WO2002004171A1

WO2002004171A1 - Method and apparatus for heating a polishing block

Info

Publication number: WO2002004171A1
Application number: PCT/US2001/017221
Authority: WO
Inventors: Kazuya Uchida
Original assignee: Memc Electronic Materials, Inc.
Priority date: 2000-07-06
Filing date: 2001-05-25
Publication date: 2002-01-17
Also published as: JP2002018703A; TW497128B

Abstract

An apparatus (11) for heating a polishing block (13) priorto wax mounting an article to be polished on the polishing block(13) comprises a heater (19) for heating the block and a chuck(15) including a surface (17) for supporting the polishing block(13). The chuck (15) is configured to hold an underside of thepolishing block (13) against the surface (17) to inhibit warpingof the block (13) and to promote uniform, rapid heating of theblock. A method of heating the polishing block (13) comprisesplacing the block on a heater (19) so that an area of a heatedsurface (14a) of the block is in contact with the heater (19) andoperating the heater to heat the block (13). The temperature ofthe block (13) is monitored and the area of the heated surface(14a) of the block (13) in contact with the heater (19) isadjusted in response to the temperature of the block (13).

Description

METHOD AND APPARATUS FOR HEATING A POLISHING BLOCK

Background of the Invention

The present invention relates generally to polishing articles, and more particularly to heating a polishing block in preparation for adhering an article such as a semiconductor wafer thereto.

Conventionally, a mechanochemical polishing method is used to polish a single surface of a semiconductor wafer. The method is performed using a suitable polishing apparatus, such as that shown in Fig. 4a. Wafers 130 are adhered to polishing blocks 120 which are rotatably mounted in the apparatus . The wafers are rotated and forced downward against a polishing cloth or pad 126 mounted on a rotating turntable 124. Abrasive liquid 128, such as alkaline colloidal silica, is applied to the polishing pad 126 during the polishing operation. A single surface of each wafer 130 is thereby polished.

Each wafer is conventionally adhered to the polishing block 120 in a three step process. Wax 122 is applied on a planar surface of the polishing block, as by spin-coating.

The spin coating operation is typically performed by placing the block in a chuck of a spin apparatus, spinning the block and applying wax while the block is spinning. In a second step, the block is transferred to a heating apparatus to heat the polishing block. The heating apparatus typically comprises a heating plate upon which the block rests during heating, or a steam-type heater including a ring for supporting the outer edge of the block and which exposes the underside of the block to the steam. The present invention particularly relates to the heating plate heating apparatus.

After heating, the block is transferred to a press for pressing the wafer 130 against the softened wax 122. (Fig. 4b shows the block with several wafers mounted thereon.)

Heating the polishing block to the correct temperature and making the temperature uniform is difficult because the block is made of a thick ceramic material, such as alumina or silicon carbide, which is a poor thermal conductor. A substantial amount of time is expended in heating the thick block to the relatively high temperature required to achieve suitable bonding of the wafer to the block. Moreover, the block may warp (Fig. 3) due to the difference in temperature between the heated lower surface of the block and the unheated upper surface of the bloc . Such warping increases the time required to heat the block, causes the block to be unevenly heated and causes the temperature at the upper surface of the block to be non-uniform. Non-uniform temperature at the upper surface also causes the hardness of the wax 122 on the polishing block 120 to be non-uniform and thereby prevents a wafer adhered to the block from lying flat on the surface. The non-uniform temperature may also lead to dimpling in the wax. Additionally, in order to speed heating of the block, the heater may be set at a temperature higher than the desired temperature for the polishing block. Thus, if the block is left on the heater for too long, the block is overheated (or "superheated) which also prevents the wafer from lying flat on the surface. Such non-flat mounting will cause the flatness and the edge roll-off characteristic of the wafer to be degraded during polishing. Summary of the Invention

Among the several objects of the present invention may be noted the provision of an apparatus and method for uniformly heating a polishing block prior to adhering a semiconductor wafer to the block; the provision of such an apparatus and method which uniformly heats wax applied to the polishing block; the provision of such an apparatus and method for rapidly heating the polishing block; the provision of such an apparatus and method for inhibiting warping of the polishing block; the provision of such an apparatus and method which promote flat mounting of the wafer on the polishing block; and the provision of such an apparatus and method which promote flatness and thickness uniformity in the wafer after polishing. Briefly, apparatus of this invention for heating a polishing block prior to wax mounting an article to be polished on the polishing block comprises a heater for heating the block and a chuck including a surface for supporting the polishing block. The chuck is configured to hold an underside of the polishing block against the surface to inhibit warping of the block and to promote uniform, rapid heating of the block.

In another aspect of the invention, the apparatus comprises a heater for heating the block and a vacuum chuck including a surface for supporting the polishing block and a groove for drawing air therethrough to hold the polishing block to the surface to inhibit warping of the block and to promote uniform, rapid heating of the block.

