Removal of Fluorocarbon Residues on  CF 4 /  H 2 Reactive‐Ion‐Etched Silicon Surfaces Using a Hydrogen Plasma

Abstract

A cleaning procedure based on a hydrogen plasma is described which removes most of the fluorocarbon passivation layer remaining on silicon surfaces exposed to CF4/H2 reactive ion etching (RIE). Real time in situ ellipsometry performed during hydrogen plasma exposure of a reactive-ion-etched silicon surface showed removal of the bulk of this residue. The contamination layer thickness was reduced from 50A to less than 10A. X-ray photoelectron spectroscopy of hydrogenplasma-cleaned silicon showed an 80% reduction in carbon contamination and a 95% reduction in fluorine without appreciable oxidation of the surface. The contamination left after cleaning is a 10A carbon film. Secondary ion mass spectrometry showed that hydrogen implantation into the silicon substrate during cleaning was negligible relative to the amount implanted during RIE. Continued exposure of the surface to the cleaning plasma resulted in a redeposition of contamination, the source of which is sputtered residue from the reactor walls that was deposited during RIE. Surface oxidation by residual water and oxygen desorbing from chamber surfaces may also take place during prolonged H2 plasma cleaning.

Patterning of silicon nitride for CMOS gate spacer technology. II. Impact of subsilicon surface carbon implantation on epitaxial regrowth

“…The reduction of C-Si bonds present at a CF x /Si interface using an in situ RF hydrogen plasma was already demonstrated by Oehrlein et al 22,23 A passivation with Si-H bonds at the extreme surface by the N 2 /H 2 plasma radicals 12 could not explain the improvement of the post-epitaxy Si thickness since a 4 nm silicon oxide is present on top of the silicon substrate, which is later removed by a "HF-last" step. The reduction of C-Si bonds present at a CF x /Si interface using an in situ RF hydrogen plasma was already demonstrated by Oehrlein et al 22,23 A passivation with Si-H bonds at the extreme surface by the N 2 /H 2 plasma radicals 12 could not explain the improvement of the post-epitaxy Si thickness since a 4 nm silicon oxide is present on top of the silicon substrate, which is later removed by a "HF-last" step.…”

Selective etching of SiO2 over polycrystalline silicon using CHF3 in an inductively coupled plasma reactor

“…This is very likely due to the presence of hydrogen and its strong affinity for reacting with fluorine. The phenomenon of ''hydrogen scavenging'' 8,[11][12][13] in fluorocarbon plasmas where hydrogen is present is a well established mechanism for the reduction of the atomic fluorine concentration. It is also observed that for any given inductive power, the atomic fluorine concentration within the plasma increases with the increasing pressure.…”

“…It has been well established that the thickness of the steady-state fluorocarbon film plays a key role in the regulation of the silicon etch rate. 3,4,[8][9][10][11] Figure 7 shows the results of the three separate ellipsometry experiments conducted at a constant pressure in which a crystalline silicon wafer was etched in CHF 3 as a function of the increasing inductive power. In each experiment the inductive power was initially low, and then increased to higher values.…”

Plasma etching: Yesterday, today, and tomorrow

“…236)], C 2 F 6 (Freon 116), and C 3 F 8 (Freon 218) were used in the early days to etch SiO 2 , 28,29 usually with addition of O 2 when selectivities to resist and/or silicon were not critical, and polymer control was important. Hydrogen addition to the above fluorocarbons was used to increase selectivity to silicon, 28,29,237 with the drawbacks of polymer formation, decreased etch rate, 237,238 and deep penetration of hydrogen into the silicon substrate [239][240][241][242][243][244][245][246][247] that can lead to device degradation if not annealed properly. In applications where this is not an issue (such as patterning of waveguides), hydrogen may be used as an additive to control selectivity to silicon and/or photoresists.…”