Investigation of Trimethylphosphine as a Source for [sup +]P[sub 31] Implantation Using a Cold-Cathode Implantation System for Silicon Device Fabrication

Abstract

Trimethylphosphine, ͑CH 3 ͒ 3 P, an organic phosphine liquid, has been investigated as a source for ϩ P 31 ion implantation in silicon using a cold-cathode implantation system. The use of trimethylphosphine has the potential to minimize safety concerns associated with other implantation sources for phosphorous. Using secondary-ion mass spectroscopy and Auger electron spectroscopy analysis the P ϩ , (CH 2 ) ϩ , and ͑CH͒P ϩ current peaks were identified. A graphical analysis procedure was then used to predict the other dominant peaks of the beam current spectrum. Using this graphical analysis the dominant species of the beam current spectrum were determined to be (CH 3 ) ϩ , (CH 2 ) ϩ , ͑CH 3 ͒2P ϩ , and ͑CH 3 ͒3P ϩ . Although the beam current spectrum for (CH 3 ͒ 3 P was found to be abundant in ionic species, the P ϩ beam current peak was easily resolved. The P ϩ peak revealed no carbon, indicating the suitability for silicon device fabrication.Ion implantation technology is extensively used for doping of silicon during semiconductor fabrication. Currently, PH 3 is widely used as an implantation source for the dopant phosphorous. However, PH 3 presents concerns from considerations of health and safety. The use of trimethylphosphine, ͑CH 3 ͒ 3 P, as an ion implantation source has the potential to minimize these hazards. This organic source, however, has two potential disadvantages; an abundant beam current spectra of ionic species, which would create difficulty in resolving the P 31 species for implantation, and carbon contamination of the P 31 peak.In this paper, we report on an investigation of the feasibility of using trimethylphosphine, ͑CH 3 ͒P, for ϩ P 31 implantation in a coldcathode implantation system. Approximate implantation dose and energy requirements for Auger electron spectroscopy ͑AES͒ and secondary-ion mass spectroscopy ͑SIMS͒ detection of implanted species were determined using computer simulations ͑SUPREM͒. Other ionic species in the beam current spectrum were determined by a graphical analysis method, in conjunction with AES and SIMS measurements, confirming selected current peaks. Ion Implantation SystemThe implantation system used in this work was an Extrion model 200-20A ion implanter, which used a gaseous source of trimethylphosphine in a Penning cold-cathode discharge system. The trimethylphosphine was purchased in a lecture bottle from Alfa Products. 1 Trimethylphosphine, ͑CH 3 ͒ 3 P, is a colorless liquid with a boiling point, at 760 mm Hg, of 37.8 C. At 20°C, the vapor pressure is 373 mm Hg, and was high enough to be effective as a gaseous source for this ion implantation system at room temperature. 2 Consequently, no external heating of the source was needed. Preacceleration mass analysis was employed in conjunction with a gridded lens and electrostatic scanning. The extraction potential was 25 keV, which permitted analysis of ions with a mass to charge ratio up to 76 amu/charge. Because the amu of ͑CH 3 ͒ 3 P is 76, the ion implanter was able to analyze all potential species. Implantat...

Surface Reactions of Molecular and Atomic Oxygen with Carbon Phosphide Films

“…TMP was purified by several freeze−pump−thaw cycles before the vapor was introduced into the ion gun through a UHV-compatible leak valve. Gas purity was routinely checked using mass spectrometry to verify the presence of the P(CH 3 ) 3 + parent ion . Following ion implantation, the surface became visibly discolored (darker).…”

“…The practical utility of phosphine is limited, however, by its toxicity. A recent study has shown that trimethylphosphine, P(CH 3 ) 3 (TMP), can also be employed as a source gas for phosphorus implantation . On the basis of this study, we have employed TMP as a cheap, commercially available, and less hazardous source of phosphorus to generate carbon phosphide coatings on polyethylene.…”