Reactions of Fluorine-Containing Compounds on Thermal SiO 2
- PDF / 294,277 Bytes
- 6 Pages / 420.48 x 639 pts Page_size
- 55 Downloads / 201 Views
REACTIONS OF FLUORINE-CONTAINING COMPOUNDS ON THERMAL SIO 2
STEPHEN JOYCE AND JEFFREY I. STEINFELD Department of Chemistry, Massachusetts Institute of Technology, Cambridge, MA 02139
ABSTRACT
The reactivity of XeF 2 and CF 3 on thermally grown SiO 2 surfaces has been investigated.
CF 3 radi-
cals were generated by infrared multiple-photon dissociation of C 2 F6 using a pulsed CO 2 laser. X-ray photoelectron spectroscopy (XPS) was used to determine the chemical state of the surface after exposure to the gases.
Both CF 3 and XeF2 are relatively inert to annealed SiO 2 surfaces.-
damaged surfaces are much more reactive. cussed.
Ion
Implications for ion enhancement of etching are dis-
XPS spectra reveal fluorine, from XeF 2 bonded to both silicon and oxygen.
The CF 3 radi-
cal appears to undergo little dissociation upon chemisorption on SiO 2. INTRODUCTION There are many examples of the enhancement of the etch taneously exposed photonI1].
rate of a solid substrate simul-
to both etchant gas and various forms of radiation,
either ion, electron, or In many cases little is known about the actual mechanism for the enhancement. Consider
the case of ion bombardment;
physical sputtering,
chemical sputtering[2],
the use of ions as an
energy source[3]. and lattice damage[4] have all been suggested as being potentially important.
In or-
der to isolate the effects of one of these mechanisms, namely lattice damage, we have intentionally damaged thermally grown SiO, films with argon ions prior to exposure to XeF 2 and the CF 3 radical. X-ray photoelectron spectroscopy (XPS) was then employed to characterize the resulting stable overlayer. XeF 2 has been shown to dissociatively chemisorb on a SiO 2 surface but will not spontaneously In the presence of an Ar+ beam, however, it has been shown that SiO 2 is
etch the substrate[5]. etched by XeF
2
with SiF 4 and 02 as the primary products[5].
silica was measured to be - 0.1f6).
The sticking coefficient of XeF 2 on
Irradiation of SiO, by an ion beam is known to introduce
defects in the form of both reduction of SiO 2 to suboxides by preferential sputtering of oxygen over silicon[7] and introduction of lattice strain[8] by rapid bond reformation after bond cleavage by an energetic ion.
Studies of the reaction of CF 3 with SiO219,10] have shown that CF 3 is capable of
etching SiO 2 , but details of the surface
reactions were not investigated.
SiF 4 , CO 2.
CO and
COF 2 I10] have been identified as the primary products of this reaction. No studies have investigated the effect of ions on the etching of SiO, by CF 3 radicals, although several workers[2,1 1] have looked at the etching of SiO, by the CF 3
4
ion and found that etching does occur under some circumstances. EXPERIMENTAL
The experimental apparatus is described in detail elsewhere[121.
Briefly, it is a two stage UHV
chamber in which the two stages can be separated by a gate valve. The upper chamber is used for sputtering, oxidation, and dosing of the substrate. The lower chamber contains an X-ra
Data Loading...
