Wafer backside reflectivity measurements at room temperature have been performed in a rapid thermal processor equipped with two rows of heating lamps by measuring, with the process optical pyrometer, the light emitted by the lower row of the heating lamps and reflected by the wafer. The differences in reflectivity have been correlated with the process temperature variations induced by emissivity changes. Optical pyrometer recalibration procedures have then been established. It has been demonstrated that the reflectivity measurement, performed automatically for each wafer prior to the thermal cycle, may drastically improve the accuracy of temperature control.

The main factors influencing the thermal performance (and thus product yield) of a rapid thermal processor are the heat source, the reaction chamber, the temperature measurement system, and as complicating factors, their total configuration and the optical wafer properties.

The characteristics of 19 currently available commercial RTP systems are highlighted with focus on temperature control including the spectral characteristics and measures to suppress perturbations due to stray radiation.

In addition recent developments and trends in the system configuration and in the optimization of temperature or layer thickness control are discussed. The improvements in temperature control focus especially on in situ temperature control, irrespective of wafer condition, and at system constructions that optimize dynamic temperature uniformity. Some novel optical process control and novel system design aspects to compensate for emissivity changes and temperature non-uniformity are included.

The applications of in situ automated ellipsometry in the measurement and control of temperature in rapid-thermal processing (RTP) equipment are investigated. This technique relies on the accurate measurement of the index of refraction of a wafer using ellipsometry and the strong temperature dependence of the index of refraction to determine the wafer temperature. In principle, this technique is not limited to silicon wafer processing and could be applied to any surface whose index of refraction has a strong and well known temperature dependence. This technique is non-invasive, non-contact, fast, accurate, compatible with ultraclean processing, and lends itself to monitoring the dynamic heating and cooling cycles encountered in rapid-thermal processing.

A novel wafer temperature and emissivity measurement technique for rapid thermal processing (RTP) is presented. The ‘Ripple Technique’ takes advantage of heating lamp AC ripple as the signature of the reflected component of the radiation from the wafer surface. This application of Optical Fiber Thermometry (OFT) allows high speed measurement of wafer surface temperatures and emissivities. This ‘Ripple Technique’ is discussed in theoretical and practical terms with wafer data presented. Results of both temperature and emissivity measurements are presented for RTP conditions with bare silicon wafers and filmed wafers.

Radiation and the resulting excess concentration of free carriers has a strong impact on several physical processes in silicon. New experimental results involving RTA are compared with previous experimental practice. Several aspects of the new result raise questions about the validity of the assumptions which were used in the past. It is concluded that radiation significantly enhances annealing processes, especially during the initial phase of RTA. Based on the study of the physical phenomena involved in the irradiated silicon, it is shown that the absorption and recombination rate are the most affected parameters and they are most likely the reason for the underestimation of the magnitude of excess free carriers.

An Extended Kalman Filter (EKF) is developed to provide an improved pyrometer-based estimate of temperature in rapid thermal processing systems. Models of the heat transfer characteristics, emissivity variations, and temperature measurement equipment, are used in formulating an EKF as a closed-loop observer to filter out noise, lessen the effects of processing variations, and to infer temperature at locations where no measurements are available. Extensive simulations are conducted to analyze the robustness of the EKF.

The electrical activation of As implanted Si has been investigated on rapid thermal annealing timescales using sheet resistance, spreading resistance and Hall Effect techniques. For high dose implants (>1015 As cm-2) differential Hall Effect and spreading resistance profiles confirm the existence of a temperature dependent electrical solubility limit. However for low dose implants, annealing schedules chosen such that the electrical solubility limit is not exceeded reveal electrical deactivation which is not accounted for in the clustering theory. Hall Effect measurements performed as a function of temperature have enabled us to reveal directly electrically inactive As which is not observable at room temperature using standard electrical techniques. The results indicate that As atoms in Si introduce deep trapping levels within the bandgap which are responsible forremoving As from the conduction process at room temperature. This temperature activated process is characterized with an activation energy of 0.4eV.

