Medium Energy Ion Scattering Analysis of Damage in Silicon Caused by Ultra-low Energy Boron Implantation at Different Substrate Temperatures

Medium Energy Ion Scattering (MEIS) has been used to determine the pre- and post- annealing damage distributions following 0.5-2.5 keV B⁺ implantation into Si (100) at different substrate temperatures. Substrates were implanted to doses of up to 3 × 10¹⁵ cm^-2at temperatures of -120 °C, 25 °C and 300 °C and annealed in a rapid thermal processing (RTP) system to temperatures between 400 °C and 1000 °C for 10 s. For the room temperature (RT) implants, two distinct damage distributions were observed. The first, was a near-surface damage peak which merges with the virgin Si surface peak, and has a width ≤ 3 nm. For B ⁺ doses above 10¹⁵ cm^-2, a second, deeper damage peak appeared at a depth of ≈ 7 nm, well below the TRIM predicted B⁺ mean projected range of R, = 5.3 nm. This peak is probably due to the formation of small interstitial (I_x) and /or B_y-I _x clusters. During implantation at 300 °C, more effective dynamic annealing results in a substantially reduced width of the near-surface damage peak. The deeper damage peak is similar to that observed for RT implantation. B⁺ implantation at -120 °C leads to a single damage peak stretching from the surface to the position of the deeper damage peak. The MEIS yield approaches random level, showing near or total amorphisation of the Si lattice, yet solid phase epitaxial regrowth is arrested at R_p. RTP at 900 °C of this implant leads to the highest degree of damage recovery, suggesting that low temperature implantation restricts the agglomeration of defects. RTP of the RT implanted samples at 400∼500 °C leads to substantial reduction in the two damage peaks, especially in the width of the near-surface peak. For RTP at 900 °C and 1000 °C, the near-surface damage region broadens as the deeper damage almost disappears, suggesting that, as the complex defects in the deeper damage region dissolve, point defects not only move into the bulk causing TED, but also towards surface, as a result of which the surface peak width increases.