JPS6194324A - Apparatus for correcting surface shape of laminar plate - Google Patents

Abstract

PURPOSE:To enable the surface shape of a laminar plate to be corrected, by providing means for fixing the laminar plate, and means for deforming the laminar plate by means of a difference between air pressures. CONSTITUTION:When a wafer 1 is disposed on a wafer chuck body 2, a vacuum is applied to a tube 3 and the wafer 1 is attractively secured to the body 2 by means of vacuum grooves 23. A pocket portion 22 whose air pressure is controllable is thereby defined between the wafer 1 and the body 2. A driving section 7 controls the supply of a vacuum from a vacuum tube 8 or of pressurized air from a pressurized tube 9 to the pocket portion 22 in accordance with a computation output from an arithmetic circuit 12, so as to change the pressure within the pocket portion 22. Consequently, the surface shape of the wafer 1 is changed to a convex, flat or concave as required, and therefore any focus deviation between a mask and the wafer can be properly corrected.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of the Invention] The present invention relates to an apparatus for correcting the surface shape of a thin plate such as a semiconductor wafer. BACKGROUND OF THE INVENTION Conventionally, in the process of exposing a wafer in a semiconductor exposure apparatus, focus deviation between a mask and a wafer has been corrected. In order to eliminate this problem, the flatness of the wafer chuck was improved, and the wafer was fixed by suction so as to follow the flatness. But in this case,
Sea urchin chucks require highly accurate flatness on the surface, and the flatness must be constantly controlled, which has the disadvantage of increasing the cost of the wafer chuck and requiring strict maintenance methods. In addition, with this method of suctioning the entire surface of the wafer, the flatness of the wafer does not necessarily follow the flatness of the sea urchin hook and is fixed.
In this case, there is a problem that a focus shift occurs between the mask and the wafer, and the image of the mask cannot be faithfully transferred to the wafer.

On the other hand, in order to eliminate such drawbacks, the vacuum suction force of each part of the wafer is adjusted independently (Japanese Patent Application Laid-Open No. 57-87129, JP-A No. 57-17753).
6, etc.) have also been proposed.

However, with such a method using only suction, the problem remains that, although correction can be performed relatively well when the wafer is warped in a convex shape, it is difficult to correct it when the wafer is warped in a concave shape.

Additionally, if the contact area between the wafer chuck and the wafer is large, there is a high probability that dust will get caught between them, and in this case, the convex part of the dust will be lifted up, causing a focus shift in this part. There was also the inconvenience that the possibility was large.

Furthermore, if the mask and wafer are out of focus on the wafer surface, that is, if the optically best focus position is not a flat surface, conventionally it has not been possible to match the wafer surface shape to the best focus surface shape.

[Object of the Invention] In view of the above-mentioned problems in the conventional example, the present invention prevents local protrusion of the wafer due to trapped dust, and also prevents the warping of the original wafer from unevenness. Another object of the present invention is to provide a surface shape correction device capable of correcting the flatness of a wafer in a fast follow-up time. In addition, even in projection exposure equipment where the best focus surface is not flat, by applying this surface shape correction device, the surface shape of the wafer to be exposed can be adjusted to the best position, and the entire surface of the wafer can be brought to the best focus position according to the shape of the focus surface. A general purpose of the present invention is to provide a surface shape correction device that can be set.

[Description of Embodiments] FIG. 1 shows the configuration of a wafer chuck to which a surface shape correction apparatus according to an embodiment of the present invention is applied.

In the figure, 1 is a wafer on which a mask image is printed;
2 is a wafer chuck main body, and 3 is a wafer fixing suction tube (hereinafter referred to as tube). The wafer chuck main body 2 is provided with a ring-shaped wafer support portion 21 on the periphery, and a recess (pocket portion) inside the wafer support portion 21.
22 is formed, and a circular wafer suction vacuum groove 23 is provided roughly along the top of the wafer support section 21. The vacuum groove 23 is connected to the tube 3, and the wafer 1 placed on the wafer support part 21 of the wafer chuck main body 2 is placed on the wafer chuck by applying a vacuum to the vacuum groove 23 via the duplex 3. It is fixed to the main body 2 by suction.

5 is a pressure sensor that detects the pressure in the pocket portion 22; 6 is a command unit that sets the surface shape of the wafer 1; 7 is a drive unit;
The drive unit 7 is composed of valves, nozzles, on/off switches, etc. that are operated by electric signals. 8.9 is a vacuum tube and a pressure tube that supply vacuum and pressurized air to the pocket portion 22, respectively; 10 is a flatness measuring device that measures the flatness of the wafer 1; The flatness measuring device 1o measures displacements at multiple locations on the wafer 1 using a displacement measuring device such as a capacitance type displacement measuring device or a laser type displacement measuring device, and compares these measured values. The flatness may be determined by determining the flatness.

11 is a tube (or pipe) that supplies air controlled by the drive section 7 to the pocket section 22; 12 is a value tp measured by the flatness measuring device 10 or a pressure sensor 5;
This is an arithmetic circuit that provides the difference between the value obtained in and the command value given from the command section 6 to the drive section 7 as an operating amount.

Next, the operation of the wafer chuck according to the above configuration will be explained.

When the wafer 1 is placed on the wafer chuck body 2, a vacuum is applied to the tube 3, and the wafer 1 is suctioned and fixed to the wafer chuck body 2 by the vacuum groove 23. This results in
A closed space whose air pressure can be controlled is formed between the wafer 1 and the pocket portion 22. This closed space or pocket part 2
2 is initially at atmospheric pressure (1 atm). Subsequently, the flatness measuring device 10 measures the surface shape of the wafer 1, such as flatness, and the output of the flatness measuring device 10 is supplied to the arithmetic circuit 12.

