Vacuum Rapid Thermal Chemical Vapor Research Articles

In Situ Phosphorus Doping during Silicon Epitaxy in an Ultrahigh Vacuum Rapid Thermal Chemical Vapor Deposition Reactor

Phosphorus incorporation during selective silicon epitaxy using the phosphine , disilane , and chlorine chemistry in a cold‐wall ultrahigh vacuum rapid thermal chemical vapor deposition reactor was investigated. We have studied the dependence of silicon growth rate and phosphorus incorporation on phosphine partial pressure and temperature in the range of to , and 650 to 800°C, respectively. Even at such low partial pressures, phosphorus concentration above was obtained due to the high sticking coefficient of phosphine. Phosphorus incorporation was found to be a strong function of temperature. Two possible incorporation mechanisms have been discussed in detail: surface electronic effects created by silicon becoming extrinsic at high phosphorus concentrations and high phosphorus surface coverage in the form of P‐P dimers. A reduction in silicon growth rate was observed due to phosphine. Doping concentration was found to be uniform in the films at low temperatures (650—750°C) accompanied with by phosphorus peaks at interfaces for growth temperatures above 800°C. A significant chamber memory effect was observed in the process which prohibits intrinsic silicon deposition following an in situ phosphorus‐doped layer. © 1999 The Electrochemical Society. All rights reserved.

Growth of Selective Silicon Epitaxy Using Disilane and Chlorine on Heavily Implanted Substrates: II. Role of Implanted Arsenic

In this report, we present results on the low thermal budget deposition of selective silicon epitaxy on heavily arsenic implanted substrates using and in an ultrahigh vacuum rapid thermal chemical vapor deposition reactor. The selectivity of silicon to as well as the silicon growth kinetics, epitaxial quality, and dopant incorporation for varying substrate implant dose conditions and varying levels of chlorine during processing were investigated. We demonstrate that an increase in the arsenic implant dose can reduce the silicon growth by means of an inherent incubation time for deposition occurring in a chlorinated ambient. The extent to which the silicon growth suppression occurs, however, can be lessened by specific changes in the system conditions, and therefore, growth reductions due to arsenic can be minimized. In addition to changes in the silicon growth kinetics, arsenic implanted substrates have demonstrated a tendency to degrade the surface morphology and enhance the density of defects within the deposited silicon epitaxial films. Furthermore, by depositing the silicon film immediately following implantation and prior to any high temperature anneal, movement of arsenic into the deposited silicon layers has been observed at growth temperatures as low as 800°C. Therefore, the incorporation of arsenic into the deposited epitaxial films has been found to be controllable such that abrupt profiles or intentional diffuse structures can be achieved by variation of the process sequence and the annealing conditions. © 1999 The Electrochemical Society. All rights reserved.

Growth of Selective Silicon Epitaxy Using Disilane and Chlorine on Heavily Implanted Substrates: I. Role of Implanted BF 2

In this report, we present results on the low thermal budget deposition of selective silicon epitaxy on heavily implanted substrates using and , in an ultrahigh vacuum rapid thermal chemical vapor deposition reactor. Si growth kinetics, selectivity to , dopant incorporation, and epitaxial quality have been investigated for varying implant dose conditions and varying levels of chlorine during processing. Contrary to published reports, no significant selectivity degradation mechanism has been observed for oxides implanted, and therefore, damaged by ions. Additionally, with heavily implanted boron substrates no reduction in silicon growth occurred despite the presence of a hydrophilic substrate surface just prior to epitaxial growth. Although the hydrophilic surface did not affect the silicon growth rate, the epitaxial defect density did increase with increasing implant dose and chlorine flow rate during processing. The nature of these defects has been studied using atomic force microscopy and transmission electron microscopy. The incorporation of boron into the deposited epitaxial films has been investigated and abrupt profiles or intentionally diffuse structures were achieved through variation of the process sequence and annealing conditions. © 1999 The Electrochemical Society. All rights reserved.

