Patent Grant
6908368
The present invention relates to manufacture of semiconductor wafers and more particularly to a method and system of polishing pad tensioning in a chemical mechanical polishing apparatus.
U.S. Pat. No. 6,103,628, assigned to the assignee of the present invention, describes a reverse linear chemical mechanical polisher, also referred to as bi-directional linear chemical mechanical polisher, that operates to use a bi-directional linear motion to perform chemical mechanical polishing. In use, a rotating wafer carrier within a polishing region holds the wafer being polished.
U.S. patent application Ser. No. 09/684,059, filed Oct. 6, 2000, which is a continuation-in-part of U.S. Pat. No. 6,103,628, describes various features of a reverse linear chemical mechanical polisher, including incrementally moving the polishing pad that is disposed between supply and receive spools.
While the inventions described in the above patent and application are advantageous, further novel refinements are described herein which provide for a more efficient drive system that creates the reverse linear (or bi-directional linear) motion.
The present invention offers many advantages, including the ability to efficiently produce reverse linear motion for a chemical mechanical polishing apparatus.
Another advantage of the present invention is to provide for the ability to efficiently produce bi-directional linear motion in a chemical mechanical polishing apparatus that also allows for the incremental movement of the polishing pad.
Another advantage of the present invention is the provision for a single casting that houses the polishing pad, including the supply spool, the receive spool, and pad path rollers.
The present invention provides the above advantages with a method and apparatus for producing bi-directional linear polishing that uses a flexible pad. In one aspect, a portion of the polishing pad is disposed under tension between a supply spool and a receive spool, with a motor providing the tension to either the supply spool or the receive spool and the other spool being locked during processing. If a new section of the polishing pad is needed, the same motor that provided the tension, if connected to the receive spool, is used to advance the polishing pad a determined amount. Further, during processing, a feedback mechanism is used to ensure that the tension of the polishing pad is consistently maintained.
The above and other objectives, features, and advantages of the present invention are further described in the detailed description which follows, with reference to the drawings by way of non-limiting exemplary embodiments of the present invention, wherein like reference numerals represent similar parts of the present invention throughout several views and wherein:
U.S. Pat. No. 6,103,628 and U.S. patent application Ser. No. 09/684,059, both of which are hereby expressly incorporated by reference, together describe, in one aspect, a reverse linear polisher that can use a polishing pad to polish a wafer.
Below the pad 30 is a platen support 50. During operation, due to a combination of tensioning of the pad 30 and the emission of a fluid, such as air, water, or a combination of different fluids from openings 54 disposed in the top surface 52 of the platen support 50, the bi-linearly moving portion of the pad 30 is supported above the platen support 50 in the processing area, such that a frontside 32 of the pad 30 contacts the front surface 12 of the wafer 10, and the backside 34 of the pad 30 levitates over the top surface 52 of the platen support 50. While the portion of the pad 30 within the processing area moves in a bi-linear manner, the two ends of the pad 30 are preferably connected to source and target spools 60 and 62 illustrated in
Further, during operation, various polishing agents without abrasive particles or slurries with abrasive particles can be introduced, depending upon the type of pad 30 and the desired type of polishing, using nozzles 80. For example, the polishing pad 30 can contain abrasives embedded in the frontside 32, and can be used with polishing agents but not a slurry being introduced, or with a polishing pad 30 that does not contain such embedded abrasives instead used with a slurry, or can use some other combination of pad, slurry and/or polishing agents. The polishing agent or slurry may include a chemical that oxidizes the material that is then mechanically removed from the wafer. A polishing agent or slurry that contains colloidal silica, fumed silica, alumina particles etc., is generally used with an abrasive or non-abrasive pad. As a result, high profiles on the wafer surface are removed until an extremely flat surface is achieved.