The arithmetic circuit 12 calculates the difference between the output of the flatness measuring device 10 and the surface shape signal of the wafer 1 output from the command unit 6. The drive unit 7 controls the supply of vacuum from the vacuum tube 8 or pressurized air from the pressure tube 9 to the pocket portion 22 in accordance with the calculation output of the calculation circuit 12, and changes the pressure in the pocket portion 22.

As a result, the portion of the wafer 1 that is in contact with the pocket portion 22 is displaced upward or downward, and the surface shape of the wafer 1 changes to be convex, flat, concave, or the like. The surface shape of the wafer 1 is corrected to the shape given by the command unit 6 by repeating the above-described flatness measurement or pressure control operation in the pocket portion 22 in a negative feedback manner, that is, by feedback control.

Note that when the surface profile measuring device shown in FIG. 1 is applied to a semiconductor exposure device, it is difficult to measure the flatness of the wafer 1 with the flatness measuring device 10 during exposure. A feedback system including a pressure sensor 5 corrects the surface shape of the wafer 1, and during and after exposure, the flatness measuring device 10 is moved out of the exposure optical path, and a feedback system including a pressure sensor 5 corrects the pressure inside the pocket portion 22. is maintained at a constant value to correct and maintain the surface shape of the wafer 1.

In this way, in the wafer chuck shown in FIG. 1, the wafer 1 is supported and fixed only at the periphery, and the pocket 22 is provided in the center, and by controlling the pressure inside this pocket 22, the wafer 1 is By driving the mask up and down, the surface shape can be corrected to a flat surface or a concave or convex shape with a desired curvature. It is possible to eliminate defocus within the plane of the wafer, and to prevent deterioration of the image transferred to the wafer due to the defocus. Further, since the central portion of the wafer is held by air pressure and does not come into contact with the wafer chuck body, there is no possibility that dust or the like will be caught in this portion and adversely affect the focus.

[Modifications of Embodiments] The present invention is not limited to the above-described embodiments, and can be implemented with appropriate modifications. For example, in the above-mentioned embodiment, there was one pocket section 22, but as shown in FIG. If the correction is performed at various positions, the surface shape can be corrected more precisely.

Further, in the above description, the wafer 1 is fixed to the wafer chuck by vacuum suction, but as shown in FIG. The wafer supporting portion 21 may be fixed by mechanically pressing the wafer 1, or as shown in FIG.
By fixing the wafer 1 more strongly, such as by charging the top part of the pocket part 22 and fixing the wafer 1 by suction,
The pressure can be made higher than that in the case of vacuum suction, and the range of surface shape correction of the wafer 1 can be expanded.

[Effects of the Invention] As described above, according to the present invention, a part of a thin plate such as a wafer is fixed, and air pressure is applied to a part of the plate to vertically displace the part. Even if the surface is uneven or warped, the surface shape can be corrected to a desired flat or curved surface. Therefore, if this surface shape correction device is applied to a semiconductor exposure device, even if the best focus surface of the projection system of the exposure device is a curved surface, the entire surface of the wafer can be set at the focus position by warping the wafer to a desired curvature. be able to. Also,
Since the surface of the thin plate is displaced by air pressure, the follow-up time for surface shape correction is also fast.

Furthermore, since the contact area between the thin plate and the means for supporting the thin plate is small, the surface shape of the thin plate is not affected by dust or the like caught between the thin plate and the supporting means.

[Brief explanation of drawings]

FIG. 1 is a schematic cross-sectional view of a wafer chuck according to an embodiment of the present invention, FIG. 2 is a schematic cross-sectional view of a wafer chuck according to another embodiment of the present invention, and FIGS. 3(a) and (b) are FIG. 6 is a schematic cross-sectional view of a wafer chuck according to still another embodiment of the present invention. DESCRIPTION OF SYMBOLS 1: Wafer, 2: Wafer chuck main body, 21... Wafer support part, 22... Pocket part, 23: Vacuum groove for wafer suction, 3: Suction pipe for wafer fixation, 5: Pressure sensor, 6
: Command unit, 7: Drive unit, 8: Vacuum tube, 9: Pressure tube, 10: Flatness measuring device, 12: Arithmetic circuit, 14:
Pressing is performed by section 15, electrical adsorption means.

Claims (1)

[Claims] 1. The thin plate is characterized by comprising a fixing means for fixing a part of the thin plate, and a means for deforming the thin plate by applying an air pressure difference to at least a part of the thin plate other than the fixed part. A thin plate surface shape correction device. 2. The thin plate surface shape correction device according to claim 1, wherein the fixing means adsorbs and fixes the thin plate using vacuum pressure. 3. The thin plate surface shape correction device according to claim 1, wherein the fixing means fixes the thin plate by mechanical pressing means. 4. The means for applying the air pressure difference consists of one or more divided recesses forming a closed space between it and the back surface of the thin plate, and controls the air pressure in the closed space to make it different from atmospheric pressure. Claim 1, in which the air pressure difference between
, 2 or 3. The thin plate surface shape correction device according to item 2 or 3. 5. The method according to any one of claims 1 to 4, wherein the fixing means fixes a peripheral portion of the thin plate, and the means for applying an air pressure difference applies an air pressure difference to a central portion of the thin plate. Surface shape correction device for thin plates. 6. The fixing means fixes a concentric circular portion centered approximately at the center of the thin plate, and the means for applying an air pressure difference applies a concentric air pressure difference to the thin plate between each of the concentric fixing portions. A thin plate surface shape correction device according to any one of claims 1 to 4 to which the invention applies. 7. The thin plate surface shape correction device according to any one of claims 1 to 6, wherein the thin plate is a wafer.