A. E. Michel

Rapid annealing and the anomalous diffusion of ion implanted boron into silicon

The anomalous diffusion of ion implanted boron into silicon is shown to be a transient effect with a decay time that decreases rapidly with increasing anneal temperature. The decay time is approximately 45 min at 800 °C and decreases to the order of a second at 1000 °C. The anomalous displacement in the low concentration region is greater at low temperatures but a larger fraction of the boron is redistributed at high temperature. Sheet resistance measurements agree with the idea that the moving fraction of the boron atoms is electrically active and limited to the intrinsic carrier concentration at the anneal temperature. The activation energy for the decay of the transient is greater than that for the diffusion coefficient, which makes an appropriate rapid thermal anneal cycle an important practical process in the fabrication of shallow p‐n junctions.

Boron, phosphorus, and arsenic diffusion in TiSi2

The diffusivities of B, P, and As implanted in TiSi2 are analyzed between 500 and 900 °C by secondary ion mass spectroscopy. It is shown that P and As have high (and almost equal) diffusivities compared with B which appears immobile. This difference is presumed to be related to the very high stability of TiB2 (as compared with TiSi2) and the probable precipitation of B in the form of a titanium boride. The lattice diffusion coefficients for As and P are deduced from the diffusion profiles; they range from 10−17 to 10−14 cm2/s between 550 and 800 ° C. The activation energies are found to be, respectively, 1.8 and 2.0 eV; values close to the activation energy for the self‐diffusion of Si in TiSi2, 1.8 eV. The diffusion profiles also show a high grain boundary diffusivity and an accumulation of dopant at the TiSi2–Si interface.

Channeling in low energy boron ion implantation

The effects of both planar and axial channeling on the profile of 5‐keV boron ions implanted into (100) oriented silicon wafers are demonstrated. A tilt angle of 12° from the (100) axis in a ‘‘random’’ crystallographic direction is required to minimize the (100) axial channeling tail. It is also shown that the effect of channeling along 100 planar channels produces a negligible addition to the channeling tail, whereas channeling along the (110) planar channels produces a measurable contribution. Implantation through a thin, 8‐nm, thermally grown silicon dioxide layer with the ion beam aligned along the (100) direction produces an ion profile comparable to an offset of 9° in a random direction.

Implantation damage and the anomalous transient diffusion of ion‐implanted boron

The effect of the implantation of silicon ions on the anomalous transient diffusion of ion‐implanted boron is investigated. It is found that silicon ion fluences well below that necessary to amorphize the lattice substantially reduce the anomalous transient diffusion of subsequently implanted boron. The sheet resistance, however, is increased by the additional silicon implant. The implantation of silicon ions into activated boron layers causes additional anomalous diffusion at substantial distances beyond the range of the silicon ions. The anomalous motion is also reduced in regions where the damage is greater. The effects can be explained in terms of the generation of point defect clusters which dissolve during anneal and the sinking of point defects in the regions of high damage by the formation of interstitial type extended defects.

GaAs Injection Laser with Novel Mode Control and Switching Properties

The effects of nonuniform current densities on the properties of GaAs injection lasers are investigated. The structure studied is an injection laser with a channel etched on the p side of the junction parallel to the reflecting ends. It is found that the threshold current is higher for nonuniform currents than for uniform currents. The mode in which the laser oscillates depends on the distribution of current. A simple model of the transition and the energy vs density of states for the semiconductor is presented to explain these effects. Bistable operation of the structure has been observed.

The poly‐single crystalline silicon interface

Cross sectional transmission electron microscopy (TEM) reveals an amorphous interfacial region of the order of 2 nm thick between chemical vapor deposition‐(CVD) deposited polycrystalline silicon films and the single‐crystal silicon substrate. The continuity of this region varies from sample to sample and plays an important role in the effects produced by subsequent heat treatment. In cases where this interfacial layer is continuous, the deposited layer remains polycrystalline. When the region is discontinuous, complete epitaxial realignment of the poly is possible. The speed of realignment depends on the implanted arsenic dose and is much greater than reported for undoped films. Various impurities are also observed at the interface and correlate with the character of the interface.

Anomalous transient diffusion of ion implanted dopants: A phenomenological model

Abstract The reduced thermal budget required for very shallow p/n junctions gives greater significance to some of the previously ignored effects occurring during the anneal of ion implanted layers. The anomalous transient displacement that is observed for some dopants during high temperature, short time anneals is a major contribution to the junction depth. The experimental evidence supports a model for the transient displacement that involves the evolution of the damage created by the implanted ions. It is thermal dissolution of small clusters of interstitial silicon atoms created by the ion implantation that produces a supersaturation of interstitial silicon atoms which is the basic cause of the anomalous transient displacement. The formation of extended defects also plays an important role in the redistribution and activation of the dopant.

Investigation of transient diffusion effects in rapid thermally processed ion implanted arsenic in silicon

Arsenic dopant profile motion in ion implanted Si samples annealed for a few seconds at 1100 °C is adequately described by a model involving concentration enhanced diffusion. There is no evidence of an initial rapid diffusive transient. Diffusion in samples preannealed at 550 °C is consistent with this result.

Transient diffusion of boron implanted in SI along random and channeling directions

Abstract We have studied anomalous diffusion of boron implanted into silicon along the [100] channeling direction versus random directions for 5, 10, and 40 keV, 2 × 1014 cm2 boron implantations. Three different annealing conditions, 800 °C for l h, 900 °C for 30 min, and 1000 °C for 10 s, were studied. Anomalous diffusion was observed for all implants annealed at all conditions. The amount of enhanced diffusion is 10–50% higher in the implants along the channeling direction than along the random directions. We attribute the mechanism of the diffusion enhancement to the annealing of ion implantation damage. The difference of diffusion enhancement between channeled implants and random implants are due to the difference in damage profile of the two different implants. Electrical activity of boron is observed for random and for channeled implantations, and the shape of the Hall profile agrees with that of SIMS.

Anomalous diffusion of boron implanted into silicon along the [100] direction

We have observed transient enhanced diffusion of boron implanted into silicon along the [100] channeling direction and compared it with that of boron implanted in a ‘‘random’’ direction. It is found that the anomalous boron displacement for the channeled implants is significantly greater than for the random counterparts. An empirical explanation for the greater displacement of the channeled implants is proposed that is related to the spatial distribution of the implanted boron and the lattice damage generated by the implantation process.