Scanning infrared microscopy study of thermal processing induced defects in low resistivity Si wafers

Abstract

Scanning infrared microscopy (SIRM) is used to study thermal processing induced oxygen precipitation in low resistivity n+ and p+ Si substrates doped with As, P, Sb or B. It is shown that SIRM allows us to investigate successfully Si samples with resistivities as low as 1.7 m cm and to measure non-destructively bulk micro spectroscopy densities between 10 7 and 10 10 cm −3 with precipitate sizes as small as 30 nm. Comparison with precipitation in moderate resistivity reference material that received the same thermal treatments reveals a strong impact of doping for concentrations above 5 × 10 18 cm −3 , in particular, in combination with rapid thermal processing pre-treatments at temperatures above 1000 • C. The observations can be understood by intrinsic point defect trapping during rapid thermal processing and release during subsequent lower temperature treatments through its impact on homogeneous oxide precipitate nucleation.

Oxide precipitate nucleation at 300 °C in low resistivity n-type Czochralski Si

“…During the subsequent 300 8C anneal, the resistivity then gradually Figure 7 BMD densities measured by SIRM for three RTP temperatures (top) [21]. Assuming an Arrhenius dependence of the BMD density on 1/T as shown in the bottom figure, yields a dopant concentration and type dependent activation energy.…”

“…It is known that the concentration of vacancies injected into silicon increases exponentially with increasing RTP temperature T which leads to the observed increase of BMD density. More detailed SIRM analyses are published elsewhere [21].…”