounted and chucked centered on a rotatable table 1 equipped with a vacuum chuck. Since the direction of the facet F of the wafer W when placed is indefinite, the wafer W is rotated together with the table 1 by a driving mechanism (not shown) so that the facet F has a predetermined orientation as shown in the drawing. When the direction is reached, the photosensors 2a and 2b detect the facet F, and the rotation is stopped by the detection.

The photosensors 2a and 2b are provided with a light emitting element and a light receiving element and are classified into a light passing type and a light reflecting type.
The position where the irradiation position of the light emitting element with respect to is inside the peripheral edge of the arc portion of the main surface of the wafer W and the facet F is detected by the disappearance of light shielding by the wafer W in the former case and the disappearance of light reflection by the latter case. Is located in.

Since the wafer W has variations in the outer diameter dimension and the length dimension of the facet F, the photosensors 2a and 2b are arranged at the position of the facet F where the distance from the center of the wafer W is maximum.

[Problems to be solved by the invention]

Therefore, when the wafer W having the facet F whose distance from the center of the wafer W is smaller than the maximum is aligned, as shown in FIG.
If the position of is within the range from the long chain line to the short chain line, the condition for alignment is satisfied, and thus there is a problem that the alignment accuracy deteriorates.

[Means for solving problems]

The problem is that a disk-shaped wafer having a facet whose outer peripheral surface is a flat surface on a part of the outer periphery is placed on a rotatable table and rotated, and the outer peripheral surface of the wafer is irradiated with a light beam, Orientation of the facet by determining the rotation stop position of the wafer by detecting the light reflected by the facet portion of the outer peripheral side surface by two light receiving elements that receive light from different directions in a plane parallel to the wafer surface Is a wafer alignment method for aligning the two light-receiving elements in a predetermined direction, wherein the two light-receiving elements receive light of the two light-receiving elements of the reflected light from the facet portion of the wafer that rotates in one direction, Is maximum before the facet is in a predetermined direction, and the other is maximum after the facet is in a predetermined direction,
Further, when the facet is in a predetermined direction, it is arranged at a position where the light receiving amounts of both light receiving elements are equal, and the position where the difference between the light receiving amounts of both light receiving elements becomes zero is the rotation stop position. A wafer alignment method according to the present invention is solved.

[Action]

In this method, light irradiation for detecting facets is applied to the outer peripheral side surface of the wafer. Then, when the irradiation position comes to the facet by the above rotation, the direction of the reflected light moves as the wafer rotates because the irradiation position is a plane. Therefore, the rotation stop position can be obtained at a predetermined point by detecting the reflected light at a predetermined position.

However, since the direction of reflected light is uniquely determined by the direction of the facet regardless of the distance from the center of the wafer to the facet, the required rotation stop position is the outer diameter of the wafer and the facet length. Even if there are variations in dimensions, the facet orientation is kept constant regardless of the variation.

Further, in general, since the plane of the facet is rougher than the mirror surface, the reflected light becomes scattered light with the center being the strongest. Therefore, it is possible to detect the reflected light and determine the rotation stop position at the two positions as described above.

Then, in this case, the maximum detected during the rotation indicates immediately before the rotation is stopped, and the stop position is clearly indicated, so that the rotation can be easily stopped at the correct position.

〔Example〕

An embodiment of the method of the present invention will be described below with reference to FIGS.

FIG. 1 is a plan view showing an embodiment, FIG. 2 is an explanatory view of obtaining a stop position in the embodiment, and FIG. 3 is a plan view showing another embodiment. Indicates a thing.

In FIG. 1, the wafer W is placed on the table 1 with its center aligned, chucked, and rotated together with the table 1 by a drive mechanism (not shown), as in the case of the conventional method. Then, when the facet F reaches a predetermined direction as shown in the drawing, the light emitting elements 3a and 3b and the light receiving element
The direction of the facet F is detected by the combination of 4a and 4b, the rotation is stopped by the detection, and desired alignment is performed.

Each of the light emitting elements 3a and 3b is formed of, for example, a light emitting diode or the like, and both of them emit the light flux 5 to the outer peripheral side surface of the wafer W so that the irradiation position comes to the facet F when the wafer W comes near the alignment position.

The light receiving element 4a is composed of, for example, a photodiode or a phototransistor, detects the reflected light 6 from the light beam 5 of the light emitting element 3a with the maximum intensity when the wafer W comes just before the alignment position, and comes to the alignment position. At this time, it is arranged at a position where the reflected light 6 is detected with an appropriate intensity.