A study of gettering and electrical activity of metallic impurities Ni, Au and Cu has been carried out on epitaxial Si/Si(2%Ge)/Si wafers containing interfacial misfit dislocations. The impurities were intentionally introduced from a backside deposited thin metal followed by rapid thermal annealing (RTA). Transmission Electron Microscopy (TEM) results indicate that the impurities were gettered along the misfit dislocations in near-surface regions either as Au precipitate colonies, or as NiSi2 and CuSi silicide precipitates. Data from Scanning Electron Microscopy (SEM) in the Electron Beam Induced Current (EBIC) mode revealed that these precipitates dominate the recombination properties of the initially inactive misfit dislocation.

Synchrotron white beam x-ray topography in transmission geometry has been used to monitor the damage accompanying a Rapid Thermal Processing (RTP) treatment of Si wafers. The behavior of low and high carbon-content Si is contrasted and discussed. The applicability of this technique to this kind of study is demonstrated, with particular emphasis being laid on its non-destructive nature. The general usefulness of the technique as a monitor for damage accompanying IC processing is discussed.

Tantalum nitride, Ta-Si-N, and tantalum silicide films were investigated for use as a diffusion barrier in Al/Si metallization. The former two films were deposited by reactive sputtering of a Ta or TaSi2 target in Ar/N2 gas mixture. The TaSix films were fabricated by sputtering of TaSi2 target. Then, the Ta-Si-N and TaSix film were annealed at temperature 950°C for 15 seconds by RTA. The resistivities of Ta-Si-N, TaN, and TaSix films are about 180, 250, and 60 µohm-cm, respectively. The X-ray photoelectron spectroscopies were made to study the chemical structure of the films. For both nitrides, TaO comprises the native oxide formed at room temperature. A large amount of silicon nitride was formed on the surface of TaSix film during the RTA. Rutherford backscattering and Auger profile were performed to understand the degradation. It was found that these three films are effective diffusion barriers at temperature 620°C.

Variations of thermal donors (TDs) in highly phosphorus-diffused n-type silicon wafers (diffused wafer) have been studied with deep-level transient spectroscopy and capacitance-voltage measurements. The introduction and annihilation of TDs have been performed with heat treatment at 450°C and rapid thermal annealing (RTA) in the temperature range 600-900°C,respectively. In diffused floating zone-grown (FZ) silicon wafer, TDs were observed. It is thought that oxygen diffuses into FZ silicon during the diffusion process, since no TDs are generally formed in FZ silicon for the low oxygen concentration. The behavior of TDs in diffused wafer corresponded with that in oxygen-rich bulk silicon. TDs were completely annihilated by RTA at 700 and 800°C for the as-diffused wafers and the heat-treated ones at 450°C for 24 h, respectively, and the annihilation rate for the as-diffused wafers was fast, as compare to that for the heat-treated ones. This results may be caused by difference in the total concentration and cluster size of TDs.

Using thermal wave mapping and imaging techniques in conjunction with x-ray transmission topography and transmission electron microscopy, precipitation behavior of various fast and slowly diffusing metallic impurities such as Au, Co, Cu, Fe, Mo, Ni, Pd, Pt, W and Zn in Czochralski Si following rapid thermal processing are investigated. Our data have shown that thermal wave signal is sensitive to certain types of metal-induced surface defects (most likely metal silicides) and associated crystallographic defects. In addition, the comparison between thermal wave and x-ray imaging methods shows an interesting speciesdependent complimentary relationship.

The effects of high temperature-time thermal cycles on the structural stability of GexSi1−x/Si and Si/GexSi1−x/Si layers are studied, using double-crystal x-ray diffraction. The temperature-time cycles chosen in this study are useful for the fabrication of submicron Si MOSFETs. The electrical characteristics of GeSi/Si p-n heterojunctions as a function of annealing temperature and time are also presented.

Introduction of oxygen during thermal oxidation and production of defects by rapid thermal annealing (RTA) in n-type epitaxial Si layers were studied with deep-level transient spectroscopy measurements. We use oxygen-related thermal donors (TDs) as a monitor for introduction of oxygen in silicon epitaxial layers. It is found that oxygen is introduced from the substrate into the epitaxial layer after thermal annealing. The TD was almost annihilated by RTA at .700°C. However, a shallow trap (Ec−0.073±0.005 eV) was induced by RTA.

