We describe the observation of a strain-induced order-disorder transition in the alloy layers of a GeSi/Si superlattice and discuss the possible implications of the transition for the opto-electronic properties of this important system.

Low temperature photoluminescence spectra measured from MBE GaAs/Aℓ_xGa_1-xAs superlattices with different excitation photon energies were analyzed to reveal superxlattice well thickness variations along the MBE growth direction. Due to their unique electrical and optical properties, semiconducting multi-quantum-well (MQW) structures are receivIng much attention fo; their applications in microstructure devices such as HEMT, SEED , and tunable lasers. The properties of MQW structures are greatly affected by the MQW heterointerface qualities, impurity contents, and layer thickness irregularities. So far, molecular-beam-epitaxy (MBE) prepared MQW structures are found to exhibit superior sample qualities i Tany respects, and a great deal of effort is being made to further advance MBE technology. The characterization of multi-layered structures, however, has not progressed as fast as the development of thin film growth methods. Among the various sample characterization methods, optical techniques offer certain advantages since the test results can be obtained in a relatively quick and simple manner. Besides, the nondestructive (or non-contact) nature of optical methods provides opportunities for repetitive evaluations, which improves accuracy in sample characterizations.

Measurements of ultrasonic attenuation and velocity as a function of temperature can yield valuable structural information on defects which lower the symmetry of the lattice site on which they are located. We report here on two such defects in GaAs: the Cr impurity and the as yet inconclusively identified defects caused by low temperature irradiation with 2.25-2.5 Mev electrons. The neutral Cr impurity (Cr³⁺-[Ar]3d³) traps an electron to become Cr²⁺. This charge state undergoes a static tetragonal Jahn-Teller distortion which can be detected ultrasonically. Ultrasonic measurements at 10 frequencies between 5 and 130 MHz for differing polarizations of the stress wave confirm the tetragonal symmetry of the defect, and provide quantatative information on the kinetics of reorientation between energetically equivalent distortions. Samples with as little as .2 appm Cr were studied. Two defects with trigonal symmetry were observed to be created after the above mentioned electron irradiation. Both have reorientation kinetics obeying the Arrhenius law. The frequency factor and activation energy is 10^11.5 (10^13.2) sec and 12.5 (54.1) meV for the low (high) temperature attenuation peak. Both defects were observed to anneal out below 340 K. The low temperature peak annealed in a complicated fashion between 208 and 334K, whereas the high temperature peak exhibited single activation energy annealing above 320K. Our results suggest that no long range migration of the radiation produced defects occurs below room temperature. There is some evidence that the low temperature attenuation peak could be caused by a Ga vacancy. Several candidates for defects which could be responsible for the high temperature peak are considered and discussed.

Transmission electron microscopy (TEM) is well established as an important technique for the examination of microelectronic materials, solid phase interfaces, and device structures. It is routinely possible to obtain microstructural images at a 1 nm level of resolution, and electron diffraction patterns and microchemical analyses at the 10 nm level. For many specimens, it is also possible to image directly the lattice structure of a material at a resolution of 0.2 - 0.3 nm, depending on the instrument available. Thus it is possible to examine structural features and defects at a near-atomic level of resolution. These capabilities not withstanding, many practicing materials engineers have had little exposure to TEM techniques. It is the purpose of this paper, then, to review briefly these techniques, and to illustrate their unique contribution to the field of microelectronic materials analysis. Particular emphasis will be placed on the study of thin films and interfaces, structures of prime importance to the semiconductor industry.

The wavelength dependence of Raman scattering from B⁺ and BF₂⁺ implanted silicon is explored as a basis for a non-destructive method of evaluating dopant concentration profiles in submicron pn junctions. Depth resolution is obtained optically by making use of the change in the absorption coefficient with wavelength in the visible region. For comparison, chemical etching of the surface layers, in steps of ≈ 50 nm, to a depth of 550 nm enabled a direct measurement of the relative dopant concentration with depth by Raman spectroscopy. It is known that the increase in the intensity of the boron local mode at 618 cm^-1 and the broadening of the silicon optical phonon at ≈520 cm^-1 correlate with the increase in concentration of substitutional boron and its electrical activation. It was also observed that the intensity of the second order Raman band at ≈980 cm^-1 is a useful indicator of the doping level. Results are compared with secondary ion mass spectrometry (SIMS) analyses. Suggestions are made for improvements in resolution, sensitivity and calibration in order to provide a rapid method of measuring simultaneously the depth profiles of electrically active and inactive dopant species after annealing or for studying implantation damage prior to annealing.

