In situ fiber optic thermometry of wafer surface etched with an electron cyclotron resonance source

Abstract

The effect of plasma heating on wafer temperature during etching has been studied. Si and InP were etched using a high ion density discharge generated by an electron cyclotron resonance source. The wafer temperature was measured using fiber optic thermometry as microwave power, rf power, chamber pressure, and gas flow were varied. Wafer temperatures increased with both rf and microwave power, and decreased with chamber pressure. For a rf power of 50 W, chamber pressure of 1 mTorr, a source distance of 13 cm, and a 10 sccm Ar flow, an increase in microwave power from 50 to 500 W caused the temperature to increase from 62 to 186 °C. An increase in the rf power from 50 to 300 W increased the wafer temperature to 145 °C. Additionally, the effectiveness of using He flowing at the backside of the wafer for temperature control was analyzed. By setting the backside He pressure at 3 Torr, the temperature increased to only 29 °C. Time dependent etch characteristics 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 °C. As the temperature increased above 150 °C, the profile became more undercut and the surface morphology improved. By setting the stage temperature to −100 °C and using 3 Torr of He pressure at the backside of the wafer, the InP etch rate remained constant during etching and undercutting was suppressed. For 500 W of microwave power, a fast InP etch rate of 2 μm/min was obtained when the wafer temperature was <110 °C, and it increased to over 4 μm/min when the temperature was ≳150 °C.