High Vacuum Chemical Vapor Deposition Research Articles

Epitaxial Silicon Growth by Load-Lock Low Pressure Chemical Vapor Deposition System for Elevated Source/Drain Formation

A silicon epitaxial layer on the active region of a Si substrate was selectively grown under a low temperature condition of 620°C with a low pressure chemical vapor deposition (LPCVD) employing SiH4 as a precursor, without high-temperature H2 annealing and ultra high vacuum chemical vapor deposition (UHV-CVD). This method was achieved by the use of a N2-purged wafer cassette and a load-lock chamber that was directly connected to the CVD chamber. A cross-sectional transmission electron microscopy (TEM) micrograph of the interface between the CVD-deposited film and the Si substrate revealed that the Si film was grown homoepitaxially, however nanometer-scaled silicon oxide islands were sparsely formed at the interface. Epitaxial film growth seemed to be achieved by lateral grain growth over oxide islands during film deposition. Polycrystalline Si was grown on the silicon oxide under the same deposition condition, and a Si epitaxial growth layer was formed on the active region selectively by wet chemical etching using HNO3, CH3COOH and HF-based solution. Since this system has higher throughput than conventional UHV-CVD or MBE systems, it is expected to become important for the development of future ULSI devices with a sub-50 nm-scale metal–oxide–semiconductor field effect transistor (MOSFET).

Study on the initial deposition of ZrO2 on hydrogen terminated silicon and native silicon oxide surfaces by high vacuum chemical vapor deposition

We used in situ spectroscopic ellipsometry to study the deposition process of ZrO2 from zirconium t-butoxide (ZTB) on both native silicon oxide and H-terminated silicon (H–Si) surfaces. The ZrO2 films deposited on native silicon oxide surfaces have higher refractive indexes and film densities. The properties of films deposited on different surfaces are affected by different nucleation and coalescence processes during the initial stage deposition. Due to the lack of reactive surface hydroxyl groups and high surface diffusivity of ZTB molecules, a three-dimensional nucleation process is predominant on H–Si surfaces. The resulting films have high surface roughness, and are inappropriate for gate dielectric applications. The highly reactive hydroxyl groups on native silicon oxide surface react with ZTB molecules to form a high-density film. At temperatures higher than the decomposition temperature of the t-butoxy group, further nucleation of ZrO2 is suppressed. The resulting films have high film density and low topology development, and are more suitable for gate dielectric applications. Additionally, we discuss the factors that influence the deposition process and film properties, and show that the deposition temperature can be used to control film density.

Spectroscopic ellipsometry characterization of ZrO2 films on Si(100) deposited by high-vacuum-metalorganic chemical vapor deposition

The integration of high-k dielectric materials into semiconductor devices requires nondestructive, fast, and accurate characterization methods. Spectroscopic ellipsometry (SE) is an outstanding candidate for this purpose. A multisample variable-angle SE method was used to characterize ZrO2 samples deposited on Si(100) by high-vacuum chemical vapor deposition. Proper modeling of the optical properties of the interfacial layer is found to be the key to accurate characterization of ZrO2 films. Based on a stacking model consisting of an effective medium approximation surface-roughness layer, a Tauc–Lorentz (TL) layer to represent the ZrO2 layer, and a second TL layer to represent the interfacial layer, we accurately extract both thickness and optical constants of each layer. The extracted surface-roughness and thickness values were confirmed by atomic force microscopy and transmission electron microscopy results. The optical constants of the interfacial layer suggest that the interfacial layer is composed of nonstoichiometric zirconium silicate.

