Patent GB-1376665-A (GB)
Title: Apparatus for pulling semoconductor crystals
IPC: C30B15/28
Filed: 1972-02-24
Abstract: 1376665 Controlling crystal growth SONY CORP 24 Feb 1972 [25 Feb 1971 8 Nov 1971] 8692/72 Heading B1S A modified crystal-pulling apparatus of the Czochralski-type wherein the rate of growth and diameter of the growing crystal is controlled by a float immersed in a liquid in a tub cooperating with means for pulling up the crystal by comparing the weights of the float and growing crystal whereby the rate of growth of the crystal is automatically controlled. As shown in the figure. Furnace 1 consists of two parts la, and 1b. Disposed in la is a crucible 2 supported by 3. Both 2 and 3 are movable vertically and rotatable by a shaft 4 and are enclosed within a fixed cylindrical heater 13 and insulator 14. In part 1b of the hermetically sealed furnace 1, through a closed bearing 15 is an outer shaft 16 through which crystal pulling shaft 17 is passed. To the lower end of shaft 17 is attached a seed chuck 18 and seed 19. When the seed 19 is immersed in the melt 12, it grows into single crystal 20. Engaged with the upper end of shaft 16 is portion 22a of a vertically moving rack 22. The shaft 16 is also rotatable in the opposite direction to crucible 2 by motor 23 and worm gear 24. The shaft 17 rotates with shaft 16 at a predetermined speed. The shaft 17 is connected to a weight detector 25 through suspension installation 26 to portion 22b of moving rack 22. The latter mesh with rotatable shaft 27 provided on shoulder lc of the furnace 1. The growth control element consists of a bath tub 32 fixedly attached to a stationary table 30 connected to furnace 1. The tub comprises a liquid intake 33 and outlet 34 arranged to maintain a liquid level 31a of the chosen liquid 31. A float 35 immersed in the liquid is connected to a lower end of a rod 38, which rod is connected to a weight detector 37, and a suspension installation 36. The installation 36 is connected as is 26 to portion 22b of the rack 22. The suspension installations 26 and 36, and the weight detectors 25 and 37 are of similar construction. The float is shaped to correspond to the final form of the crystal. The outputs from the weight detectors are compared by circuit 40, passed to processing circuit 41 from which they are delivered to power controller 42, a lift speed controller 43 and a pull up speed controller 44 which respectively control the heater 13, the lift motor 8 and the crystal pull motor 28. In operation at the start of the crystal pulling operation the seed is in contact with the melt whilst the upper end of the float 35 coincides with liquid level 31a. Growth of crystal 20 produces an increase in weight which is shown by detector 25, whilst because of the upward movement of 22a, the float 35 is lifted above liquid level 31a, and accordingly detector 37 shows an increase in weight. If not identical the comparator circuit adjusts the pulling up speed of the crystal. Various other automtaic methods of adjusting the rate of growth of the crystal are also described, e.g. movement of the crucible and temperature adjustment thereof and also movement of the tub upwards to'maintain the float immersed.