Further, the light receiving element 4b is the same as the light receiving element 4a, and when the wafer W comes right after the alignment position, the reflected light 6 by the light flux 5 of the light emitting element 3b is detected to the maximum intensity and the alignment position is set. When it comes, it is arranged at a position where the reflected light 6 is detected with the same intensity as in the case of the light receiving element 4a.

The reason why the light receiving elements 4a and 4b can detect the reflected light 6 in this manner is that the facet F has a rougher plane than the mirror surface, and the reflected light 6 becomes scattered light having the strongest center as described above. .

Then, when the wafer W comes to the alignment position, the difference in the intensity of light detected by the light receiving elements 4a and 4b becomes zero.

Therefore, by detecting the difference in light intensity with respect to the rotation of the wafer W in real time, the stop position of the rotation, which is the alignment position of the wafer W, can be obtained as the point where the difference becomes zero. .

The rotation of the wafer W is plotted along the horizontal axis in FIG. 2, and the light intensity detected by the light receiving element 4a is a long chain line, and the light intensity detected by the light receiving element 4b is positive or negative. The inverted one is shown by a short chain line, and the difference in intensity of both lights is shown by a solid line which is the sum of the long chain line and the short chain line.

This solid line traces the maximum, the minimum, and the minimum as the wafer W rotates, and the point of 0 indicates the rotation stop position.
However, since the inclination in the vicinity is large, the stop position is clearly shown. Further, the above-mentioned maximum indicates that the stop position is close because it is immediately before the stop position.
It can be used to slow down the rotation speed of, and makes it easy to stop accurately at the position of rotation stop.

In this alignment method, as described above, the outer peripheral side surface of the wafer W is irradiated with the light beam 5 and the rotation stop position is obtained by the reflected light 6. Therefore, the obtained stop position is the wafer. Even if there are variations in the outer diameter dimension and the length dimension of the facet F in W, the direction of the facet F is kept constant, and the alignment accuracy does not deteriorate as in the conventional method example.

According to the experiment by the inventor, the variation in the direction of the facet F when the alignment is performed according to the above-described embodiment is
Approximately 1/5 of the case of the conventional method example, the alignment accuracy is greatly improved.

In another embodiment shown in FIG. 3, the light emitting elements 3a and 3b of the previous embodiment are commonly used and the light emitting element 3a also serves as 3b. In FIG. 6A, the light receiving elements 4a and 4b are arranged on both sides of the light emitting element 3a so that the light flux 5 irradiates the facet F substantially vertically when the wafer W is at the alignment position. Further, in FIG. 6B, the light receiving elements 4a and 4b are arranged so as to irradiate the facet F obliquely.
It is placed on one side of.

In any case, the mechanism for detecting the orientation of the facet F is the same as that in the previous embodiment, and the alignment accuracy is also the same.

〔The invention's effect〕

As described above, according to the configuration of the present invention, a disk-shaped wafer having a facet on a part of its outer periphery is placed on a rotatable table and rotated to align the facet with a predetermined direction. In alignment, even if there are variations in the outer diameter dimension and facet length dimension of the wafer, it is possible to improve the alignment accuracy that is not affected by such variations, and It has the effect of facilitating correspondence.

[Brief description of drawings]

 FIG. 1 is a plan view showing an embodiment of the method of the present invention, FIG. 2 is an explanatory view of obtaining a stop position in the embodiment, FIG. 3 is a plan view showing another embodiment, and FIG. 4 is a conventional method example. FIG. 5 is a plan view of FIG. 5, and FIG. In the drawing, 1 is a table, 2a and 2b are photosensors, 3a and 3b are light emitting elements, 4a and 4b are light receiving elements, 5 is a luminous flux, 6 is reflected light, W is a wafer, and F is a facet.

Claims (1)

[Claims] 1. A disk-shaped wafer having a facet whose outer peripheral surface is a flat surface on a part of the outer periphery is placed on a rotatable table and rotated, and the outer peripheral surface of the wafer is irradiated with a light beam. Orientation of the facet by determining the rotation stop position of the wafer by detecting the light reflected by the facet portion of the outer peripheral side surface by two light receiving elements that receive light from different directions in a plane parallel to the wafer surface Is a wafer alignment method for aligning the two light-receiving elements in a predetermined direction, wherein the two light-receiving elements have one received light amount of reflected light from the facet portion of the wafer that rotates in one direction. Is the maximum before the facet is in the predetermined direction, the other is maximum after the facet is in the predetermined direction, and at the time when the facet is in the predetermined direction, the light receiving amounts of both light receiving elements are equal. The wafer alignment method is characterized in that the rotation stop position is set at a position where the difference in the amount of light received by both light receiving elements becomes zero.