LOW-ENERGY PLASMA ENHANCED CHEMICAL VAPOR DEPOSITION CARSTEN ROSENBLAD 1 , THOMAS GRAF 1 , ALEX DOMMANN 2 , HANS VON KANEL' 'Laboratorium ffir Festkbrperphysik, ETH Zurich, CH-8093 Zurich, Switzerland 2 Neu-Technikum Buchs, CH-9470 Buchs, Switzerland ABSTRACT We discuss a new method for plasma enhanced chemical vapor deposition, applied to the epitaxial growth of Si and of Si-Ge heterostructures. Growth rates up to 5 nm/s become possible at substrate temperatures below 6000 C, by utilizing very intense but low energy plasmas to crack the reactive gases, SiH 4 and GeH 4 , and to speed up the surface kinetics. The method is applied to the synthesis of step-graded Si-Ge buffer layers, exhibiting the well known cross-hatched surface morphology. INTRODUCTION Deposition techniques which can be used at comparatively low substrate temperatures are required in order to suppress, e.g., islanding of strained-layer semiconductor heterostructures and dopant segregation. The methods most commonly used in Si-Ge heteroepitaxy are ultrahigh-vacuum chemical vapor deposition (UHV-CVD) [1] and molecular beam epitaxy (MBE) [2]. While material of excellent quality can be produced by both, neither is well suited for production. Thus MBE is hampered by the frequent need to replenish the source materials for the electron beam evaporators, while in UHV-CVD the growth rates become exceedingly low at substrate temperatures below 6000 C. Plasma enhancement has been recognized long ago to be a possibility to overcome this shortcoming [3, 4]. Ion-induced damage is, however, often a serious problem, unless the energy of ions impinging on the growing film is carefully controlled [5]. In this paper we describe a new process for plasma-enhanced CVD, based on a low-voltage DC arc discharge. The process is called low-energy plasma enhanced chemical vapor deposition (LEPECVD), in order to emphasize the exceptionally low ion energies created in this kind of plasma. While ion energies are low, the plasma densities at the position of the substrate can be exceedingly large, leading to very efficient cracking of the reactive gases and to greatly enhanced surface kinetics. In this way, exceptionally high growth rates of several nm/s become possible at substrate temperatures below 600' C. We have applied LEPECVD to the synthesis of homoepitaxial Si films and of step-graded Si- Ge buffer layers used as virtual substrates for the modulation doped field effect transistor (MODFET). EXPERIMENTAL The plasma source used for LEPECVD has been used previously for hydrogen plasma cleaning of Si substrates [6]. The essence of it is a low voltage arc discharge sustained by a hot Ta filament. The plasma source is connected to the UHV deposition chamber through an orifice '-. 1 cm in diameter. Typical voltages between the filament and the grounded chamber walls are in the range of 20-30 V, leading to arc currents of up to 70 A. This, together with an externally applied substrate bias [7], limits the energy of ions impinging on the substrate to typically 10 eV or even less. In order to gain better control over the plasma distribution, the deposition chamber is equipped with an auxiliary grounded 301 Mat. Res. Soc. Symp. Proc. Vol. 533 01998 Materials Research Society