JPS6063929A - Optical processor for plate object - Google Patents

Abstract

PURPOSE:To put the entire surface of a wafer within the focal depth of an aligner, etc. by a method wherein the relative position of the plate object to be processed and the focal plane is detected in the state of non contact. CONSTITUTION:The wafer 27 is raised by rotation of a pulse motor 21. When the wafer comes to partial contact with a reference ring 28, parallel leading is performed by the action of a spherical base 25. Further rise of a precise screw 22 in a slight amount causes the very small deformation of a pressure sensing element 23 and leads to the detection of the set pressure, when the motor 21 is stopped. The wafer 27 is pushed to the ring 28 under the set pressure. The degree o displacement of the wafer surface at each part to the lower surface 30 of the ring, i.e., the reference surface is measured by means of an air micrometer 29. If the focal plane of an optical system is at its average position, the entire surface of the wafer comes sufficiently into the range of exposure.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a wafer positioning method and apparatus, particularly to an exposure apparatus such as a projection aligner. For example, an exposure apparatus for optically transferring a mask pattern is disclosed in Japanese Patent Application No. 4973/1983.

As shown in FIG. 1, in the conventional positioning method, the lower surface of the reference ring 1 is accurately positioned and fixed at the focal plane 3 (
・Ru. On the other hand, the wafer 2 is vacuum-adsorbed onto the wafer chuck 4. The wafer chuck holder 5 has a built-in spring 6, and this pressing force causes the unino
The area around the area is being pushed to a standard/gu. This means that the wafer is aligned with the focal plane.

When the mirror polishing of the wafer is completed, the flatness of the top surface is measured by placing it on a wafer chuck and vacuum suction.
It is within 5μ. However, after heat treatment such as diffusion or CVD, the difference may be about ±15 μm when measured under the same conditions. The depth of focus is ±10μ as shown by Vc11 above and below the focal plane 10 as shown in FIG.
be. If the flatness of the wafer is within ±5μm, Unino
The entire surface will be within the depth of focus. However, in the actual process, the diameter of the wafer is ±15μ, and as shown in FIG. , the problem here is that sufficient resolution cannot be obtained.

An object of the present invention is to provide a technique for bringing the entire surface of a wafer, which has a flatness of approximately ±15 μm in reality, into the depth of focus of an aligner or the like.

In the present invention, after pressing the periphery of the wafer against a reference surface and aligning it, the wafer is measured at several points on the wafer using an air micrometer or the like to determine whether the wafer is convex or concave. Melt. Next, it is calculated at what height on the wafer the focal plane would most effectively fit the entire surface within the depth of focus.

Calculate how far the ideal focal plane for this wafer deviates from the reference plane, and then move the wafer on the wafer chunk so that the ideal focal plane coincides with the reference plane. Then it is exposed. If the reference plane is aligned with the focal point of the optical system, the depth of focus is 20 μm with resin.
Therefore, both the +15 .mu.m convex wafer and the -15 .mu.m concave wafer have their surfaces completely included within the depth of focus, so that good projection printing can be performed over the entire surface. That is,
The gist of the present invention is an optical processing apparatus (aligner or exposure apparatus) having a device for detecting the relative position of a plate-shaped object (wafer) to be processed and a focal plane in a non-contact state.

An example of this method will be described below. In FIG. 3, 21 is a pulse motor, and 23 is a pressure sensitive element connected to a precision screw part 22 via a joint.
The surface between 23 and 22 is made sufficiently small so that 220 rotations are not transmitted to 24. 25 is a spherical seat for parallelization, and 24 is its receiver.

A wafer chuck 26 holds the wafer 27 under vacuum. 28 is a reference ring for parallel alignment. 29 is an air micrometer.

Initially, the rotation of the pulse motor 21 causes the motor 22 to rise, thereby raising the wafer 27. When a part of the wafer comes into contact with the reference ring 28, parallelization is achieved by the action of the spherical seat 25. When the precision screw 22 further rises slightly, the pressure sensitive element is deformed very slightly (within 1 μm), and when the set pressure is detected, the motor 21 is stopped. The wafer will now be pressed against the reference ring 28 with the set pressure.

Thereafter, the air micrometer 29 measures how much the wafer surface is displaced at each portion with respect to the lower surface 30 of the reference ring, that is, the reference surface.

For example, let us take the average of those displacement amounts.

If the focal plane of the optical system is located at this average position, the entire surface of the wafer will be sufficiently within the optical range.

Kokote considered the average, but there are many ways to calculate the most effective focal position for each unit of displacement, depending on the installation location of the air micrometer, the curve of the wafer surface, etc.

Now, the focal plane 31 of the optical system is set parallel to the reference plane 30 and lowered by, for example, 100 μm. The above-mentioned average value of the displacement unit is determined to be positive when the wafer is convex and negative when the wafer is concave, and the pulse motor is driven by the value of this average displacement plus 100 μm. and lower the wafer.

In this way, the focal plane of the optical system can be set at the average height of the unevenness of the wafer, and the entire surface of the wafer can be placed within the depth of focus. During actual exposure, the micrometer 29 will get in the way, so move the wafer and its entire holding system parallel to the focal plane using air bearings or the like so that the height does not change so that the micrometer 29
7- It is necessary to expose at a position that does not come to H.

In this way, the entire surface of the wafer with large irregularities can be exposed within the depth of focus.

If deformation of the pressure sensitive element 23 is also a problem, assuming that the amount of deformation is, for example, 1 μIn, the pulse motor may be driven until the deformation is further reduced by 1 μIn from the calculated value.

According to the present invention, the entire surface of the wafer, which currently has a flatness of approximately ±15 μm, will be within the focal range of the optical system of ±10 μm, and pattern resolution defects will no longer occur in fine processes such as 3 μm processes. , the yield of LSI chips is improved.

[Brief explanation of drawings]

FIG. 1 is a sectional view showing a method of positioning the surface of a wafer according to the prior art; FIG. FIG. 3 is a sectional view of a surface positioning mechanism for a sea urchin, showing an embodiment of the present invention. 2... Wafer, 10... Focal plane, 23... Pressure sensitive element section. Agent Patent Attorney Akira Takahashi Mistake 1 Figure 2 Part 2

Claims (1)

[Claims] IJa) A plate-shaped object holding section that holds a plate-shaped object to be processed; and (1)
) an optical system for performing predetermined optical processing on the plate-like object to be processed; and (C) an optical system for detecting the relative position of the focal plane of the optical system and the plate-like object to be processed; On the other hand, an optical processing device for a plate-shaped object includes a non-contact position detection means.