Effects of oxygen on selective silicon deposition using disilane

Using Si 2H 6 in an ultrahigh vacuum rapid thermal chemical vapor deposition reactor, we have investigated the role of high levels of oxygen (>5×10 −6 Torr) introduced during selective silicon deposition. The effects of oxygen have been investigated with regard to oxygen incorporation, selectivity with respect to thermal SiO 2, growth rate, and epitaxial quality. The addition of oxygen was found to enhance the inherent process selectivity of Si 2H 6 to SiO 2 while causing no reduction in the silicon growth rate or measurable oxygen incorporation into the growing film for oxygen pressures below 5×10 −5 Torr. Contrary to published reports, the silicon film was devoid of the pyramidal defects usually characteristic to highly oxygenated processes. The silicon surface morphology, however, exhibited increased roughness with increasing oxygen partial pressure. The surface roughness is believed to be a result of the high levels of oxygen adsorbed at the initial growth surface.

Optimization of Process Conditions for Selective Silicon Epitaxy Using Disilane, Hydrogen, and Chlorine

We have previously reported a process for low temperature selective silicon epitaxy using , and in an ultrahigh vacuum rapid thermal chemical vapor deposition reactor. Selective deposition implies that growth occurs on the Si surface but not on any of the surrounding insulator surfaces. Using this method and process chemistry, the level of Cl species required to maintain adequate selectivity has been greatly reduced in comparison to ‐based, conventional CVD approaches. In this report, we have extended upon the previous work and provide information regarding the selectivity of the silicon deposition process to variations in the growth conditions. We have investigated the selectivity of the process to variations in disilane flow/partial pressure, growth temperature, and system contamination. We demonstrate that increases in either the partial pressure or flow rate, the process temperature, or the source contamination levels can lead to selectivity degradation. In regard to the structural quality of the selective epitaxial layers, we have observed epitaxial defects that have appeared to be a strong function of two basic conditions: the contamination level of the process and the chlorine flow rate or chlorine partial pressure. Overall, the results in this study indicate several process conditions that can inhibit the quality of a selective silicon deposition process developed for single‐wafer manufacturing.

On the Role of Chlorine in Selective Silicon Epitaxy by Chemical Vapor Deposition

Si thermal etching studies have been performed using pure in an ultrahigh vacuum rapid thermal chemical vapor deposition reactor in the temperature range of 650–850°C and the flow rate range of 1–10 sccm which corresponds to a pressure range of 0.5–3.5 mTorr. The effects of temperature and flow were investigated with thermodynamic equilibrium calculations performed to determine possible reaction pathways. The effect of adding , up to 500 sccm, on Si etch rates at 800 and 850°C was also obtained experimentally. Thermodynamic equilibrium calculations were used to support the experimental results and determine the reaction by‐products. It is proposed that equilibrium partial pressure can be used as a means to compare the etching ability, thus the selectivity, of different selective Si processes. The results from the etching studies were used to explain the behavior of Si epitaxy growth rate from the and system in the 650–850°C, 22–24 mTorr processing regime. The implications of the etching studies for selective silicon epitaxy with the and chemistry are discussed and then extended to the based chemistry.

Low temperature selective silicon epitaxy by ultra high vacuum rapid thermal chemical vapor deposition using Si2H6, H2 and Cl2

We present the use of the Si2H6/H2/CL2 chemistry for selective silicon epitaxy by rapid thermal chemical vapor deposition (RTCVD). The experiments were carried out in an ultrahigh vacuum rapid thermal chemical vapor deposition reactor. Epitaxial layers were grown selectively with growth rates above 150 nm/min at 800 °C and 24 mTorr using 10% Si2H6 and H2 and Cl2 with a minimum Si:Cl ratio of 1. Excellent selectivity with respect to SiO2 and Si3N4 was obtained indicating that very low Cl2 partial pressures are sufficient to preserve selectivity. In situ doping results with B2H6 show that sharp doping transitions and a wide range of B concentrations can be obtained with a slight B incorporation rate reduction with Cl2 addition. Our results indicate that UHV-RTCVD with the Si2H6/H2/Cl2 chemistry yields highly selective Si epitaxy with growth rates well within the practical throughput limits of single wafer manufacturing and with a potential to reduce the Cl content below the levels used in conventional SiH2Cl2 based selective epitaxy processes.

