O. W. Holland

Ion beams in silicon processing and characterization

General trends in integrated circuit technology toward smaller device dimensions, lower thermal budgets, and simplified processing steps present severe physical and engineering challenges to ion implantation. These challenges, together with the need for physically based models at exceedingly small dimensions, are leading to a new level of understanding of fundamental defect science in Si. In this article, we review the current status and future trends in ion implantation of Si at low and high energies with particular emphasis on areas where recent advances have been made and where further understanding is needed. Particularly interesting are the emerging approaches to defect and dopant distribution modeling, transient enhanced diffusion, high energy implantation and defect accumulation, and metal impurity gettering. Developments in the use of ion beams for analysis indicate much progress has been made in one-dimensional analysis, but that severe challenges for two-dimensional characterization remain. The ...

Efficient production of silicon-on-insulator films by co-implantation of He+ with H+

We have investigated the process of thin film separation by gas ion implantation and wafer bonding, as well as the more basic phenomenon of blistering, on which the technique is based. We show that when H and He gas implants are combined they produce a synergistic effect which enables thin-film separation at a much lower total implantation dose than that required for either H or He alone. By varying the H and He implantation doses we have been able to isolate the physical and chemical contributions of the gases to the blistering processes. We find that the essential role of H is to interact chemically with the implantation damage and create H-stabilized platelet-like defects, or microvoids. The efficiency of H in this action is linked to its effective lowering of the silicon internal surface energy. The second key component of the process is physical; it consists of diffusion of gas into the microvoids and gas expansion during annealing, which drives growth and the eventual intersection of the microvoids ...

Formation of epitaxial layers of Ge on Si substrates by Ge implantation and oxidation

Thin epitaxial layers of Ge‐Si alloys have been formed on Si(100) substrates by steam oxidation of Ge‐implanted samples. During the oxidation, the Ge is totally piled up ahead of the SiO2/Si interface. This segregation of Ge leads to the formation of a distinct, Ge‐rich layer which is epitaxial with the underlying Si. The thickness of the Ge layer is dependent on the implantation dose. This layer and its two bounding interfaces with the oxide and Si are characterized as a function of the implantation dose and energy, using Rutherford backscattering and high‐resolution transmission electron microscopy.

Novel oxidation process in Ge+‐implanted Si and its effect on oxidation kinetics

Thermal oxidation of Si is shown to be substantially affected by the implantation of Ge+ ions. A unique morphology develops during steam oxidation due to the rejection of Ge from the oxide at the growth interface. The Ge pile‐up leads to the formation of a distinct layer of almost pure Ge between the oxide and the underlying Si. Oxidation rates are enhanced due to the presence of this film which is shown to increase the interfacial reaction rate. This increase is attributed to a decrease in the binding energy of Si atoms at the interface as a result of alloying with the Ge film. A model is proposed to account for the enhanced oxidation kinetics and is shown to be in good agreement with experimental data.

Ion implantation and thermal annealing of α‐Al2O3 single crystals

The effects of ion implantation and post‐implantation thermal annealing of α‐Al2O3 have been characterized using ion scattering‐channeling techniques, and correlated with electron paramagnetic resonance (EPR) and microhardness measurements. Although most of the work was done on 52Cr implanted specimens, preliminary results have been obtained also for implanted 90Zr and 48Ti. For Cr implantation, the Al2O3 lattice damage saturates at relatively low doses, but the near‐surface region never becomes amorphous. A preferential annealing behavior begins in the Al sublattice after ∼800 °C annealing, and in the oxygen sublattice, only after 1000 °C annealing. Lattice location measurements show that after annealing to 1500 °C, Cr is greater than 95% substitutional in the Al sublattice. Above 1500 °C, implanted Cr atoms redistribute by substitutional diffusion processes. EPR measurements show that part, if not all, of the implanted Cr is trivalent and substitutional after annealing to 1600 °C. Microhardness measurem...