While the polishing pad can have differences in terms of whether it contains abrasives or not, any polishing pad 30 according to the present invention needs to be sufficiently flexible and light so that a variable fluid flow from various openings 54 on the platen support can affect the polishing profile at various locations on the wafer. Further, it is preferable that the pad 30 is made from a single body material, which may or may not have abrasives impregnated therein. By single body material is meant a single layer of material, or, if more than one layer is introduced, maintains flexibility such as obtained by a thin polymeric material as described herein. An example of a polishing pad that contains these characteristics is the fixed abrasive pad such as MWR66 marketed by 3M company that is 6.7 mils (0.0067 inches) thick and has a density of 1.18 g/cm3. Such polishing pads are made of a flexible material, such as a polymer, that are typically within the range of only 4-15 mils thick. Therefore, fluid that is ejected from the openings 54 on the platen support 50 can vary by less than 1 psi and significantly impact the amount of polishing that will occur on the front face 12 of the wafer 10 that is being polished, as explained further hereinafter. With respect to the pad 30, the environment that the pad 30 is used in, such as whether a linear, bi-linear, or non-constant velocity environment will allow other pads to be used, although not necessarily with the same effectiveness. It has been determined, further, that pads having a construction that has a low weight per cm2 of the pad, such as less than 0.5 g/cm2, coupled with the type of flexibility that a polymeric pad achieves, also can be acceptable.
Another consideration with respect to the pad 30 is its width with respect to the diameter of the wafer 10 being polished, which width can substantially correspond to the width of the wafer 10, or be greater or less than the width of the wafer 10.
As will also be noted hereinafter, the pad 30 is preferably substantially optically transparent at some wavelength, so that a continuous pad 30, without any cut-out windows, can allow for detection of the removal of a material layer (end point detection) from the front surface 12 of the wafer 10 that is being polished, and the implementation of a feedback loop based upon the detected signals in order to ensure that the polishing that is performed results in a wafer 10 that has all of its various regions polished to the desired extent.
The platen support 50 is made of a hard and machineable material, such as titanium, stainless steel or hard polymeric material. The machineable material allows formation of the openings 54, as well as channels that allow the fluid to be transmitted through the platen support 50 to the openings 54. With the fluid that is ejected from the openings 54, the platen support 50 is capable of levitating the pad. In operation, the platen support 50 will provide for the ejection of a fluid medium, preferably air, but water or some other fluid can also be used. This ejected fluid will thus cause the bi-linearly moving pad 30 to levitate above the platen support 50 and pushed against the wafer surface when chemical mechanical polishing is being performed.
A pad drive system 100 that is preferably used to cause the bi-linear reciprocating movement of the portion of the polishing pad within the processing area will now be described.
As an initial overview, as illustrated by
With the path 36 and the bi-linear pad movement mechanism having been described, a further description of the components within the path 36, and the horizontal movement drive assembly 150 associated therewith, will now be provided.
As illustrated in
With respect to the horizontal slide member 120, as illustrated in
Furthermore, a pin 130 is downwardly disposed from the pin connection piece 122A as shown in
The horizontal drive assembly 150, as shown in
Thus, operation of the horizontal drive assembly 150 will result in the bi-directional linear movement of the horizontal slide member 120, and the corresponding horizontal bi-directional linear movement of a portion of the polishing pad 30 within the processing area.
As described in U.S. application entitled “Drive System For A Bi-Directional Linear Chemical Mechanical Polishing Apparatus” attorney reference 042496/0293224 mentioned above, during processing the polishing pad can be locked in position between the supply spool 60 and the receive spool 62. As such, while a portion of the pad 30 within the processing area moves in the horizontal bi-directional linear manner, the pad can also be unlocked so that another portion of the polishing pad will move within the processing area, allowing incremental portions of the pad to be placed into and then taken out of the processing area, as describe in U.S. patent application Ser. No. 09/684,059 referenced above.
