AVS 45th International Symposium
    Plasma Science and Technology Division Wednesday Sessions
       Session PS-WeA

Paper PS-WeA5
The Role of Etching Products on the Chemical Composition and Thickness of the Chlorinated Surface Layer That Forms During Etching of Silicon in a Chlorine Plasma

Wednesday, November 4, 1998, 3:20 pm, Room 318/319/320

Session: Plasma-Surface Interactions I
Presenter: K.H.A. Bogart, Bell Laboratories, Lucent Technologies
Authors: K.H.A. Bogart, Bell Laboratories, Lucent Technologies
V.M. Donnelly, Bell Laboratories, Lucent Technologies
Correspondent: Click to Email
The influence of etching products on the surface layer formed during chlorine (Cl@sub 2@) plasma etching of unmasked and silicon dioxide (SiO@sub 2@) masked p-type Si (100) was investigated using vacuum-sample-transfer and angle-resolved x-ray photoelectron spectroscopy (XPS). The etch product concentration was controlled by varying the Cl@sub 2@ flow rate from 0.5 to 10.0 sccm at constant pressure. Gas phase Si, Cl, Cl@sub 2@, SiCl, SiCl@sub 2@, and SiCl@sub 3@ were monitored by optical emission spectroscopy (OES). The Si etching rate increased linearly with Cl@sub 2@ flow from 1917 Å/min at 0.5 sccm to 2848 Å/min at 10 sccm. From these rates, mass balance, and the Si area (4.62 cm@super 2@), the product-to-etchant ratio, defined as SiCl@sub x@(g)/(Cl(g) + Cl@sub 2@(g)) varied from 3.64 to 0.027 between 0.5 and 10.0 sccm, respectively, and was qualitatively confirmed by OES. On unmasked substrates, Cl was present as SiCl@sub x@ (x = 1-3) at XPS Si2p@sub 3/2@ binding energies of 99.9, 101.0, and 102.0 eV, respectively, relative to Si at 99.1 eV. Surprisingly, the amounts of the three components and the total Cl (also derived from its 2p peak) were nearly independent of the product-to-etchant flux ratio. Depth profiles were obtained from an inversion of the observed take-off angle dependencies of the XPS signals. The chlorinated layer was approximately 20 Å thick, with Cl falling off in a graded fashion. The Cl areal density was 2.5 x 10@super 15@ Cl/cm@super 2@ and the average stoichiometry was [SiCl]:[SiCl@sub 2@]:[SiCl@sub 3@] = 1.0:0.25:0.20. SiCl@sub 2@ and SiCl@sub 3@ were in the top 75% of the layer, while SiCl was throughout the layer. On SiO@sub 2@ masked samples, less SiCl@sub x@ was found on exposed Si sidewalls, as well as on trench bottoms, than on unmasked samples. SiCl@sub x@ coverage in the features was also independent of the product-to-etchant flux ratio, suggesting that redeposition of SiCl@sub x@ plays no role in etched profile evolution.