AVS 51st International Symposium
    Plasma Science and Technology Wednesday Sessions
       Session PS-WeA

Paper PS-WeA9
Investigation of Correlation between Etching Profiles and Neutral Density in Cl@sub 2@/O@SUB 2@ Plasmas

Wednesday, November 17, 2004, 4:40 pm, Room 213A

Session: Plasma Diagnostics
Presenter: M. Mori, Hitachi Ltd., Japan
Authors: M. Mori, Hitachi Ltd., Japan
G. Cunge, CNRS/LSP, France
M. Kogelschatz, CNRS/LSP, France
L. Vallier, CNRS/LTM, France
Correspondent: Click to Email
Cl@sub 2@/O@sub 2@ plasmas are basically used in Shallow Trench Isolation (STI) etching of ULSI device fabrication. In STI etching, precise taper angle control is one of the issues for good coverage without stress damage to Si substrate at following deposition process. The taper angle is determined by the sidewall passivation layer during etching. Hence etching by-products (SiCl@sub x@) are thought to play an important role in taper angle control, because they are believed to be the precursors to the deposition of sidewall passivation layers. In this study, we have investigated the correlation between SiCl@sub x@ density and etching profiles in Cl@sub 2@/O@sub 2@ plasmas. The SiCl@sub x@(X=0-2) absolute densities are measured by UV broad band absorption spectroscopy. The thickness of the sidewall passivation layer is measured by comparing the etched profiles before and after removal of the passivation layer. The SEM results firstly confirm that good correlation between the taper angles and the thickness of the passivation layer on feature sidewalls over a wide range of plasma operating conditions (pressure, source power, O@SUB 2@ flow rate and total gas flow rate). By contrast, there is no correlation between the thickness of sidewall passivation layers and the SiCl@sub x@ densities in the plasma. For example, the passivation layer thickness increases rapidly while the SiCl@sub x@ density decrease with increasing O@SUB 2@ gas flow. Indeed, our data suggests that the growth rate of sidewall passivation layers is limited only by the O density in the plasma, which thus controls the etching profile. By roughly calculating O atom density as a function of electron temperature and density, we are then able to explain the trend of passivation layer thickness with pressure and source power. The role of O is to oxidize SiCl@sub x@ species chemisorbed on the surfaces exposed to the plasma, which, without oxidation are etched back into the plasma by Cl atoms.