Boron mediation on the growth of Ge quantum dots on Si (1 0 0) by ultra high vacuum chemical vapor deposition system

Self-assembled Ge quantum dots (QDs) with boron mediation are grown on Si (1 0 0) by an industrial hot wall ultra-high-vacuum chemical vapor deposition (UHV/CVD) system with different growth temperatures and dopant gas flow rates. Diborane (B 2H 6) gas is applied as a surfactant on the Si (1 0 0) prior to the growth of Ge QDs. Small dome and pyramid shaped Ge QDs are observed after boron treatment as compared to the hut shaped Ge cluster without boron pre-treatment at 525 and 550 °C. The Ge QDs have a typical base width and height of about 30 and 6 nm, respectively, and the density is about 2.5×10 10 cm −2 for the growth temperature of 525 °C. Through weakening the SiH bond during the epitaxy growth and changing the stress field on the surface of the Si (1 0 0) buffer, boron mediation can modify the growth mode of Ge QDs. When the growth temperature is low (525–550 °C), the former factor is dominate, as the growth temperature is raised (600 °C), the latter parameter may play an important role on the formation of Ge QDs. Optical transition from Ge QDs is demonstrated from photoluminescence (PL) spectra. Furthermore, multifold Ge/Si layers are also carried out to enhance the PL intensity with first Ge layer treated by B 2H 6 and avoid the generation of threading dislocations.

Growth of cubic SiC thin films on Si(001) by high vacuum chemical vapor deposition using 1,3-disilabutane and an investigation of the effect of deposition pressure

We have deposited cubic SiC thin films on Si(001) substrates by high vacuum chemical vapor deposition (CVD) using a single molecular precursor of 1,3-disilabutane (DSB) at various temperatures (600–1000 °C) and pressures in the range of 1×10−6–1×10−5 Torr. A single-crystalline cubic SiC thin film with stoichiometric composition can be obtained under deposition conditions of 900–1000 °C and 4.0–6.5×10−6 Torr. However, on increasing the deposition pressure and decreasing the growth temperature to 1×10−5 Torr and 600 °C, respectively, the film became polycrystalline. The effect of deposition pressure on the film growth rate and crystallinity was also studied. Based on the experimental results from x-ray diffraction, x-ray photoelectron spectroscopy, scanning electron microscopy (SEM), transmission electron microscopy, and transmission electron diffraction, the best SiC film was grown at 900 °C and 6.5×10−6 Torr of DSB at a maximum growth rate of 0.1 μm/h. The thicknesses of as-grown films were determined by cross-sectional SEM and Rutherford backscattering spectroscopy. Two different activation energies for cubic SiC film formation were obtained from Arrhenius plots. The deposition temperatures and pressures used in this study are lower by as much as 200 °C and a factor of 102, respectively, compared with those grown by conventional CVD methods.

Thermal desorption effects in chemical vapor deposition of silicon nanoparticles

Silicon nanoparticles are grown via ultra high vacuum chemical vapor deposition (UHV-CVD) on SiO 2 and Si 3N 4 covered Si(1 0 0) substrates using disilane. Temperature programmed desorption spectra demonstrate the presence of H 2 and SiO desorption features at 770 and 900 K, respectively, which are in the 750–1000 K temperature range that is typical for nanoparticle growth via CVD. The lower temperature limit (∼750 K) for nanoparticle growth is related to hydrogen desorption from the nanoparticle surface just as in epitaxial growth. SiO desorption is shown to hinder silicon adatom accumulation and nanoparticle nucleation on SiO 2 at temperatures as low as 875 K, giving an upper temperature limit for dense nanoparticle growth. Optimum conditions for nanoparticle growth on SiO 2 are found within this narrow temperature window (750–875 K), and densities up to 8×10 11 cm −2 are obtained within. Depletion of surface silicon is not observed on Si 3N 4 substrates, and this allows high-density nanoparticles to be grown at much higher temperatures.

Effect of carbon on lattice strain and hole mobility in Si1-xGex alloys

Pseudomorphic Si1-x Ge x and partially strain compensated $${\text{Si}}_{1 - x - y} {\text{Ge}}_x {\text{C}}_y $$ layers with different Ge and C fractions have been grown at 500 °C by ultra high vacuum chemical vapor deposition on Si (100) substrates. The degree of strain compensation of the layers has been investigated by high resolution X-ray diffraction and simple application of the linear elasticity theory. The surface morphology of the layers has been characterized by atomic force microscopy. The dependence of Si–Si Raman mode vibrations on strain and composition of binary and ternary alloys have been explained with experimental and theoretically calculated results. The Hall hole mobility is found to increase with decreasing compressive strain or effective Ge content in the layer throughout the temperature range of 120–300 K.

