Highly anisotropic microwave plasma etching for high packing density silicon patterns

Anisotropic etching which can be performed effectively with a low-pressure and high-density plasma may sometimes produce nonuniform patterns. Such a phenomenon has been observed in Si trench etching and poly-Si etching. Although this phenomenon is thought to be based on the local electric field, the mechanism for its generation is not clear. The nonuniformity of the ion direction, which is a serious problem in the fabrication of higher-packing-density patterns of future ULSIs such as 256 M DRAMs is considered. Time-modulated (TM) etching based on a model featuring pattern-plasma interaction is also discussed. It was found that peripheral patterns are inclined by the local electric field generated by the secondary electron effect. Using TM etching with an alternately supplied bias, such nonuniformity was reduced, and quarter-micron-level anisotropic etching of dense Si patterns was achieved.<>