Development and Evaluation of die Materials for Use in the Growth of Silicon Ribbons by the Inverted Ribbon Growth Process. Task II: LSSA Project. Quarterly Report No. 4

摘要

The results of emission spectroscopic analysis indicate that molten silicon (sessile drop) can remain in contact with hot-pressed Si sub 3 N sub 4 (99.2% theoretical density) for prolonged periods without attaining the impurity content level of the nitride. It is interesting to note that, although MgO was used as binder (approx. 3.8%), Mg was not found present in the silicon sessile drop in quantities much above the level initially present in the silicon source material. The conversion of CVD silicon oxynitride to beta -Si sub 3 N sub 4 can be carried out at high temperature in N sub 2 (approx. 1600 exp 0 C), by contact with molten silicon or by a combination of these steps. Conversion in the presence of molten silicon appears preferable. Preliminary experiments with EFG-type dies coated with CVD Si sub 3 N sub 4 or CVD SiO/sub x/N/sub y/ indicate that capillary rise does not occur readily in these dies. The same was found to be true of hot-pressed and reaction-sintered Si sub 3 N sub 4 obtained commercially. However, when dies were formed by depositing CVD layers on shaped silicon slabs, a column of molten silicon (approx. 2.5 cm high) was maintained in each CVD die while being heated (approx. 30 min) in contact with a crucible of molten silicon. Preliminary wetting of dies appears necessary for EFG growth. Several ribbon growth experiments were performed in our new ribbon growth facility from V-shaped dies. Both CVD Si sub 3 N sub 4 and CVD SiO/sub x/N/sub y/ coatings were used on the die parts. There is also a problem with the wetting of SiO/sub x/N/sub y/ in the inverted ribbon growth process but not with Si sub 3 N sub 4 layers. After about 90 min in contact with the melt, however, silicon flows into the defining slot in the case of SiO/sub x/N/sub y/ coatings. (ERA citation 04:051242)