Apparatus for controlled growth of silicon and germanium crystal ribbons

Claim 1

Apparatus for growing a ribbon shaped crystalline body of silicon or germanium so that said body has a selected cross-sectional shape for a selected distance along its length, said material being at least partially reflective to radiation at a preselected wavelength, said apparatus comprising means for growing and pulling said crystalline body from a growth pool of melt supplied by a capillary die and means for replenishing said growth pool with melt provided from a reservoir supply of melt, said body and said growth pool of melt forming a solid/liquid interface and said growth pool being characterized by a meniscus which extends from said die and joins said body at said interface to form a solid/liquid/vapor junction above said die at which the liquid surface of said meniscus intersects the solid surface of said body at a predetermined meniscus angle when the growth of said crystalline body is under steady state conditions, said apparatus further comprising: means for observing a plurality of preselected points on at least the portion of the surfaces of said body and said meniscus adjacent said junction for the quantity of radiation of said preselected wavelength emitted and reflected from each of said points in a direction along an axis substantially perpendicular to the meniscus surface formed at said junction when the growth of said crystalline body is under steady state conditions, and for producing a like plurality of first electrical signals, each corresponding to the observed quantity of radiation reflected from a respective one of said points; means for comparing each of said first electrical signals with a predetermined first reference signal so as to determine which of the observed points exhibit a sharp change in the amount of reflected radiation of said preselected wavelength and for generating a control signal as a function of the spatial position of said points exhibiting a sharp change in the amount of reflected radiation; and means, responsive to said control signal, for controlling the speed at which said body is being pulled or the temperature of said growth pool of melt so as to maintain those points exhibiting said sharp change at a preselected spatial position relative to a predetermined reference position.