Silicon trench undercutting caused by the preferential plasma etching of surface-implanted-regions

It is shown that the residual surface damage present in heavily implanted n⁺ regions causes severe undercutting during the reactive ion etching (RIE) of silicon trenches in a SiCl₄-N ₂ plasma. The trench sidewall undercutting was not observed when the trenches were etched in unimplanted silicon wafers. For specific implant does of arsenic and phosphorus, optimal thermal activation cycles were identified that resulted in negligible trench undercutting. The trench undercutting profiles traced the n⁺ junction profiles and the undercutting was more pronounced in phosphorus-implanted samples