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NOVEL USES OF A SILICON CARBIDE SUSCEPTOR FOR RAPID THERMAL PROCESSOR

IP.com Disclosure Number: IPCOM000007317D
Original Publication Date: 1994-Oct-01
Included in the Prior Art Database: 2002-Mar-14
Document File: 5 page(s) / 243K

Publishing Venue

Motorola

Related People

Craig Jasper: AUTHOR [+5]

Abstract

One of the major problems with using a Rapid Thermal Annealer (RTA) in a manufacturing area is the tool's ability to accurately measure and con- trol temperature. The temperature measurement is made on the backside of each wafer processed in the RTA. Product wafers in a manufacturing line have a variety of processing steps that will change the emissivity of each wafer. For example the sili- con vendor growth and polish techniques, dielectric deposition, RIE etching, wet processing, will change the emissivity reading. Any variation in the back- side condition of the wafers will cause a change in the emissivity reading resulting in different wafer temperatures.

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MOTOROLA Technical Developments Volume 23 October 1994

NOVEL USES OF A SILICON CARBIDE SUSCEPTOR FOR RAPID THERMAL PROCESSOR

by Craig Jasper, Edouard De Fresart, Carl D'Acosta, Steve King and Dan Banks

  One of the major problems with using a Rapid Thermal Annealer (RTA) in a manufacturing area is the tool's ability to accurately measure and con- trol temperature. The temperature measurement is made on the backside of each wafer processed in the RTA. Product wafers in a manufacturing line have a variety of processing steps that will change the emissivity of each wafer. For example the sili- con vendor growth and polish techniques, dielectric deposition, RIE etching, wet processing, will change the emissivity reading. Any variation in the back- side condition of the wafers will cause a change in the emissivity reading resulting in different wafer temperatures.

  The emissivity measurements are made by using an optical pyrometer to measure the optical wave length of each wafer processed, (Figure #l, RTP over- view). The susceptor looks like a black body to the optical pyrometer, providing a strong and consistence signal. The use of a susceptor eliminates the prob- lem of wafer backside emissivity variations seen in typical semiconductor fabrication lines.

  Current methods to maintain temperature con- trol is to perform a wafer backside etch or create a large calibration file for each process flow. Rapid Thermal Processing (RTP) companies are working on new ways to control the temperature with Open Loop Intensity Control (OLIC), Closed Loop Inten- sity Control (CLIC), and Direct Thermocouple Con- trol (DTC). This is an attempt to minimize the tem- perature drift seen in the current RTA processing.

  To eliminate the variation of wafer backside con- ditions seen in a typical manufacturing line, a sili- con carbide susceptor is used which provides a con- stant source of emissivity, (Figure #2, Susceptor Layout). The product or test wafers are placed between the upper and lower susceptor plates, The lower susceptor plate is recessed so that the wafer will not slide around, and it provides a good ther- mal mass to eliminate wafer slippage. The top plate

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rests on top of the bottom plate, but does not touch the wafer that is resting on the bottom plate. The susceptor and the wafer inside the susceptor are then placed inside the RTA chamber by a robot. Any RTA process can now be performed regardless of what the previous wafer processing step has been.

  The RTA's temperature is calibrated with a ther- mocouple wafer sandwiched between the top and bottom plates ofthe susceptor, and with the susceptor placed inside the oven, The optical pyrometer is cal- ibrated to match the thermocouple inside the susceptor. The RTA system is now calibrated for a wide range of temperatures from -400°C to 1150°C. No hrrther calibrations or emissivity changes are required regardless of the previous processing on the wafers. In addition to the...