U. Lambert

Influence of boron concentration on the oxidation-induced stacking fault ring in Czochralski silicon crystals

The influence of the boron doping level in the range of 1 x 10(15)-2 x 10(19) cm(-3) on the position of the oxidation-induced stacking fault ring (R-OSF) in silicon crystals has been investigated by experiments and numerical simulation. For low boron-doped crystals, the position of the R-OSF is described by a critical value C-crit defined by the ratio of the pull rate and the temperature gradient in the crystal at the solid/liquid interface. Boron concentrations higher-than 10(17) cm(-3) shift the position of the R-OSF towards the wafer center without change of growth parameters. The critical value C-crit converts into a function C-crit(C-B), depending linearly on the boron concentration C-B. Crystal-originated particles (COP) and gate oxide integrity (GOI) yield distributions which are consistent with the R-OSF pattern. A low COP density and a high GOI yield are observed outside the ring; a high COP density and a medium GOI yield in the inner region bordered by the ring. It is assumed that boron atoms modify the thermodynamical properties of vacancies and self-interstitials.

Lock-In IR-Thermography – A Novel Tool for Material and Device Characterization

A novel non-destructive and non-contacting technique for the spatially resolved detection of small leakage currents in electronic devices and MOS materials is presented. Highly-sensitive lock-in infrared (IR-) thermography is used to localize leakage current induced temperature variations down to 10 μK at a lateral resolution down to 5 μm. Leakage currents of about 1 mA can be localized within seconds and some μA may be detected after less than 1 h measurement.

Characterization of Crystal Quality by Crystal Originated Particle Delineation and the Impact on the Silicon Wafer Surface

Characterization of Si wafers by delineation of crystal originated particles (COP) provides insight into size and radial distribution of crystal related defects. A good correlation of the COP densities with gate oxide integrity and flow pattern defect densities is observed. The density and size distribution of COP in Czochralski Si ingots can be modified by the pulling rate and the cooling conditions of the crystal and is further influenced by high doping concentrations. The COP densities are comparable on wafers with (100) Si and (111) Si orientation as well as on p- and n-type wafers with moderate doping level. No COP are found on float zone (FZ) and on epitaxially grown wafers. Crystal defects are also delineated by chemomechanical polishing and can be detected on the wafer surface as light point defects (LPD). LPD densities, however, do not necessarily correlate with the corresponding COP densities after SC1 treatment and do not reflect the quality of the crystals because polishing delineates only part of the larger crystal defects to a size which is above the detection limits of commercially available scanning surface inspection systems. High temperature annealing results in reduction of defect sizes and partial dissolution of COP Investigations of FZ and oxygen doped float zone indicate that oxygen is participating in the formation of COP.

Key influence of the thermal history on process-induced defects in Czochralski silicon wafers

Using a method to study the grown-in defect density spectra in Czochralski silicon wafers by infrared light scattering tomography, we elucidate the changes in the size distribution of grown-in oxide precipitate nuclei caused by thermal processing at the beginning of a common CMOS device process. The first thermal step, screen oxidation at , determines which parts of the grown-in defects grow to large stable defect formations and which of them shrink. The cooling rate of the crystal has a considerable influence on the defect evolution during CMOS processing. Low cooling rates result in lower defect densities than high cooling rates, although the total density of as-grown nuclei is the same. However, the maximum of their size distribution is located at a lower stability temperature for the low cooling rate than for the high cooling rate. This is important for their ability to grow during the first thermal step of the CMOS process. It also demonstrates that the choice of the appropriate silicon material is important for defect generation during processing and consequently also for the device yield.

Grown‐in Oxide Precipitate Nuclei in Czochralski Silicon Substrates and Their Role in Device Processing

Using a method to study the grown-in defect density spectra in Czochralski silicon wafers, we elucidate the changes in the size distribution of grown-in oxide precipitate nuclei caused by thermal processing in a common complementary metal-oxide semiconductor device process. The first thermal step determines which parts of the grown-in defects grow to large stable defects and how many harmful defects appear in the defect-denuded zone. The cooling rate of the crystal considerably influences the defect evolution during complementary metal oxide semiconductor processing. The choice of appropriate silicon material for a device process or adjusting processing conditions to suit the material are important for defect generation during processing and, consequently, also for device yield.

Influence of Residual Point Defect Supersaturation on the Formation of Grown‐In Oxide Precipitate Nuclei in CZ‐Si

Density spectra of grown-in oxide precipitate nuclei were measured along the radius of a silicon wafer with a stacking fault ring. A first-order approximation model allows us to explain the experimental observations. By fitting growth rate curves to the defect density spectra, the residual point defect supersaturation present during formation of oxide precipitate nuclei can be estimated. We show that the ring region is the region where the vacancy supersaturation remains subcritical and no vacancy agglomeration occurs, resulting in the highest residual vacancy supersaturation, and finally leading to the largest grown-in oxide precipitate nuclei. These nuclei first reach the critical size for stacking fault formation during subsequent thermal treatments.

Oxygen Precipitation in Nitrogen Doped CZ Silicon

Nitrogen doping of CZ silicon results in an early formation of large precipitate nuclei during crystal cooling, which are stable at 900°C. These are prone to develop stacking faults and high densities of defects inside defect denuded zones of CZ silicon wafers. Simultaneous doping of FZ silicon with nitrogen and oxygen results in two main stages of precipitate nucleation during crystal cooling, an enhanced nucleation around 800°C, which is nitrogen induced, and a second enhancement around 600°C, which depends on the concentration of residual oxygen on interstitial sites. A combined technique of ramping with 1K/min from 500-1000°C with a final anneal at 1000°C for 2h and lateral BMD measurement by SIRM provides a possibility to delineate v/G on nitrogen-doped silicon wafers. Surface segregation of nitrogen and oxygen during out-diffusion can explain the enhanced BMD formation in about 105m depth and the suppressed BMD formation in about 405m depth below the surface. The precipitate growth is enhanced in regions where nitrogen is filled up again after a preceding out-diffusion.

Conditions for the Formation of Ring-Like Distributed Stacking Faults in CZ-Si Wafers

The influence of ramp rate and starting temperature of the ramp on the generation of ring-like distributed stacking faults during wet oxidation of CZ-Si wafers was investigated. These parameters determine the average emission rate of interstitials required to maintain strain-free growth of oxide precipitates. This emission rate correlates well with the density of oxidation induced stacking faults. It indicates that the higher the required emission rate, the more strain is built into the growing oxide precipitates because of insufficient interstitial generation. This results in an increased nucleation of stacking faults.