Plastic deformation of several covalently-bound materials has been studied during ion irradiation. In all of these materials, namely crystalline and amorphous silicon, crystalline and amorphous Si0.9Ge0.1, and amorphous SiO2, the damage created by the ion beam causes density changes in the irradiated region which eventually saturate with ion dose. In the crystalline materials, the density changes were accompanied by a transformation to the amorphous phase. Superimposed on the density changes is plastic deformation which occurs during irradiation of both crystalline and amorphous materials to relieve stresses in the irradiated region. A wafer curvature measurement technique has been developed which allows the contributions from density changes and plastic deformation to be distinguished and the stress dependence of the plastic deformation to be determined.

In all of the amorphous materials, the plastic deformation is Newtonian viscous shear flow, which is characteristic of solids where deformation is governed by the diffusive motion of point defects. The radiation-enhanced shear viscosity per ion was flux-independent, revealing that flow occurs rapidly, probably within the localized damaged regions created by each ion. This viscosity does not depend strongly on the material. In fact, similar viscosities were obtained during measurements of radiation-enhanced plastic deformation of crystalline covalent samples and polycrystalline aluminum films.

Crystalline silicon (c-Si) and structurally relaxed amorphous silicon (a-Si) were implanted with 1 MeV Si+ at liquid nitrogen temperature. The photocarrier lifetime τ in the implanted samples was determined with sub-picosecond resolution through pump-probe reflectivity measurements. At low damage levels (i.e. <1014 ions/cm2), τ decreases with increasing ion dose in both materials, indicating a build up of trapping and recombination centers. The dominant centers in c-Si appear to be related to simple defects. The generation rate of electrically active defects is found to be the same in relaxed a-Si and c-Si, which suggests that the structural defects formed in a-Si strongly resemble the simple defects in c-Si. For ion doses > 1014 /cm2, τ saturates at a level of 0.8 ps for both materials. Strikingly, the saturation sets in far below the dose needed to amorphize (>1015 /cm2). The defect density in a-Si at saturation is estimated to be ≈1.6 at.%.

The dynamics of relaxation of amorphous silicon after unrelaxation (creation of defects) by irradiation with 600 KeV Kr++ ions is investigated using the changes in electrical conductivity of amorphous silicon. By measuring the conductivity of such unrelaxed amorphous silicon after being partially relaxed by isochronal anneals in a temperature range from 383 to 873° K, it is shown that conductivity of amorphous silicon decreases monotonically by up to 3 orders of magnitude as it relaxes; i.e. that conductivity is a measure of the degree of relaxation. Furthermore, it is found that such change in conductivity can be completely reversed by a subsequent unrelaxation with ion irradiation. Continuous in situ measurements of conductivity of amorphous silicon before, during and immediately after irradiation in a temperature range from 77 to 573° K show that relaxation occurs even at 77°K. Finally, the relaxation of amorphous silicon thus measured is linear when plotted against ln(t), a behavior that is characteristic of relaxation with a spectrum of activation energies.

Isolated amorphous zones produced in GaAs, GaP, Si, and Ge by the implantation of 50 keV Kr+ or Xe+ ions have been induced to recrystallize under the influence of the electron beam in the transmission electron microscope. This effect has been investigated as a function of electron irradiation temperature and beam energy in the TEM. Temperature effects were investigated through irradiations performed at 30 and 300 K. The electron energies used ranged from 50–300 keV in the 300 K experiments and 200 keV electrons were used at 30 K.

Recovery was induced in all of the materials even at electron energies below the threshold displacement energy indicating production of point defects within the crystalline material is not required to induce regrowth. In GaAs and GaP, recovery occurred for all electron energies studied, down to 50 keV. In Si, the beam induced regrowth rate approaches zero at an energy of 80 keV with the recovery rate increasing with increasing electron energy. At 30 K, the 200 keV electron beam induced recrystallization in all cases studied (GaAs, GaP, and Si).

Detailed measurements of the stresses induced by implantation of ions of different types, such as light ions: boron and nitrogen, and heavy ions: argon, krypton and xenon, were carried out in situ on thin silicon films. The measurement were made for keV energy of ions, for a wide range of doses and for different values of the dose rate. Experimental results indicate that the ion-beam-induced transformation in silicon is dose-rate dependent for light ions, as well as for heavy ions. The last conclusion contradicts the classical ideas of amorphization of elemental semiconductors by heavy ions that are based on the concepts of a heterogeneous mechanism of formation of the amorphous state during implantation. Heavy-ion implantation behaves similarly with light-ion implantation at a higher sample temperature. A comparison TEM investigation with stress measurement was made. The results indicate that i) the ion-beam-induced deformation correlates with structural changes and ii) both homogeneous and heterogeneous mechanisms are involved in the structural changes. The results are discussed in terms of non-equilibrium phase transitions in silicon under irradiation.