While have the pad 30 locked in position at both the supply spool 60 and the receive spool 62 will work, it has been found that more effective results can be achieved using a tensioning mechanism at one end of the portion of pad 30 in cooperation with the drive system described in the Drive System application referenced above. In particular, as illustrated in
Further, as shown in
The control system for controlling the tensioning and incrementing motor 270 and the lock mechanism 280 is illustrated in further detail in FIG. 6. As shown, power for the motor 270 and a controller 320 is provided by power source 310, which provides appropriate power along line 314 to a driver 324 and likely a different appropriate power along line 312 to controller 320. Controller 320 includes a computer or microcontroller of some type, as is known. Further, line 322 from the controller inputs the predetermined torque value to the motor control unit 304 as a TORQUE signal, specifically to torque control unit 326. The predetermined torque value for the motor 270 may be a torque value that is about 10% less than the rated torque value of the lock mechanism 280. The line 323 from the torque control unit inputs the TORQUE signal to the driver 324. Line 316 returns the TORQUE signal that is received from the driver 324 to the controller for feed-back or self-check purposes. If self-check is not desired, the line 316 is removed. As will be described hereinafter, the TORQUE signal is used to maintain the tension on the receive spool 62 at a desired level during processing. The driver 324, through the line 328a, applies this torque value to the motor 270 as electrical current.
If the pad needs to be incremented, however, with an appropriate signal from the controller, the motor 270 is rotated, preferably at a low rpm, and the pad is advanced. As the motor rotates, it generates predetermined number of encoder pulses per revolution. The encoder pulses generated by the motor 270 are fed back to the driver 324 through the line 328b and then from the driver 324 to the controller 320 through the line 328c. By counting the pulses, the controller 320 tracks the position of the pad, as it is advanced by the motor 270. In one example, a single revolution of the motor 270 advances the pad 280 millimeters. An exemplary motor may be Model no. SG255SA-GA05ACC which is available from Yaskawa Electric Co., Tokyo, Japan. In this particular example, the motor 270 generates 8192 pulses per revolution. These pulses are sent to the driver serially. However, encoder pulses are ignored by the controller when performing tensioning, because the motor 270 will try to rotate at a certain speed, but of course it will not be able to move since pad is constrained by the lock mechanism 280 on the supply spool.
Upon receipt of process sequence commands and external signals, such as the TORQUE signal discussed above, controller 320 will generate control signals along line 322 that are used by the motor control unit 304 to control the motor 270. In particular, the signals generated include an ON/OFF signal, as well as a TENSION signal that is used to supply the motor control unit 304 with an indication of the proper amount of power to supply to the motor 270 in order to achieve the desired tension on the receive spool 62 during processing. Controller 320 will also generate a BRAKE signal along line 330, which preferably passes through relay 332 to the lock mechanism 280, which is preferably implemented as an electromagnetic clamp brake that is used to lock the supply spool 60 in position. A monitor 340 and a user-input device 350 such as a keyboard are also preferably connected to the controller 320.
The motor control unit 304 includes a driver 324 and a torque adjustment unit 326. Power supplied to the driver 324 is varied in dependence upon a signal that is generated by the torque adjustment unit 326.
Operation of the tensioning and incrementing of the portion of the pad 30 according to the present invention will now be further described with reference to the flowchart illustrated in
As illustrated, during processing, initially in step 410, the controller 320 provides an OFF signal to both the motor control unit 304 and the lock mechanism 280. This causes both the supply spool 60 and the receive spool 62 to rotate freely, thereby allowing the initial threading of the pad 30 through the pad path 36 as described above with reference to FIG. 5A. Once threaded and processing is to occur, step 420 follows, at which time controller 320 provides an ON signal to the lock mechanism 280, followed by a TENSION signal to the motor control unit 304, which TENSION signal turns on the motor 270 and applies tension to the receive spool 62. Thus, the supply spool 60 becomes locked, and the receive spool 62 is held under tension, thereby appropriately tensioning the entire portion of the pad 30 therebetween, including that portion of the pad 30 that is in the processing area 20 illustrated in FIG. 1.
