Isotropic silicon etch characteristics in a purely inductively coupled SF6 plasma

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The characteristics of isotropic etching of silicon in a purely inductively coupled SF6 plasma are quantitatively studied. Since the etch results are strongly dependent on mask features, the authors investigated both large area and narrow trench etch characteristics. Circles of diameter 500 μm were used as a proxy for unpatterned surfaces and etched for different durations to establish the material etch rate and surface roughness. The average etch rate using the chosen recipe was found to be 2.27 μm/min. Arrays of narrow trenches ranging from 8 to 28 μm were also etched to analyze the effect of trench size on etch rate and degree of anisotropy. The etch rate of the trenches was found to strongly decrease with decreasing trench width. The results demonstrate that isotropic SF6 etch can be readily used as a replacement for more exotic silicon vapor phase etch chemistries such as XeF2.