Amorphous Si has been investigated by variable-energy positron annihilation spectroscopy (PAS) and lifetime measurements of optically generated free carriers. The density of positron-trapping defects can be reduced by thermal annealing at 500°C. Simultaneously, the density of bandgap states is reduced as indicated by an increased photocarrier lifetime. Hydrogen, implanted and annealed at 150°C, leads to an increased photocarrier lifetime and reduced positron trapping. It appears that (some of) the electrical defects are associated with positron-trapping, and therefore possibly vacancy-type, structural defects. Finally, both methods have been used to detect small amounts of ion irradiation damage in amorphous Si.

An in situ method for determining the ion implantation dose necessary to make Si amorphous is developed and utilized. This method is based on measuring ion-implantation-induced in-plane stress. Measurements are carried out for various low energy ions implanted into thin p-type (100) Si. The doses necessary to make Si amorphous obtained by this method are in good agreement with previous data. This technique is sensitive, informative, quick, visual and nondestructive.

Photoluminescence of erbium in ion-implanted amorphous Si has been observed after annealing at 400°C. In addition, a broad band of luminescence attributed to intrinsic defects in amorphous Si is present. The background level steadily increases with increasing anneal temperature. The fluorescence lifetimes of either the Er or the background in all samples are ≤150μsec.

The solid phase epitaxial regrowth (SPER) process of implantation amorphized Si0.7Ge0.3 layers (850± Å thick) grown on (100) Si has been studied by cross-sectional transmission electron microscopy. For amorphous layers produced by 40 Ar+ implantation highly defective three dimensional regrowth was observed in both Si0.7Ge0.3 and Si. Stacking faults were the principle defect formed of both materials during regrowth. SPER after amorphization via 73 Ge+ implantation was also investigated. It was found that the SPER velocity of the 73 Ge+ implanted Si0.7 Ge0.7 Ge0.3 was about twice the velocity of the 40 Ar+ implanted samples; for 73 Ge+ implanted Si it was about three times that of the 40Ar+ implanted samples. The activation energy for SPER in 40Ar+ and in 73 Ge+ implanted Si0.7 Geo0.3 was about 1.6 and 2.6 eV, respectively. The defect density was significantly reduced in 73 Ge+ amorphized Si but not in the 73 Ge+ amorphized Si0.7 Ge0.3. It is proposed that limited Ar solubility inhibits high quality regrowth in both SiGe and Si. Upon 73 Ge+ amorphization and solid phase epitaxy the interfacial strain between the SiGe and Si cannot be accommodated. Thus the epitaxial process is poor in these SiGe strained layers regardless of the amorphizing species.

By performing scaling experiments [1] and examining the evolution of the spatial second moment of the concentration profile, it was shown that the diffusion coefficient of gold in amorphous silicon is both concentration and time dependent. The second moment curves for different temperature anneals can be scaled to a master curve using a factor with an activation enthalpy of 2.0 eV.

In situ TEM observations of defects and. the amorphous phase in Si wafer during 150 keV Ar+ ion implantation were made which elucidated their characteristic behavior in Si. Defects introduced by ion implantation were eliminated by amorphous phase formation and then new defects did not form in the amorphous phase. Microstructural evolution in Si wafers under high dose implantation (2E16 ions/cm2) of 400 keV Si* ions was also investigated at temperatures of -70, -30, 20, 100 and 200 °C using a cross-section 1 TEM observation technique. At temperature of 20 °C and above, a defect layer was formed in each specimen, and the defect density was observed to decrease as temperature increased. At temperture of -30 °C and below the amorphous phase was formed and a defect layer which made contact with this phase was also observed. After annealing of these implanted specimens at 850 °C for 20 min, the amorphous phase had crystallized and the defect layer in contact with the amorphous phase was almost eliminated. But another defect layer was formed during annealing in the region where the amorphous phase had existed.

The transition between relaxed and unrelaxed amorphous silicon can be obtained by thermal treatment of the unrelaxed amorphous or by low dose ion irradiation of the relaxed material. In both cases a variation in the short range order has been invoked to explain the behavior of the structural changes probed by various techniques. In this work we study the influence of such changes on the optical properties of a-Si in the region of the transition between the relaxed and the unrelaxed states. We show that a progressive variation of the optical constant in the visible-near infrared region upon derelaxation occurs. Therefore, significant modifications of the electron density of state in the region above the optical gap are associated with the changes in the short range order probed by Raman spectroscopy.

