For an ideal Si‐Ge solid solution deposited from an ideal vapor phase in a two phase solid solution‐vapor system, the equilibrium constant, KnormalSiSS/NnormalSiSS , for the global process has been derived in terms of the equilibrium constant for the deposition of a pure solid phase. KnormalSiS ,and the solid solution mole fraction of silicon species, NnormalSiSS , and has been shown to be KnormalSiSS=KnormalSiSS . Derivation of the relationship for the germanium species is symmetrical to that for silicon and given by KnormalGeSS=KnormalGeS/NnormalGeSS=KnormalGeS/false(1−NnormalSiSSfalse) . © 1999 The Electrochemical Society. All rights reserved.

Alternating cyclic (AC), selective area deposition of Si 1Ϫx Ge x thin and thick films, 0.1 to 3.5 m, via the reaction of SiCl 4 , GeCl 4 , and H 2 using Ar as a carrier gas, was carried out in a hot-wall, low pressure epitaxial reactor, using oxide masked silicon wafers. The AC process is based on the existence of an embedded disproportionation reaction within the overall deposition chemistry, which provides an effective mechanism for preventing the formation of nuclei in the areas where deposition is not desired. This disproportionation reaction is made dominant cyclically, by pulsing the hydrogen on and off periodically, in order to eliminate incipient nucleation. Experiments were carried out over a large portion of the available parameter space, as determined by extensive thermodynamic analyses, using a reference non-AC process as a control, and comparing the results with different AC frequencies. The [GeCl 4 /(SiCl 4 ϩ GeCl 4 )] mole fractions used were 0.0012, 0.0025, 0.005, 0.01, 0.02, 0.03, and 0.05, the temperature was varied from 700 to 950ЊC, and the Ar/H 2 ratio varied from 1 to 9. The range of alloy composition deposited was from 0 to 30 mol %, Ge. Total gas flow rate was varied from 2 standard liters per min (slpm) to 20 slpm to modulate gas hydrodynamics. To varying degrees, various experimental conditions influenced the tendency for formation of spurious nuclei on the oxide surface. However, under all conditions, the AC technique was capable of preventing the formation of spurious nuclei on the oxide, guaranteeing essentially 100% selectivity control, for both nonimplanted wafers and ion-implanted wafers.

The last few years have seen considerable advancement in SiGe technology due to the potential for achieving device speeds greater than those obtained with silicon only devices. 1-3 Si 1Ϫx Ge x heterostructures have found applications in fabricating heterojunction bipolar transistors (HBTs), 4-17 and in channel engineering, 18 as gate material, 19 and in contact resistance applications 20 in insulated gate field effect transistors (IGFETs). In order to fabricate such devices, excellent control over the morphology and composition of epitaxial Si 1Ϫx Ge x films is mandatory. For Si 1Ϫx Ge x films to be useful, they should be microscopically smooth and exhibit good crystalline quality.Si and Ge are completely miscible over the entire composition range. 5 Hence, they can be intermixed to form a stable alloy, Si 1Ϫx Ge x , where x represents the mole fraction of Ge in the alloy. However, the lattice constant of Si is about 4.2% smaller than that of Ge, leading to a number of practical difficulties in deposition of SiGe alloys for use in semiconductor applications. 21 In order to retain crystal perfection at low Ge compositions, e.g., less than 30 mol %, the Si 1Ϫx Ge x films need to adopt the smaller lattice constant of the host material without relaxing. This accommodation, known as strained layer epitaxy, induces compressive strain in the overlying film. Strained layer epitaxial films are stable only under a narrow range of conditions, dependent on the film's effective strain, which increases with increasing Ge composition and film thickness, and also depends on the temperature of subsequent treatment. Films with a high Ge content must be deposited at low temperatures to prevent relaxation, and they must be very thin if they are to be stable. 22,23 Band structure, optical properties, and the carrier mobility are determined by the homogeneous strain in the lattice structure. The homogeneous strain is, therefore, a key factor in determining the usefulness of the layers. The strain can relax by forming crystalline defects and/or three-dimensional growth, which degrade the electrical characteristics.The film thickness, t m , at which transition from smooth to rough morphology takes place, depends on the mole fraction of Ge in the Si 1Ϫx Ge x films and the temperature of deposition. The choice of temperature for deposition of Si 1Ϫx Ge x films requires the balancing of two competing temperature requirements. The atoms should have sufficient mobility to achieve good quality epitaxy. The mobility of atoms increases with increase in temperature. However, the transition from smooth to rough surface morphology, which tends to degrade morphological quality and which is needed for current device applications, is enhanced at a given film thickness at higher growth temperatures.In this paper, we investigate the effect of processing conditions such as deposition temperature, input gas phase composition, flow rates, and deposition time, on the resulting Si 1Ϫx Ge x film composition, morphology, and crystalline perfection, using the ...

As a starting point, for a system of minimum chemical complexity, the analysis of the Si-Ge-Cl-H system 1 is a good introduction for setting up an experimental alternating cyclic (A.C.) process. However, in the experimental implementation of such a system, it may be somewhat difficult to reestablish flow equilibrium every time the hydrogen flow is terminated abruptly and then restarted, particularly if on-off cycles are very short. Experimentally, it would be advantageous to have a continuous flow of an inert carrier gas present, such as argon, to act as a flow rate buffer to the abrupt hydrogen flow cycling and to minimize back diffusion. 2 In the present paper we discuss the effect of including an inert gas such as argon on the behavior of the Si-Ge-Cl-H system. This paper describes thermodynamic analysis of the Si-Ge-Cl-H-Ar system and employs a first principles analysis as an integrity check. The approach is identical to that employed for the Si-Ge-Cl-H system described in Ref 1. In addition, the several potential advantages in using an inert carrier gas such as argon are discussed, and this was the system employed for the experimental studies described recently. 3,4 The Si-Ge-Cl-H-Ar System The Si-Ge-Cl-H-Ar system contains five chemical components (Si, Ge, Cl, H, Ar) present in two phases (vapor and solid). From the Gibbs' phase rule, the system possesses five degrees of freedom. The five independent variables can be chosen as total system pressure, p t , three different hypothetical component partial pressure ratios, e.g.,