Mahesh K. Sanganeria

Growth Kinetics, Silicon Nucleation on Silicon Dioxide, and Selective Epitaxy Using Disilane and Hydrogen in an Ultrahigh Vacuum Rapid Thermal Chemical Vapor Deposition Reactor

Silicon nucleation on silicon dioxide and selective silicon epitaxial growth (SEG) were studied in an ultrahigh vaccuum rapid thermal chemical vapor deposition (UHV-RTCVD) reactor using 10% Si 2 H 6 diluted in H 2 . Silicon was deposited on SiO 2 patterned Si(100) substrates over a pressure range of 10-100 mTorr and a temperature range of 650 and 850 o C. Under these conditions, the growth rate ranged from 50 to 330 nm/minute, demonstrating compatibility with single wafer manufacturing throughput requirement. A pressure dependence in the activation energy in the surface reaction limited regime was observed and attributed to a variation in the steady-state hydrogen coverage on the growing surface

Rapid thermal chemical vapor deposition of in-situ boron doped polycrystalline Si x Ge 1- x

In-situ doped polycrystalline SixGe1-x(x = 0.7) alloys were deposited by rapid thermal chemical vapor deposition (RTCVD) using the reactive gases SiH2Cl2, GeH4 and B2H6 in a H2 carrier gas. The depositions were performed at a total pressure of 4.0 Torr and at temperatures 600° C, 650° C and 700° C and different B2H6 flow rates. The conditions were chosen to achieve high doping levels in the deposited films. Our results indicate negligible effect of B2H6 flow on the deposition rate. The depositions follow an Arrhenius type behavior with an activation energy of 25 kcal/mole. Boron incorporation in the films was found to follow a simple kinetic model with higher boron levels at lower deposition rates and higher B2H6 flow rates. As-deposited resistivities as low as 2 mΩ-cm were obtained. Rapid thermal annealing (RTA) in the temperature range 800-1000° C was found to reduce the resistivity only marginally due to the high levels of boron activation achieved during the deposition process. The results indicate that polycrystalline SixGe1-x films can be deposited by RTCVD with resistivities comparable to those reported for in-situ doped polysilicon.

Low temperature silicon epitaxy in an ultrahigh vacuum rapid thermal chemical vapor deposition reactor using disilane

Epitaxial silicon films have been deposited by a new technique which combines an ultrahigh vacuum (UHV) environment with rapid thermal chemical vapor deposition (RTCVD). The technique is referred to as UHV/RTCVD. Using Si2H6, B2H6, and H2 as process gases, low temperature (T≤800 °C) and high throughput (growth rate ≳0.25 μm/min) processing have been achieved in the 90 mTorr (1 Pa=133.32 Torr) total pressure regime. Epitaxial growth was achieved on hydrogen passivated silicon surfaces without using a high temperature in situ clean. Effect of the growth temperature on the generation lifetime of the films grown on 4–11 Ω cm (100) silicon substrates was studied at three different temperatures of 700, 750, and 800 °C using the Zerbst technique. The epitaxial films were in situ doped with boron to a doping level of 1–2×1016 cm−3. Generation lifetimes, as high as 400 μs, were measured with no strong dependence on the growth temperature. Chemical purity of the films was studied using secondary ion mass spectrosco...

Ultrahigh Vacuum Rapid Thermal Chemical Vapor Deposition of Epitaxial Silicon onto (100) Silicon I . The Influence of Prebake on (Epitaxy/Substrate) Interfacial Oxygen and Carbon Levels

This investigation is concerned with the influence of a vacuum prebake on oxygen and carbon levels at epitaxial silicon/silicon (100) interfaces. The epitaxial layers are deposited in an ultrahigh vacuum, rapid thermal reactor using chemical vapor deposition techniques. Secondary ion mass spectroscopy (SIMS) is used to evaluate carbon and oxygen levels at the epitaxy/substrate interface. We show that a vacuum prebake can be effectively used following a standard ex situ clean that consists of an RCA clean, a dilute (5%) HF dip, and a rinse in deionized water. The results show that if epitaxial deposition is initiated by introducing the reactive gases into the chamber at the prebake temperature, oxygen and carbon levels below the sensitivity limits of secondary ion mass spectroscopy are obtained at the epitaxy/substrate interface. This result can be reproducibly achieved with a low thermal budget prebake of 750°C/15 s even after a relatively long rinse (∼300 s) in deionized water. We propose that the mechanism responsible for cleaning is thermal desorption of oxygen and hydrocarbons from the (100) surface of silicon. We show that the surface obtained with this ex situ clean is very stable and, hence, the wafer can be left in a clean ultrahigh vacuum environment for many hours without detectable changes in the oxygen and carbon levels. On the other hand, results indicate that when the prebake is terminated by cooling the wafer to the ambient temperature of the reactor, carbon is readsorbed on the silicon surface at a peak concentration of 3 to 6 x 10 18 cm -3 . We also show that when a small amount of hydrogen is introduced into the reactor during the prebake, a higher thermal budget is required to remove oxygen from the surface. This observation is attributed to a higher H 2 O background associated with the presence of hydrogen. It is concluded that vacuum prebake is an attractive surface preparation technique which effectively reduces oxygen and carbon levels on a silicon (100) surface below the SIMS sensitivity limits.

A uniformity degradation mechanism in rapid thermal chemical vapor deposition

In this letter, a new physical mechanism that can significantly degrade the thickness uniformity in rapid thermal chemical vapor deposition (RTCVD) has been identified and experimentally verified using polycrystalline silicon (polysilicon) deposition on silicon dioxide. The mechanism is initiated by small temperature variations across the wafer typically caused by edge cooling or large area patterns. The amount of light absorbed in a silicon wafer is determined by the wafer absorptivity weighted by the emission spectrum of the heat lamp. The absorptivity is a strong function of the thickness and optical properties of the layers on the wafer surface. Consequently, during RTCVD, once a nonuniform deposition pattern is established, the absorptivity and hence, the temperature uniformity become strongly dependent upon the thickness uniformity. This causes the nonuniformity to increase with process time and the thickness of the deposited layer.

