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

Paper PS-WeA10
Optical Monitoring of Surface Adlayers by Laser-induced Thermal Desorption during Plasma Etching of Si and Ge

Wednesday, November 4, 1998, 5:00 pm, Room 318/319/320

Session: Plasma-Surface Interactions I
Presenter: I.P. Herman, Columbia University
Authors: J.Y. Choe, Columbia University
I.P. Herman, Columbia University
V.M. Donnelly, Bell Laboratories, Lucent Technologies
Correspondent: Click to Email
Laser-induced thermal desorption, with detection by laser-induced fluorescence (LD-LIF) and transient plasma-induced emission (LD-PIE), was used to analyze the surface during the chlorine plasma etching of Si and Ge in an inductively-coupled plasma (ICP) source. Quantitative information about the formation and ion-induced removal of this surface layer was obtained from the optical signals. A pulsed XeCl excimer laser (308 nm) was used to desorb the surface layer and (for LIF) to excite the desorbed species. LD-LIF was used to probe SiCl (292.4 nm) and GeCl (289.12 nm) to compare Si and Ge etching. The surface adlayer did not change with ion density for both Si and Ge, but the rate of adlayer chlorination for Ge was much faster (< 0.1 s) than that for Si (~ 5 s), as was indicated by the signal size when the laser repetition rate was varied. The chlorine content of the adlayer did not change with ion energy (16 - 116 eV) during Ge etching, as confirmed by XPS analysis; in contrast, for Si the adlayer became more chlorinated with increasing ion energy. The etch yield for ion sputtering from Ge increased from 1 to 3 atoms/ion from 16 to 116 eV ion energy. LD-PIE was also used to probe SiCl, SiCl@sub 2@, and Si atoms during Si etching. No LD-PIE signal from Cl or Cl@sub 2@ was detected, suggesting that steady-state chlorine desorption is negligible during the plasma etching of Si. LD-LIF and LD-PIE signals during Si etching by Cl@sub 2@ have been compared for various processing conditions. The work at Columbia was supported by NSF grant DMR-94-11504.