Peter Krottenthaler

Oxygen Precipitation in Nitrogen Doped CZ Silicon

Nitrogen doping of CZ silicon results in an early formation of large precipitate nuclei during crystal cooling, which are stable at 900°C. These are prone to develop stacking faults and high densities of defects inside defect denuded zones of CZ silicon wafers. Simultaneous doping of FZ silicon with nitrogen and oxygen results in two main stages of precipitate nucleation during crystal cooling, an enhanced nucleation around 800°C, which is nitrogen induced, and a second enhancement around 600°C, which depends on the concentration of residual oxygen on interstitial sites. A combined technique of ramping with 1K/min from 500-1000°C with a final anneal at 1000°C for 2h and lateral BMD measurement by SIRM provides a possibility to delineate v/G on nitrogen-doped silicon wafers. Surface segregation of nitrogen and oxygen during out-diffusion can explain the enhanced BMD formation in about 105m depth and the suppressed BMD formation in about 405m depth below the surface. The precipitate growth is enhanced in regions where nitrogen is filled up again after a preceding out-diffusion.

Processing and Characterization of 300 mm Argon-Annealed Wafers

High nitrogen doped 300 mm silicon wafers annealed in 100 % argon ambient were investigated whether modified pulling conditions will lead to improved slip behavior and homogeneous radial oxygen precipitation. It turned out that increasing of the cooling rate during crystal pulling is beneficial on these wafer defect parameters. The void morphology was investigated by TEM and oxygen precipitation profiler measurements. Remarkably changes in the morphology of grown-in defects (voids) with varying the ingot cooling rate of these crystals can be observed.

Precipitation enhancement of so called defect-free Czochralski silicon material

Thermal treatments to enhance precipitation like RTA, ramp anneal and argon anneal were performed on low oxygen 300 mm wafers without vacancy or interstitial agglomerates (“so called” defect-free material). Best results were achieved using high temperature argon anneal leading to a homogenous BMD and denuded zone formation. Furthermore the getter efficiency was positively tested by intentional Ni-contamination. Concepts to overcome the slip danger like improved support geometries and nitrogen codoping were also evaluated and are seen to be beneficial.