C. A. Evans

Physical and electrical properties of laser‐annealed ion‐implanted silicon

The use of a laser as a tool for annealing of ion‐implantation damage is described. The principal results obtained are as follows: (1) electrical measurements show that activity comparable to that of a 1000 °C 30‐min anneal can be obtained; (2) TEM measurements show that complete recrystallization of the damaged layer occurs during the laser anneal; (3) impurity profiles obtained from SIMS measurments show that the dopant atoms remain in the LSS profile during annealing. Simple diodes were fabricated to examine the feasibility of the method for device fabrication.

Mechanism of the SIMS matrix effect

Quantization of ion microprobe mass spectrometric analyses has been complicated by the variation in the ion yield of an element contained in different matrices. This work demonstrates that, for O− and Cs+ bombardment, these ion‐yield variations are solely attributable to variations in the matrix sputtering yield. It is argued that the matrix sputtering yield determines the near‐surface concentration of the ion‐yield‐enhancing species O and Cs.

Recrystallization of implanted amorphous silicon layers. II. Migration of fluorine in BF+2‐implanted silicon

Fluorine distribution profiles for silicon implanted with BF+2 have been measured by SIMS as a function of anneal temperature and time. Anomalous migration of fluorine is observed in samples having amorphized layers after implantation. Outdiffusion of fluorine occurs during recrystallization of the amorphous layer, and fluorine collects in regions of residual damage during annealing. This gettering of fluorine by defects illustrates the residual damage below the amorphized layer in samples implanted at room temperature is more difficult to anneal out than that in samples implanted at lower temperture (∼−110 °C).

A unified explanation for secondary ion yields

The pure element secondary ion yields under oxygen and cesium ion bombardment are shown to be solely dependent on a) the ionization potential (or electron affinity for negative ionization) of the sputtered atom and b) the reciprocal of the matrix sputtering yield which determines the equilibrium concentration of implanted oxygen or cesium. This unified approach accounts for the yields of C±, Si±, Ge± and Sn± from the pure elements as well as of Ga± and As± from gallium arsenide.

Redistribution of Cr during annealing of 80Se‐implanted GaAs

Cr in‐depth distributions have been measured in Se‐ion‐implanted GaAs as a function of postimplant annealing using secondary‐ion mass spectrometry (SIMS). Analysis shows that Cr redistributes into regions of residual damage following 800 °C annealing. As the damage anneals at higher temperatures, however, the Cr tends toward the GaAs surface. This phenomenon offers a plausible explanation of the discrepancies between the observed electrical and chemical distributions of ion‐implanted Se.

Surface cesium concentrations in cesium‐ion‐bombarded elemental and compound targets

Auger electron spectrometry has been used to characterize the atomic cesium concentration [Cs]a at the surface of cesium ion bombarded silicon and various metal silicides. The Si− ion yield was found to be proportional to [Cs]v2.8±0.1. Surface cesium concentration was also found to increase with increasing inverse sputtering yield S−1 of the substrate. Deviations from a linear dependence of [Cs]v on S−1 are ascribed to differential sputtering effects.

Use of a scanning cw Kr laser to obtain diffusion‐free annealing of B‐implanted silicon

The use of a continuous scanned Kr ion laser as a tool for annealing of boron‐implanted silicon is described. Conditions were found that produce high electrical activity and crystallinity of the implanted layer without redistribution of the boron from the as‐implanted profile.

Anomalous migration of fluorine and electrical activation of boron in BF+2‐implanted silicon

Fluorine distribution profiles for silicon implanted with 150‐keV 1×1015‐cm−2 BF+2 at room temperature or at −110 °C have been measured by SIMS as a function of anneal temperature. Anomalous migration of fluorine during annealing is observed, and is explained in terms of recrystallization and impurity‐gettering effects. Electrical carrier distribution profiles of room‐temperature BF+2‐implanted silicon, measured by differential Hall effect methods, demonstrate that boron is electrically activated by epitaxial recrystallization during 550 °C annealing. However, a damaged region near the crystalline‐amorphous interface remains after recrystallization. This damaged layer is apparently responsible for the fluorine gettering.

Stoichiometric disturbances in ion implanted GaAs and redistribution of Cr during annealing

Using the Boltzmann transport equation, calculations were obtained predicting the zones of stoichiometric imbalance produced in GaAs after ion implantation at energies of 50, 100, and 300 keV. The recoiling Ga and As atoms were shown to produce a zone of interstitials at depths exceeding Rp . Secondary‐ion mass spectrometry profiling indicated that Cr was rapidly redistributed into these regions at temperatures ⩽500 °C. Transmission electron microscopic analyses obtained on horizontally sectioned and vertical cross section samples indicated that the interstitials coalesced into small clustered sites (50–100 A) and were responsible for the development of Cr gettering at depths ≳Rp .

Gettering of mobile oxygen and defect stability within back‐surface damage regions in Si

Motion and gettering of oxygen into damage regions created by back‐surface mechanical abrasion in Si has been investigated using transmission electron microscopy (TEM), scanning electron microscopy, secondary‐ion mass spectrometry profiling and secondary‐ion microscopy. Redistribution and gettering of oxygen have been detected along dislocation lines after annealing at 600 °C by both TEM and direct ion imaging. Subsequent annealing at 1050 °C produces additional gettering, SiOx nucleation, and a dramatic increase in dislocation‐line density within the initial damage region. Secondary dislocation lines extending to a depth ≃ 40 μm are also generated by the two‐stage anneal, resulting in additional gettering sites for oxygen and other impurities. In comparison, single anneals at 1050 °C produce rapid defect annihilation, oxygen outdiffusion, and loss of additional gettering efficiency.