In yet another aspect of the present invention, a heater to heat the block. The temperature of the block is monitored and the area of the heated surface of the block in contact with the heater is adjusted in response to the temperature of the block. Other objects and features of the present invention will be in part apparent and in part pointed out hereinafter.

Brief Description of the Drawings

Fig. 1 is a schematic elevational view of a heating apparatus of the invention illustrating internal components of a polishing block chuck thereof;

Fig. 2 is a top view of a chuck;

Fig. 3 is an elevational view of the chuck and polishing block showing warping (exaggerated for illustration purposes) ;

Fig. 4a is a schematic elevational view of a single surface polishing apparatus; and

Fig. 4b is a schematic perspective view of the polishing block having wafers mounted thereon. Corresponding reference characters indicate corresponding parts throughout the several views of the drawings .

Detailed Description of the Preferred Embodiment

Referring now to the drawings and in particular to Fig. 1, a heating apparatus of the present invention is designated in its entirety by the reference numeral 11. The heating apparatus is constructed and configured to heat a includes an upper plate portion 17 for supporting the polishing block 13. The apparatus also comprises heating elements 19 (collectively, a heater) , preferably disposed within the chuck 15, for heating the block. Note that the invention is not limited to a vacuum chuck and use of other types of chucks is contemplated. For example, the chuck may comprise mechanical clamps which engage the peripheral edge of the polishing block.

Preferably, the plate portion 17 of the chuck 15 is planar and includes a circumferential groove 21 (Fig. 2) disposed near its peripheral edge for positioning generally opposite an edge 23 of the polishing block 13. A tube 25 connects the groove 21 to an electromagnetic valve 27. When the valve is opened to the tube 25, air is drawn through the groove (as by a pump or vacuum source) to draw a vacuum under the block 13 to hold the block to the plate portion 17 and thereby inhibit warping of the block during heating and promote uniform, rapid heating of the block.

As shown in Fig. 1, the apparatus 11 further comprises a lift mechanism 29 adapted to lift the block 13 off the plate portion 17. Preferably, the lift mechanism 29 includes three lift pins 31 extendable through openings 35 in the chuck 15 to contact and lift the block 13. The lift pins are supported at bottom ends by a base 33. A vertically movable piston rod 37 is attached to the base 33 for raising and lowering the lift pins 31. The piston rod 37 preferably extends from a pneumatic cylinder 39 connected via a tube 41 to the electromagnetic valve 27. Opening the valve 27 causes air to be forced into the cylinder and be used to support the block 13, though three is preferred. Other types of lift mechanisms are contemplated, including a lift mechanism using air pressure directly against the block. Preferably, the chuck 15 is made of aluminum, and the heating elements 19 are positioned within the chuck beneath the upper plate portion 17. The elements are connected to a suitable electrical power source (not shown) .

A pyrometer 45 (generally, temperature sensor) is positioned to sense the temperature of wax 46 on the surface 14b and transmit the temperature data to a controller 47. A suitable pyrometer is an infrared radiation pyrometer which need not contact the wax 46 to sense the wax temperature. The controller 47 is, for example, a microcontroller, and is adapted to receive temperature data (generally, signals) from the pyrometer 45 and to control the electromagnetic valve 27 to actuate the vacuum chuck or the lift mechanism in response to the temperature data.

In a method of the invention, the polishing .block 13 is placed on the plate portion 17 (generally, the heating surface) so that an area of the lower surface 14a (the heated surface) of the block is in contact with the plate portion 17. Preferably, wax 46 has been applied to the block 13 prior to placement on the chuck. The vacuum chuck 15 is operated to hold the block against the plate portion 17 so that, preferably, substantially all of the lower surface 14a is in contact with the plate portion 17 and is heated uniformly. In other words, the chuck 15 prevents the block 13 from warping and maintains the block in contact 13 to "thermal shock" which may damage the block, but which is also high enough to heat the block relatively quickly. Preferably, the elements are operated at a temperature of between 100° and 200°C (between 212° and 392°F), and more preferably between 130° and 150°C (between 266° and 302 °F) . The pyrometer 45 operates to sense the temperature of the wax 46 on the upper surface 14b and transmits temperature data to the controller 47. Generally, the controller monitors the temperature data and adjusts the area of the lower surface 14a of the block 13 in contact with the plate portion 17 in response to the temperature data so that the wax temperature is maintained at a desired temperature, plus or minus a relatively small temperature range such as 4°C (7°F) . As an example, a desired temperature is selected and the block is heated to the desired temperature with the block held by the vacuum chuck. When the wax temperature is 4°C above the desired temperature, the controller 47 actuates the valve 27 to stop drawing the vacuum against the block and to cause the lift mechanism to lift the block off the plate portion 17 and thereby reduce the area of the lower surface 14a of the block 13 in contact with the plate portion 17 to zero. If the wax temperature falls 4°C below the desired temperature, the controller actuates the valve to lower the block to the plate portion and to draw a vacuum once again and thereby hold the block to the plate portion 17. Note that the vacuum may be operated, e.g., at a reduced vacuum force, so that less than all of the lower surface 14a of the block is in contact with the plate portion 17. Moreover, the lift mechanism may be made to even when the block is lifted, a portion of the lower surface 14a remains in contact with the plate portion 17.

