Porous silicon damage enhanced phosphorus and aluminium gettering of p-type Czochralski silicon

Abstract

In this work, porous silicon damage (PSD) is presented as a simple sequence for efficient external purification techniques. The method consists of using thin nanoporous p-type silicon on both sides of the silicon substrates with randomly hemispherical voids. Then, two main sample types are processed. In the first type, thin aluminium layers (≥1 μm) are thermally evaporated followed by photo-thermal annealing treatments in N 2 atmosphere at one of several temperatures ranging between 600 and 800 °C. In the second type, phosphorus is continually diffused in N 2/O 2 ambient in a solid phase from POCl 3 solution during heating at one of several temperatures ranging between 750 and 1000 °C for 1 h. Hall Effect and Van Der Pauw methods prove the existence of an optimum temperature in the case of phosphorus gettering at 900 °C yielding a Hall mobility of about 982 cm 2 V −1 s −1. However, in the case of aluminium gettering, there is no gettering limit in the as mentioned temperature range. Metal/Si Schottky diodes are elaborated to clarify these improvements. In this study, we demonstrate that enhanced metal solubility model cannot explain the gettering effect. The solid solubility of aluminium is higher than that of P atoms in silicon; however, the device yield confirms the effectiveness of phosphorus as compared to aluminium.