Photoluminescence images of Czochralski grown GaAs reveal large fluctuations in the concentration of defects that lower the lifetime of photogenerated electrons or holes. Images made with ^~1 μm spatial resolution in the vicinity of isolated dislocations in low-dislocation-density In-alloyed GaAs reveal bright rings ^~300μm in diameter. The features have an interior dark spot approximately 100 ym across centered on the dislocation. The ratio of intensity in the bright ring to that of regions far from dislocations is as large as 10³. The intensity of the dark region in the center of the feature is up to a factor of ten lower than the peak intensity. These observations demonstrate that dislocations play an important role in generating or absorbing defects that lower the electron or hole lifetime.

Electrolyte electroreflectance and photocapacitance measurements have been performed on In-doped and on undoped GaAs. They verify that In doping generates large inhomogeneous strains which locally lower the stability of the zincblende structure compared to the chalcopyrite structure, but that it lowers the density of dislocations and of antisites. They also show that the EL2 complex is intimately associated with As antisites.

Characterization of metal-insulator-semiconductor (MIS) interfaces by capacitance-voltage (C-V) analysis is reviewed. Particular emphasis is placed upon III-V semiconductor inter-faces which are compared to the nearly ideal thermal Si0₂/Si system.

Sheet resistance has become an industry standard for monitoring high and medium dose ion implants. For low dose there are two sheet resistance techniques available, the direct implant technique and the double implant technique. Careful processing has extended the range of direct sheet resistance measurements down to doses of 2E11 ions/cm2. The double implant technique requires an initial implant to create an easily measured sheet resistance layer that serves as the test vehicle for the second implant. The dose of the second implant is measured by monitoring the change in the sheet resistance due to the implant damage created by the second implant into the first. This double implant technique is not limited to low dose nor to species that are electrically active in the substrate.

The use of scanning deep level transient spectroscopy (SDLTS) in the investigation of deep level trap distributions in LEC GaAs is described. Technique is based on electron beam induced current transients in a Schottky barrier, allowing approx. 1 micron spatial resolution. Results indicating enhanced hole trap concentrations around dislocation cores and walls are presented.

Fourier Transform Infra-Red Spectroscopy (FTIR) along with total and partial pressure measurements have been used to characterize the severe resist outgassing that occurs during high current ion implantation. This outgassing is confirmed to be mainly the evolution of hydrogen as shown by Residual Gas Analysis(RGA). Hydrogen is liberated by the breaking of C-H bonds present in the polymeric component of the resist, thus resulting in carbon layer formation. This effect is clearly observed by FTIR. Due to this mechanism, outgassing is found to be independent of the heat treatments used to cure the resists for temperatures above that necessary to evolve solvents (90C). This study concentrates on high-dose, high current conditions. The outgassing behaviorfor these cases is saturated as a function of energy, current, and dose and the results indicate near total conversion of the resist to carbon.

CZ wafers have been heat treated with either a 2 step anneal (16 hrs. @ 800°C/16 hrs. @ 1050°C) or a single step anneal (16 hrs. @ 1050°C). Deep level transient spectroscopy and minority carrier lifetime measurements were obtained on processed wafers containing diode-capacitor arrays. Wafers from the seed end of the crystal (initial oxygen concentration [O_i ~ 40 ppm) with the 2 step anneal showed 2 electron traps E 1 (E_C-E_T = 0.41 ± 0.02 eV), and E2 (E_C-E_T = 0.23 ± 0.03 eV), the dominant trap E 1 is shown to correlate with generation lifetime. Wafers implanted with oxygen at 400 keV or 3.5 MeV with doses of 3 X 10¹⁵ and 1 X 10¹⁶ atoms cm^-2 with similar heat treatments reveal electron traps with the same energies as those observed in the unimplanted samples. The high dose samples show a much more complicated spectra, in which E1 and E2 are present. TEM analysis of the seed end unimplanted samples with 2 step anneal show plate type precipitates with punched out loops and dislocations. The tang-end showed octahedral precipitates. The cross sectional view of the implanted samples reveal the precipitates and dislocation loops in a well defined layer. ESR measurements on similar samples with similar anneals reveal residual phosphorus and thermal donors and a new, broad resonance in some of the 2 step annealed samples. This board peak which is not fully analyzed suggests a signature that is not typical of isolated paramagnetic point defects.

