Heat treatment apparatus

Abstract

A support table holds a working fluid in an inner space thereof, and has four cylindrical heaters arranged to surround a cooling plate disposed centrally of the support table. In time of heating, vapor generated from each cylindrical heater spreads toward a central region and peripheral regions of the support table (as schematically shown in two-dot chain line arrows). The vapor can reach peripheral ends, without flows of the vapor colliding with one another, in a way to suppress generation of stagnation points. Since the support table can be heated uniformly, a substrate is heat-treated uniformly over the entire surface thereof. The support table is cooled efficiently by the cooling plate disposed centrally of the support table.

Description

BACKGROUND OF THE INVENTION

(1) Field of the Invention

This invention relates to a heat treatment apparatus for heat-treating semiconductor substrates, glass substrates for liquid crystal displays, glass substrates for photomasks, substrates for optical disks, and so on (hereinafter simply called “substrates”).

(2) Description of the Related Art

A conventional apparatus of the type noted above has a support table for supporting substrates, and a heater and a cooling plate provided for the support table (as disclosed in Japanese Unexamined Patent Publication No. 2003-297738, for example).

This support table defines a space inside, and a working fluid is enclosed in this space. FIG. 1A refers. FIG. 1A is a cross-sectional view of a support table of a conventional heat treatment apparatus. As shown, the support table 41 has two parallel groove-like working fluid chambers 43 arranged on the bottom of an inner space thereof and opposed to each other across the center of the support table 41. A working fluid is stored in these working fluid chambers 43. Each working fluid chamber 43 has a heater 45 for heating the working fluid. Thus, the support table 41 has a heat pipe structure. The support table 41 includes a cooling plate (not shown) attached to the lower surface thereof for cooling the support table 41.

The heat treatment apparatus of such construction causes the heaters 45 to generate heat for heating the support table 41. A substrate is placed and heated on an upper surface acting as a support surface of the support table 41. At this time, the working fluid evaporates inside the support table 41, and its vapor convects and condenses in the space, thereby giving heat uniformly to the support table 41. Consequently, the temperature of the support surface increases uniformly.

The above conventional example has the following drawbacks.

The vapor cannot flow smoothly through the entire space, but tends to stagnate in certain regions in the space. FIG. 1A shows vapor flows with two-dot chain line arrows. The vapor generated adjacent the heaters 45 and working fluid chambers 43 spreads toward the peripheries. At this time, the vapor flows collide on a central line between the two heaters 45. The vapor flows stagnate markedly on this central line and adjacent peripheral walls of the support table 41 (the regions of stagnation being affixed with reference “Q” in FIG. 1A). In the regions where the vapor flows stagnate (hereinafter called “stagnation points”), a reduced quantity of heat is transferred from the vapor to the support table 41. When impurities such as nitrogen are present in the space, the impurities collect at the stagnation points to prevent the vapor condensation reaction. As a result, the temperature of the support surface of the support table 41 cannot be appropriately increased at the stagnation points, causing nonuniformity of the temperature over the support surface. Further, heat can radiate more easily from the peripheral walls than from the central region of the support table 41, thereby promoting the temperature difference between the peripheral walls and the central region, within the support surface.

To cope with the above drawback, it is conceivable to increase the heaters 45 to three as shown in FIG. 1B. However, even such a construction cannot produce an effect of suppressing generation of the stagnation points (referenced “Q” in FIG. 1B). This measure cannot solve the problem of temperature nonuniformity of the support surface.

SUMMARY OF THE INVENTION

This invention has been made having regard to the state of the art noted above, and its object is to provide a heat treatment apparatus for suppressing stagnation of flows of the vapor of a working fluid stored inside a support table, thereby performing uniform heat treatment over an entire substrate surface.

The above object is fulfilled, according to this invention, by a heat treatment apparatus for heat-treating substrates, comprising a support table for supporting the substrates and holding a working fluid inside, a cooling device disposed centrally of the support table in plan view for cooling the support table, and a heating device disposed to surround the cooling device for heating the working fluid.

