LASER-INDUCED THERMAL-DESORPTION ANALYSIS OF THE SURFACE DURING GE ETCHING IN A CL-2 INDUCTIVELY-COUPLED PLASMA

Laser desorption laser-induced fluorescence (LD-LIF) detection of GeCl was used to determine in situ the surface coverage of chlorine during the etching of germanium by Cl-2 in an inductively coupled plasma (IC P) reactor. The ICP operated in the dim mode for radio frequency (rf) power less than or similar to 350 W and in the bright mode for higher powers. The etch rate was 3.5 mu m/min with 540 W rf power and -40 V s ubstrate bias. The chlorine surface coverage was about 2X that with ch lorine how only and the plasma off both with dim- and bright-mode oper ation, and was independent of rf power within each mode for laser repe tition rates of 0.2, 5, and 15 Hz. Similarly, the chlorination of the adlayer did not change when the ion energy was increased from 16 to 11 6 eV by increasing the substrate bias voltage, both with dim- and brig ht-mode operation. This was confirmed by x-ray photoelectron spectrosc opy measurements in a similar high density reactor, where it was found that the surface density of chlorine was similar to 2.6X10(15) Cl/cm( 2). As the ion energy increases from 16 to 116 eV, the etch yield of i ons increases from 1 to 3 atoms/ion; ''Wait and probe'' measurements s how that the GeClx adlayer is quite stable. Since the same adlayer chl orine content was measured by LD-LIF under high ion current/fast etch conditions (bright mode) and low ion current/slow etch conditions (dim mode), both the adlayer chlorine content and the etch rate seem to be controlled by the ion current to the wafer. Previously reported work in Si etching,in this ICP [J. Vac. Sci, Technol. A 15, 3024 (1997)] sh owed a similar independence of adlayer chlorination with rf power, but much slower chlorination and an increasing chlorination of the adlaye r with increasing ion energy. (C) 1998 American Vacuum Society. [S0734 -2101 (98)05006-4].