Thereafter, step 430 is begun and processing will occur. During processing, the controller 320 will initiate the bi-directional linear movement of the pad 30 using the pad drive system 100 discussed above with reference to
At some point, however, the portion of the pad 30 used for polishing will need to be replaced, and another portion of pad 30 provided. While an entirely new portion of pad 30 will be described as being provided, it will be understood that incremental portions can also be provided. When any new portion of pad 30 is needed from the supply spool 60, the same operation will apply. In particular, the controller 320 will first provide in step 430 an OFF signal to the motor control unit to signal that the motor 270 should be turned off. Thereafter follows step 440, in which an OFF signal will also be provided to the lock mechanism 280, thereby turning off the brake and unlocking the supply spool 60. Step 460 then follows, in which the controller 320 signals to the motor control unit 304 to increment the pad 30 some specified amount, which amount will correspond to the linear distance the pad 30 is desired to move. Upon this signal, the motor control unit 304 turns on the motor 270 and advances the pad by rotating the receive spool 62. As previously mentioned this specific amount that the pad is incremented may be determined through the encoder pulses generated by the rotating motor 270. Once the pad advancement occurs, step 420 is then initiated again, so that the supply spool 60 can be locked and the receive spool tensioned as described above.
The above provided description illustrates a preferred manner of providing tension during processing for the portion of the pad 30 that is in the processing area, as well as the incrementing of the pad 30, using the same motor 270. It is understood that although described as tensioning the receive spool 62 and locking the supply spool 60 during processing, that tensioning the supply spool 60 and locking the receive spool 62 during processing is another manner of implementing the present invention.
While the tensioning and incrementing is preferably accomplished using the single motor 270, it is understood that if two motors, one attached to the receive spool and the other to the supply spool, that a variety of arrangements for tensioning and incrementing would also exist.
Further, although various preferred embodiments have been described in detail above, those skilled in the art will readily appreciate that many modifications of the exemplary embodiment are possible without materially departing from the novel teachings and advantages of this invention.
This is application is a continuation of U.S. patent Ser. No. 10/126,464 filed Apr. 18, 2002, now U.S. Pat. No. 6,589,105, and related to (U.S. Patent Application entitled “Drive System For a Bi-Directional Linear Chemical Mechanical Polishing Apparatus” Ser. No. 10/126,469 filed Apr. 18, 2002, all incorporated herein by reference. This application is a continuation-in-part of and claims the benefit of priority under 35 USC 119/120 to the following: Ser. No. 10/252,149 filed Sep. 20, 2002, now U.S. Pat. No. 6,604,988, entitled “Polishing Apparatus and Method With Belt Drive System Adapted to Extend the Lifetime of a Refreshing Polishing Belt Provided Therein”, which is a continuation of Ser. No. 09/880,730 filed Jun. 12, 2001, now U.S. Pat. No. 6,464,571 Entitled “Polishing Apparatus and Method With Belt Drive System Adapted to Extend the Lifetime of a Refreshing Polishing Belt Provided Therein”, which is a continuation-in-part of Ser. No. 09/684,059 filed Oct. 6, 2000 now U.S. Pat. No. 6,468,139 entitled “Chemical Mechanical Polishing Apparatus and Method with Loadable Housing”, which is a continuation-in-part of Ser. No. 09/576,064 filed May 22, 2000 now U.S. Pat. No. 6,207,572 entitled “Reverse Linear Chemical Mechanical Polisher with Loadable Housing”, which is a continuation of Ser. No. 09/201,928 filed Dec. 1, 1998 now U.S. Pat. No. 6,103,628 entitled “Reverse Linear Polisher With Loadable Housing”, all incorporated herein by reference.
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| Number | Date | Country | |
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| Parent | 09684059 | Oct 2000 | US |
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