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Mask Aligning

IP.com Disclosure Number: IPCOM000092050D
Original Publication Date: 1968-Aug-01
Included in the Prior Art Database: 2005-Mar-05
Document File: 2 page(s) / 26K

Publishing Venue

IBM

Related People

Hallas, CE: AUTHOR

Abstract

The method is used for locating buried diffused regions in semiconductor wafers and locating a mask relative to such regions. One method of locating such buried diffused regions involves reoxidizing this wafer after the diffusion, and subsequently chemically removing the oxide. This leaves a depression in the surface of the wafer at the diffused area which is used to locate the region. However, after the growing of an epitaxial layer, this depression is often displaced away from the vertical over the diffusion as a result of epitaxial growth in a nonperpendicular direction. This constitutes a problem in accurately locating masks over the wafer. In this method, infrared radiation is transmitted through the wafer.

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Mask Aligning

The method is used for locating buried diffused regions in semiconductor wafers and locating a mask relative to such regions. One method of locating such buried diffused regions involves reoxidizing this wafer after the diffusion, and subsequently chemically removing the oxide. This leaves a depression in the surface of the wafer at the diffused area which is used to locate the region. However, after the growing of an epitaxial layer, this depression is often displaced away from the vertical over the diffusion as a result of epitaxial growth in a nonperpendicular direction. This constitutes a problem in accurately locating masks over the wafer. In this method, infrared radiation is transmitted through the wafer. The buried diffused region, having a higher impurity concentration than silicon, absorbs more radiation and is visible with an IR detector. The greatest contrast is observed for the infrared radiation in the 10 to 30 microns range. The method can also be used with reflected light. The arrangement consists of infrared light source 1 disposed beneath wafer 2 containing buried diffused regions 3. Mask 4, to be aligned over regions 3, is disposed over wafer
2. Infrared light inverter 5 is disposed over mask 4 and adapted to receive light transmitted from source 1 through wafer 2. Observation of regions 3 through inverter 5 enables accurate location of mask 4 relative to regions 3.

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