K. Christensen

Oxygen gettering and precipitation at MeV Si+ ion implantation induced damage in silicon

The interaction of intrinsic oxygen in Czhochralski silicon with implantation damage induced by 2.0 MeV Si+ ions has been investigated as a function of annealing temperature and time. Four distinct regions of oxygen localization are revealed by secondary ion mass spectrometry following sample annealing. The different regions are correlated with either a near surface vacancy‐rich region or the buried layer of extended defects near the projected range. The relative concentration of oxygen in each region depends on the competition between oxygen gettering in each region and out‐diffusion to the surface. It has been established, using quasikinematical and dynamical contrast transmission electron microscopy imaging techniques, that the oxygen in regions containing extended dislocations is in the form of fine precipitates. The precipitates decorate both the dislocations and, for faulted loops, the stacking fault planes.

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 SiH2C...

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

Si thermal etching studies have been performed using pure Cl 2 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 Cl 2 flow were investigated with thermodynamic equilibrium calculations performed to determine possible reaction pathways. The effect of a ding H 2 , 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 SiCl 2 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 be avior of Si epitaxy growth rate from the Si 2 H 6 , H 2 , and Cl 2 system in the 650-850°C, 22-24 mTorr processing regime. The implications of the etching studies for selective silicon epitaxy with the Si 2 H 6 and Cl 2 chemistry are discussed and then extended to the SiH 2 Cl 2 based chemistry.

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 Si 2 H 6 , H 2 , and Cl 2 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 SiH 2 Cl 3 -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 Si 2 H 6 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.

EFFECTS OF CARBON IMPLANTATION ON GENERATION LIFETIME IN SILICON

In this study, we present characterization of metal–oxide–silicon (MOS) capacitors fabricated on carbon (C12) implanted Si substrates. Carbon was implanted at an energy of 50 keV with doses ranging from 1×1012 cm−2 to 4.1×1015 cm−2. Metal–oxide silicon capacitors were fabricated and used to determine the MOS capacitance–voltage (C–V) and capacitance–time (C–t) behavior. These measurements revealed a strong correlation between carrier lifetime and the C dose. Degradation in lifetime was observed for C dose levels as low as 4×1012 cm−2. At C doses equal to and above 6.4×1013 cm−2, extremely low generation lifetimes were obtained (∼10−7 s). On the other hand, for C dose levels higher than 2.7×1014 cm−2, a low accumulation capacitance was observed at high frequencies and attributed to hole traps. Below this dose, both flatband voltage and interface trap density of the C implanted samples were comparable to those of the monitors.

Silicon Nucleation and Film Evolution on Silicon Dioxide Using Disilane Rapid Thermal Chemical Vapor Deposition of Very Smooth Silicon at High Deposition Rates

An investigation of Si{sub 2}H{sub 6} and H{sub 2} for rapid thermal chemical vapor deposition (RTCVD) of silicon on SiO{sub 2} has been performed at temperatures ranging from 590 to 900 C and pressures ranging from 0.1 to 1.5 Torr. Deposition at 590 C yields amorphous silicon films with the corresponding ultrasmooth surface with a deposition rate of 68 nm/min. Cross-sectional transmission electron microscopy of a sample deposited at 625 C and 1 Torr reveals a bilayer structure which is amorphous at the growth surface and crystallized at the oxide interface. Higher temperatures yield polycrystalline films where the surface roughness depends strongly on both deposition pressure and temperature. Silane-based amorphous silicon deposition in conventional systems yields the expected ultrasmooth surfaces, but at greatly reduced deposition rates unsuitable for single-wafer processing. However, disilane, over the process window considered here, yields growth rates high enough to be appropriate for single-wafer manufacturing, thus providing a viable means for deposition of very smooth silicon films on SiO{sub 2} in a single-wafer environment.

Rapid thermal chemical vapor deposition of in situ boron-doped polycrystalline silicon-germanium films on silicon dioxide for complimentary-metal-oxide-semiconductor applications

In situ boron-doped polycrystalline Si1−xGex (x>0.4) films have been formed on the thermally grown oxides in a rapid thermal chemical vapor deposition processor using SiH4-GeH4-B2H6-H2 gas system. Our results showed that in situ boron-doped Si1−xGex films can be directly deposited on the oxide surface, in contrast to the rapid thermal deposition of undoped silicon-germanium (Si1−xGex) films on oxides which is a partially selective process and requires a thin silicon film pre-deposition to form a continuous film. For the in situ boron-doped Si1−xGex films, we observed that with the increase of the germane percentage in the gas source, the Ge content and the deposition rate of the film are increased, while its resistivity is decreased down to 0.66 mΩ cm for a Ge content of 73%. Capacitance-voltage characteristics of p-type metal-oxide-semiconductor capacitors with p+-Si1−xGex gates showed negligible polydepletion effect for a 75 A gate oxide, indicating that a high doping level of boron at the poly-Si1−xGex...

Smooth amorphous silicon deposition on silicon dioxide with high deposition rates by rapid thermal chemical vapor deposition using disilane

In this paper, we report amorphous silicon (α-Si) deposition on SiO2 by rapid thermal chemical vapor deposition for the first time at rates compatible with single wafer manufacturing. Depositions were performed using 10% Si2H6 in H2 at 1 Torr in the temperature range 550 to 750 °C. Very high deposition rates are achieved and these rates range from 45 nm/min to as high as 650 nm/min. Analysis of the films by transmission electron microscopy indicates α-Si deposition at temperatures below approximately 600 °C. At temperatures around 625 °C, films with a bilayer amorphous-polycrystalline composite microstructure were obtained which was attributed to a deposition rate greater than the crystallization rate. Analysis of these low temperature films by atomic force microscopy yields rms roughness values, in general, that are less than 1.5 nm and as low as 0.3 nm. The smoothness of the films is comparable to the best α-Si films obtained by conventional low pressure chemical vapor deposition using SiH4 or Si2H6. In summary, by using an efficient source gas, we are able to deposit very smooth Si films by rapid thermal chemical vapor deposition which we believe is a viable option for high quality MOS gate stack formation in a single wafer manufacturing environment.

Suppression of self-interstitials in silicon during ion implantation via in-situ photoexcitation

The influence of in-situ photoexcitation during low temperature implantation on self-interstitial agglomeration following annealing has been investigated using transmission electron microscopy (TEM). A reduction in the level of as-implanted damage determined by RBS and TEM occurs athermally during 150 keV self-ion implantation. The damage reduction following a 300 C anneal suggests that it is mostly divacancy related. Subsequent thermal annealing at 800 C resulted in the formation of (311) rod like defects or dislocation loops for samples with and without in-situ photoexcitation, respectively. Estimation of the number of self-interstitials bound by these defects in the sample without in-situ photoexcitation corresponds to the implanted dose; whereas for the in-situ photoexcitation sample a suppression of {approx}2 orders in magnitude is found. The kinetics of the athermal annealing process are discussed within the framework of either a recombination enhanced defect reaction mechanism, or a charge state enhanced defect migration and Coulomb interaction.