The desired temperature is selected based on the most suitable temperature for adhering the wafer to the block, which varies depending upon the type of wax 46 applied to the block 13. Maintaining the wax at the desired temperature range promotes flatness of the polished wafer, the most desirable nanotopology for the polished wafer, inhibits formation of dimples in the wax and thereby inhibits imperfections in the polished wafer, and promotes a desirable wafer roll-off characteristic (or roll-off value) . Preferably, the desired temperature of the wax 46 is selected from the range of temperatures between about 60° to 100° C (140° to 212°F) and more preferably between about 80° to 95°C (176° to 203°F) . The wax 46 attains such a temperature in less time and has a more uniform temperature due at least in part to the chuck which operates to hold a larger area of the block, especially the edges of the block, in contact with the plate portion and thereby inhibit warping of the block. For example, when a heating plate has a temperature of 115°C (239°F) , the polishing block 13 can reach the desired temperature in about 60 seconds or less, and the variance in wax temperature over the upper surface of the polishing block can be made +4°C or less as described above .

In view of the above, it will be seen that the several objects of the invention are achieved and other advantageous results attained.

When introducing elements of the present invention or there may be additional elements other than the listed elements .

As various changes could be made in the above constructions without departing from the scope of the invention, it is intended that all matter contained in the above description or shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense .

Claims

WHAT IS CLAIMED IS:

1. An apparatus for heating a polishing block prior to wax mounting an article to be polished on the polishing block, the apparatus comprising: a heater for heating the block, and a chuck including a surface for supporting the polishing block, the chuck configured to substantially hold an underside of the polishing block against the surface to inhibit warping of the block and to promote uniform, rapid heating of the block.

2. Apparatus as set forth in claim 1 further comprising a vacuum source in fluid communication with the chuck surface to apply a vacuum to the polishing block.

3. Apparatus as set forth in claim 2 wherein the chuck surface has at least one opening through which a vacuum is applied from the vacuum source to the polishing block.

4. Apparatus as set forth in claim 3 wherein the opening in the chuck surface comprises an annular groove in the chuck surface disposed for positioning generally opposite the edge of the polishing block to hold the edge of the block against the chuck surface to inhibit warping of the edge of the block.

5. Apparatus as set forth in claim 1 wherein the

6. Apparatus as set forth in claim 1 wherein the surface of the chuck is generally planar for supporting a generally planar surface of the polishing block.

7. Apparatus as set forth in claim 2 further comprising a lift mechanism adapted to lift the block off the surface of the chuck.

8. Apparatus as set forth in claim 7 further comprising a temperature sensor for sensing the temperature of the block.

9. Apparatus as set forth in claim 8 wherein the apparatus further comprises a controller for receiving signals from the temperature sensor, the controller being adapted to control the vacuum source and the lift mechanism in response to said signals during heating of the polishing block to help maintain a constant temperature of the polishing block and to inhibit warping of the edge of the block.

10. An apparatus for heating a polishing block prior to wax mounting a semiconductor wafer on the polishing block, the apparatus comprising: a heater for heating the block, and a vacuum chuck including a surface for supporting the polishing block and a groove for drawing air therethrough to hold the polishing block to the surface to inhibit warping of the block and to promote uniform, rapid heating of the

11. Apparatus as set forth in claim 10 wherein the apparatus further comprises a lift mechanism adapted to lift the block off the surface of the chuck.

12. Apparatus as set forth in claim 10 wherein the apparatus further comprises a controller adapted to control the vacuum chuck and the lift mechanism during heating of the polishing block to help maintain a uniform temperature of the polishing block and to inhibit warping of the edge of the block.

13. A method of heating a polishing block prior to adhering a semiconductor wafer on the polishing block, the method comprising: placing the block on a heater so that an area of a heated surface of the block is in contact with the heater, operating the heater to heat the block, monitoring the temperature of the block, and adjusting the area of the heated surface of the block in contact with the heater in response to the temperature of the block.

14. A method as set forth in claim 13 wherein the adjustment step is performed by subjecting at least a portion of the heated surface of the polishing block to a vacuum chuck.

15. A method as set forth in claim 13 wherein the adjustment step is performed by lifting at least a portion

16. A method as set forth in claim 13 wherein the adjustment step is performed using a controller.

17. A method as set forth in claim 13 further comprising the step of subjecting at least a portion of the heated surface of the polishing block to a vacuum chuck after said placement step and prior to said adjustment step,