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. 1

Abstract

Listen

Translate article

Silicon sessile drop experiments were performed on a variety of commercially available refractory carbides, nitrides, oxides, and borides to examine the potential of these materials for applications involving either direct contact with molten silicon or as substrates for CVD coatings in the fabrication of dies and crucibles for containing molten silicon. Simultaneous experiments were also conducted with CVD layers of SiC, Si/sub 3/N/sub 4/, and SiO/sub x/N/sub y/. The latter two materials proved superior for purposes of contact with the silicon melt in relation to chemical reactivity and reduced impurity content. Silicon nitride layers, deposited with NH/sub 3/ : SiH/sub 4/ ratios ranging from 100 : 1 down to 5 : 1, were examined in sessile drop experiments to determine if the layers are degraded as a result of using lower reagent ratios. The cost of ammonia (5 nines purity) at the higher ratios represents the major cost in the production of these layers, and a reduction in the above ratio could result in a substantial reduction in cost. Preliminary experiments were undertaken on the stability of CVD Si/sub 3/N/sub 4/ near the melting point of silicon. From our initial experiments it appears that the rate of decomposition is less than 100 A/h just below the melting point of silicon. Silicon ribbon segments were grown from vitreous carbon dies which had been coated with CVD Si/sub 3/N/sub 4/. Depending upon the purity of the die materials, ribbon resistivity values up to 40 ..cap omega..-cm were obtained.