An investigation of thermally-sprayed aluminum oxide coatings for high-temperature electrostatic chucks (ESCs)

Thermally-sprayed aluminum oxide (Al₂O₃) coatings were investigated as candidate materials for high temperature electrostatic chucks (ESCs). Electrical resistivities and dielectric constants of Al₂O₃ coatings deposited on test coupons were measured at temperatures up to 500°C. Limited breakdown voltage testing was also performed. To examine the effect of impurities on electrical resistivity over the test temperature range, data for plasma-sprayed alumina coatings of various purity levels were compared. Resistivity data for plasma- and high velocity oxy-fuel (HVOF)-sprayed coatings were compared to data reported for sintered alumina of various purity levels, with the coatings generally exhibiting higher resistivities than bulk alumina for similar purity levels. The effect of plasma-spray power level and feed angle on electrical resistivity of coatings deposited using two types of high purity alumina was also examined. Results of these tests were used to select a coating and spray process to fabricate a pair of small-scale ESCs. When evaluated in a test chamber, these ESCs showed promising behavior by maintaining adequate wafer holding pressures after testing up to 24 hours at a maximum test temperature of 400°C. Results of test coupon and small-scale ESC testing suggest that it may be possible to produce an effective alumina coating for high temperature ESCs through proper control of coating impurities and thermal spray process characteristics, although further work is needed to more fully characterize coatings and optimize process conditions