Low Temperature Selective Si Epitaxy Using Si2H6 and Cl2: Investigations into Selectivity Robustness and Epitaxial Film Quality

AbstractIn this paper, we explore selective Si epitaxy by UltraHigh Vacuum Rapid Thermal Chemical Vapor Deposition (UHV-RTCVD) using Si2H6, H2, and C12 with particular emphasis on selectivity robustness. Two key parameters considered in this study were partial pressures of Si2H6 and H2. It was found that excessive increases in either partial pressure could lead to selectivity degradation. The two mechanisms by which the observed selectivity degradation can be explained are as follows: A higher Si2H6 partial pressure provides a larger flux of Si atoms which directly influences the probability of reaching the critical nuclei size for stable nuclei formation while an increase in H2 partial pressure reduces the desorption rate of Si adatoms from the insulator surface by reducing the available Cl in the gas phase for SiC12 formation. The impact of process parameters on epitaxial defect density was also evaluated using darkfield imaging. The results clearly indicate increasing defect density upon increases in both the chlorine flow rate and the level of contamination introduced through the silicon source gas.

Sub-Half Micron Elevated SourceDrain NMOSFETS by Low Temperature Selective Epitaxial Deposition

AbstractIn this paper we report the first NMOSFETs with elevated S/D selectively deposited by ultra high vacuum rapid thermal chemical vapor deposition (UHV-RTCVD). The deposition process included an in-situ vacuum prebake (750 °C for 10 sec) followed by selective epitaxial growth (SEG) at 800 °C. Si2H6 was used as the silicon gas source instead of the more commonly used SiH4 and SiH2Cl2 in order to achieve high growth rates at low pressure. To prevent nucleation from occurring on insulator surfaces during growth, an etching mechanism was introduced by the addition of Cl2. The gases included 100 sccm of 10% Si2H6 in H2 and 2 sccm of Cl2 at a process pressure of 24 mTorr. An epitaxial growth rate of 160 nm/min has been achieved. The final epi thickness was around 0.1 μm. The S/D junctions were formed via ion implantation into the epi. The subsequent RTA (10 sec at 950 °C) resulted in an effective junction depth about 75 nm beneath the starting Si substrate. Process and device simulations reveal the importance of maintaining a shallow LDD junction for deep submicron devices by using low temperature selective deposition. MOSFETs exhibit good subthreshold characteristics with subthreshold swing of 86 mV/dec at a drain bias of 2.5 V, and threshold variations due to charge sharing and drain-induced-barrierlowering (DIBL) were moderate for Leff down to 0.35 μm. The gate-induced junction leakage current is below 2 pA/μm at a bias of 2.5 V.

Ultrahigh Vacuum Rapid Thermal Chemical Vapor Deposition of Epitaxial Silicon on (100) Silicon: II . Carbon Incorporation info Layers and at Interfaces of Multilayer Structures

In this study, we have investigated carbon incorporation in epitaxial Si layers and at interfaces of multilayer epitaxial structures due to desorption of hydrocarbons from chamber walls at elevated temperatures. The experiments were conducted in an ultrahigh vacuum rapid thermal chemical vapor deposition (UHV‐RTCVD) reactor. We have investigated carbon contamination as a function of deposition temperature, film growth rate, and partial pressure of hydrocarbons. The results show that at higher deposition temperatures (750 and 800°C) carbon levels in epitaxial layers are lower compared to levels in layers grown at lower temperatures (650 and 700°C). It is proposed that at higher temperatures, the carbon concentration in Si is determined by the adsorption‐desorption equilibrium and this results in a growth rate independent incorporation process. At lower temperatures, carbon incorporation is limited by the availability of sites for chemisorption. Site availability is determined by hydrogen coverage on Si during growth, and this produces a growth rate dependent incorporation process. Hydrocarbon desorption from the chamber walls increases with increasing hold time at elevated temperatures, resulting in a time dependent increase in the carbon level within epitaxial layers. Carbon contamination at interfaces of multilayer structures was found to depend strongly on the growth temperature. Higher interfacial carbon levels were obtained following growth at higher temperatures when temperature cycling was used to start and stop the growth processes. When gas switching was used for this purpose, interfacial carbon contamination was observed at lower temperatures (650 and 700°C). This is tentatively attributed to loss of hydrogen coverage when is evacuated from the chamber for gas switching and inefficient desorption of physisorbed species from the surface at lower temperatures.