According to this invention, the heating device surrounds the cooling device disposed centrally of the support table. With this arrangement, when the working fluid inside the support table evaporates, the vapor forms, in plan view, flows directed toward the central region of the support table, and flows directed toward peripheral walls of the support table. The flows to the central region collide with one another, whereby the flows of vapor could stagnate in the central region of the support table. However, the central region of the support table is less subject to the influence of heat dissipation than peripheral regions, and therefore the vapor stagnation will not impair uniformity of the temperature of the support table. On the other hand, the flows to the peripheral walls of the support table can reach the peripheral walls of the support table without colliding with one another. That is, stagnation of the working fluid vapor is restrained. Consequently, the flows of vapor can convect smoothly through the entire support table, thereby heating the support table uniformly. Each substrate placed on the support table is thereby heat-treated uniformly over the entire surface thereof.

The peripheral regions of the support table are more influenced by heat dissipation than the central region, and therefore are subject to a relatively large temperature change. It is difficult to maintain the uniformity of the temperature of the support table. However, according to this invention, the heating device is disposed outwardly of the cooling device disposed in the central region. This arrangement can control the temperature of the peripheral regions with increased accuracy, to secure the uniformity of the temperature of the support table with ease.

The cooling device for cooling the support table is disposed in the central region in plan view. This arrangement can effectively cool the central region which is subject to less temperature change (i.e. has higher heat retention) than the peripheral regions. The temperature of the support table can be lowered efficiently.

“Cooling the support table” with the cooling device includes a direct cooling of the support table, and an indirect cooling of the support table through cooling of the working fluid.

In the invention described above, the heating device, preferably, includes at least n (n being an integer 3 or more) cylindrical heaters, the cylindrical heaters being arranged to form sides of an n-sided polygon centering on the cooling device. The cylindrical heaters constituting the heating device can restrain the flows of vapor from colliding with one another.

The support table may define therein a common working fluid chamber for storing the working fluid and accommodating all of the cylindrical heaters. Then, any differences in the heat value among the cylindrical heaters may be absorbed. Consequently, vapor can be generated uniformly throughout the working fluid chamber.

The heating device may be a planar heater. The planar heater acting as the heating device can restrain the flows of vapor from colliding with one another.

The planar heater may have a ringlike shape surrounding the cooling device. This shape provides an increased effect of restraining the collision among the flows of vapor.

BRIEF DESCRIPTION OF THE DRAWINGS

For the purpose of illustrating the invention, there are shown in the drawings several forms which are presently preferred, it being understood, however, that the invention is not limited to the precise arrangement and instrumentalities shown.

FIG. 1A is a cross-sectional view of a support table of a conventional heat treatment apparatus schematically showing vapor flows;

FIG. 1B is a cross-sectional view of a different support table of a conventional heat treatment apparatus schematically showing vapor flows;

FIG. 2 is a view in vertical section showing an outline of a heat treatment apparatus in a first embodiment of the invention;

FIG. 3 is a cross-sectional view of a support table;

FIG. 4 is a cross-sectional view of a cooling plate;

FIG. 5 is a cross-sectional view of the support table schematically showing vapor flows;

FIG. 6 is a view in vertical section showing an outline of a principal portion of a heat treatment apparatus in a second embodiment; and

FIG. 7 is a cross-sectional view of a support table schematically showing vapor flows.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Preferred embodiments of this invention will be described in detail hereinafter with reference to the drawings.

First Embodiment

FIG. 2 is a view in vertical section showing an outline of a heat treatment apparatus in a first embodiment of the invention. FIG. 3 is a cross-sectional view of a support table. FIG. 4 is a cross-sectional view of a cooling plate.

The heat treatment apparatus in the first embodiment, broadly, includes a support table 1 for supporting a wafer W under heat treatment, cylindrical heaters 3 and a cooling plate 5 provided for the support table 1, and a controller 7 for operating the cylindrical heaters 3 and cooling plate 5 to control the temperature of the support table 1.

The support table 1 has a plurality of small ceramic balls 1b projecting from an upper surface thereof for contacting and supporting the wafer W. These small balls 1b are fitted in recesses formed in the upper surface of the support table 1. The wafer W is supported in a state of point contact on the support table 1. This support mode can prevent variations of the heat treatment. The small balls 1b may be omitted, in which case the wafer W is supported in a state of surface contact.

The support table 1 includes a temperature sensor 11 for detecting the temperature of a support surface 1a which is the upper surface of the support table 1.

The support table 1 defines a closed space A therein which accommodates a working fluid 13 in a decompressed state. A groove-like working fluid chamber 15 is formed in the bottom of the space A for storing the working fluid 13. The working fluid chamber 15 is formed to extend continuously, describing a square surrounding the central region of the support table 1 in plan view. The space A includes a plurality of pillars 17 erected to provide reinforcement.