Rapid thermal processing of silicon in oxygen and ammonia reactive ambients has been performed successfully to grow thin layers of Si0₂, silicon nitride, and silicon nitroxide for high quality gate insulators of submicron CMOS VLSI.

Thin oxides with thicknesses in the range of 100 - 350 Å have been grown by rapid thermal oxidation using an ambient gas mixture of oxygen and argon, and pure oxygen. Growth rates as a function of temperature and time have been studied. Silicon samples of both <111> and <100> crystal orientation have been studied. Thickness uniformities for steady state and transient annealing have also been measured.

Polycrystalline silicon films on oxidized silicon wafers have been subjected to rapid thermal processing before arsenic or boron ion implantation (pre-implant anneal). The films have then been ion implanted and given another rapid thermal process step to activate the dopant and repair the implant damage. The pre-implant anneal has caused the as-deposited grain size to increase by approximately a factor of ten. After the activation anneal these films have shown a 10 to 100% lower sheet resistance than films which did not receive a pre-implant anneal. The increase in grain size by the pre-implant anneal reduced the grain boundary area and as a result reduced the amount of dopant trapped in the grain boundaries relative to that which was actually inside the grains.

Using transmission electron microscopy, we show that melting and subsequent defect-free recrystallization can be obtained in silicon by absorbing the pulse energy via free-carrier transitions. We use a pulsed CO₂ laser to anneal extended lattice defects caused by high-temperature diffusion of phosphorus into lightly doped silicon. For pulse energy densities exceeding a threshold value, we find that the spherical precipitates and dislocation loops in the diffused layer are dissolved by C0₂ laser-induced melting, which results in a large increase in the electrically active phosphorus in the near-surface region. We also used the differential absorption between layers with different free-carrier concentrations to achieve melting of a buried ion-implanted layer, without melting the material that encapsulates the molten layer. This type of melting phenomenon is likely not obtainable using a laser where the absorption is dominated by an intrinsic mechanism. New applications using free-carrier absorption as a means to process silicon samples are discussed.

Temperature and temperature uniformity measurements in rapid thermal processing (RTP) require accurate, non-contact methods which operate over the temperature range of approximately 300-1400°C with accuracies and reproducibilities of better than 5°C. Non-contact methods for temperature measurements include [optical and infrared pyrometry] comparison measurements made by thermocouples inserted into dummy samples, and methods for temperature uniformity measurement include multiple sensor measurements over the wafer and a variety of process tests which include oxide growth, silicide sintering, polysilicon annealing, partial activation recrystallization and localized melting. Once the temperature measurement has been successfully completed, the results can be used for temperature control. Temperature control techniques include a mixture of optimal nonlinear, PID, and computer control.

Proton bombardment of doped gallium arsenide is known to produce electrical compensation and optical changes within the implanted material. In semi-conductor processing this technique has found wide application ranging from electrical device isolation to laser fabrication. This paper addresses recent advances in this technology with emphasis on opto-electronic developments. Components and devices formed through this process are reviewed as well as the optical and electrical properties of the bombarded material.

The production and annealing of damage in (100) InP implanted with Si ions at 77K, room temperature and 200°C have been studied by channeling, Secondary Ion Mass Spectrometry (SIMS), Hall measurement and electrochemical profiling. An ion energy of 180 keV and a fluence of 10¹⁴cm^-2 produces an amorphous layer which extends to the surface in samples implanted at 77K or room temperature, while samples implanted at 200°C with a fluence as high as 10¹⁵cm^-2 remain crystalline. For room temperature or 77K implants, the maximum epitaxial regrowth thickness is about 2000Å. An amorphous layer less than 2000Å thick can be nearly completely recrystallized by epitaxial growth, at a temperature of 250°C. The post-anneal residual disorder of thicker layers, following furnace annealing (FA) at 750°C for 15 minutes, is linearly dependent on the initial amorphous layer thickness. A high degree of electrical activation is reached for high temperature implants and low annealing temperature (500°-600°C). In contrast, for room temperature implants annealing at higher temperature using furnace or rapid thermal annealing was required to activate the dopants. The percentage of electrical activation of both low and high fluence ion doses is nearly the same at the optimal condition for rapid thermal annealing (RTA) or furnace annealing, even for the case of residual disorder layers following room temperature implants and furnace annealing. Comparison of the SIMS Si profile with the carrier concentration profile shows compensation at the damage-crystalline interface.

