Alternative Chemistries for MOCVD Growth of III/V Materials
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ALTERNATIVE CHEMISTRIES FOR MOCVD GROWTH OF IrVv MATERIALS R.M. LUM AND J.K. KLINGERT AT&T Bell Laboratories, Crawfords Corner Rd., Holmdel, NJ 07733.
ABSTRACT are attractive alternatives to arsine, AsH 3 . for Alkyl substituted arsine compounds, R.AsH3.. metalorganic chemical vapor deposition (MOCVD) of GaAs-based compounds because they are typically low vapor pressure liquids which can be stored and handled more safely than the high-pressure gas cylinders used for AsH 3 . Despite their increased safety, the alkylarsines have not been widely used due to carbon incorporation problems and high background doping levels in the deposited films. To determine the impact of alternative growth chemistries on MOCVD processes we have investigated the thermochemistry controlling the decomposition of AsH 3 and its alkyl substitutes. Data are presented on the thermal stability of the Ascompounds, their resulting growth properties, and the composition and formation kinetics of the volatile products formed during thermal decomposition in an H2 ambient. The gas phase reactions controlling decomposition are identified. The implications of our results for CVD growth models and the potential of alkylarsine compounds for different CVD processes are discussed.
INTRODUCTION There is increasing interest in replacing the Group V hydrides, AsH3 and PH 3 , used in metalorganic chemical vapor deposition (MOCVD) with less hazardous reactants. The hydrides are highly toxic gases stored at high-pressure. Group V alkyl compounds have been investigated as hydride replacements because they are typically low vapor pressure liquids which can be stored and handled more safely than the high-pressure gas cylinders used for AsH 3 and PH 3 . In particular, the methyl, ethyl and butyl derivatives of AsH 3 (RnAsH3..,; R=Me, Et, Bu) have received the most attention [1-11]. In general, the lowest quality films are obtained when fully substituted alkylarsines (n=3) are used. Use of mono and di-substituted compounds yield films with improved surface morphology, lower carbon contamination and higher electron mobilities. This suggests that the underlying growth chemistry and reaction kinetics are greatly affected by the molecular configuration and degree of hydrogen atom substitution in the alkylarsine compound. In this paper we report mass spectrometric studies of the thermochemistry of arsine and the alkylarsines in hydrogen. Data are presented on the thermal stability of the As-compounds, their resulting growth properties, and the composition and formation kinetics of the volatile products formed during thermal decomposition in an H2 ambient. The reactions controlling decomposition of the precursor compounds are identified, and insights are obtained on the potential of alkylarsine reactants for different CVD processes.
EXPERIMENTAL A schematic of the gas handling and control equipment used in these experiments is shown in Fig. 1. The reactant gases can be switched either into the MOCVD growth chamber, or into a quartz flow-tube (0.5 cm diam, 100 cm long) f
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