Buried Layer Diffusion Research Articles

Determination of silicon point defect properties from oxidation enhanced diffusion of buried layers

In order to characterize fundamental silicon point defect properties, the enhanced diffusion of phosphorous buried layers as a function of depth into the silicon substrate was measured during interstitial injection via thermal oxidation of the wafer surface. The measurements were used to calculate the effective interstitial diffusivity in epitaxial silicon at 1100 °C. The experimental results were also interpreted using a physical model which includes bulk recombination of interstitials with vacancies and a fast interstitial diffusivity calculated from metal gettering. The model effectively accounted for the experimental data, and through comparison of the data with model simulations, the ratio of the concentrations of vacancies and interstitials in equilibrium was obtained.

Switching properties of polysilicon emitter transistor operating in saturation

Saturation behaviour of a polysilicon emitter transistor is studied using the analysis of the most fundamental parameter, the saturation time constant, and correlated with the physical structure. The analysis takes into account the effect of the polysilicon/monosilicon interface in the emitter and n/n/sup +/ type transition interface due to be buried layer diffusion in the collector. The effect of the polysilicon/monosilicon interface becomes crucial to the transistor behaviour at smaller emitter junction depths. The interface contributes to a significant amount of charge storage in the emitter region and is independent of charge storage in the collector region bounded by the n/n/sup +/ interface recombination velocity. The increase in saturation time constant because of charge storage in the emitter and collector regions should be taken into consideration in the design of BiCMOS VLSI circuits.

Silicon Nitride Masking Integrity Characterization

The masking integrity of a mask against an Sb diffusion is characterized as a function of ratio during the deposition and the oxygen partial pressure during the subsequent high‐temperature buried layer diffusion. Localized masking failure occurs with Si rich ratio during deposition equals 1.0. Sb penetration depth through the mask, measured by SIMS, increases by a factor of two‐three when the oxygen partial pressure during the buried layer diffusion is increased from 0.0145 to 0.0822 atmospheres. Total masking failure results with oxygen partial pressures greater than 0.100 atmospheres. The oxidation of is responsible for the oxygen partial pressure dependence of the Sb penetration depth.

Measurements of Enhanced Diffusion of Buried Layers in Silicon Membrane Structures During Oxidation

AbstractReported calculations of the diffusion coefficient of silicon self interstitials vary over several orders of magnitude at temperatures of interest for integrated circuit fabrication. In this work, we measure the enhanced diffusion of phosphorus buried layers while interstitials are injected at a wafer surface via thermal oxidation. The starting substrates were either float-zone silicon or Czochralski silicon with a pre-treatment to precipitate excess oxygen. The samples were prepared by implantation of phosphorus followed by the growth of a 40-60µm epitaxial layer. They were then etched anisotropically from the frontside or backside to yield membrane structures. Local oxidation was performed at 1100°C on either the frontside or backside of each wafer and buried layer diffusion was monitored, yielding information about interstitial diffusion in silicon and it’s dependence on bulk properties.

Measurement of silicon interstitial diffusivity

A conceptually simple experiment to measure silicon interstitial diffusivity is described. The structure uses a silicon wafer with buried layers deep in the bulk. Oxidation of the wafer surface generates interstitials that diffuse into the wafer and enhance the buried layer diffusion. The results show that the interstitial profiles are flat out to 40 μm for the times and temperatures investigated. We can thus conclude that the interstitials move significantly faster than previously thought.