Patent Application
20050217586
The present inventions relate to methods and apparatus for lifting a workpiece from the surface of a workpiece support in a semiconductor processing system, and to methods and apparatus for aligning lifting apparatus in a semiconductor processing system.
A conventional semiconductor processing system contains one or more chambers including processing and transfer chambers, within which a wafer is supported by a pedestal or other workpiece support. One example of a pedestal is a heater plate in an annealing chamber in which the heater plate heats a semiconductor wafer which is supported on the plate. The wafer or other semiconductor workpiece is typically transported into the chamber through a slit valve by a transport robot which positions the wafer above the pedestal. A lift mechanism which often includes a plurality of lift fingers, is raised within the chamber until the lift fingers engage the underside of the wafer and lift the wafer from the robot arm. After the robot arm is withdrawn from the chamber, the lift mechanism, typically under control of a computer control system, then lowers the lift fingers below the pedestal so that the wafer is placed onto the surface of the pedestal
After the wafer is placed onto the support surface of the pedestal, the lift fingers typically continue to descend into the pedestal to a fully retracted position. The wafer is usually chucked by a mechanical or electrostatic chuck which clamps or chucks, the wafer to the pedestal. Then one or more semiconductor fabrication process steps are performed in the chamber, such as annealing the wafer or depositing or etching films on the wafer. After completion of the process steps, the lift mechanism extends the lift fingers to raise the wafer above the pedestal so that the wafer can be removed from the chamber via the robotic transport.
However, some chambers including anneal chambers often include a cooling plate positioned above the pedestal to cool the wafer prior to removing the wafer from the chamber. The lift mechanism may be used to lift the wafer from the pedestal following annealing or other processes which heat the wafer, and to position the wafer adjacent to the cooling plate to facilitate cooling of the wafer prior to removal of the wafer from the chamber. In many such chambers, it is preferred that the wafer not actually touch the cooling plate since such may damage the processed wafer surface. Accordingly, the actuation of the lift fingers is typically carefully controlled to avoid contact between the wafer and the cooling plate. To facilitate such control, the lift fingers are usually aligned with respect to a chamber interior surface to provide a baseline or “zero” location for the lift mechanism control system.
To align the lift mechanism to the cooling plate 30 of the chamber, a technician fastens the lift mechanism upper assembly 10 to the underside of the chamber lid 32 as shown in
Following alignment, the chamber 30 may be pumped down to the desired processing vacuum pressure by a pump 64 which evacuates the chamber 30 through an exhaust line 66. The pump 64, the lift motor 62 and other controllable components of the processing system are usually controlled by a system controller 70 which is typically a programmed workstation. To cool a wafer, the lift fingers 12 may be positioned by the system controller 70 at a vertical location offset from the zero location such that the wafer has the desired spacing from the cooling plate.
The following is a description of a specific embodiment of the inventions, reference being made to the accompanying drawings, in which:
a is a perspective view of a lift pin subassembly of the lift mechanism of
b is a front view of the lift pin subassembly of
A semiconductor processing system in accordance with one embodiment of the present invention is indicated generally at 100 in
In the illustrated embodiment, each lift pin 110 includes a piston 120 which is exposed to the internal chamber pressure on one side of the piston 120 (
In another aspect of the present inventions, each lift pin 110 has a curved engagement surface 122 positioned to engage the chamber alignment surface 116. In the illustrated embodiment, and as best seen in
In yet another aspect of the present inventions, the linking mechanism 112 includes a plurality of floating joints 124, each of which, as best seen in
In still another aspect of the present inventions, the lift mechanism 104 further includes one or more pressure cylinders 128 coupled to the linking mechanism 112. As noted above, each piston 120 of the lift pins 110 provides an upward force as a result of the net pressure differential between the internal chamber pressure and the ambient atmospheric pressure external to the chamber. After the initial alignment procedure and the lift pins 110 are coupled to the linking mechanism 112, this upward force produced by the ambient atmospheric pressure on the lift pins 110 is opposed by the motor 114, particularly when the motor 114 is directed to lower the lift pins 110. To counter-balance the upward force produced by the ambient atmospheric pressure on the lift pins 110, a pump 130 can provide air or other fluid under pressure to the pressure cylinders 128 to produce a downward directed force on the linking mechanism 112. The magnitude of the downward force can be controlled by controlling the pressure of the fluid supplied to the pressure cylinders 128. In the illustrated embodiment, a pressure regulator 132 controlled by the system controller 140 maintains the pressure to the pressure cylinders 128 substantially constant at a first value such as 10 p.s.i. (0.7 kilogram-force per square centimeter (kgf/cm2)), for example, when raising the lift pins 110. Conversely, the pressure is maintained substantially constant at a second value, such as 20 p.s.i. (1.4 kgf/cm2) for example, which is higher than that of the first pressure value, when lowering the lift pins.