Self-assembled Ge quantum dots on SiC substrates grown by UHV-CVD

AbstractWe report our first results using a ultra high vacuum chemical vapor deposition (UHV-CVD) system to form Ge quantum dots on off-axis SiC substrates. Pure SiH4 and hydrogen-diluted GeH4 were used as gas precursors. The SiC substrates were chemically cleaned using the modified RCA process and the SiO2 layer was removed in-situ under a low SiH4 flow rate at a temperature between 1030°C and 1080°C. The Ge quantum dots were grown at a temperature of 750°C. In-situ reflection high-energy electron diffraction (RHEED) was used to monitor the surface cleaning and the Ge quantum dot growth. Ex-situ scanning electron microscope and atomic force microscopy were used to confirm the presence of Ge dots. The observed dots are smaller (350 Å width and 100 Å height) than similar Ge dots grown on Si.

Reduction of source/drain series resistance and its impact on device performance for PMOS transistors with raised Si/sub 1-x/Gex source/drain

P-channel MOS transistors with raised Si/sub 1-x/Ge/sub x/ and Si source/drain (S/D) structure selectively grown by ultra high vacuum chemical vapor deposition (UHVCVD) were fabricated for the first time. The impact of Si/sub 1-x/Ge/sub x/ and Si epitaxial S/D layers on S/D series resistance and drain current of p-channel transistors were studied. Our results show that devices with the raised Si/sub 1-x/Ge/sub x/ S/D layer display only half the value of the specific contact resistivity and S/D series resistance (R/sub SD/), compared with those with a Si raised S/D layer. The improvement is even more dramatic when comparing with conventional devices without any raised S/D layer, i.e., R/sub SD/ of devices with Si/sub 1-x/Ge/sub x/ raised S/D is only about one fourth that of conventional devices. Moreover, the raised SiGe S/D structure produces a 29% improvement in transconductance (g/sub m/) at an effective channel length of 0.16 /spl mu/m. These performance improvements, together with several inherent advantages, such as self-aligned selective epitaxial growth (SEG) and the resultant T-shaped gate structure, make the new device with raised Si/sub 1-x/Ge/sub x/ S/D structure very attractive for future sub-0.1 /spl mu/m p-channel MOS transistors.

Investigation of Si/SiGe heterostructure material using non-destructive optical techniques

Characterisation of UHV-CVD (ultra high vacuum chemical vapour deposition) grown Si/SiGe heterostructure field-effect transistor (HFET) material with a buried, strained silicon layer has been carried out using non-destructive optical techniques. The effect of thermal budget on the heterostructure was investigated by annealing samples at temperatures up to 900°C for 5 min and carrying out analysis using Raman back-scattering spectroscopy. An investigation of silicon cap loss due to native oxide removal etches was carried out using phase-modulated variable angle spectroscopic ellipsometry (VASE) and correlated with Rutherford back-scattering spectroscopy (RBS) measurements.

Characterization of SiGe base layer in Si/SiGe heterojunction bipolar transistor layer structure

Si/SiGe heterojunction bipolar transistor (HBT) layer structures, grown by ultra high vacuum chemical vapor deposition (UHVCVD), were investigated by high resolution X-ray diffraction (HRXRD) and cross-sectional transmission electron microscopy (XTEM). The SiGe base layer thickness in the Si/SiGe HBT structure is determined by HRXRD and confirmed by XTEM. HRXRD indicates that the high quality SiGe base layer and abrupt interfaces between Si and SiGe were obtained. The Ge content in the SiGe base layer, determined by HRXRD, is 16% for sample #a and #b and 10% for sample #c. XTEM shows no defects in both the strained SiGe base layer and the HBT structure. Mesa-type Si/SiGe HBT was fabricated and ideal base current over several orders was obtained.

