Cryogenic etching of deep narrow trenches in silicon

Deep and narrow anisotropic etching of silicon structures has been investig ated in a low-pressure high density plasma reactor working with a cryogenic chuck. We have previously demonstrated the feasibility of this technique o n such structures. Improvement of etch rate and profiles has been studied a nd new results show 2 mu m wide trenches etched to a depth of 50 mu m at an average etch rate of 5 mu m/min with highly anisotropic profiles and very high selectivity (>500:1) toward the SiO2 mask. An evaluation of a commerci ally available reactor from Alcatel has been carried out and similar result s an obtained. A phosphosilicate glass mask has been used to study the effe ct on profiles. It is shown that undercut is reduced while bowing is indepe ndent of the mask material. Since surface temperature strongly affects the profiles, wafer deformations in our cryogenic chuck have been measured and temperature evolution across the wafer has been estimated. A significant te mperature difference of 10 degrees C between the chuck and the wafer is exp ected for thin wafers (210 mu m). (C) 2000 American Vacuum Society. [S0734- 2101(00)16804-6].