Infrared studies of the crystallinity of ion-implanted Si

Abstract

The crystallinity of ion-implanted silicon has been investigated using ion mass and ion fluence dependences of divacancy formation as measured by the characteristic 1.8 μ absorption band. Room temperature, nonchanneled implants of 400-keV B¹¹, Zn⁶⁴, and Sb¹²¹ ions were performed to maximum fluences of 10¹⁴ ions/crn² for Sb and Zn and to 2 × 10¹⁵ ions/cm² for B. The results are interpreted on the basis of ion energy spent in atomic processes per unit volume, ε, within the implanted layer. For ε ≤ 10¹⁹ keV/cm³ the energy to form a divacancy (1.5 ± 0.5 keV) is nearly ion independent. Maxima appear in the divacancy densities at ∼10¹³ Sb ions/cm² and ∼2 × 10¹³ Zn ions/cm² where ε ≤ 10²⁰ keV/cm³. The divacancy density for B implantation did not exhibit a distinct maximum at E = 10²⁰ keV/cm³, but continued to increase with fluence. The B results are attributed to defect motion because divacancies are observed beyond the calculated depth for energy deposition after a high fluence B implant. In addition to the 1.8 μ band, absorption extending from the band edge to at least 3.5μ is observed to increase with fluence for all ions. Analysis of the divacancy density data indicates that 1.8μ band quenching occurs for divacancy concentrations ≥ 7 × 10¹⁹ cm⁻³. The results of this investigation are consistent with crystal lattice defect domination of the ion-produced disorder when the energy spent in atomic processes is ∼ 10²⁰ keV/cm³ at room temperature, and with amorphous layer formation when the energy deposition is∼10²¹ keV/cm³ at room temperature, providing the defects remain near the position of the initial energy deposition.