Selective Area Chemical Vapor Deposition of Si[sub 1−x]Ge[sub x] Thin Film Alloys by the Alternating Cyclic Method: Experimental Data: II. Morphology and Composition as a Function of Deposition Parameters

Abstract

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 ...

Selective Area Chemical Vapor Deposition of Si[sub 1−x]Ge[sub x] Thin Film Alloys by the Alternating Cyclic Method: Experimental Data: I. Deposition Parameters

“…More detailed description of TEM studies is presented in the companion paper, Part II. 40 To verify absence of any interface contamination in deposition of Si-Ge alloy films, we have studied effects of Si buffer layers deposited sequentially with and prior to deposition of the alloy film. We found that the buffer layers had no effect on surface morphology of the deposited films, indicating absence of surface contamination at the Si substrate/epitaxial film interface.…”

“…Results obtained below 950ЊC are discussed in the companion paper, Part II. 40 The thickness of deposited Si 1Ϫx Ge x films was measured using a profilometer. Quantitative analysis of the film composition was performed using energy dispersive X-ray spectroscopy (EDS) coupled with an environmental scanning electron microscope (N-SEM) technique as developed earlier.…”

Selective Area Chemical Vapor Deposition of Si[sub 1−x]Ge[sub x] Thin Film Alloys by the Alternating Cyclic Method: A Thermodynamic Analysis. I. The System Si-Ge-Cl-H

“…Two recently published papers describing experimental work based on the present thermodynamic analysis support the conclusions arrived at herein. 12,13 The Alternating Cyclic (A.C.) Process for Selective Area Deposition of Si 1Ϫx Ge x The A.C. technique is based on the existence of an embedded disproportionation reaction within the framework of an overall hydrogen reduction process. 14,15 By simply pulsing the hydrogen on and off in the embedded disproportionation reaction process, at a predetermined frequency and at a predetermined on to off cycle ratio, the embedded disproportionation reaction can be suppressed or made dominant, causing deposition and etching to occur in a cyclic fash-ion, respectively.…”

Selective Area Chemical Vapor Deposition of Si[sub 1−x]Ge[sub x] Thin Film Alloys by the Alternating Cyclic Method: A Thermodynamic Analysis. II. The System Si-Ge-Cl-H-Ar

“…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.…”