Probing radicals in hot wire decomposition of silane using single photon ionization

Abstract

Radicals produced by the hot wire-induced decomposition of silane have been identified using vacuum ultraviolet single photon ionization (SPI). This laser-based technique uses 118 nm photons (10.5 eV) to ionize gas phase species; the resulting photoions are detected using time-of-flight mass spectrometry. The major silicon-containing gas-phase species identified by SPI during hot-wire activation of silane gas are Si, SiH3, and Si2H6. These results demonstrate that single photon ionization can be a powerful probe for in situ, real-time detection of multiple species in hot wire chemical vapor deposition.

The aging of tungsten filaments and its effect on wire surface kinetics in hot-wire chemical vapor deposition

“…2 are Si and SiH 3 , as they were the predominant species in the present study, as well as in that of Doyle et al 7 In the study of Tange et al, 4 the SiH 2 signal exhibited very similar characteristics as SiH 3 and thus is omitted for clarity. Similar to the other studies, 4,5,7 we find that Si is the predominant radical desorbed from the wire for wire temperatures above 1500 K. Above 1800 K, a saturation in the Si signal is noted, with a slight decrease above 2300 K, an effect also observed in previous studies. 4,5,7 This phenomenon has been attributed to competition between desorption and decomposition; 16 it should be pointed out that diffusion of Si through the wire may also be important at these high temperatures.…”

“…Similar to the other studies, 4,5,7 we find that Si is the predominant radical desorbed from the wire for wire temperatures above 1500 K. Above 1800 K, a saturation in the Si signal is noted, with a slight decrease above 2300 K, an effect also observed in previous studies. 4,5,7 This phenomenon has been attributed to competition between desorption and decomposition; 16 it should be pointed out that diffusion of Si through the wire may also be important at these high temperatures. The observation of primarily Si desorption at high temperatures indicates that surface decomposition of SiH 4 is faster than evaporation of SiH x at these temperatures.…”

“…There have been a number of recent reports [3][4][5][6] of the distribution of wire-desorbed radicals, following the early report by Doyle et al 7 Experiments conducted using similar detection schemes, such as vacuum ultraviolet photoionization mass spectrometry, have shown quite different results in some cases. 4,5 Whether these differences are due to the different histories of the wire used or differences in the reactor condition ͑e.g., amorphous silicon-coated walls͒ is unclear.…”

“…In the report of Doyle et al, 7 SiH 3 was the next most abundant radical to Si. Duan et al 5 report disilicon species (Si 2 H x ) as the next most abundant, followed by SiH 3 ; the presence of Si 2 H x was thought to be related to wall reactions, however, and not a result of wire processes. Tange et al 4 report SiH 2 as the next most abundant radical, followed by SiH 3 .…”

“…4,5 Whether these differences are due to the different histories of the wire used or differences in the reactor condition ͑e.g., amorphous silicon-coated walls͒ is unclear.…”