The cylindrical heaters 3 are arranged at the four sides of the working fluid chambers 15, respectively. The cylindrical heaters 3 generate heat for heating the working fluid 13. The cylindrical heaters 3 arranged in the working fluid chamber 15 as described above remain immersed in the working fluid 13 even when the support table 1 tilts. Thus, the cylindrical heaters 3 can heat the working fluid 13 appropriately.

The cylindrical heaters 3 are electrically connected to a power source 21 which outputs AC power through a switch 23. When this switch 23 is “on”, AC power is supplied to the cylindrical heaters 3. The switch 23 is operable by the controller 7.

The cooling plate 5 is disposed centrally of the support table 1 in plan view. The cooling plate 5 is formed of two metal plates of high thermal conductivity joined together, with a channel 5a cut in mating surfaces thereof. The channel 5a has a meandering form, with opposite ends thereof defining an inlet 5b and an outlet 5c.

The inlet 5b of the cooling plate 5 is connected through an electromagnetic switch valve 35 to a cooling water source 31 provided as a utility of a factory, for example. When the electromagnetic switch valve 35 is opened, cooling water is supplied to the channel 5a. The electromagnetic switch valve 35 also is operable by the controller 7. The cooling water flowing through the channel 5a is drained from the cooling plate 5 via the outlet 5c. The cooling plate 5 corresponds to the cooling device in this invention.

Results of detection by the temperature sensor 11, indicating temperatures of the support surface la, are inputted to the controller 7. Based on a predetermined target temperature and a temperature of the support surface 1a, the controller 7 operates the switch 23 and electromagnetic switch valve 35 to control the temperature of the support surface 1a which is the upper surface of the support table 1. The controller 7 corresponds to the control device in this invention.

Operation of the above heat treatment apparatus for raising and lowering the temperature of the support surface 1a will be described next.

When raising the temperature of the support surface 1a to the target temperature, the controller 7 turns the switch 23 to “on” state based on the target temperature and the temperature of the support surface 1a. At this time, the electromagnetic switch valve 35 is closed. AC power is supplied to the cylindrical heaters 3, whereby the cylindrical heaters 3 generate heat. The cylindrical heaters 3 heat and evaporate the working fluid 13 stored in the working fluid chamber 15.

Since the four cylindrical heaters 3 are arranged in the common working fluid chamber 15, any differences in the heat value among the cylindrical heaters 3 may be absorbed. Consequently, vapor can be generated uniformly throughout the working fluid chamber 15.

FIG. 5 refers. FIG. 5 is a cross-sectional view of the support table 1 schematically showing vapor flows. In FIG. 5, two-dot chain line arrows indicate flows of the vapor of the working fluid.

The vapor generated spreads about. In the first embodiment, the cylindrical heaters 3 are arranged to surround the central region. The vapor therefore flows to the central region and peripheral regions of the support table 1.

To the central region of the support table 1, the vapor flows in from all directions and the flows collide with one another. The vapor may stagnate at this time. However, since the vapor is flowing in from all directions, and since less heat dissipation and higher heat retention occur in the central region than in the peripheral regions, the vapor stagnation will not impair the uniformity of the temperature of the support surface 1a.

On the other hand, the peripheral regions of the support table 1 are reached by the vapor generated from the nearby cylindrical heaters 3 without the vapor flows colliding with one another. Thus, vapor stagnation hardly occurs in the peripheral regions.

Owing to the heat generation characteristic of the opposite end regions of each cylindrical heater 3, relatively weak parts may be present among the vapor flows to the peripheral regions of the support table 1. As a result of the vapor flowing in to the weak parts, the vapor flows collide with one another to cause stagnation (in FIG. 5, reference “P” schematically indicates regions where the vapor flows stagnate). However, the regions where the vapor flows stagnate (hereinafter called “stagnation points”) are limited to the peripheral regions adjacent where normals pass through the ends of the cylindrical heaters 3. Thus, the stagnation is trivial enough to leave the uniformity of the temperature of the support surface 1a intact.

Even when a gas (hereinafter called impurities) heterogeneous to the working fluid 13 and its vapor has mixed into the space A, the impurities are distributed at least to the four stagnation points. The impurities present at each stagnation point are reduced in quantity. Thus, the condensation reaction of the working fluid is not impaired, and the uniformity of the temperature of the support surface la remains intact.