In the illustrated embodiment, the processing chamber 102 is an anneal chamber which treats the wafer 106 by heating it to a prescribed temperature for a prescribed length of time. The wafer is heated by the pedestal 108 which includes a heater plate on which the wafer rests in the chamber 102. Because some wafers are subject to oxidation, particularly at high temperatures, in some applications it is preferred to anneal the wafer in an oxygen free atmosphere in the chamber. For example, a wafer having a deposited copper film may be heated to 100 to 600 degrees C. Upon completion of the anneal process, the wafer may be transferred by a robot 150 in an adjoining transfer or buffer chamber 152 (
In order to cool the wafer following annealing, the lift mechanism 104 lifts the wafer 106 from the pedestal heating plate 108 and moves the wafer 106 to an upper position adjacent to the cooling plate 154. In many applications, it is appropriate to bring the upper surface of the wafer close to the cooling plate to facilitate heat transfer from the wafer to the cooling plate. However, it is often preferred that the upper surface of the wafer not actually touch the cooling plate because the cooling plate may scratch or otherwise damage the deposited films on the wafer. Thus, in many applications it is desirable to closely control the spacing between the wafer and the cooling plate. For example, a parallel spacing of as little as 0.5 mm to 1 mm between the upper surface of the wafer and the lower surface of the cooling plate may be appropriate in some applications. As will be made more clear below, a lift mechanism and alignment procedure in accordance with the present inventions are believed to facilitate precise control of the spacing between the wafer and the cooling plate, which spacing may be maintained over many wafer cooling operations.
To lift a wafer from the pedestal 108, the lift pins 110 of the lift mechanism 104, each have a lift finger 170 which is carried by the piston 120 of each lift pin 110. Each lift finger 170 in turn has a finger tip 172 which is positioned to engage the underside of the perimeter of the wafer 106. When the lift pins 110 are positioned in a fully retracted position as shown in
a,
5
b and 6 show the piston 120 of the lift pins 110 in greater detail. As shown therein, each piston 120 includes a flange-shaped piston head 190 and a piston shaft 192 extending below the piston head 190. The piston shaft 192 vertically slides within a flange member 194 having a barrel portion 196 which is received in an aperture 198 in the bottom floor 200 of the processing chamber 102. A shoulder 202 of the flange member 194 is carried by the top surface of the chamber floor 200. The flange member 194 guides the vertical movement of the piston shaft 192 and has a pair of bushings 204 which facilitate the piston shaft 192 sliding within the flange member.
Above the piston head 190 of the piston 120 is a generally cylindrically-shaped base portion 206 which carries a lift finger 170. The base portion 206 has a flat registration surface 208 which engages a similarly shaped registration surface 210 of the lift finger 170 to align the lift finger with respect to the piston 120 so that the lift finger tip 172 is oriented radially inward toward the wafer position as shown in
The lift pin 110 further includes a bellows 220 which is welded and sealed to the piston head 190 at one end, and welded and sealed to the lift pin flange member 194 at the other end of the bellows. The bellows 220 defines a piston chamber 224 on the underside 222 of the piston head 190. The flange member 194 defines a channel 230 which is aligned with a corresponding channel 232 in the bottom floor 200 of the chamber 102. The channels 230 and 232 vent the piston chamber 224 to the exterior of the chamber 102 so that the piston chamber 224 and hence the underside 222 of the piston head 190 are exposed to the ambient atmospheric pressure exterior to the chamber 102.
