Damage and contamination in low‐temperature electron cyclotron resonance plasma etching

Abstract

An electron cyclotron resonance (ECR) plasma etching system has been built to study the damage and contamination inherent to the high density ECR etching. The temperature of the substrate can be lowered to −150 °C by the backside cooling of the substrate with the liquid‐nitrogen cooled helium. The substrate temperature during etching was monitored by a sheathed thermocouple and IR laser interference thermometry. Gate polysilicon etching by SF6 plasma had been carried out and the effect of the substrate temperature on the anisotropy, selectivity, and etch rate was examined with special emphasis on the damage and contamination incurred by the plasma etching. Secondary ion mass spectroscopy (SIMS) analysis shows that the depth of the contaminated layer decreases when the substrate temperature is lowered to −120 °C. Also, the measurement of the gate oxide breakdown voltage shows much less oxide damage when the substrate temperature is lowered during ECR etching.