Compared with the central region, the peripheral regions of the support surface 1a are subject to temperature change under the influence of heat dissipation and the like. However, since the cylindrical heaters 3 are arranged outwardly of the cooling plate 5 in this embodiment, the peripheral regions are heated more accurately than where the cylindrical heaters 3 are arranged in the central region. In this way, the uniformity of the temperature of the support table 1 is secured easily.

The support surface 1a is set to the target temperature beforehand by raising the temperature of the support surface 1a as described above. Then, a wafer W may be placed on the support surface 1a to be heat-treated appropriately. While the operation to place the wafer W is in progress, the temperature of the support surface 1a may be raised to the target temperature for heating treatment.

When lowering the temperature of the support surface 1a to a new target temperature, the controller 7 opens the electromagnetic switch valve 35 based on this target temperature and the temperature of the support surface 1a. Through the electromagnetic switch valve 35 opened, cooling water is supplied from the cooling water source 31 to the cooling plate 5. The cooling water supplied flows through the inlet 5b into the channel 5a. The cooling water flowing through the channel 5a collects heat from the support table 1. This cools the entire support table 1 from the central region of the lower surface of the support table 1. The switch 23 is in “off” state at this time.

The central region of the support table 1 is subject to less temperature change (i.e. has higher heat retention) than the peripheral regions. Thus, the temperature of the support table 1 can be lowered efficiently by the cooling plate 5 disposed centrally of the support table 1.

The support surface 1a is set to the target temperature beforehand by lowering the temperature of the support surface 1a as described above. Then, a wafer W may be placed on the support surface 1a to be heat-treated appropriately. While the operation to place the wafer W is in progress, the temperature of the support surface 1a may be lowered to the target temperature for cooling treatment.

Second Embodiment

A second embodiment of this invention will be described next. The second embodiment employs a planar heater 4 in place of the cylindrical heaters 3 of the first embodiment. The following description will be made, centering on this aspect. FIG. 6 is a view in vertical section showing an outline of a principal portion of a heat treatment apparatus in the second embodiment. Like reference numerals will be used to identify like parts which are the same as in the first embodiment and will not be described again.

The heat treatment apparatus in the second embodiment, broadly, includes a support table 2 for supporting a wafer W under heat treatment, a planar heater 4 and a cooling plate 5 provided for the support table 2, and a controller (not shown) for operating the planar heater 4 and cooling plate 5 to control the temperature of the support table 2. Though not shown in FIG. 6, the AC power supply system (including the power source and switch) electrically connected to the planar heater 4, the cooling water supply-drain system (including the cooling water source and electromagnetic switch valve) connected to the cooling plate 5, and the controller for operating these components are the same as in the first embodiment.

The support table 2 defines a working fluid chamber 16 therein, which has an annular (ringlike) shape having a smaller outside diameter than a support surface 2a. The working fluid chamber 16 has an inside diameter to surround the cooling plate 5 disposed centrally of the support surface 2a.

The planar heater 4 is disposed on the lower surface of the support table 2, over a range corresponding to the bottom of the working fluid chamber 16. Thus, the planar heater 4 has an annular shape similar to the working fluid chamber 16. With the planar heater 4 disposed in this way, the bottom of the working fluid chamber 16 is not exposed even when the support table 1 tilts. Thus, the planar heater 4 can heat the working fluid chamber 16 appropriately. The planar heater 4 may comprise a mica heater or silicone rubber heater, for example.

Operation of the above heat treatment apparatus for raising the temperature of the support surface 2a will be described next.

When raising the temperature of the support surface 2a to a target temperature, the controller not shown supplies AC power to the planar heater 4 based on the target temperature and the temperature of the support surface 2a. The planar heater 4 generates heat to heat and evaporate the working fluid 13 stored in the working fluid chamber 16.

FIG. 7 refers. FIG. 7 is a cross-sectional view of the support table 2 schematically showing vapor flows. In FIG. 7, two-dot chain line arrows indicate flows of the vapor of the working fluid. As shown, the vapor generated in the working fluid chamber 16 spreads toward the central region and peripheral regions of the support table 2.

To the central region of the support table 2, the vapor flows in from all directions and the flows collide with one another. The vapor may stagnate at this time. However, since the vapor keeps flowing in, and since less heat dissipation and higher heat retention occur in the central region than in the peripheral regions, the vapor stagnation will not impair the uniformity of the temperature of the support surface 2a.

