ADVANCED SOLAR® CRUCIBLE FOR HIGHER PRODUCTION YIELD AND RELIABLE CRYSTALLINE SILICON INGOT QUALITY

摘要

Multi-crystallized wafers are produced by directional solidification of molten silicon in fused silica cruciblepreviously coated with a releasing agent mainly composed of silicon nitride. The interaction between the crucible/coatingand silicon results in the degradation of the electrical properties of a significant ingot border layer, called “red zone” thatcannot be directly processed into wafers.Electronic grade (EG) transparent fused quartz crucible exhibiting excellent purity is known to be the lesscontaminating material that generates the lowest ingot red zone but cannot be produced in industrial size. The presentstudy aims to close the gap between the EG fused quartz crucibles and the commercial grade fused silica ones. Standardand newly developed Advanced SOLAR® crucibles (ASC) were coated with the same silicon nitride coating and used togrow 3 kg silicon ingot. Red zone area, lifetime mapping and impurity contaminations were compared to reference ingotcrystallized in electronic fused quartz crucible.Results demonstrate that the new Advanced SOLAR® crucible shows up to 30% reduced red zone than previousstandard reaching comparable benefice as electronic fused quartz (the bottom red zone is 14 mm thick instead of 21 mm).The minority carrier lifetime is significantly improved but the max value remains below the values obtained in the case ofthe electronic fused quartz (125 μs instead of 160 μs).Minority carrier lifetime values and red zone reduction correlates well with the interstitial iron concentration.Indeed the interstitial iron concentration (measured by the iron-boron dissociation method) is around 4×10~(13) cm~(-3) in thered zone and around 10~(11) cm~(-3) in the center of the ingots.