JPH04280619A - Wafer retaining method and retaining device - Google Patents

Abstract

PURPOSE:To improve accuracy of transfer of a mask pattern by suppressing the temperature rise and thermal strain of a wafer being exposed. CONSTITUTION:Four suction regions 4, divided by partition walls 1, are formed on the wafer suction surface of a main structural member 3. A vacuum piping 5 is independently connected to each suction region 4, an outside air introducing pipe 7 and a vacuum source 8 are connected to each vacuum piping 5 respectively through the intermediary of three-way valves 11. A valve controller 12 is connected to each three-way valve 11. Each suction region 4 can be selectively communicated independently to the outside air introducing pipe 7 or the vacuum source 8 in a selective manner by switching the three-way valves 11 using a valve controller 12.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a wafer holding method and apparatus for an exposure apparatus, which holds a wafer by vacuum suctioning the back surface of the wafer.

0002

Conventionally, when transferring a mask pattern onto a wafer, a wafer holding device used to hold the wafer generally holds the wafer by vacuum suctioning the back surface of the wafer to the wafer suction surface of a main structural member. A wafer holding device (for example, Japanese Patent Publication No. 1-14703) is known.

However, if a wafer holding device using vacuum suction is used as is, gas, which is a heat medium for releasing heat, will exist in the suction area formed between the back surface of the wafer and the wafer suction surface after vacuum suction. As a result, the following problems arise.

[0004] When a wafer is held by a wafer holding device,
Since the contact thermal resistance between the wafer and the main structural member increases, the exposure energy when transferring the mask pattern to the wafer does not escape from the wafer to the main structural member, resulting in an increase in the temperature of the wafer. In addition, thermal distortion occurs and mask pattern transfer accuracy deteriorates.

As a means of solving the above problems, for example, as described in Japanese Patent Application Laid-Open No. 63-98119, a flow path is provided in which temperature-controlled water is provided in the main structural member of the wafer holding device. It has been proposed to control the temperature of the wafer during exposure by flowing the wafer through the wafer.

[0006]

However, even in the vacuum suction type wafer holding device that uses temperature-controlled water to control the temperature of the wafer, the wafer holding device uses synchrotron radiation as a light source. When used in an X-ray exposure apparatus, the following problems still remain regarding thermal distortion of the wafer.

[0007] In the X-ray exposure apparatus, the wafer holding device usually has two
It is installed in a chamber filled with He gas whose pressure is reduced to about 0.00 Torr. Therefore, in order to increase the difference between the pressure on the front surface of the wafer (200 Torr) and the pressure on the back surface after vacuum suction, and to obtain a large suction force, the exhaust gas is pumped to an ultimate vacuum of about 10-2 Torr. Using a capable rotary pump as a vacuum evacuation means, the He gas in the adsorption area on the back surface of the wafer is evacuated until the pressure on the back surface of the wafer becomes 10 [Torr] or less. However, the pressure within the adsorption region is reduced to 1
When the temperature is 0 [Torr] or less, the thermal conductivity of the adsorption area is approximately 2×10-2 [W/m・K], which is about 10-1 [W/m・K] which is the thermal conductivity before vacuum adsorption. ], the heat generated in the wafer during exposure becomes difficult to escape to the main structural members, causing a temperature rise and thermal distortion of the wafer.

Furthermore, in a proximity type exposure apparatus, the mask and the wafer are placed at a very small distance of several tens of μm, so that the temperature of the wafer is easily transmitted to the mask. Therefore, an increase in the temperature of the wafer also causes an increase in the temperature of the mask, and there is a problem in that the mask pattern transfer accuracy deteriorates due to thermal distortion of the mask due to the increase in the temperature of the mask.

SUMMARY OF THE INVENTION An object of the present invention is to provide a wafer holding method and a wafer holding device that improve mask pattern transfer accuracy by suppressing temperature rise and thermal distortion of the wafer during exposure.

0010

Means for Solving the Problems In order to achieve the above object, the wafer holding method of the present invention uses a wafer holding device having a plurality of suction areas separated from each other on the wafer suction surface, and during exposure of the wafer. Among the plurality of suction areas, at least the suction area immediately below the exposed portion of the wafer is not vacuum-suctioned, but the other suction areas are vacuum-suctioned to hold the wafer.