Al and B ion‐implantations in 6H‐ and 3C‐SiC

Low (keV) and high (MeV) energy Al and B implants were performed into n‐type 6H‐ and 3C‐SiC at both room temperature and 850 °C. The material was annealed at 1100, 1200, or 1400 °C for 10 min and characterized by secondary ion mass spectrometry, Rutherford backscattering (RBS), photoluminescence, Hall and capacitance‐voltage measurement techniques. For both Al and B implants, the implant species was gettered at 0.7 Rp (where Rp is the projected range) in samples implanted at 850 °C and annealed at 1400 °C. In the samples that were amorphized by the room temperature implantation, a distinct damage peak remained in the RBS spectrum even after 1400 °C annealing. For the samples implanted at 850 °C, which were not amorphized, the damage peak disappeared after 1400 °C annealing. P‐type conduction is observed only in samples implanted by Al at 850 °C and annealed at 1400 °C in Ar, with 1% dopant electrical activation.

Ion implantation damage and annealing in germanium

We have observed a unique damage structure, which forms within the amorphous phase, in ion‐implanted Ge above a certain ion dose. This structure, which represents a drastic alteration of the near‐surface morphology, is responsible for the adsorption of large quantities of C and O onto the surface of the implanted area. Results are presented of a systematic study of this effect and possible mechanisms for its information are discussed. Ion implantation conditions desirable for device applications are established and deleterious effects due to the presence of this damage upon both solid‐ and liquid‐phase epitaxial growth of the implanted layers are discussed.

Solid-phase-epitaxial growth and formation of metastable alloys in ion implanted silicon

Transmission electron microscopy (cross‐section and plan‐view) and ion backscattering techniques have been combined to study the details of solid‐phase‐epitaxial (SPE) growth in Sb+, In+, Bi+, Ga+, and As+ implanted silicon after furnace annealing in the temperature range 450 to 650 °C. The ion implanted amorphous layer grew ‘‘defect‐free’’ in 〈001〉 orientations and the crystalline–amorphous (c–a) interface during growth contained undulations ∼5 A over the intervals of 200–500 A. During SPE growth in 〈111〉 orientations, the c–a interface was atomically smooth initially, but eventually became nonplanar due to the formation of twins. From SPE growth rates at different temperatures, the activation energy associated with the growth was determined to be 2.6±0.3 eV. The dopant concentrations in defect‐free SPE grown layers were found to exceed equilibrium solid solubility limits by as much as a factor of 560 in the Si–Bi system. The absolute maximum concentrations, corresponding to the intersections of free‐ene...

Ion-induced damage and amorphization in Si

Abstract Ion-induced damage growth in high-energy, self-ion irradiated Si was studied using electron microscopy and Rutherford backscattering spectrometry. The results show that there is a marked variation in the rate of damage growth, as well as the damage morphology, along the path of the ion. Near the ion end-of-range (eor), damage increases monotonically with ion fluence until a buried amorphous layer is formed, while damage growth saturates at a low level in the region ahead. Damage growth remains saturated ahead of the eor until expansion of the buried amorphous layer encroaches into the region. The morphology of the damage in the saturated region is shown to consist predominantly of simple defect clusters such as the divacancy. A homogeneous nucleation and growth model, presented to account for damage saturation, is shown to also predict the dose-rate dependence of the saturation level. Mechanisms are identified which contribute to the unconstrained damage growth observed near the eor prior to amorphization, and subsequently at the interface of the buried amorphous layer. The effects of an imbalance in the generation rates of interstitials and vacancies on damage growth in the eor region are discussed. This imbalance is shown to arise either as a result of added atoms during implantation or spatial separation of the Frenkel defect pairs created during ion impact. A local, uniaxial strain field in the interfacial region of the amorphous layer is identified, and the possibility of its contribution to growth at that location is discussed.

New model for damage accumulation in Si during self‐ion irradiation

The dependence of the damage produced by self‐ion implantation in Si on dose is determined and is shown to exhibit two distinct behaviors: an initial sublinear increase of damage with dose, followed by a period of greatly accelerated growth. Ion backscattering analysis using both single‐ and double‐alignment channeling measurements is used to determine the distribution of damage in the samples. The nature of the damage is determined from its thermal annealing behavior and differences in the spectra recorded in the two channeling configurations. Damage is found to consist predominantly of two components: simple defects, such as divacancies, and regions of amorphous Si. The behavior of these components is shown to be divergent at the fluence which separates the two different growth regimes. A model is proposed which considers the amorphization process in Si as a critical‐point phenomenon, one in which the onset of amorphization leads to a cooperative behavior among the various types of damage resulting in a...