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 desorption and avoid Si overgrowth on the O and C sites.

N-Channel Mos Transistors below 0.5 μm with Ultra-Shallow Channels formed by Low Temperature Selective Silicon Epitaxy

AbstractIn this paper, we present an application of ultra high Vacuum Rapid Thermal Chemical Vapor Deposition (UHV-RTCVD) to MOSFET channel engineering. MOSFETs were fabricated on ultra-thin (200 Å), moderately doped (l×1017 - 6×1018 cm−3) p-type epitaxial layers selectively grown in active areas defined by standard LOCOS isolation. The selective epitaxy was achieved using a novel Si2H6Cl2/B2H6 process at 800°C and at a total pressure under 30 mtorr. Low thermal budget processing techniques were emphasized to minimize spread in the channel doping profile. Threshold voltages below 0.6 V were obtained. Transistors with effective channel lengths of 0.45 μm exhibit subthreshold slopes from 78 to 92 mV/decade determined by the epitaxial channel doping density. We have found that by using ultra-thin channels, expected transconductance degradation at high channel doping densities can be minimized. Furthermore, ultra-thin channels help reduce the sensitivity of the threshold voltage on substrate bias. The results show that low temperature selective silicon epitaxy can be used to form ultra-shallow channel doping profiles that can enhance the performance of MOSFETs in the deep submicron regime.

Low Temperature Selective Silicon Epitaxy Using Si2H6, H2 and Cl2 in Ultra High Vacuum Rapid Thermal Chemical Vapor Deposition

In this paper we present for the first time the use of the Si2H6/H2/Cl2 chemistry for selective silicon epitaxy in a rapid thermal CVD reactor. Depositions were carried out in an ultra-high vacuum rapid thermal chemical vapor deposition (UHV-RTCVD) system designed and constructed at North Carolina State University. Experiments were performed over a temperature range of 650°C to 850°C and over a pressure range of 22 to 25 mTorr using a flow rate 100 sccm of 10% Si2H6 in H2 and 0 to 10 sccm of Cl2. Deposited layer thicknesses were evaluated using a combination of interferometry and profilometry. Without Cl2 over the range of 650°C to 850°C, the growth rate is approximately constant at 160 nm/min. exhibiting a weak dependence on temperature. A clear advantage of Si2H6 is that high growth rates compatible with single wafer manufacturing can be obtained at very low pressures thus minimizing the introduction of contaminants by the process gases. With the addition of C12, the growth rate is suppressed at temperatures below 800°C, but, at 800°C and above, it is affected only slightly for Cl2 flow rates below 5 sccm. As the Cl2 flow rate is increased past 5 sccm, the growth rate at higher temperatures becomes a strong function of Si2H6:Cl2 ratio. Excellent selectivity with respect to patterned SiO2 and Si3N4 was obtained over the entire Cl2 flow rate range suggesting that even lower Cl levels may be sufficient for selective deposition. This implies that selectivity can be obtained with Si:Cl ratios much lower than those introduced by the more commonly used SiH2Cl2 chemistry. Furthermore, because Si2H6 can provide high growth rates at very low pressures, the total partial pressures of Cl2 and resulting chlorinated species can be significantly lower than typically required for selectivity. Our results indicate that C12 successfully enhances selectivity and yields highly selective depositions for process durations well within the practical limits of single wafer manufacturing.

