IN-SITU FIBER OPTIC THERMOMETRY OF WAFER SURFACE ETCHED WITH AN ELECTRON-CYCLOTRON-RESONANCE SOURCE

The effect of plasma heating on wafer temperature during etching has b een studied. Si and InP were etched using a high ion density discharge generated by an electron cyclotron resonance source. The wafer temper ature was measured using fiber optic thermometry as microwave power, r f power, chamber pressure, and gas flow were varied. Wafer temperature s increased with both rf and microwave power, and decreased with chamb er pressure. For a rf power of 50 W, chamber pressure of 1 mTorr, a so urce distance of 13 cm, and a 10 seem Ar flow, an increase in microwav e power from 50 to 500 W caused the temperature to increase from 62 to 186 degrees C. An increase in the rf power from 50 to 300 W increased the wafer temperature to 145 degrees C. Additionally, the effectivene ss of using He flowing at the backside of the wafer for temperature co ntrol was analyzed. By setting the backside He pressure at 3 Torr, the temperature increased to only 29 degrees C. Time dependent etch chara cteristics of InP were studied and related to the in situ temperature measurements. At 100 W of microwave power, the InP etch rate increased from 100 to 400 nm/min as the wafer temperature rose from 20 to 150 d egrees C. As the temperature increased above 150 degrees C, the profil e became more undercut and the surface morphology improved. By setting the stage temperature to -100 degrees C and using 3 Torr of He pressu re at the backside of the wafer, the W? etch rate remained constant du ring etching and undercutting was suppressed. For 500 W of microwave p ower, a fast InP etch rate of 2 mu m/min was obtained when the wafer t emperature was <110 degrees C, and it increased to over 4 mu m/min whe n the temperature was >150 degrees C. (C) 1996 American Vacuum Society .