Study on Boron‐Hydrogen Pairs in Bare and Passivated Float‐Zone Silicon Wafers

Abstract

This study deals with the dynamics of the formation and dissociation of boron-hydrogen (BH) pairs in crystalline silicon during a rapid high temperature treatment and subsequent dark annealing between 200°C and 300°C. Highly accurate resistivity measurements were used to detect BH pairs in chemically polished B-doped FZ-Si(ρ ≈ 1 Ω cm). An unexpectedly high amount of hydrogen is present in the as-purchased wafers. Hydrogen is initially mostly paired to boron but can be dissolved by a high temperature firing step. If a firing step with a peak temperature of around 530°C is applied to bare Si wafers, most of the initial BH pairs are dissolved and hydrogen dimers (H2) form. With increasing peak temperature, an increasing amount of hydrogen leaves the H2 = BH system. The proportion of BH increases with decreasing total hydrogen content. Additional hydrogen can be introduced by firing a wafer passivated with PECVD SiNx:H. The mathematical description with a three-state-model shows a good agreement with the measured data for both bare and coated samples as well as for different annealing temperatures. With increasing dark annealing temperatures, the BH dynamics accelerates while the maximum BH concentration reached decreases. For temperatures above 280°C, significant changes in the reaction dynamics are observed.