An alignment pin 234 extending from the bottom of the flange member 194 is received in a corresponding recess in the chamber bottom floor 200 to align the channels 230 and 232 and also the angular orientation of the lift pin 110 in general. To facilitate alignment between the piston 120 and the flange member 194 of each lift pin 110 as the bellows 220 is welded to the piston and flange member, the flange member 194 has a flat surface 240 on which the flange member 194 may rest on a support surface during the welding operation. The base portion registration surface 208 of the piston 190 may rest on a support surface with the lift finger 170 removed. In this manner, a desired orientation between the piston 120 and the flange member 194 may be maintained as the bellows 220 is welded to these members. It is recognized that other techniques for permanently attaching the bellows to the piston and flange member may be used as well.
The lift finger 170 may then be clamped to the base portion 206 of the piston 120 and the lift pin 110 installed into the chamber in the angular alignment orientation discussed above. Each lift pin may be fastened to the bottom wall 200 of the chamber using fasteners 241 which pass through the bottom wall 200 as shown in
During normal processing operations in which the lift mechanism 104 is used to raise and lower wafers for processing and transfer, the lift pins 110 are normally linked together by attachment to the linking member 126 of the linking mechanism 112 so that the motor 114 can lift raise and lower the lift pins in unison. However, during an initial alignment procedure, the lift pins 110 are preferably disconnected from the linking mechanism 104 so that each lift pin 110 is free to vertically slide independently of the other lift pins 110. As previously mentioned, the piston chamber 224 of each lift pin is exposed to ambient atmospheric pressure. In accordance with one aspect of the present inventions, each lift pin may be raised independently, using the ambient atmospheric pressure, to align each lift pin independently. This may be achieved by activating the pump 118 (
The internal chamber pressure exerts a downward force on each lift pin 110 including the piston head 190. In addition, gravity exerts a downward force on the lift pins 110. Conversely, the ambient atmospheric pressure in the piston chamber exerts an upward force on the piston head 190 of each lift pin 110. In the illustrated embodiment, the lift pins when first installed are at an initial position above the retracted position illustrated in
In this manner, the lift pins may be raised independently until the engagement surface 122 of each lift pin 110 engages the alignment surface 116 of the chamber as shown in
Once each lift pin has securely engaged the associated alignment surface 116, each lift pin 110 may be secured to the linking mechanism 112 so that the motor 114 can lower the lift pins from physical height 0 to other heights including the fully retracted position illustrated in
It is preferred that the vertical movement of the linking member 126 of the linking mechanism 112 move the cylindrical body 250 of the float joint 124 in a vertical direction as represented by an arrow 253 which is coaxial with the lift pin vertical movement as represented by the arrow 242. However, due to various misalignments, the linking member 126 may shift laterally or angularly as the linking member 126 is raised and lowered by the motor. The float joint 124 can accommodate a degree of this lateral and angular shifting as the float joint moves vertically because the cylindrical body 250 can slide eccentrically with respect to the stem 246 as represented by the eccentric or lateral direction arrow 254, and can also deflect radially or angularly, as represented by the angular direction arrow 256.
A float joint typically includes a ball and socket joint in which the ball portion is enclosed within the cylindrical body 250 which provides a clamping surface for the clamp 252. In the illustrated embodiment, it is preferred that the ratio L/D of the length L of the cylindrical surface of the body 250 to the diameter D of the cylindrical body 250 be at least 1 and more preferably greater than 1.5. It is recognized that the body 250 enclosing the ball of the float joint may have other shapes as well but it is preferred that the length to width ratio of the joint body which is fastened to the link member, be at least 1 and more preferably greater than 1.5.