Further, the wafer holding device of the present invention includes a plurality of suction areas separated from each other on the wafer suction surface of the main structural member, vacuum piping each independently connected to each of the suction areas; Switching means respectively connected to the ends of the vacuum piping, and a vacuum source and a vacuum release means selectively connected to the vacuum piping via the switching means, and switching the switching means. According to the present invention, each of the suction regions independently communicates with either the vacuum source or the vacuum release means.
Furthermore, a groove may be formed along the outer periphery of the wafer suction surface and the groove may be communicated with a vacuum source, or three or more suction areas may be used instead of multiple suction areas, and each vacuum piping At least one of the vacuum pipes may be connected to a plurality of adsorption areas.

0012

[Operation] In the invention as set forth in claim 1 constructed as described above, a wafer holding device having a plurality of suction areas separated from each other on the wafer suction surface is used, and during exposure of the wafer,
Among the plurality of suction areas, at least the suction area directly below the exposed portion of the wafer is not vacuum-suctioned, and the other suction areas are vacuum-suctioned, so that the wafer is held by being vacuum-suctioned in the other suction areas. However, gas is always present in the suction area directly below the exposed area of the wafer, and this gas acts as a heat transfer medium, so the exposure energy applied to the wafer during exposure causes the exposed area of the wafer to Heat generated near the wafer is easily transferred to the wafer suction surface. As a result, wafer temperature rise and wafer thermal distortion are suppressed, and mask pattern transfer accuracy is improved.

[0013]

Embodiments Next, embodiments of the present invention will be described with reference to the drawings. (First Embodiment) First, a first embodiment of a wafer holding device used to carry out the wafer holding method of the present invention will be described with reference to FIG.

A partition wall 1 is integrally provided on the upper surface of the main structural member 3, which is the wafer suction surface, and divides the suction surface into four areas, and the areas surrounded by the partition wall 1 are divided from each other. Four adsorption areas 4 are formed. On the bottom surface of each suction area 4, a large number of protrusions 2 are protruded at a predetermined interval at the same height as the partition wall 1 for flattening the wafer 9 when the wafer 9 is vacuum suctioned. , vacuum piping 5 that opens independently is connected to each suction region 4 .

Each vacuum pipe 5 is connected to a valve device 6, and the valve device 6 includes an outside air introduction pipe 7 whose one end is open to the outside air and the other end of which serves as a vacuum release means, and a vacuum pump or the like. A vacuum source 8 is connected. One end of the outside air introduction pipe 7 may be connected to a cylinder (not shown) filled with gas. However, in that case, it is necessary to provide means for adjusting the pressure when introducing gas into the adsorption region 4.

The configuration of the valve device 6 will now be explained. Inside the valve device 6, each vacuum pipe 5 is
They are each independently connected to the outside air introduction pipe 7 and the vacuum source 8 via a three-way valve 11 as a switching means provided for each vacuum pipe 5. Each three-way valve 11 has a valve controller 12 provided outside the valve device 6.
By switching each three-way valve 11 by the valve controller 12, each vacuum pipe 5 can be independently communicated with either the outside air introduction pipe 7 or the vacuum source 8.

With the above configuration, when the wafer 9 is on the wafer suction surface of the main structural member 3, the arbitrary vacuum piping 5 is connected to the vacuum source 8 so that the arbitrary vacuum pipe 5 communicates with the vacuum source 8. When the three-way valve 11 installed in the vacuum pipe 5 is switched, the interior of the suction region 4 connected to the arbitrary vacuum pipe 5 is evacuated by the vacuum source 6. Moreover, when the three-way valve 11 interposed in the arbitrary vacuum pipe 5 is switched so that the arbitrary vacuum pipe 5 and the outside air introduction pipe 7 communicate with each other,
Gas is introduced into the adsorption region 4 connected to the arbitrary vacuum pipe 5 from the outside air introduction pipe 7.

The number of suction regions 4 is not limited to four, and the number can be increased or decreased as necessary. Furthermore, the configuration of the valve device is not limited to the one described above, and the vacuum release means and the vacuum source can be provided for each vacuum pipe through a three-way valve, and the switching means is not limited to a three-way valve, but a two-way valve. Combinations of valves or other means may also be used.

Next, a wafer holding process using the wafer holding device of this embodiment will be explained. First, the wafer 9 is placed on the wafer suction surface of the main structural member 3, all three-way valves 11 are opened to the vacuum source 8 side, all suction areas 4 are vacuum-suctioned, and the wafer 9 is vacuum-suctioned and held.

Next, exposure is performed, and during the exposure, the vacuum pipe 5 connected to the suction area 4 directly below the exposed area of the wafer is
A three-way valve 11 provided in the wafer is opened to the outside air introduction pipe 7 side, and gas is introduced into the suction area 4 directly below the wafer exposure area. The other suction areas 4 are kept in vacuum and the wafer 9 is
It is held by vacuum suction.

