The Effect of Pull Speed and Heat Treatment on Thermal Donors in Czhocralski Silicon

Abstract

In silicon crystals manufactured by the Czochralski method, oxygen is incorporated as a contaminant originating primarily from dissolution of the quartz crucible used to contain the molten silicon feedstock. The oxygen can be found either as interstitials, agglomerates, or as oxide particles. Particular kinds of agglomerates are known to lead to the formation of thermal donors—electronic states in the bandgap of the silicon base material. These can act as sites for recombination of excited charge carriers and are called thermal donors due to their ability to inject two electrons into the conduction band of silicon by thermal excitation, leading to enhanced electrical conductivity. Neither of these features are desirable in Cz‐Si manufacture. Herein, the behavior of thermal donors as a function of the pull speed, and the position in the ingot, is investigated. Thermal treatment is provided, first for the formation of thermal donors and then for their removal. The aim is to investigate methods for minimalizing their incorporation in the crystal in the first place and then how they can be removed. Hyperspectral imaging and spectroscopy combined with Fourier‐transform infrared spectroscopy are used.

Comprehensive Model for Charge Carrier Recombination in Czochralski‐Grown Silicon Due to Oxygen Precipitation in Industrial Solar Cell Manufacturing

“…[2,3,23] TDs are known to be aggregates of a few O i atoms, whose density (number per volume) increases with duration within the generation temperature range, similar to OP nuclei. [16,17] Recently, Olsen et al found an inverse correlation of TD density with pulling rate during Cz manufacturing, [24] which can be attributed to a change in duration within the generation temperature range. Furthermore, TDs act as double donors and therefore influence the resistivity of the wafers below 500 °C.…”