Low-resistance bandgap-engineered W/Si/sub 1-x/Ge/sub x//Si contacts

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 ...

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confidence: 99%

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

Soman

Reisman

Temple

et al. 2000

“…[4][5][6][7][8] Si-Ge heterojunction bipolar transistors are beginning to commercially compete with GaAs heterojunction bipolar transistors. 1,9 Si-Ge is also finding applications in channel engineering, 5 as gate material, 6 and in contact resistance applications 10 in insulated gate field effect transistors (IGFETs). Selective epitaxial deposition (SED) of Si 1Ϫx Ge x offers potential for use in fabricating these novel devices as well as in reducing the number of processing steps.…”

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confidence: 99%

“…Various CVD techniques such as ultrahigh vacuum CVD, low pressure CVD, rapid thermal CVD, and atmospheric pressure CVD have been employed for deposition of Si 1Ϫx Ge x thin films. 10,[13][14][15][16][17][18][19][20][21] Although varying degrees of success have been reported, most selective deposition processes rely on natural selectivity, i.e., incubation time, or the use of HCl or Cl 2 in the process to etch nuclei (see, for example, Ref. 22).…”

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confidence: 99%

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

Soman

Reisman

Temple

et al. 2000

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 interest in the growth of Si-Ge alloy epitaxial layers because of their potential for fabricating novel devices. [1][2][3][4][5][6] Silicon and germanium are completely miscible over the entire composition range. 1 The variable bandgap of the alloys in Si 1Ϫx Ge x /Si heterostructures holds promise for the formation of high speed devices.…”

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confidence: 99%

“…1 The variable bandgap of the alloys in Si 1Ϫx Ge x /Si heterostructures holds promise for the formation of high speed devices. 2 It is anticipated that the extensive amount of development performed for silicon devices can be applied to fabricate the heterostructures for heterojunction bipolar transistors, [1][2][3] modulation doped field effect transistors, 4 low resistance contacts, 5 and photodiodes, 6 to name several.…”

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confidence: 99%

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

Soman¹,

Reisman²,

Temple³

2000

To investigate selective area chemical vapor deposition of Si 1Ϫx Ge x thin films by the alternating cyclic (A.C.) process, a thermodynamic analysis has been performed over extensive temperature, pressure, input gas ratio, and deposited solid composition ranges. In the A.C. approach Si 1Ϫx Ge x thin film deposition via the hydrogen reduction of SiCl 4 and GeCl 4 is followed cyclically by etching of spurious nuclei from mask regions via an embedded disproportionation reaction. The embedded disproportionation reaction between SiCl 4 , GeCl 4 , and the Si 1Ϫx Ge x nuclei is made dominant when the hydrogen flow is interrupted cyclically. The thermodynamic calculations have been carried out via the computer program, SOLGASMIX, which is based on the minimization of the system's Gibbs free energy, and also using a first principles approach as an integrity check. These calculations have indicated that selective area deposition of Si 1Ϫx Ge x thin films by the A.C. method is feasible. The analysis has also defined the parameter space in which to conduct the selective area deposition using the A.C. process.