Exposure is performed sequentially while determining the position of the exposure light beam 10 on the wafer 9. When the exposure light beam 10 deviates from above the adsorption area 4 into which the gas has been introduced, the three-way valve 11 provided in the vacuum piping 5 connected to the adsorption area 4 from which the exposure light beam 10 has deviated is connected to the vacuum source 8 side. The suction area 4 is opened to vacuum the inside of the suction area 4. At the same time, the three-way valve 11 provided in the vacuum pipe 5 connected to the suction area 4 directly below the exposed area of the wafer newly hit by the exposure light beam 10 is opened to the outside air introduction pipe 7 side, and gas is introduced into the suction area 4. will be introduced.

By repeating the above-mentioned procedure, the wafer 9 is vacuum-adsorbed to the main structural member 3 during exposure.
Gas always exists in the suction region 4 directly below the exposed portion of the wafer.

Therefore, when the wafer 7 is vacuum-adsorbed by the wafer holding method of the present invention, the contact thermal resistance that occurs when solids are brought into contact does not occur, and instead, the gas introduced into the adsorption area 4 only thermal resistance occurs.

By the way, with the conventional wafer holding method, the wafer 9
It has been experimentally confirmed that the contact thermal resistance generated at the contact surface between the wafer 9 and the main structural member 3 when the wafer 9 is held is approximately 10-2 [m2 K/W], and that it does not depend on the type of solid material. There is. On the other hand, the thermal resistance R generated when the wafer 9 is held by the wafer holding method of the present invention is determined by the thermal conductivity of the gas existing in the adsorption area 4 being λ [W/m·K], and the thermal conductivity of the gas existing in the adsorption area 4 being If the depth is d [m], then R=d/λ[m2 K/
W]. For example, in the adsorption area 4 of depth d = 100 [μm], H with thermal conductivity λ = 0.13 [W/m・K]
When e-gas is introduced, the thermal resistance is R = 7.7 x 10-4 [
m2 K/W], and the thermal resistance can be significantly reduced compared to conventional vacuum suction.

As described above, by reducing the thermal resistance of the contact surface between the main structural member 3 and the wafer 9, the heat generated in the exposed area of the wafer 9 during exposure is reduced by the gas present in the adsorption area 4 acting as a medium. As a result, the temperature of the wafer 9 can be suppressed and the resulting thermal distortion of the wafer 9 can be suppressed, and the accuracy of mask pattern transfer can be improved.

Further, since the wafer 9 is vacuum suctioned in the suction area 4 excluding the suction area 4 directly below the exposed area, sufficient wafer suction force can be obtained. (Second Embodiment) A second embodiment of a wafer holding device used to carry out the wafer holding method of the present invention will be described with reference to FIG.

The configuration of the wafer holding device of this embodiment includes a suction groove 33 as a groove formed by the partition wall 21 along the outer periphery of the wafer suction surface of the main structural member 23, and a suction groove 33 as a groove formed by the partition wall 21.
This embodiment differs from the first embodiment in that an adsorption pipe 34 that communicates with the vacuum source 28 and is connected to the vacuum source 28 is added. The adsorption area 24, the vacuum pipe 25, the valve device 26, and the outside air introduction pipe 27 may be the same as those in the first embodiment, so a description thereof will be omitted.

The wafer holding process using the wafer holding device described above is the same as in the first embodiment with respect to the exposed portion of the wafer 29, but the outer peripheral portion of the wafer 29 is always vacuum-adsorbed by the suction groove 33 during exposure. This differs from the first embodiment in this point. Therefore, deformations such as warpage that occur in the wafer 29 due to residual stress after film formation on the wafer 29 during the semiconductor manufacturing process can be more reliably corrected to a flat surface, and transfer accuracy can be improved. (Third Embodiment) A third embodiment of a wafer holding device used to carry out the wafer holding method of the present invention will be described with reference to FIG.

In this embodiment, the wafer suction surface is the partition wall 4.
1 into 16 adsorption areas 4 in a grid pattern.
4A, 44B, 44C, and 44D are formed. Each suction region 44A, 44B, 44C, and 44D has the same number and is connected to one vacuum pipe (not shown), and adjacent suction regions are not connected to the same vacuum pipe. . Other configurations are the first
Since it may be the same as that in the embodiment, its explanation will be omitted.

