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AUTO INCREMENTAL MICROSHAPING (AIM) FOR SILICON ON INSULATOR (SOI) THICKNESS CONTROL

IP.com Disclosure Number: IPCOM000006712D
Original Publication Date: 1992-Dec-01
Included in the Prior Art Database: 2002-Jan-24
Document File: 3 page(s) / 147K

Publishing Venue

Motorola

Related People

Raymond C. Wells: AUTHOR

Abstract

Wafer Bonding has become a weU known and pre- ferred process for producing Silicon on Insulator (SOI) materials used in various new device design applications. The process for manufacture of SOI Wafers is shown in Figure 1. In the old process the thickness of the base wafer is known and the bonded wafer is ground to this thickness, plus that of the oxide, the SOI layer desired and the polish removal required to remove grind dam- age. After grind the wafers are measured for SOI layer thickness by FTIR. The wafers are then sorted for SO1 thickness and polished to the desired thickness by adjustig polish time for each sort catagory. Due to pol- ish removal rate variables this measure and sort process typically results in a large variance from the desired thickness.

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INC. Technical Developments Volume17 December 1992

AUTO INCREMENTAL MICROSHAPING (AIM) FOR SILICON ON INSULATOR (SOI) THICKNESS CONTROL

by Raymond C. Wells

   Wafer Bonding has become a weU known and pre- ferred process for producing Silicon on Insulator (SOI) materials used in various new device design applications. The process for manufacture of SOI Wafers is shown in Figure 1. In the old process the thickness of the base wafer is known and the bonded wafer is ground to this thickness, plus that of the oxide, the SOI layer desired and the polish removal required to remove grind dam- age. After grind the wafers are measured for SOI layer thickness by FTIR. The wafers are then sorted for SO1 thickness and polished to the desired thickness by adjustig polish time for each sort catagory. Due to pol- ish removal rate variables this measure and sort process typically results in a large variance from the desired thickness.

  In the present status of the new process an in-situ SO1 measurement and control at polish has been dem- onstrated. A Nanometric 210 unit, combined with a microprocessor controlled polisher is used for this pur- pose. The polisher is typically capable of completing both the primary and finishing slurry polish on a single wafer in an automated sequence. The flexible fibre optic meas- urement sensor of the Nanometric was easy to install on the polish machine. The sensor allows SO1 thickness to be measured on the polisher at any time between load and unload operations, and as many times as desired. The typical process measures the wafer at least twice alIowing for the removal rate variable in the first pri- mary polish. This provides an SOI thickness that is usu- ally slightly above the target value after the iirst polish, and which has a very low variance from target after the second primary polish. An example of data from this process is shown in Figure 2.

  In the future operation of the new process the in-situ measurement and control will be added to the grind operation. Both grind and polish machines will then be programmed to automatically adjust the control param- eters to obtain the target thickness. The grinder will remove the bulk of the active wafer in its initial plunge using its present thickness feedback system. The final grind wiIl then be halted, the wheel will back away just enough to break...