On the other hand, the peripheral regions of the support table 2 are reached by the vapor from the directions of normals without the vapor flows colliding with one another. Thus, no vapor stagnation occurs in the peripheral regions. The temperature of the support surface 2a may be raised with increased uniformity.

This invention is not limited to the foregoing embodiments, but may be modified as follows:

(1) In the first embodiment described above, the four cylindrical heaters 3 share the common working fluid chamber 15. Instead, separate working fluid chambers may be formed for the respective cylindrical heaters 3. This modification will facilitate sealing work that accompanies installation of the cylindrical heaters 3.

(2) The first embodiment described above uses four cylindrical heaters 3. The construction may be modified as appropriate to use three, five or more such heaters. Where three cylindrical heaters are used, these heaters may be arranged to form the three sides of a triangle surrounding the central region of the support table 1 in plan view.

(3) In the second embodiment described above, the planar heater 4 has a shape of circular ring. This shape may be modified as appropriate as long as it retains a ring-like shape. The shape of the working fluid chamber 16 may also be changed accordingly. For example, the inner circumference of the ringlike planar heater 4 may be changed into a rectangular shape to match the cooling plate 5. The outer circumference of the ringlike planar heater 4 may be extended to the edges of the support table 2.

This invention may be embodied in other specific forms without departing from the spirit or essential attributes thereof and, accordingly, reference should be made to the appended claims, rather than to the foregoing specification, as indicating the scope of the invention.

Claims

1. A heat treatment apparatus for heat-treating substrates, comprising:

a support table for supporting the substrates and holding a working fluid inside;

a cooling device disposed centrally of said support table in plan view for cooling said support table; and

a heating device disposed to surround said cooling device for heating said working fluid.

2. An apparatus as defined in claim 1, wherein said heating device includes at least n (n being an integer 3 or more) cylindrical heaters, said cylindrical heaters being arranged to form sides of an n-sided polygon centering on said cooling device.

3. An apparatus as defined in claim 2, wherein each of said cylindrical heaters forms a side of a triangle or rectangle.

4. An apparatus as defined in claim 2, wherein said support table defines therein a common working fluid chamber for storing said working fluid and accommodating all of said cylindrical heaters.

5. An apparatus as defined in claim 2, wherein said support table defines therein a plurality of separate working fluid chambers for storing said working fluid and accommodating said cylindrical heaters.

6. An apparatus as defined in claim 1, wherein said heating device is a planar heater.

7. An apparatus as defined in claim 6, wherein said planar heater has a ringlike shape surrounding said cooling device.

8. An apparatus as defined in claim 7, wherein said planar heater has an annular shape surrounding said cooling device.

9. An apparatus as defined in claim 6, wherein said planar heater has an outer circumference thereof extending to edges of said support table.

10. An apparatus as defined in claim 6, wherein said support table defines therein a working fluid chamber for storing said working fluid, said planar heater being disposed on a lower surface of said support table corresponding to a bottom of said working fluid chamber.

11. An apparatus as defined in claim 10, wherein said working fluid chamber has a ringlike shape surrounding said cooling device.

12. An apparatus as defined in claim 6, wherein said planar heater comprises one of a mica heater and a silicone rubber heater.

13. An apparatus as defined in claim 1, wherein said cooling device comprises a cooling plate defining a cooling water channel.

14. An apparatus as defined in claim 1, further comprising a control device for operating said heating device and said cooling device to control temperature of an upper surface of said support table.

15. An apparatus as defined in claim 14, further comprising a temperature sensor for detecting the temperature of said upper surface of said support table, said control device being operable based on detection results received from said temperature sensor.

16. An apparatus as defined in claim 14, wherein:

said heating device comprises an electric heater;

said heat treatment apparatus further comprising:

a power source electrically connected to said heating device; and

a switch disposed between said heating device and said power source;

said control device being arranged to operate said switch.

17. An apparatus as defined in claim 14, wherein:

said cooling device comprises a heat exchanger using cooling water;

said heat treatment apparatus further comprising:

a cooling water source communicating with said cooling device; and

an electromagnetic switch valve disposed between said cooling device and said cooling water source;

said control device being arranged to operate said electromagnetic switch valve.

18. An apparatus as defined in claim 1, wherein said support table includes a support device projecting from an upper surface thereof for contacting and supporting the substrates.

19. An apparatus as defined in claim 18, wherein said support device comprises small balls.

20. An apparatus as defined in claim 18, wherein said support device comprises ceramics.