Method for circumferential dimension measuring and control in crystal rod pulling
AssigneeFerrofluidics Corporation
InventorsRichard A. Scholl, John L. Cole
Life of this patent
Estimating the term…
Abstract
The circumference of a crystal rod is monitored and controlled during the rod growing process by providing relative rotation between the growing crystal rod and a melt of the crystal material as the rod is being pulled from the melt according to the Czochralski method, and by using a radiation-sensitive control system for adjusting growth conditions of the rod in response to variations in a radiation signal which is indicative of the circumferential dimension of the rod. An electronic circuit integrates the radiation signal over each complete rotation of the rod, thereby eliminating unnecessary adjustment of the growth conditions in response to diametric variations of the rod which recur regularly in each rotation.
Claims18
A method for controlling the growth of a crystal rod in a direction transverse to the axis of said rod, as said rod is being drawn from a melt in a substantially vertical direction, which method comprises:
- (a) providing relative rotation of said rod with respect to the melt, while drawing the crystal rod from the melt;
- (b) sensing electromagnetic radiation from the circumference of the meniscus, which occurs at the interface between said rod and said melt, and obtaining a signal responsive to a substantial circumferential dimension of said crystal rod, for successive rotations thereof;
- (c) integrating successive circumferential signals to generate a correction signal indicative of the change of any circumferential dimensions of said drawn rod;
- and
- (d) adjusting the rate at which the rod is drawn from the melt, to provide for a rod of controlled growth in the transverse direction.
The method of cliam 1 which includes rotating the rod relative to the melt at from about 30 to 120 degrees per second.
A method for controlling the growth of a crystal rod in the plane transverse to the axis of said rod, as said rod is being drawn by a crystal-growing apparatus from a melt, said method comprising the steps of:
- (a) providing relative rotation of said rod with respect to said melt;
- (b) measuring the circumferential dimension of a cross-section of said rod in said plane, said measuring comprising causing electromagnetic radiation to impinge upon a meniscus occurring at the interface between said rod and said melt, and producing an electrical signal responsive to electromagnetic radiation reflected from said meniscus, and integrating said signal over an angular interval of said rotation from 0 to 2.pi.n radians, where n is an integer;
- (c) distinguishing any change which occurs in said circumferential dimension during successive rotations of said rod and generating a correction signal proportional to any said change;
- and
- (d) adjusting the rate at which said crystal rod is drawn from said melt, which affects the growth of said rod in said plane in response to said correction signal.
Dependencies are inferred from the claim text.