Plasma processing of the silicon surface: A novel method to reduce transient enhanced diffusion of boron

We investigate in detail the effect of plasma processing on the transient e nhanced diffusion of implanted boron in silicon. Thermally oxidized silicon wafers were first processed with CHF3/CF4 plasma and subsequently implante d with boron, with energies ranging from 3 to 20 keV and a dose of 1 x 10(1 3)/cm(2). Chemical profiles were measured by secondary ion mass spectrometr y while lattice extended defects induced in silicon by plasma processing we re characterized by transmission electron microscopy. Secondary ion mass sp ectrometry measurements reveal that the transient enhanced diffusion of bor on after rapid thermal annealing is strongly reduced in plasma processed sa mples with respect to unprocessed samples. Defects induced by plasma proces sing are responsible for the reduction by acting as very efficient traps fo r the interstitial atoms generated during the implant. We note that the tra pping efficiency is critically dependent on the projected range of the boro n implant, being extremely evident at low energies and less marked as the e nergy is increased (i.e., when the interstitials generated by the B implant are far away from the trapping sites). By varying the plasma conditions (a n argon plasma is used instead of a CHF3/CF4 plasma), we are able to establ ish a general correlation between trapping defect centers and transient enh anced diffusion reduction. Finally, spreading resistance measurements revea l that the amount of electrically active boron in plasma processed pure epi taxial Si is almost equal to that obtained in samples not exposed to plasma bombardment, thus demonstrating that the plasma processing has no detrimen tal effect on the boron electrical activation. (C) 1998 American Institute of Physics. [S0021-8979(98)05623-0].