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 vacuum rapid thermal chemical vapor deposition (UHV‐RTCVD) reactor using 10% diluted in . Silicon was deposited on patterned Si (100) substrates over a pressure range of 10–100 mTorr and a temperature range of 650 and 850°C. Under these conditions, the growth rate ranged from 50 to 330 nm/minute, demonstrating compatibility with single wafer manufacturing throughput requirements. 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. The incubation time for loss of selectivity via Si nucleation on was found to increase at lower pressure and remained constant over the experimental temperature range. However, the incubation thickness defined as the film thickness that can be deposited before loss of selectivity occurs was found to increase both at low pressures and high temperatures. We show that a 100 nm thick epitaxial film can be grown selectively with no Cl addition at 750°C/10 mTorr.

Nucleation and Growth of Polycrystalline Silicon Films in an Ultra high Vacuum Rapid Thermal Chemical Vapor Deposition Reactor Using Disilane and Hydrogen

A study of Si nucleation and deposition on SiO2 was performed using disilane and hydrogen in an ultra high vacuum rapid thermal chemical vapor deposition reactor in pressure and temperature ranges of 0.1 – 1.5 Torr and 625 – 750°C. The film analysis was carried out using scanning electron microscopy, transmission electron microscopy and atomic force microscopy. At lower pressures, an incubation time exists which leads to a retardation in film nucleation. At 750°C, the incubation time is 10s at 0.1 Torr and decreases to less than Is at 1.5 Torr. The nuclei grow and form three dimensional islands on S1O2, and as they coalesce, result in a rough surface morphology. At higher pressures, the inherent selectivity is lost resulting in a higher nucleation density and smoother surface morphology. For ˜ 2000 Å thick films, the root-mean-square surface roughness at 750ÅC ranges from 110Å at 0.1 Torr to 40Å at 1.5 Torr. Temperature also strongly influences the film structure through surface mobility and grain growth. At 1 Torr, the roughness ranges from 3Å at 625°C to 60Å at 750°C. The grain structure at 625°C/1Torr appears to be amorphous, whereas at 750°C the structure is columnar. The growth rate at 625°C/1.5 Torr is 1200 Å/min provides a surface roughness on the order of atomic dimensions which is comparable to or better than amorphous silicon deposited in LPCVD furnaces.

Oxide Removal on Silicon by Rapid Thermal Processing Using SiH2CI2 and H2

In this paper, we report in-situ oxygen removal on Si using SiH2Cl2 and H2 in a high vacuum rapid thermal chemical vapor deposition reactor. The system consists of a main process chamber and a load-lock with base pressures of ∼ 1×10−7 Torr and 1×10−5 Torr respectively. The experiments were conducted in the temperature range of 750°C to 865 °C, and SiH2Cl2/H2 flow ratios of 1% to 7%. For comparison, samples were also prepared with only H2 prebaking in the same temperature and pressure range as well as with no in-situ cleaning. With no in-situ cleaning, the oxygen content was found to decrease at higher temperatures suggesting partial oxygen removal during early stages of growth. The results indicate a strong temperature dependence for the H2 clean with an increased effectiveness at higher temperatures which is believed to be due to temperature dependence of oxygen desorption from Si. In the temperature range studied, the SiH2Cl2 clean was found to be effective at 750°C. An additional oxygen removal mechanism appears to be introduced by the addition of SiH2Cl2. Using this approach, at 750°C, the peak oxygen concentration can be reduced to 4×1018 cm−3 whereas the H2 anneal at the same temperature results in a concentration of 6×1018 cm−3. At higher temperatures, the oxide can be removed in pure H2 just as efficiently or desorbed during initial stages of growth. The results show that the efficiency of the process increases as more SiH2 Cl2 is added to the system up to a critical pressure. However, if the SiH2Cl2 partial pressure is above this critical value, Si deposition can occur on the Si surface yielding an optimum partial pressure which is a function of temperature. The results indicate that the use of a small amount of SiH2Cl2 as a cleaning agent may provide a low temperature pre-epi clean.

