A Comparison of CH 4 :H 2 and C 2 H 6 :H 2 Morie of GaAs
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A COMPARISON OF CH4 :H 2 AND C2 H6 :H2 MORIE OF GaAs V. J. Law, G. A. C. Jones, M. Tewordt, and H. Royal*. Cavendish Laboratory, Madingley Rd, Cambridge, CB3 OHE, *Plasma Technology, Yatton, Bristol, BS19 4AP, U.K.
U.K.
ABSTRACT A comparative study is made of CH 4 :H 2 and CH3 -CH 3 :H 2 metal-organic reactive ion etching of molecular beam epitaxially grown GaAs. The etch rates are measured to be proportional to both CH 4 and CH 3 -CH 3 concentrations, with empirically determined order of reactions at 1.1 W.cm- 2 of, 0.57 ± 0.1 and 0.32 ± 0,01. Approximately twice the number of CH4 molecules are required to produce the equivalent etch rate as CH3 -CH 3 molecules. The measured apparent activation energies are low, Ea • 6 meV, and GaAs area loading effects are the same. These results indicate that methyl radicals are predominately responsible for the reaction. INTRODUCTION The technological development of hydrocarbon based plasmas has undergone a dramatic change in the last decade; they are now used in the production of amorphous and diamond-like films, the repair of lithographic masks, and etching of III-V semiconductor materials. In this paper, we focus on the latter, in particular the metal-oganic reactive ion etching (MORIE) of Gallium Arsenide (GaAs). Dilute mixtures of methane (CH4 ) - ethane (CH3 -CH 3 ) with hydrogen (H2 ) in non-equilibrium rf plasmas, have been shown to etch all the III-V semiconductor materials with a high degree of anisotropy and smooth morphology [1-8). There are, however, a number of deleterious effects associated with the etching process: (i) near-surface In enrichment of InP based materials, due to the preferential etching of P [9), and (ii) hydrogen passivation of donors. These effects can be reduced by slow etching of In based materials, and post-etch thermal annealing [4,10,11]. It should be noted that an In rich near-surface can be desirable in the fabrication ohmic contacts. It has also been established that these gases can produce a significant degree of etch selectivity between the III-V materials, particularly AlxGal.As for different values of x (12,13). Furthermore, a review of published literature shows that the etch rates follow an unidirectional periodic trend with the Group IIIB metals (Al
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