Rugged Surface Polycrystalline Silicon Film Formed by Rapid Thermal Chemical Vapor Deposition for Dynamic Random Access Memory Stacked Capacitor Aplication

Polycrystalline silicon films with a rugged surface (rugged poly-Si), deposited by a single-wafer rapid thermal chemical vapor deposition (RTCVD) system suitable for 12 inch wafer fabrication, are studied and the films have been successfully applied to bottom storage electrodes for stacked capacitors in dynamic random access memory cells. Our data show that the rugged poly-Si is actually formed by the nucleation generation on the amorphous silicon surface and subsequent crystalline growth during the annealing step following deposition. We also determined that a wide temperature window exists for the formation of rugged poly-Si (i.e., ±15°C) using RTCVD, which is wider than that using low pressure chemical vapor deposition (LPCVD) (i.e., ±3°C) and ultra high vacuum chemical vapor deposition (UHVCVD) (i.e., ±10°C). Stacked capacitors fabricated using rugged poly-Si and thin silicon oxide/silicon nitride dielectric film show that for a rugged poly-Si storage electrode with a 60 nm top-layer and 645°C annealing, an effective surface area of approximately 2.9 times that of a conventional poly-Si film electrode is obtained.

X-ray study of UHV-CVD filling of porous silicon by Ge

Using ultra high vacuum chemical vapour deposition (UHV-CVD), the pore network of porous silicon layers is filled with Ge. The evolution of the resulting structure, as a function of the Ge content, is investigated by X-ray diffraction. Information on the Ge crystallite size and orientation as well as on the porous layer strains is obtained from (0 0 4) rocking curve and reciprocal space mapping measurements. The observation of the (2̄ 2̄ 4) asymmetric reflection allows the determination of the relaxation state of the Ge/Si layer. The Ge growth inside the pores is epitaxial, giving a composite layer of good crystalline quality. After a review of the relaxation modes of the Ge deposition on Si substrates, we propose a model for the filling of porous silicon by Ge.

Neutron radiation tolerance of advanced UHV/CVD SiGe HBT BiCMOS technology

The effects of 1.0 MeV neutron irradiation on both SiGe heterojunction bipolar transistors (HBTs) and Si CMOS transistors from an advanced ultra high vacuum chemical vapour deposition (UHV/CVD) SiGe BiCMOS technology are examined for the first time over the temperature range of 300 K to 84 K. Results at 300 K indicate that this SiGe technology is robust with respect to neutron radiation. At fluences as high as 10/sup 15/ n/cm/sup 2/ (1.0 MeV equivalent) the devices exhibited a degradation of less than 30% in peak current gain. The SiGe HBTs maintain a current gain of 60 after 10/sup 15/ n/cm/sup 2/ at 84 K, compared to the Si BJT which degrades with cooling to a current gain of 20 at 84 K. The cutoff frequencies of both the Si and SiGe transistors are unaffected by neutron irradiation, and only a slight degradation in the maximum oscillation frequency of the transistors was observed.

Heteroepitaxial growth of 3C-SiC on Si(0 0 1) without carbonization

Epitaxial cubic SiC films were grown on Si(0 0 1) substrates without carbonization at temperatures of 900-1000°C by high-vacuum chemical vapor deposition using 1,3-disilabutane (H3SiCH2SiH2CH3). The films were characterized by in situ RHEED, TEM, XRD, SEM, RBS, AES and ERD analyses. The electron and X-ray diffraction results showed that the crystalline structure of the deposited films depends on the heating rate of the substrate from ∼ 100°C to the growth temperature. The films grown only with a temperature ramp slower than 1.5°C/s were found to be single-crystalline over this temperature range. RBS, AES and ERD analyses showed that our films are stoichiometric and homogeneous in depth and have low levels of impurities, especially hydrogen.