High Quality Silicon Epitaxy In An Ultra High Vacuum Rapid Thermal Cvd Reactor: An Application to Single Wafer Processing

ABSTRACTIn this paper, we report epitaxial growth of silicon in an ultra high vacuum rapid thermal chemical vapor deposition (UHV/RTCVD) equipment. In this study, our objectives were low temperature/low thermal budget processing and a high throughput compatible with single wafer manufacturing. The reactor consists of a load lock, a main process chamber and an intermediate cryopumped vacuum buffer chamber between the two chambers. An ultra-clean process environment was achieved using oil free pumps and point of use gas purifiers. The wafer is heated by a Peak Systems LXU-35 arc lamp through a quartz window. In this system, we achieved good quality silicon epitaxy at low temperature (T≤800°C) in the very low, 100 mTorr, pressure regime with high throughput (Growth rate>0.25 μm/min.). High growth rate was achieved using Si2H6 as the reactant gas instead of SiH4 or SiH2C12 which are more commonly used gases for epitaxial growth. High temperature in-situ cleaning was completely eliminated by initiating film growth on a hydrogen passivated surface obtained via dilute HF etching. Generation lifetimes in the 200-400μs range were measured for deposition temperatures of 700°C, 750°C and 800°C with no strong dependence on the deposition temperature.

Cleaning during Initial Stages of Epitaxial Growth in an Ultrahigh Vacuum Rapid Thermal Chemical Vapor Deposition Reactor

AbstractIn this paper, we report our results on surface preparation for the growth of epitaxial Si films. Hydrogen passivated surfaces are currently being investigated for application in Si epitaxy to eliminate the high temperature in-situ bake necessary to remove the native oxide. Hydrogen passivation is obtained by a dilute HF dip before the substrate is loaded in the process chamber. However the passivation is partially lost when the HF dip is followed by a water rinse which results in oxygen absorption on the substrate. It was found that the peak oxygen concentration at the epitaxy substrate interface increase by an order of magnitude due to a five minute water rinse. We report here that oxygen and carbon at the epitaxy substrate interface can be desorbed during initial stage of epitaxial growth by reducing epitaxial growth rate. In this work, epitaxial Si films were deposited over a wide range of growth rates obtained by varying Si2H6 flow rates. The peak oxygen concentration decreases by an order of magnitude by changing the growth rate from 3000 to 700Å/kminute for a deposition temperature of 800°C. We believe that at higher growth rates Si overgrows on absorbed oxygen maintaining epitaxial alignment reflected in the good electrical quality of the epitaxial films. However, at low growth rates oxygen has sufficient time to desorb before overgrowth can take place, improving the epitaxy substrate interface quality.

Silicon Nucleation on Silicon Dioxide and Selective Epitaxy In An Ultra-High Vacuum Raptid Thermal Chemical Vapor Deposition Reactor Using Disilane In Hydrogen

AbstractSilicon nucleation on silicon dioxide and selective silicon epitaxial growth (SEG) were studied in an ultra high vacuum rapid thermal chemical vapor deposition (UHV-RTCVD) reactor. Experiments were performed using 10% Si2H6 in H2 in a pressure range of 10 - 100 mTorr at 760°C. Under these conditions, the growth rate ranged from 75 to 330 nm/minute. Loss of selectivity via Si island formation on SiO2 was studied using scanning electron microscopy (SEM) and atomic force microscopy (AFM) revealing a strong dependence on deposition pressure. Cross sectional transmission electron microscopy (XTEM) was employed to study the vertical oxide/epitaxy interface where faceting can occur. The incubation time for nucleation was found to increase from 10s to 70s as pressure is reduced from 100 mTorr to 10 mTorr, allowing thicker selective epitaxial film growth in spite of the reduced growth rates. This was attributed to the reduction in gas phase supersaturation of the Si containing species resulting in a lower density of adsorbed atoms on the SiO2 surface. This process shows a potential for chlorine free selective epitaxial growth and provides insight to the surface morphology of polycrystalline films deposited at low pressures.