Effects of plasma conditions on the shapes of features etched in Cl2 and HBr plasmas. I. Bulk crystalline silicon etching

Abstract

We have studied the effects of source and bias powers, pressure, and feed gas composition on the shapes of SiO2-masked crystalline silicon features etched in a transformer-coupled high density plasma system. Higher etching rates were obtained at higher source and bias powers, and higher pressure. The etching rates of isolated and nested trenches, isolated lines, and holes were nearly the same, indicating a negligible pattern density dependence. We did, however, observe a very weak decrease in etch rates with increasing aspect ratio at 2 mTorr in a pure Cl2 plasma. At 10 mTorr, no aspect ratio dependence was observed, except at the highest source and bias powers. Microtrenching was observed under certain plasma conditions and could be reduced by using higher bias powers. At 10 mTorr in a pure chlorine plasma, we observed a slight taper at the bottoms of the etched features and the formation of narrow microtrenches near feature corners. At 2 mTorr, the microtrenches were broader and overlapped near the center of narrow trenches to form pyramid-shaped trench bottoms. When a HBr plasma was used instead of Cl2, the etching rate decreased by 50% but the etching profiles were more vertical and the trench bottoms were flat. Isolated lines etched in the HBr plasma, however, revealed broad but shallow microtrenches near the edges of the line, suggesting that the flat trench bottoms were a result of broad microtrenches that overlapped. Trenches of 3 μm depth and aspect ratios of 7 have been obtained using either HBr or Cl2, exhibiting similar microfeatures as observed when etching shallower trenches.

Photo-assisted etching of silicon in chlorine- and bromine-containing plasmas

“…[32][33][34][35][36][37][38] Undercutting in HBr-containing plasmas is usually not observed. [39][40][41][42][43][44] Perhaps this is a result of the erosion of photoresist and chamber materials (with no Faraday shield, as in most commercial etching tools), resulting in passivating layers on the Si sidewalls 42 that could slow or block isotropic etching by H atoms. Haverlag et al 42 reported undercutting of poly-Si beneath a photoresist mask exposed in an electron cyclotron resonance 5 mTorr HBr plasma at a modest substrate temperature (48 C) and low rf bias voltage (50 V).…”

Nanoscale pattern transfer for templates, NEMS, and nano-optics

“…5 Experimental studies and modeling of profile development in sub-micron patterned Si undergoing Cl 2 and HBr dry etching have evolved over the last 10 years. 5,[7][8][9][10][11][12][13][14][15] For the purpose of precisely controlling profiles for imprint templates for nanodevices, we extended the experimental studies to the nanoscale regime. 16,17 Here we discuss how ion interactions with the feature sidewalls and mask can completely dominate the overall feature shape as features shrink.…”

Effects of Mask Pattern Geometry on Plasma Etching Profiles

“…Vyvoda et al studied the effects of source and bias powers, pressure, and feed gas composition on the feature profiles of SiO 2 -masked crystalline silicon etched in Cl 2 /HBr transformer-coupled plasmas (TCP). 3) They obtained higher etch rates at higher source powers, bias powers, and pressures. When HBr was used instead of Cl 2 , etch rate decreased substantially, but the etch profile became more vertical and the trench bottom became flatter.…”