An investigation of the heating behavior of GaAs and InP in a Rapid Thermal Annealing (RTA) system shows a significant variation in the temperature response of these materials. These compound semiconductors are heated with incoherent light in an RTA system where a Si sample is used for temperature feedback. The temperatures of GaAs and InP samples thermally isolated from the Si control sample during heating may overshoot or undershoot the desired temperature by hundreds of degrees. When the samples are thermally connected to the Si control sample by means of a susceptor, the temperatures of the III-V semiconductors follow the programmed temperature closely. Much of the variation in temperature response can be correlated with free carrier concentrations in the materials, but other material properties also play a role. This significant variation in temperature response has practical implications for the design and application of RTA systems.

Undoped and Cr-doped LEC GaAs substrates were implanted with Si at 150 keV with doses from 4x10¹² to 1x10¹⁴/cm². The wafers were encapsulated with sputtered Si3Nt1 and annealed in a flash-lamp system at temperatures from 850 to 1025°C for times between 5 and 80 seconds. Channel dose implants into undoped LEC wafers give mobilities between 4700 and 4800 cm²/V-s for 1000°C, 5 sec. anneals, which are comparable with furnace annealed wafers. A sheet resistance of 61 ohms/sq and a mobility of 2500 cm2/V-s was obtained for a 1x10¹⁴/cm² implant dose. Reproducible threshold voltages can be obtained for both undoped and Cr-doped substrates using rapid thermal annealing.

The top silicon layer in as-implanted SIMOX wafer is usually too thin to support device fabrication. Hence, an epitaxial layer is usually grown on a SIMOX wafer after oxygen ion implantation and anneal. Because this epitaxial layer is typically very thin (less than 500 nm) and because of the material structure of the SIMOX wafer, special care has to be exercised in order to obtain desirable epitaxial growth. This paper describes the unique problems of epitaxial growth on SIMOX.

Progress in the growth and fabrication of silicon-on-insulator (SOI) structures, based on heteroepitaxial growth of CaF₂ films on silicon, is reviewed. This approach has led to prototype SOI structures, such as MOSFETS, with promising performance. The combination of silicide and fluoride heteroepitaxy on silicon may lead eventually to multiple level SOI device structures.

The present understanding of the properties of heteroepitaxial Si films grown on yttria stabilized zirconia single crystals (YSZ) is reviewed with particular emphasis on the properties of Si films resulting from high temperature post oxidation treatment. The crystalline, physic() chemical and electrical properties of Si films obtained by pyrolysis of SiH4 have been characterized by various analytical techniques. The results indicate that under carefully controlled deposition conditions, the crystalline quality (density of defects, of grain boundaries ....) is better for Si deposited on YSZ (SOZ structure), than for Si deposited on sapphire (SOS structure). The Si films, as deposited on YSZ, are highly resistive (cil -,_, 105 Q cm) ; a high temperature annealing in neutral atmosphere improves the quality of the films. In contrast to SOS, self doping is absent in SOZ structures (p lir O. cm). Further

The purpose of the novel zone-melting recrystallization process (ZMR) is to produce single crystalline Si films on Si0₂ of high crystalline perfection, which are suitable for device fabrication and subsequent industrial applications. However, silicon films grown on amorphous insulating substrates without seeding contain regularly spaced subgrain boundaries as their predominant growth defect and to a lesser degree twin boundaries and some grain boundaries. Detailed materials studies have revealed the core structure of these extended defects and the fundamental mechanisms responsible for subgrain boundary formation. The nature and origin of subgrain boundaries is reviewed and a model for polygonization of the initial dislocation arrays is presented. In addition to subgrain boundary formation, silicon films on quartz are subject to microcracking due to thermal mismatch with the substrate. The influence of these residual growth defects and the inherent tensile stress on device performance is evaluated.

The novel approach to increase the performance of semiconductor devices is proposed. This approach is based on the concept of three-dimensional device fabrication where a single-crystalline Si layer is electrically isolated from a similar Si layer by a Si0₂ film. The growth of this single-crystalline Si layer is accomplished by an epitaxial growth of Si on slots of the seed region of a Si substrate bordered with a Si0₂ film and the overgrowth of Si on top of the Si0₂ surface by the CVD technique. The single-crystallinity of the epilayer has been revealed by the presence of Kikuchi lines on its surface.

