Evolution of hillocks during silicon etching in TMAH

The evolution of hillocks on (100)-silicon etched in 4 wt% tetramethyl ammo nium hydroxide is studied through a detailed examination of hillock size di stribution and individual hillock features using low-voltage scanning elect ron microscopy. Silicon samples etched for periods of 1.5, 3 and 5 min show that the population of hillocks initially comprises small, square-based py ramids with a wide distribution of aspect ratios ranging up to tall pyramid s typifying {111}-bounded pyramids. As etching progresses, the population e xtends to larger pyramids, the majority of which are somewhat flatter than expected of {111}-bounded pyramids. Detailed examination of individual hill ocks suggests that some {111}-bounded pyramids undergo a transformation tha t eventually leads to a quasi-stable bow-faced hillock configuration. Other s collapse from the apex through erosion of the main faces. A number of dis solution routes are observed, and it is postulated that a hillock may under go a series of fast transformations during its lifetime with intermediate c onfigurations that are quasi-stable.