Low thermal budget in situ removal of oxygen and carbon on silicon for silicon epitaxy in an ultrahigh vacuum rapid thermal chemical vapor deposition reactor

In this letter, we present experimental evidence on desorption of O and C from a Si surface resulting in impurity levels below the detection levels of secondary ion mass spectroscopy. We then propose a surface preperation method for silicon epitaxy that consists of an ex situ clean and an in situ low thermal budget prebake in an ultrahigh vacuum rapid thermal chemical vapor deposition (UHV‐RTCVD) reactor. The ex situ clean consists of a standard RCA clean followed by a dilute HF dip and rinse in de‐ionized water. The in situ clean is either carried out in vacuum or in a low partial pressure of 10% Si2H6 in H2. The experiments were conducted in an UHV‐RTCVD reactor equipped with oil‐free vacuum pumps. We propose that the responsible mechanism is desorption of oxygen and hydrocarbons from the Si surface due to the low partial pressures of these contaminants in the growth chamber. If Si2H6 is used during the prebake, a sufficiently low growth rate is required in order to provide sufficient time for desorptio...

On the Mechanism of Boron Incorporation during Silicon Epitaxy by Means of Chemical Vapor Deposition

A careful reexamination of experimental results on in situ boron-doping during silicon epitaxy which have been previously published permits the authors to discuss how boron adsorption rate, desorption, and incorporation rate are dependent on silicon growth rate. It is shown for the first time that boron incorporation covers the whole range from equilibrium-limited to kinetically controlled incorporation when certain deposition conditions are met. in the transition region boron incorporation is affected by the reduction of boron adsorption not only due to the consumption of adsorbed boron species by the doping process but also by the increasing hindrance of boron adsorption due to the increase in the film growth rate. At other deposition conditions the known adsorption-desorption model of silicon doping describes boron incorporation completely.

A Novel Implantation Free Raised Source/Drain Mosfet Process Using Selective Rapid Thermal Chemical Vapor Deposition Of In-Situ Boron Doped Si x Ge 1-x

In this paper, we report electrical characterization of raised source/drain MOS transistors fabricated using selectively deposited, in-situ boron doped Si x Ge 1-x as a solid diffusion source to form the source/drain junctions. The alloy can be deposited with an enhanced selectivity at temperatures as low as 600°C resulting in an abrupt doping profile at the Si x Ge 1-x /Si interface. After deposition, junctions are formed by diffusion of boron from the deposited layer into the silicon substrate. The selectively deposited alloy can serve as a sacrificial layer for self-aligned silicide formation elimintaing the problem of silicon consumption in the substrate. In this work, selective depositions were performed in a typical cold-walled, lamp heated rapid thermal chemical vapor deposition (RTCVD) system at ∼ 610 °C using SiH 2 C1 2 , GeH 4 and B 2 H 6 as the reactive gases. Using this process, MOS transistors with effective channel lengths down to 0.45 gtm were successfully fabricated.

Low thermal budget in situ cleaning and passivation for silicon epitaxy in a multichamber rapid thermal processing cluster tool

Abstract In this Letter, we report our results on surface preparation, involving in situ cleaning and passivation for low-temperature Si epitaxy in a multichamber cluster tool. The experiments were carried out in a three-chamber reactor which mimics a cluster tool. The results indicate that residual O on the dilute HF-treated Si surface (ex situ cleaned) can be reduced below the detection limit of secondary ion mass spectroscopy (SIMS) by in situ baking at 750°C for 15 s in an ultra-high vacuum environment or in H2 (pressure = 240 mTorr). We show that the extremely reactive Si surface can be passivated against recontamination by exposing it to a low-pressure Si2H6 environment at the ambient temperature immediately following the in situ clean. When the unpassivated samples are exposed to an air pressure of 10−6 Torr in the load-lock, O adsorbs on the surface up to 50% of a monolayer within 10 min. Under the same conditions, with passivation, the oxygen levels remain below the detection level of SIMS. Surface passivation will be extremely useful in applications that require wafer transfer between chambers such as in multichamber cluster tools.

Selective deposition of polycrystalline SixGe1-x by rapid thermal processing

Low pressure chemical vapor deposition (LPCVD) of polycrystalline SixGei. . x alloys in a cold-wall lamp heated rapid thermal processor was studied. SiGei. . alloys were deposited using the reactive gases GeHz and SiH2C12 in a hydrogen carrier gas. The depositions were performed at a total pressure of 2. 5Ton and at temperatures between 500C and 800C using GeH : SiH2C12 ratios ranging from 0. 025 to 1. 00. An enhancement in the deposition rate due to the addition of GeH was observed in agreement with earlier reports. The activation energy for deposition in the surface reaction limited regime varied from 20-30 Kcal/mole with the gas flow ratios used in this study. Results showed that SiGei. . alloys could be deposited selectively on silicon with no nucleation on Si02. Selective depositions were obtained when the GeH:SiH2Cl2 gas flow ratio was greater than 0. 2 regardless of the deposition temperature corresponding to a Ge content of 20 or higher in the films as determined by Auger Electron Spectroscopy (AES). Enhancement of the selectivity was attributed to the formation of highly volatile GeO. It was also shown that selectively deposited alloys could be used as diffusion sources to form very shallow ( 1000 A) pLn junctions in silicon by ion-implantation and rapid thermal annealing. 1.