Mechanism of Residue Formation in Silicon Trench Etching Using a Bromine-Based Plasma

Abstract

The formation mechanism of residues observed in HBr-based Si trench etching has been investigated. The residues were characterized using an optical microscope and a scanning electron microscope (SEM), and the residue density dependence on the interstitial oxygen concentration in the Si substrate, the formation process of etching masks and the etching condition was examined. It was confirmed that needle-shaped silicon residues of various heights had a disorderly distribution at the trench bottom. The density of the silicon needles strongly depended on both the interstitial oxygen concentration in the Si substrate and the mask formation process: numerous needles were observed when the oxygen concentration was sufficiently high and the mask formation process included oxidation. It was also found that the residue density increased with etching depth and selectivity to silicon oxide controlled by the etching condition. All the experimental results were successfully explained by a model in which oxygen precipitates nucleate in the Si substrate during the mask formation process, acting as micromasks in trench etching.