P. M. Rousseau

Arsenic deactivation enhanced diffusion: A time, temperature, and concentration study

The electrical deactivation of arsenic in silicon has been studied with regard to its effect on enhanced diffusion. Experimental structures consist of a buried boron layer as an interstitial detector, and a fully activated arsenic doped laser annealed surface layer. As these structures are annealed at temperatures between 500 and 750 °C, arsenic in the surface layer deactivates and we observe enhanced diffusion of the buried boron layer. A study with time reveals that the enhanced diffusion transient and the deactivation transient are similar, indicating a strong correlation between both phenomena. The dependence on concentration shows a maximum enhanced diffusion for concentrations between 3 and 4×1020 cm−3 of initially active arsenic. Above these concentrations, the large supersaturation of interstitials nucleates dislocation loops and lowers the overall enhancement measured in the buried boron layer. Temperature data show that even for temperatures as low as 500 °C, enhanced diffusion is observed. Thes...

Vacancy generation resulting from electrical deactivation of arsenic

Electrical deactivation of arsenic in highly doped silicon has been studied using the positron‐beam technique. Direct experimental evidence linking the formation of arsenic‐vacancy complexes (i.e., Asn‐v) to the deactivation process is reported. The average number of arsenic atoms per complex, n≳2, was determined by comparing the observed complex concentrations with those of the deactivated arsenic inferred from Hall‐effect measurements.

Electrical deactivation of arsenic as a source of point defects

The effect of electrical deactivation of arsenic in silicon has been studied. High concentrations of arsenic were implanted and laser melt annealed, creating boxlike fully electrically active arsenic layers, with no residual implant damage. Wafers were then subjected to low temperature thermal cycles while a buried boron layer monitored point defects. Strong enhancements in the boron diffusion were observed suggesting that arsenic deactivation releases large numbers of interstitials. This is explained by a process where the vacancies required by the deactivated arsenic structures are created through a deactivation assisted Frenkel pair generation process, thus injecting interstitials.

The effect of source/drain processing on the reverse short channel effect of deep sub-micron bulk and SOI NMOSFETs

This study presents a systematic investigation of the effects of source/drain processing on the reverse short channel effect (RSCE) and is the first to demonstrate significant differences in the electrical behavior of identically processed silicon-on-insulator (SOI) and bulk devices due to dopant diffusion kinetics. In bulk and SOI devices, the RCSE due to implantation damage enhanced diffusion is minimized if a high temperature rapid thermal anneal follows the source/drain implantation. The magnitude of the V/sub th/ roll-up is significantly smaller in SOI than in bulk. When arsenic concentrations greater than 2.5/spl times/10/sup 20/ cm/sup -3/ are used, arsenic deactivation enhanced diffusion can cause a significant increase in V/sub th/ rollup.

Deactivation in heavily arsenic-doped silicon

We have combined ab initio calculations with a general statistical theory to predict the properties of heavily arsenic-doped silicon. Although we find that a lattice vacancy surrounded by four arsenic (VAs4) is the dominant deactivating complex at high arsenic concentrations in equilibrium, vacancy clusters with fewer arsenic neighbors are present in significant quantities. These smaller complexes are essential not only to the establishment of equilibrium, since SiAs4 clusters are extremely rare, but can also explain deactivation even if VAs4 formation is kinetically inhibited. This suggests that materials with similar arsenic concentration and deactivation fractions can have different microscopic states, and therefore behave differently in subsequent processing. Good agreement is found between theory and experiment for the electronic concentration as a function of temperature and total arsenic concentration. We also show that for low arsenic concentrations, full activation is the equilibrium condition.

Arsenic deactivation enhanced diffusion and the reverse short-channel effect

The effect of enhanced diffusion caused by the electrical deactivation of arsenic on the reverse short-channel effect (RSCE) in NMOS devices is investigated. A simple four-mask process was utilized to fabricate deep sub-micron NMOS devices. Source/drain (S/D) implant and anneal conditions were varied in order to determine their implications on the RSCE. Results indicate that when high concentrations of arsenic deactivate, enhanced diffusion occurs, leading to significantly more RSCE. This implies that the dose of the arsenic implant and the subsequent anneals should be carefully considered in source/drain engineering.

Evolution of the crystallographic position of As impurities in heavily doped Si crystals as their electrical activity changes

Arsenic impurities in silicon can be electrically activated beyond their electrical solubility to as high as 4×1021/cm3 by ion implantation and laser melting; further annealing decreases this activity to its equilibrium saturation level. To characterize the deactivation process, we used x‐ray standing‐wave spectroscopy. Hall effect, and secondary‐ion‐mass spectroscopy. Our results indicate that the As impurities remain in substitutional positions even after 85% of the activation has been lost, so deactivation cannot be due to As migration to interstitial sites or to large precipitates.

Lattice compression of Si crystals and crystallographic position of As impurities measured with x-ray standing wave spectroscopy

In an earlier letter [Appl. Phys. Lett. 68, 3090 (1996)] we reported results about heavily arsenic doped silicon crystals, where we unambiguously showed, based on x-ray standing wave spectroscopy (XSW) and other techniques, that electrically deactivated As remains essentially substitutional. In this article we present the analysis methodology that led us to said conclusion, and show how from further analysis it is possible to extract the compression or expansion of thin epitaxial layers. We report the evolution of the compression of highly As doped Si epitaxial layers as deactivation takes place. The XSW measurements required a very small thickness of the doped layer and a perfect registry between the substrate and the surface layer. We found larger values for compression than previously reported, which may be explained by the absence of structural defects on our samples that relax the interface stress. Our results show a saturation on the compression as the electron concentration increases. We also repor...

Enhanced diffusion by electrical deactivation of arsenic and its implications for bipolar devices

In this paper, we present experiments designed to show enhanced diffusion of dopants due to the electrical deactivation of implanted arsenic or arsenic in-diffused from polysilicon. Results show a clear enhancement of diffusion in a nearby boron layer as well as an enhancement for the arsenic itself at an annealing temperature of 750/spl deg/C. At 500/spl deg/C, more typical of backend processing, no enhancement is detected in accordance with the very slow deactivation process at this temperature. Implications for bipolar devices were also investigated. Large differences in device characteristics were measured due to the enhanced diffusion. Secondary ion mass spectrometry (SIMS) analysis and simulation confirmed that enhanced diffusion of both arsenic and boron is the cause for the change in device characteristics. Evidence is also presented demonstrating that the order of the anneals is crucial, thereby rejecting the hypothesis of a full coupled diffusion effect as seen for phosphorus.

On the electrical deactivation of arsenic in silicon

Previous work on thermally induced arsenic deactivation in highly doped silicon has proven the generation of vacancies and suggests the formation of arsenic-vacancy clusters as the deactivation mechanism. Using positron annihilation spectroscopy in the two-detector coincidence geometry, we are able to show that the thermally generated vacancies are indeed surrounded by arsenic atoms.