Metal silicides are now being used as an integral part of microelectronic technology. The possiblility of epitaxial deposition affords additional potentials for many device and integrated circuit applications. Molecular beam epitaxy (MBE) has been successfully used to grow morphologically uniform epi-CoSi₂ and Ni₂Si₂ films on Si although a significant lattice mismatch is present. Using MBE, multi-layered structures have also been demonstrated without observable interdiffusion among the layers. Apparently, the strain is totally accommodated in the pseudomorphic growth. In this review, the crystallinity and morphological quality of epitaxial heterostructures grown by MBE and solid phase epitaxy will be discussed. The crystallinity is characterized with Rutherford backscattering spectroscopy, electron loss spectroscopy and x-ray diffraction while the surface morphology is determined from scanning electron microscopy. Uniform silicide films are grown successfully if the film thickness is limited. More recent works on the study of Si/Silicide/Si along with other multi-quantum well structures are discussed. Demonstrated and potential device applications using these MBE films are described.

The structure and related electrical properties of ohmic Au-Ni-Ge contacts, and Schottky: TiSi₂ and Au contacts are reviewed in this paper. Defects present in GaAs beneath the metal (anion rich - As accumulation) were suggested to be responsible for Schottky level pinning. It was shown that residual oxygen on the GaAs surface prior to metal deposition can strongly influence the interface abruptness, contact parameters and reliability of both ohmic and Schottky contacts.

Thin film properties of niobium silicide (Si/Nb ~ 2.1) on SiO₂/Si substrates after rapid thermal annealing in two different systems were investigated. The structural and compositional properties were examined with X-ray diffraction and Rutherford backscatter-ing spectrometry. X-ray diffraction revealed that NbSi₂ was the predominant silicide phase present, as the grain size increased from 10 to 160Å before and after annealing at 1100°C for 10 sec. Isochronal and isothermal annealing at 800-1200°C for 10-120 sec showed that over 50% decrease in resistivity occurred in the first 10 sec and the lowest resistivity value of 85μO-cm was obtained after annealing at 1200°C for 120 sec. Also, a corresponding increase in film reflectance was observed with the decrease in sheet resistivity. Furthermore, annealing at 1300°C led to precipitate formation on the silicide surface.

The properties and structures of tantalum and niobium silicides formed by rapid annealing of scanning Electron Beam have been investigated. The fine layers of tantalum and silicon Niobium and silicon were deposited by co-sputtering system and co-evaporating system, respectively. The Scanning Electron beam Equipment with quasi-linear source was used to realize the rapid annealing for forming the TaSi₂ and NbSi₂. The x-ray diffraction RBS and TEM have been used to characterize the Composition and structure of silicide film. The best conditions of forming silicides has been presented. The single phase TaSi₂ and NbSi₂ and the resistivity of 50 Micro Ohm-Cm have been obtained in annealing time of 10-100 seconds. The results have been compared with those of furnace thermal annealing.

The elastic resonance scattering of 3.05 MeV ⁴He⁺⁺by ¹⁶0 is studied for the case where the oxygen is present as an interfacial impurity between a Si substrate and a metallic overlain film. A simple model is developed and experimentally tested to describe the effect of the overlayer on the excitation curve and on the incident beam energy required to obtain resonance. This analytical method is very useful to study the influence of interfacial oxygen on the reaction of metallic overlayers, as shown by specific results with Al.

Chemical and electrical changes in Co/Si and Ni/Si bilayered films on Si0₂ substrates are investigated. The Si thicknesses chosen correspond to 0 to 11 atomic percent of the total film. After the films were vacuum annealed at 400, 500, 600, 700, 800, and 900°C for 1 hour, they were examined by means of ⁴He⁺ backscattering spectrometry, x-ray Read camera and diffractometer, scanning electron and optical microscopy, and four point probe resistivity measurements. At low annealing temperatures, we observe the Ni₅Si₂, Ni₃Si and Co₂Si phases. At 800 and 900°C, Si dissolves in the film. The film resistivity increses rapidly as the amount of dissolved Si in the film rises. For example, 2 at.% and 3.6 at.% suffice to double the film resistivity of Co and Ni, respectively. The lattice parameter perpendicular to the plane of the film for films annealed at 900°C was determined at room temperature and found to decrease with increasing Si content. The surface of a pure metal film becomes nonuniform upon 900°C annealing; adding as little as 2.5 at.% Si stabilizes the film morphology.