Crystallization of amorphous GexSi100−x on SiO2

Crystallization of amorphous GexSi100−x on SiO2

Thin Solid Films, 82 (1981) 343-345 343 PREPARATION AND CHARACTERIZATION C R Y S T A L L I Z A T I O N OF A M O R P H O U S GexSil0o_ ~ ON SiO 2 M...

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Thin Solid Films, 82 (1981) 343-345

343

PREPARATION AND CHARACTERIZATION

C R Y S T A L L I Z A T I O N OF A M O R P H O U S GexSil0o_ ~ ON SiO 2 M. M ~ N P , ~ A *

California Institute of Technology, Pasadena, CA 91125 (U.S.A.) S. S. LAU

University of California, San Diego, La Jolla, CA 92093 (U.S.A.) (Received March 9, 1981 ; accepted April 30, 1981)

The growth kinetics of amorphous GexSil0o_ x (x ~< 0 ~< 100) films were studied using electrical measurements. The growth rate increases with increasing germanium content in the film and the activation energies change from 2.5 to 2.0 eV as the composition changes from x = 0 to x = i00.

In this study we investigate the growth kinetics of amorphous alloy films of composition GexSilo0_x (0 ~< x ~< 100) deposited onto SiO2 substrates. The samples consist of multiple layers of germanium and silicon films deposited by electron gun evaporation which are then subjected to ion beam mixing 1 to homogenize the individual layers. The details of the sample preparation are reported in an accompanying paper 2. The growth kinetics of the alloy film are determined by measuring the electrical conductance with a four-point probe at room temperature after the samples have been vacuum annealed for various periods of time. For surface-induced crystallization and if the diameters of the growing nuclei are larger than the thickness of the amorphous layer, the electrical conductance of a crystallizing layer is linearly proportional to the growth time 3. We performed such conductance measurements on five different films of compositions with x = 0, 25, 50, 75 and 100. The results were similar to those for x = 50 shown in Fig. 3 of the accompanying paper z. Figure 1 shows the Arrhenius plots of the growth rates versus 1/T derived from those measurements. These samples were implanted with 6x1015 As + ions cm -2 at liquid nitrogen temperatures. The energies of the implantation were chosen such that Rp + 2 ARp (where Rp is the projected range and AR v the standard deviation) was comparable with the thickness (about 1500 A) of the deposited layers. The growth rates are observed to increase with increasing germanium content in the alloy. The activation energy changes from 2.5 to 2.0 eV as the composition changes from x = 0 to x = 10t3, compared with 2.3 eV and 2.0 eV for self-ion-implanted amorphous silicon and germanium layers on single-crystal silicon and germanium respectively, which are also shown in Fig. 1 (thin lineS). * Permanent address: Semiconductor Laboratory, Technical Research Centre of Finland, Otakaari 5A, SF-02150 Espoo 15, Finland. 0040-6090/81/0000-0000/$02.50

© Elsevier Sequoia/Printed in The Netherlands

344

M. M~;~NP~,S.S. LAU

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25

50

75

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TEMPERATURE,

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Fig. 1. Growth rates as functions of the reciprocal temperature for various films: + , GexSi~0o_x (1500 A) on SiO 2 implanted with 6 × 101 s As + ions cm- 2; - - , self-ion-implanted amorphous layers on Si(100), Si(111), Ge(100) and Ge(111). Figure 2 s h o w s the regrowth rates for three GesoSiso samples with different implantation conditions. It can be seen that the growth rate increases with the concentration of arsenic in the alloy layer. This enhancement effect of arsenic was observed for all samples with c o m p o s i t i o n ranging from x = 0 to x = 100.

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Fig. 2. Growth rates of G%oSiso alloy films (1500 A) o n different implantation conditions (AE = 2.3 -+0.1 eV).

SiO 2

vs.

the reciprocal temperatures for three

Our results s h o w that the crystalline growth from the a m o r p h o u s phase extends throughout the c o m p o s i t i o n range of x = 0 100, and that the growth rates and activation energies change m o n o t o n i c a l l y over the whole c o m p o s i t i o n range, Previous experiments on the regrowth of an a m o r p h o u s silicon layer implanted with 2 at.% G e s h o w e d no significant effect on the growth rates 4. H o w e v e r , the results of

CRYSTALLIZATIONOF AMORPHOUSGexSi 1oo-x ON S i O 2

345

this study show that if the germanium content in the alloy is significant (25 a t . ~ or higher) the growth rate is enhanced. The opposite result has been reported for the regrowth of single-crystal silicon amorphized by high dose germanium implantation (about 14 at.~o Ge) 5, Subsequent investigation, however, revealed that these samples were contaminated by fluorine 6. Our results further establish that the growth rate of this alloy can be accelerated by arsenic, as is known to be the case for the growth of silicon films 4. It therefore appears that the growth of Ge-Si alloys can be influenced in a similar manner to the epitaxial regrowth of a m o r p h o u s silicon 4. ACKNOWLEDGMENTS We acknowledge the financial support for the ion implantation aspect of this work by the U.S. Department of Energy through an agreement with the National Aeronautics and Space Administration and monitored by the Jet Propulsion Laboratory, California Institute of Technology (D. Fitzgerald). The authors also thank Dr. M.-A. Nicolet and Mr. L. S. H u n g for fruitful discussions, and R. Fernandez and R. Gorris for technical assistance. REFERENCES 1 B.Y. Tsaur, in J. E. E. Baglin and J. M. Poate (eds.), Proc. Syrup. on Thin Film Interfaces and Interactions, Los Angeles, 1979, Vol. 80-2, ElectrochemicalSociety, Princeton, NJ, 1980, p. 205. 2 M. Miienp/iii, L. S. Hung, M. G. Grimaldi, I. Suni, J. W. Mayer, M.-A. Nicolet and S. S. Lau, Thin Solid Films, 82 (1981). 3 P. Germain, S. Squelard, J. C. Bourgoin and A. Gheorghiu, J. Non-Cryst. Solids, 23 (1977) 93. 4 S.S. Lau and W. van der Weg. Solid-phaseepitaxy. In J. M. Poate, K. N. Tu and J. W. Mayer (eds.), Thin Films--Interdiffusion and Reactions, Wiley, New York, 1978, Chap. 12. 5 G. Mezey, S. Matteson and J. Gyulai, Nucl. Instrum. Methods, 182-183 (1981) 587. 6 P. Williams, personal communication, University of Illinois, 1980.