High depth resolution characterization of the damage and annealing behaviour of ultra shallow As implants in Si

The relationship between damage formation/annealing and As profile redistribution has been studied using low energy As implants into Si at 2.5 keV at doses between 3 × 10¹³ cm^-2 and 2 × 10¹⁵ cm^-2 at room temperature. Samples were annealed at temperatures between 600 and 1050°C. High depth resolution medium energy ion scattering (MEIS) and secondary ion mass spectrometry (SIMS) were used to characterise the damage build up and As profiles as a function of implant dose and anneal temperature. MEIS studies showed that damage does not accumulate according to the energy deposition function but proceeds from the surface inwards. This is ascribed to the accumulation of collision cascade produced interstitials that are attracted to and settle at initially the oxide/Si interface and later to the advancing amorphous/crystalline interface. Dopant depth profiles agreed well with TRIM calculations for doses ≥ 4 × 10¹⁴ cm^-2. However, for lower doses the dopant was observed to have a profile nearer to the surface, due to trapping in the narrow surface damaged layer, in which it is more easily accommodated. Following epitaxial regrowth at 700°C, MEIS showed that -50 % of the As has moved into substitutional sites, consistent with activation and/or the formation of inactive As_nV clusters (n ≤ 4), while the remainder had segregated to and become trapped in a ≤1 nm wide layer, clearly located on the Si side of the oxide/Si interface. Very low energy SIMS analysis at normal incidence is able to resolve these ultra shallow peaks, including the As pileup following epitaxial regrowth. They also confirmed that As retention was complete during dose build up and annealing.