As best seen in
The linking member 126 has an additional pair of platform legs 306 to which the pressure cylinders 128 are attached. Each pressure cylinder 128 has a piston shaft 310 (
As noted above, each piston 120 of the lift pins 110 provides an upward force on the linking member 126 as a result of the net pressure differential between the internal chamber pressure and the ambient atmospheric pressure external to the chamber. This upward force produced by the ambient atmospheric pressure on the lift pins 110 is opposed by the motor 114, particularly when the motor 114 is directed to lower the lift pins 110. To counter-balance the upward force produced by the ambient atmospheric pressure on the lift pins 110, the pump 130 (
The magnitude of the downward force can be controlled by controlling the pressure of the fluid supplied to the pressure cylinders 128. In one embodiment, the downward force provided by the pressure cylinders may be maintained relatively constant at a first value when raising the pins 110 and at a second, larger substantially constant value when lowering the pins 110. Thus, for example, in the illustrated embodiment, the pressure regulator 132 controlled by the system controller 140 can maintain the pressure to the pressure cylinders 128 substantially constant at a first value such as 10 p.s.i. (0.7 kilogram-force per square centimeter (kgf/cm2)), when raising the lift pins 110. Conversely, the pressure is maintained substantially constant at a second value, such as 20 p.s.i. (1.4 kgf/cm2) for example, which is higher than that of the first pressure value, when lowering the lift pins. The pressure cylinders may be omitted in some applications. However, a larger motor may be appropriate where counter balancing pressure cylinders are not utilized.
The linking member 126 may be formed of a single integral piece of a strong, light-weight material such as aluminum or steel. Alternatively, the linking member may be assembled from component pieces. In the illustrated embodiment, the linking member 126 has a large central aperture 320 to permit various external components attached to the chamber to pass through. The legs 302 and 306 are shown arranged in opposing pairs to facilitate balancing the linking member. Other shapes may be utilized, depending upon the particular application including the number of motors, guides, lift pins and pressure cylinders coupled to the linking member.
As best seen in
The processing chamber of the illustrated embodiment has been described as an anneal chamber in which a workpiece is heated and then cooled. However, the present inventions are applicable to a variety of other semiconductor fabrication processes. For example, in the manufacture of many electronic or electrical components such as integrated circuits, there is a need to deposit thin films on various workpieces such as substrates. Materials such as copper, aluminum, titanium, tungsten, tantalum, tantalum nitride, cobalt, and silica may be deposited on ceramic, glass or silicon-derived substrates using physical vapor deposition (PVD) processes such as a physical sputtering process. Another method of deposition of solid materials upon a substrate is chemical vapor deposition (CVD), wherein a solid material is deposited from a gaseous phase onto a substrate by means of a chemical reaction. The deposition reaction involved is generally thermal decomposition, chemical oxidation, or chemical reduction. The CVD process can be used to deposit many elements and alloys as well as compounds including oxides, nitrides and carbides. The thin film deposited may be subsequently etched or otherwise fabricated into circuits and/or other electrical components. The workpieces may be transferred from one chamber to another for the various processing steps. The present inventions are applicable to each of the above-described processes as well as others used in the fabrication of semiconductor devices in which a workpiece is to be lifted.
It will, of course, be understood that modifications of the illustrated embodiments, in their various aspects, will be apparent to those skilled in the art, some being apparent only after study others being matters of routine mechanical and electronic design. Other embodiments are also possible, their specific designs depending upon the particular application. As such, the scope of the invention should not be limited by the particular embodiments described herein but should be defined by the appended claims and equivalents thereof.
| Number | Date | Country | |
|---|---|---|---|
| Parent | 09797459 | Mar 2001 | US |
| Child | 11146687 | Jun 2005 | US |
