small motors provide critical motion for process module

When designing the process for its latest semiconductor process station, Plasma-Therm required high quality motors for smooth, accurate motion control.

by Steve O'Neil, VP Advanced Research and Planning, Micro Mo Electronics

The technologies of Plasma-Therm, Inc., St. Petersburg, FL, deliver robust, repeatable thin film processes. Systems are scaleable and software-upgradeable from R&D to manual pilot production to automated high-throughput manufacturing. As customer needs evolve, initial efforts can progressively move into higher production volumes. To further service its customers, Plasma-Therm provides an unparalleled depth of expertise and performance in processing special substrate materials and sizes, as well as standard substrates.

The company's Versalock 700 is a field-proven cluster platform which integrates Plasma-Therm's leading edge process technologies. A variety of configurations are available, ranging from simple parallel plate RIE etchers to high-density Inductively Coupled Plasma (ICP) Process Modules. Configuration options are supported by the use of industry-recognized components and user-friendly software.

Process Module Design

The company is proud of the fact that all critical components are manufactured by leading suppliers to ensure the highest in reliability for the user. For the Versalock 700, senior mechanical systems development engineer Mark Kenney needed to select components that would meet those standards of quality. Because of past experience with other semiconductor processing equipment designs, Mark felt comfortable selecting motors, gearmotors and encoders from Micro Mo Electronics, Clearwater, FL, when focusing on the moving components of the machine, particularly for the process module.

The transport module is an independently-pumped vacuum module, which houses the robot used to transport substrates to the process chambers. Isolation valves present on all process modules allow for parallel processing and high throughputs. The design for this application required that three Model 2230 gearmotors be used for Z-axis motion and one Model 1624 be used in a theta operation. The Z-axis design in the Versalock 700 is for use in a simple substrate lifting device. Each Z-axis is remotely engaged because the system operates within a vacuum.

The Versalock 700 is a cluster platform, manufactured by Plasma-Therm, which integrates some of the company's leading edge process technologies.

For each Z-axis operation, three guide rods located outside the vacuum chamber are engaged by the 2233 gearmotor. Each rod operates through a bellows to push a pin in a vertical direction. The pins, connected to a single plate, lift a semiconductor wafer into the air until a limit switch sends a signal to halt movement.

Inside the vacuum chamber, the robot's end effector moves to a position under the semiconductor to be processed. Once the end effector is in position, the Micro Mo 2233 is driven in a reverse direction, lowering the semiconductor wafer onto the end effector, which takes the part to the next stage of processing.

The Model 2233 motor provides an average torque of 0.354 oz.-in. (before the reducer) and speeds to about 3000 rpm for this application (up to 8000 rpm is possible), allowing the wafer to be lifted quickly, increasing throughput. The motor is rated at two watts of power. Its size, a factor in the overall design of the process system, is 22mm diameter and only 30mm in length. Smooth, quiet operation of the gearmotor was necessary to protect the delicate cargo from damage.

The second gearmotor, Model 5540A, is used in a theta operation where a feed arm fills a tray with six semiconductor wafers. The six wafers are placed into the machine for processing, and rotated one by one as the Z-axis operation raises and lowers the tray into a pickup position. Again, small size is a key feature of the motor. At only 16mm in diameter and only 24mm in length, the Model 5540A provides a lot of power. Although Plasma-Therm runs the motor at about 3000 rpm, maximum speed for the motor is 12,000 rpm at a continuous torque of 0.212 oz.-in -- all this with a power consumption of only 0.9 watts.

When "rim feeding" the wafers in this way, it is very important that a tight address be maintained. An encoder located on the theta axis gearmotor provides feedback data to a controller as the device sequences. After each sequence, the position counter zeroes prior to performing the next sequence. Because a variety of feed tray sizes can be used, the theta controller is calibrated using "learned position" electronics. For example, once the 1, then to learned position 2, etc. The theta then moves in, say, 60 degree movements until all six wafers have been processed. Completed, the Z-axis gearmotor takes over to allow for the removal of the tray.

For more information:

Circle 535 - MicroMo Electronics Inc., 800-403-1772, or connect directly to their website via the Online Reader Service Program at http://www.1rs.com/004df-535

Circle 585 - Plasma-Therm, Inc. or connect directly to their website via the Online Reader Service Program at http://www.1rs.com/004df-585