AVS 47th International Symposium
    Plasma Science and Technology Wednesday Sessions
       Session PS2-WeA

Paper PS2-WeA1
Undercut and Bowing Characterisation in High Aspect Ratio Trenches of Poly-Si Etched in an ICP Reactor using Cryogenic SF6/O2 Chemistry Process

Wednesday, October 4, 2000, 2:00 pm, Room 311

Session: Feature Evolution
Presenter: M. Boufnichel, University of Orleans, CNRS, France
Authors: M. Boufnichel, University of Orleans, CNRS, France
S. Aachboun, ST Microelectronics, France
G. Marcos, GREMI, France
P. Ranson, GREMI, France
Correspondent: Click to Email
In the last few years, deep trenches in silicon obtained by plasma etching have been widely studied for MEMS and/or microelectronics applications. A cryogenic method with an SF6/O2 chemistry plasma in an Alcatel ICP reactor is used to achieve deep trenches with high aspect ratio (>10) and high anisotropy. The etching rate in 2 µm wide and 100 µm deep trenches is about 3.5µm/min. The slope of the trenches can be adjusted from 88° to 90° and selectivity is higher than 300. However, profiles need to be improved, mainly by reducing the undercut and the bowing effects. Undercut is a lateral etching occurring under the mask which enlarges the trench opening and bowing is a local lateral etching located on the sidewalls and resulting in profiles destruction. This study deals with improvements in these effects. We investigated the outcome of process parameters (pressure, bias voltage, temperature, oxygen flow rate) and mask characteristics (nature, thickness, side slope, trench width and length). We tested several more or less conducting masks: oxide, thermal oxide created from TEOS gas, PSG (Poly-Silicate Glass containing 4% of phosphor), Sandwich (one layer of Si between two layers of SiO2) and Al. The different mechanisms responsible for undercut and bowing are finally discussed and evaluated.