Laser-induced thermal desorption analysis of the surface during Ge etching in a Cl2 inductively coupled plasma

Abstract

Articles you may be interested inTransition between two states of surface coverage and etch rate during Si etching in inductively coupled Cl 2 -Ar plasmas with changing mixtures Laser desorption laser-induced fluorescence ͑LD-LIF͒ 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 ͑ICP͒ reactor. The ICP operated in the dim mode for radio frequency ͑rf͒ power Շ350 W and in the bright mode for higher powers. The etch rate was 3.5 m/min with 540 W rf power and Ϫ40 V substrate bias. The chlorine surface coverage was about 2ϫ that with chlorine flow only and the plasma off, both with dim-and bright-mode operation, and was independent of rf power within each mode for laser repetition 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 116 eV by increasing the substrate bias voltage, both with dim-and bright-mode operation. This was confirmed by x-ray photoelectron spectroscopy measurements in a similar high density reactor, where it was found that the surface density of chlorine was ϳ2.6ϫ10 15 Cl/cm 2 . As the ion energy increases from 16 to 116 eV, the etch yield of ions increases from 1 to 3 atoms/ion. ''Wait and probe'' measurements show that the GeCl x adlayer is quite stable. Since the same adlayer chlorine content was measured by LD-LIF under high ion current/fast etch conditions ͑bright mode͒ and low ion current/slow etch conditions ͑dim mode͒, 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 ͑1997͔͒ showed a similar independence of adlayer chlorination with rf power, but much slower chlorination and an increasing chlorination of the adlayer with increasing ion energy.