Browse Prior Art Database

Measuring Asymmetries of Silicon Wafers

IP.com Disclosure Number: IPCOM000087118D
Original Publication Date: 1976-Dec-01
Included in the Prior Art Database: 2005-Mar-03
Document File: 2 page(s) / 29K

Publishing Venue

IBM

Related People

Bohg, A: AUTHOR

Abstract

Flat silicon wafers sliced from a cylindrical rod, lapped and polished still show a residual cross-sectional asymmetry which may be detrimental to the processing of integrated circuits on their surface. Thus, the extent of this asymmetry must be checked. By applying heat to the center region of the wafer, which results in a temperature gradient extending radially, a given asymmetry is amplified in such a manner that rapid measuring with a simple sensing tool is possible, without using complex optical equipment.

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Measuring Asymmetries of Silicon Wafers

Flat silicon wafers sliced from a cylindrical rod, lapped and polished still show a residual cross-sectional asymmetry which may be detrimental to the processing of integrated circuits on their surface. Thus, the extent of this asymmetry must be checked. By applying heat to the center region of the wafer, which results in a temperature gradient extending radially, a given asymmetry is amplified in such a manner that rapid measuring with a simple sensing tool is possible, without using complex optical equipment.

The cross-sectional view in Fig. 1 shows a wafer having an asymmetry (largely exaggerated) which may be defined by distance "a" between the ordinates of midpoints Zm, relating to cross-section Zr-Zv near the center, and Rm, relating to cross-section Rr-Rv near the edge. The device allows measuring asymmetries indicated by distance "a" which are less than 1 Micron.

As shown in Fig. 2, wafer 1 is placed on a cooled base plate 2 having a circular opening 3 and a ring-shaped radiation shield 4. Heat is applied to the center region of the wafer through opening 3 by halogen lamp 6 with a focusing spherical mirror 7. After a stationary temperature gradient extending radially has been established in wafer 1, displacement measuring tool 8, such as a caliper with a micrometer scale, is brought into contact with the upper side of wafer 1. An asymmetry of some Micron will result in a displacement of about 50 Micron. Bernoulli pr...