Multiple-energy implantation of fluorine into rf glow discharge deposited hydrogenated amorphous silicon (a-Si:H) thin films has been performed. It is found that the optical gap decreases with the implanted fluorine concentration CF from 1.56 eV for the unimplanted sample to 1.40 eV for the sample with CF of 3×1021 cm−3. Results of the Staebler-Wronski experiment show that the ratio between the electrical conductivity before and after illumination, as well as the ratio between the photo- and dark conductivity, decrease also with Cp. Electrical measurements show that there is significant decrease in the conductivity activation energy Ea with CF for samples annealed at or below the substrate temperature TS during deposition. But for samples annealed at temperatures higher than TS, Ea was found to change back to values close to that of the unimplanted sample. A large shift to higher energy for one peak in the photoluminescence spectra at 77K has been observed, from 1.34 eV of the unimplanted sample to around 1.6 eV for the implanted samples, though with almost one order of magnitude weakening in intensity. It is also observed that ESR splitting has been induced in the fluorine implanted samples. The g-factors of the two resonances are determined to be 2.003 and 2.006, respectively. For the g=2.006 resonance, the spin density increases markedly after implantation but is essentially independent on CF before annealing and effectively reduced or eliminated after annealing. For the g=2.003 resonance, the spin density increases rapidly with CFp especially in the range from CF = 1×1020 to 1×1021 cm−3 before annealing and reduces only slightly after annealing.

Amorphization of silicon films occurred through homogeneous solidification of molten silicon layers on quartz substrates induced by irradiation with a 30ns-XeCl excimer laser. The crystalline nucleation rate was obtained to be 8×1030m−3s−1. Silicon films were completely amorphized for films thinner than 18nm. Complete amorphizatoin is brought about by reduced grain size and reduced recalescence as the film thickness decreases. Recalescence was observed in situusing transient thermometry with a platinum-temperature-sensing layer when a 15nm-thick silicon film was amorphized.

Melting and solidification of a silicon film by continuous wave laser beam irradiation has been studied. The silicon film melting and recrystallization is controlled by the temperature distribution in the semiconductor. Calculations have been carried out for a range of laser beam parameters and material translational speeds. The results for the melt pool size have been compared with experimental data. The temperature field development has also been monitored with localized transient reflectivity measurements.

Lattice strain and defect formation in oxygen implanted silicon (SIMOX) were investigated as a function of dose and annealing conditions by high resolution x-ray diffraction and transmission electron microscopy. X-ray rocking curves revealed the presence of two distinct strained layers. Self-interstitial clusters and oxygen interstitials gave rise to a buried strain layer in unidirectional tension centered around the projected range at low doses (l×1016 and 3×1016 cm−2. As the dose was increased to 1×1017 and 3×1017 cm−2 a supersaturation of vacancies near the surface produced a second strain layer with a unidirectional lattice contraction at the wafer surface. Annealing at 900°C, 0.5 hr. reduced this surface strain as the defects coarsened into observable cavities. The development of cavities upon annealing was used in a sequential implantation and low temperature annealing process to produce low threading dislocation density SIMOX. Possible mechanisms for threading dislocation formation are discussed.

Although silicon-on-insulator (SOI) materials made by standard energy (150–200 keV) SIMOX processes have shown great promise for meeting the needs of radiation hard microelectronics, there are still problems relating to the radiation hardness and economic viability of standard SIMOX. A low energy SIMOX (LES) process reduces cost and improves radiation hardness and increased throughput of any implanter because much smaller doses are required. In addition, the process is uniquely able to produce high quality thin SIMOX structures that are of particular interest for fully depleted device structures. In this paper, we address the formation of high quality ultrathin SIMOX structures by low energy implantation.

Device grade single crystal <100> silicon wafers have been implanted with 40keV oxygen ions over a dose range of 2×1017 to 8×1017/cm2 at a temperature of 5507±10°C. The specimens have been analyzed, both before and after high-temperature annealing at 1320°C for six hours, using SIMS, RBS, and TEM. During implantation a continuous buried SiO2 layer forms when the dose after which the buried SiO2 layer grows primarily toward the surface. After annealing samples implanted with the doses of both 2×1017 and 3×1017/cm2 it was observed that a defective SIMOX like structure was formed. Implanting with a dose of 4×1017/cm2 results in pit formation in the silicon overlayer. For the sample implanted with a higher dose of 5×1017/cm2, a non-continuous poly-crystalline silicon “overlayer” was formed. It would thus appear that when a single step implantation route is chosen, there is a dose (or layer thickness) limit for the production of a thin film SIMOX structure.

The analysis of SIMOX structures obtained by doing the implantation with different thicknesses of thermal oxide (screen oxide) has been perfomed by Raman scattering, and the results have been correlated with those previously obtained by TEM. The use of a microRaman system on low angle bevelled sample has allowed to directly observe the different regions in the structures, corroborating the structural differences observed by TEM as a function of the screen oxide thickness. For as implanted structures, strong non homogeneous strain and disorder effects are observed in the top Si layers. After the High Temperature Anneal (HTA) process, crystalline quality of the structures is improved. The analysis of the spectra obtained at different excitation powers points out the dependence of the thermal effects of the spectra on the structural features of the scattering volume, as the dislocation density in the annealed layers. This dependence allows the assesment of the crystalline quality of these structures to be made.

We report on the formation and properties of a new type of a buried insulator using combined nitrogen/oxygen implantation with two different implantation energies. In this manner, a stacked layer consisting of silicon dioxide above silicon oxynitride above silicon nitride is formed. Experimental results concerning the impurity profiles, the microstructure and compound formation are presented.