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Selective Etching of Carbon From Silicon Surfaces

IP.com Disclosure Number: IPCOM000053007D
Original Publication Date: 1981-Aug-01
Included in the Prior Art Database: 2005-Feb-12
Document File: 4 page(s) / 51K

Publishing Venue

IBM

Related People

Gambino, RJ: AUTHOR [+2]

Abstract

Carbon is an ubiquitous contaminant on silicon surfaces. It has many sources of origin including photoresist residues, organics in deionized water, and pump oil polymerized on the surface as in ion implantation. On the other hand, carbon is well suited as a sputter etch mask because of its low sputter yield (0.072 atoms/ion @ 1 KeV, Ar/+/[1]. Its use as a mask is limited, in part, because it is so difficult to remove for subsequent processing steps.

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Selective Etching of Carbon From Silicon Surfaces

Carbon is an ubiquitous contaminant on silicon surfaces. It has many sources of origin including photoresist residues, organics in deionized water, and pump oil polymerized on the surface as in ion implantation. On the other hand, carbon is well suited as a sputter etch mask because of its low sputter yield
(0.072 atoms/ion @ 1 KeV, Ar/+/[1]. Its use as a mask is limited, in part, because it is so difficult to remove for subsequent processing steps.

Carbon contamination has many detrimental effects in electronic device processing. It acts as a diffusion barrier, and causes adhesion problems and poor wetting in LPE processing. The most common method of removing carbon from silicon is ashing. The ashing process consists of exposing the surface to an oxygen-rich plasma. This procedure has the disadvantage that it also produces a thick oxide on the surface of the silicon. Steps used to remove the oxide expose the surface to recontamination with carbon, e.g., chemical or sputter etching. Other reactive gases have been used including CO(2), H(2), H(2)O, halogens and noble gases. The selectivity of these mixtures and reactive gases for etching carbon preferentially has not been established previously.

This process selectively removes carbon from silicon by exposing the surface to an argon-hydrogen plasma. We find that preferential etching occurs only in a critical range of hydrogen concentrations and of ion acceleration energy. The proposed mechanism of the selective reaction based on these observations is the synergistic action of argon ion bombardment in the presence of hydrogen.

The carbon etching rate is enhanced by (1) Ar/+/ bombardment which breaks carbon-carbon bonds creating active sites for hydrogen reaction, (2) H/+/ bombardment (H(2)/+/) to form CH(x) (where x = 1, 2, 3, or 4) molecular units which are weakly bonded to the surface, and (3) the use of further Ar/+/ bombardment to remove these weakly bound CH(x) units by sputtering with a greatly enhanced effective sputtering yield for carbon. At the silicon surface, the sputter yield is reduced by adding hydrogen to an argon plasma.

In the case of silicon, the Si-H bond is relatively weak so Ar/+/ bombardment causes bond breaking at the Si-H bond rather than at the silicon-SiH(x) bond so there is no net removal of silicon by this mechanism. Also, the flux of H/+/ ions which form the Ar-H(2) plasma is very ineffective in the sputter removal of silicon because of the large mass difference between Si and H. The net effect is to reduce the net etching rate of silicon.

Text samples were prepared by depositing diamond-like amorphous carbon films onto polished single crystal silicon substrates. This form of amorphous carbon is very inert. It resists etching in all mineral acid and oxidizing etching solutions and all the common organic solvents. It is representative of the most highly cross-linked organic residues, such as overbaked, io...