Effect of inner-shell excitation of disilane on the reaction yield of synchrotron-radiation excited high-vacuum chemical vapor deposition

The reaction yields of synchrotron-radiation excited high-vacuum chemical vapor deposition at the core-excitation and valence-excitation regions of disilane are obtained by measuring both the incident photon numbers of the synchrotron-radiation beams which pass through C and Al filters and the rates of Si deposition induced by these synchroton-radiation beams. It is confirmed that the reaction yield for the core-excitation energy region is about three times larger than the value for the valence-excitation region. It is also demonstrated that synchrotron-radiation excited high-vacuum chemical vapor deposition proceeds by the pure-photochemical reaction, not by the reaction induced by secondary electrons due to synchrotron-radiation irradiation on the substrate.

Structures on Si(100) 2 × 1 at the Initial Stages of Homoepitaxy by SiH 4 Decomposition

The initial stages of homoepitaxial island formation on Si(100)2×1 by SiH4 decomposition under ultra high vacuum chemical vapor deposition conditions are studied by scanning tunneling microscopy and kinetic model calculations. The concentrations of the intermediate species formed on the surface during SiH4 decomposition are calculated from the kinetic parameters of the dissociation cascade leading to Si film growth in the temperature regime of 500 to 800 K and for SiH4 pressures in the range of 2×10-7 to 2×10-5 mbar. Experimental results showing the surface topography after interaction with SiH4 at various surface temperatures and deposition rates are presented, and the observed surface structures are related to the different surface conditions, i.e., deposition flux and sample temperature, under which islands are formed.

Collective excitations of electron disks in laterally patterned Si/SiGe modulation-doped heterojunctions

Square lattices of isolated electron disks of diameters 0.2–2 μm were obtained by laterally patterning n-type modulation-doped Si/SiGe heterojunctions grown by ultra high vacuum chemical vapor deposition. The disk lattices were fabricated by electron-beam lithography and reactive ion etching. The collective excitations in the disks were studied by microwave magnetotransmission experiments. The resonance dispersion as well as the disk plasma frequencies are theoretically analysed assuming a nearly parabolic confining potential.

UHV-CVD heteroepitaxial growth of Si 1− xGe x alloys on Si(100) using silane and germane

In this paper, we investigate the growth rate and strain relaxation of Si 1− x Ge x layers grown on Si substrates by UHV-CVD. The Si 1− x Ge x growth rate is found to exhibit two different behaviors as a function of growth temperature. Above the temperature corresponding to hydrogen desorption ( T H), the SiGe growth rate first decreases with x, and finally becomes almost independent of x at higher values of x. Below T H, the SiGe growth rate first increases with x, then shows a maximum and finally becomes almost independent of x at higher values of x. Using in-situ reflection high-energy electron diffraction (RHEED), transmission electron microscopy and photoluminescence, we have clearly identified two distinct mechanisms for strain relaxation as a function of Ge content: at x=0.15 strain is relaxed by nucleation of misfit dislocations while the film surface remains smooth throughout growth and relaxation process. The introduction of dislocations is found to occur before lattice relaxation. At x=0.22, strain is first relaxed via formation of coherent islands before reaching the equilibrium critical thickness for dislocation nucleation. We also show that in-situ RHEED is a powerful technique to probe the evolution of film morphology in an ultra high vacuum chemical vapour deposition system. © 1997 Elsevier Science S.A. All rights reserved.

Surface morphology of homoepitaxial silicon thin films grown using energetic supersonic jets of disilane

The effect of different chemical mechanisms for adsorption, which depend on the incidence energy of disilane, on the film morphology is investigated by comparing deposition by high (∼2 eV) kinetic energy disilane jets, direct chemisorption; low (∼0.09 eV) kinetic energy disilane jets and ultra high vacuum chemical vapor deposition, trapping-mediated chemisorption. For substrate temperatures of 500–550 °C the mechanism for adsorption does not influence the film morphology as observed for films up to 3300 Å thick, which are comparable in smoothness to the starting substrate, as determined by atomic force microscopy.