200 keV Co+ ions have been implanted into (100), (110) and (111) single crystal silicon substrates to doses of 2 × 1017 Co+ cm−2 and 5 × 1017 Co+ cm−2. During implantation the substrates were tilted at an angle of 70 to the incident ions and maintained at a temperature of 350°C. The experimental results, after implantation, are in close agreement with those obtained by computer simulations, which allow the single crystal orientation of the target and its position with respect to the incident ions to be specified. 5s RTA treatment at 1100°C was found to give CoSi2 layers of similar crystalline quality and resistivity to those produced by conventional furnace annealing.

Uniform CoSi2 surface layers 30nm thick have been realized through room temperature implantation of Co+ through a resist or an oxide mask and low temperature (600°C) annealing. TEM studies show that the surface layers are polycrystalline with large, uniformly thick grains. Resistivity values as low as 181µΩ-cm have been obtained. Surface layers of TiSi2 have also been synthesized using a similar process. The ease of formation, the low resistivity and the smooth interfaces of the CoSi2 and TiSi2 surface layers make this technique a promising candidate for contacting source and drain junctions in sub-half-micron CMOS processes.

The transformation of TiSi2 from the C49 phase to the C54 crystallographic phase is an irreversible, polymorphic transformation that occurs by a nucleation and growth process. Typical of polymorphic transformations, the transition occurs readily once a stable embryo of the thermodynamically favored phase is formed. Future VLSI applications requiring control of the resistivity and thermodynamic stability of thin TiSi2 films formed on submicron features will necessitate understanding this nucleation and transformation process to a greater extent. We have found that the C54 phase nucleation site density, the resulting microstructure and thermal stability of the film can be strongly influenced by the initial silicide formation conditions. Rapid thermal processing (RTP) has been found to offer a significant advantage over conventional furnace annealing for the silicide formation process.

The reaction between titanium and ammonia to form titanium nitride in a rapid thermal annealer has been studied as a function of process temperature and substrate conditions. The films produced have been characterized by Rutherford Backscattering, Sputtered Neutral Mass Spectroscopy and four point probe electrical resistivity measurements. On oxide substrates, below 720°C only dissolution of nitrogen within the titanium is observed leading to an increase in the specific resistance of the film. Above 720°C, stoichiometric titanium nitride begins forming leading to a drop in the specific resistance of the film. Only in the vicinity of 800°C is all the titanium consumed to form TiN. However, temperatures beyond 700°C cause dissolution of oxygen within the titanium. On silicon substrates, the competing reactions of nitridation and silicidation at the two interfaces govern the extent of nitridation.

Titanium silicide was formed on the top of Si wafers by arsenic ion beam mixing and rapid thermal annealing. Three different arsenic-ion mixing conditions were examined in this work. The sheet resistance, residue As concentration post annealing and TiSi2 phase were characterized by using the* four-point probe, RBS and electron diffraction, respectively. TiSi2 of C54 phase was identified in the doubly implanted samples. The thickness of the Ti silicide and the TiSi2/Si interface were observed by the cross-sectional TEM.

Amorphous thin films were deposited by co-sputtering Mo and Si on Si(100) single crystals. Rapid thermal annealing at 700, 800 and 1050°C for 30 sec. resulted in the growth of hexagonal and tetragonal phases of MoSi2 as revealed by glancing angle x-ray diffraction. The optical properties of these films were studied by spectroscopic ellipsometry in the range 1.0 to 5.0 eV. As deposited films showed both metallic and semiconducting features in the <ε1> and <ε2> spectra. As a result of annealing at 700 and 800°C, pronounced increase in <ε1> was obtained. Annealing at 1050°C resulted in decrease of the values of <ε2>. Surface morphology, density changes and stress variations associated with recrystallization and compound formation are proposed to account for these observations. The peaks in <ε2> spectra are found to be interband transitions in the MoSi2 structures. These results are in confirmity with the EELS and UPS studies and theoretically calculated band structure of MoSi2.