Statistical analysis of structure loss in Czochralski silicon growth

Abstract

In Czochralski monocrystalline silicon growth, structure loss (SL) is the loss of the mono-crystalline structure. It represents a significant loss of productivity. In this work, this phenomenon is investigated by statistical analysis of production data of roughly 14000 ingots produced over a year of time at NorSun factory in Årdal, Norway. It is found that ingots with structure loss typically have lower heater power and temperature fluctuations than ingots without structure loss after four hours of body (ca. 240 mm). Particularly, ingots without manual adjustment by furnace operator have significantly higher frequency of structure loss than ingots for which the operator has increased the temperature one or more times. Most ingots with structure loss are also found to have a higher pull speed on average than ingots without structure loss, and that there is a threshold below which no ingots had structure loss. A binary logistic regression was used for classification of ingots with and without structure loss and 30% of the data was used to comparison of predictions of the model. Using only the standard deviation of the temperature fluctuations around a moving average provided a prediction accuracy of 99.6%, for ingots that have passed six hours of body (ca. 360 mm).