With the above configuration, for example, the suction area 44
Gas is introduced into A, and other adsorption areas 44B, 44C,
When a wafer (not shown) is vacuum-suctioned at 44D, the suction area 44A into which gas is introduced becomes the suction area 44 that was vacuum-suctioned.
It will be surrounded by B, 44C, and 44D. Therefore, thermal distortion of the wafer due to a rise in the temperature of the wafer can be further suppressed. In addition, since one vacuum piping connects to multiple adsorption areas, there is no need to install vacuum piping for each adsorption area, which reduces the number of vacuum piping and switching means, simplifying the equipment configuration. become.

[0031] Here, the adsorption areas 44A, 44B, 44C
, 44D is not limited to 16, and the number can be increased or decreased as necessary. In addition, each adsorption area 44A, 44
The piping combinations of B, 44C, 44D and each vacuum piping and the number of vacuum piping are not limited to those described above.

The wafer holding device of the present invention described in each of the embodiments above can also be installed in an exposure apparatus using a proximity method. In exposure equipment using the proximity method, the wafer and mask are placed at a very small distance.
The temperature of the wafer is easily transmitted to the mask. Therefore, by suppressing the temperature rise of the wafer, it is possible to suppress the temperature rise of the mask due to heat transfer from the wafer and the accompanying thermal distortion of the mask, and it is possible to more effectively improve mask pattern transfer accuracy.

[0033]

[Effects of the Invention] Since the present invention is constructed as described above, it produces the following effects.

According to the first aspect of the invention, during exposure of a wafer, among the plurality of suction areas, at least the suction area immediately below the exposed area of the wafer is not vacuum-suctioned, but the other suction areas are vacuum-suctioned. Therefore, although the wafer is suctioned and held by the other suction area, since gas is present in the suction area directly below the exposure area, heat generated near the exposure area is easily transferred to the wafer suction surface. As a result, temperature rise and thermal distortion of the wafer can be suppressed, and mask pattern transfer accuracy can be improved.

The wafer holding device according to the second aspect of the present invention is suitable for carrying out the method according to the first aspect because vacuum suction or vacuum release of each suction area can be reliably performed.

[0036] In addition to the above effects, the invention according to claim 3 also has the following effects:
By forming a groove along the outer periphery of the wafer suction surface and communicating the groove with a vacuum source, the outer periphery of the wafer is vacuum-adsorbed to the main structural member. It is possible to more reliably correct flatness of deformations such as warpage, and to improve transfer accuracy.

[0037] In addition to the effects of the invention described in claim 2, the invention described in claim 4 can simplify the configuration of the apparatus since it is not necessary to provide each vacuum pipe for each adsorption area. .

[Brief explanation of the drawing]

FIG. 1 shows a first embodiment of a wafer holding device used to carry out the wafer holding method of the present invention, and (A) is a schematic diagram showing the structure of its wafer suction surface, showing the symmetrical part from the center line. The omitted figure (B) is a schematic configuration diagram of the wafer holding device.

FIG. 2 shows a second embodiment of the wafer holding device used to carry out the wafer holding method of the present invention, and (A) is a schematic diagram showing the structure of the wafer suction surface, showing the symmetrical part from the center line. The omitted figure (B) is a schematic configuration diagram of the wafer holding device.

FIG. 3 is a schematic diagram showing the structure of a wafer suction surface of a third embodiment of a wafer holding device used to carry out the wafer holding method of the present invention.

[Explanation of symbols]

1, 21 Partition wall 2
Protrusions 3, 23, 43
Main structural members 4, 24, 44A, 44B, 44C, 4
4D adsorption area

Claims (4)

[Claims] 1. A wafer holding device having a plurality of suction areas separated from each other on a wafer suction surface is used, and during exposure of a wafer, at least one of the plurality of suction areas immediately below the exposed area of the wafer is used. The suction area is not vacuum suctioned,
A wafer holding method characterized in that the wafer is held by vacuum suctioning another suction area. 2. A wafer suction surface of the main structural member is provided with a plurality of suction areas separated from each other, vacuum piping is connected independently to each of the suction areas, and an end portion of each vacuum piping is provided with a plurality of suction areas separated from each other. It includes switching means connected to each other, and a vacuum source and a vacuum release means selectively connected to each of the vacuum pipes via each of the switching means, and by switching each of the switching means, each of the adsorption areas is A wafer holding device, characterized in that it independently communicates with either the vacuum source or the vacuum release means. 3. The wafer holding device according to claim 2, wherein a groove is formed along the outer periphery of the wafer suction surface, and the groove is communicated with a vacuum source. 4. The wafer holder according to claim 2 or 3, wherein three or more suction areas are used instead of the plurality of suction areas, and at least one of the vacuum pipes is connected to the plurality of suction areas. Device.