Measurement of temperature fluctuations and microscopic growth rates in a silicon floating zone under microgravity

A silicon crystal growth experiment has been accomplished using the floatin g-zone technique under microgravity on a sounding rocket (TEXUS 36). Measur ements of temperature fluctuations in the silicon melt zone due to time-dep endent thermocapillary convection (Marangoni convection) and an observation of the microscopic growth rate were simultaneously performed during the ex periment. Temperature fluctuations of about 0.5-0.7 degrees C with a freque ncy range <0.5 Hz were detectable. The microscopic growth rate fluctuates c onsiderably around the average growth rate of I mm/min: Growth rates up to 3-4 mm/min, close to zero mm/min, as well as negative values (backmelting) were observed. Dopant striations are clearly visible in the Sb-doped crysta l. They were characterized by spreading resistance measurements and differe ntial interference contrast microscopy. The frequencies of temperature fluc tuations, microscopic growth rates, and the dopant inhomogeneities correspo nd quite well, with main frequencies between 0.1 sind 0.3 Wt. 3D numerical simulations were performed to predict the optimum position of the temperatu re sensor, and the characteristic temperature amplitudes and frequencies. A t a position 3.4 mm above the interface and 1.4 mm inside the melt, equival ent to the sensor tip position in the experiment, temperature fluctuations up to 1.8 degrees C and frequencies less than or equal to 0.25 Hz were foun d in the simulations. (C) 1999 Elsevier Science B.V. All rights reserved.