Ulrich Lambert

• Dr. rer. nat.
• Lecturer at Heidelberg University (Ruprecht-Karls -Universität Heidelberg)

We have developed a method for studying the as-grown defect density spectra of Czochralski silicon wafers by infrared light scattering tomography These spectra show the defect density vs. size or stability temperature. Different annealing procedures were used to reveal both parts of the spectra, one stable at high (1000 to 1280 degrees C) and the o...

Based on Fourier transform infrared (FTIR) spectroscopy and bulk micro-defect investigations, in relation to earlier results of other groups, we suggest the following model for oxide precipitate nucleation in N-doped silicon. Around 600 °C a nucleation maximum exists where oxide precipitates are formed via oxygen attachment to both NOO and NNO comp...

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...

Float zone crystals without nitrogen (N) and with increasing axial nitrogen doping have been grown. Vacancy agglomerates have been delineated in FZ wafers in the low nitrogen doping level with various measurement techniques like flow pattern defects, localized light scattering defects and A- and B-mode failures in MOS capacitors. All these measurem...

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...

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...

Grown-in crystal defects like crystal originated particles (COPs) in Czochralski grown silicon wafers deteriorate the yield of metal oxide semiconductor devices by causing dielectric breakdown of the insulating oxide layer. The technique of lock-in IR-thermography is presented, which allows the localization of active gate oxide integrity (GOI) defe...

Si(113) may be a competitive substrate material for Si integrated circuits. High-quality SiO2/Si(113) films can be produced by standard oxidation techniques. Based on investigations of the initial stages of oxidation by Scanning Tunneling Microscopy and ab initio calculations, we interpret this result as an effect of tensile stress and reduced diff...

The temperature and shear strain rate dependence of the upper yield point of a few kinds of large diameter silicon crystals was studied. Crucial material attributes, such as doping level, initial oxygen content, and the state of oxygen aggregation after thermal treatment, were taken into account. Overall experimental results show that the deformati...

Yield and reliability of MOS devices are strongly affected by crystal-originated particles which may generate gate oxide integrity (GOI) defects. For the semiconductor industry it is highly desirable not only to measure the density, but also to image the lateral distribution of GOI-defects. A novel technique to image GOI defects across large gate a...

A technique to image gate oxide integrity (GOI) defects across large gate areas has been developed. First, a low-ohmic bias pulse is used in order to break down nearly all GOI defects in a large area metal-oxide-semiconductor (MOS) structure. Then a periodic bias of typically 2 V is applied and the local heating caused by the leakage current throug...

300 mm device requirements are getting more demanding with decreasing design rule of future generations. Special emphasis is put on the improvements of local wafer geometry, on bulk related defects in the near surface region, e.g. Crystal Originated Particle (COP), and on surface Localized Light Scatterer (LLS) while keeping the demand for getterin...

For standard epitaxial processes, developed for layers with a thickness > 1 μm, the dominating part of the time that the wafer spends in the reactor is needed for the deposition itself. Therefore, only little variability is left to improve throughput. In contrast, for a layer thickness below 1 μm, reduction of the overall process time can be achiev...

The dependence of the gate oxide integrity on the grown-in defect density is demonstrated using Czochralski grown crystals with different as grown defect densities and by varying the gate oxide thickness in the range of 5-25 nm. The Poisson distribution -ln(1-F)=rho(A)A(gate) (F: ratio of failures, rho(A): area defect density, A(gate): gate area) i...

The changeover from 200 mm to 300 mm is required by the semiconductor industry due to the necessity for larger chip sizes and demand for decreasing cost. However, the cost for 300 mm crystal growth is likely to rise owing to larger puller, enlargement of hot zone, expensive silica crucibles and longer growth process times caused by lower growth rat...

In the present stage of development, 300 mm crystals often contain a transition from vacancy-rich to interstitial-rich. Due to this radially varying concentration of intrinsic point defects, the radial size distribution of grown-in oxide precipitate nuclei is also inhomogeneous in these wafers. In order to achieve a radially uniform bulk defect den...

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...

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 , determi...

The thermal diffuse scattering around reflection 220 of a thick, perfect silicon crystal has been studied quantitatively by means of a triple-crystal diffractometer and 100 keV synchrotron radiation. The necessary fitting procedures were simplified by deriving an analytic solution to the instrumental resolution function for nondispersive setting of...

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 ox...

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...

Fast pulled Czochralski silicon crystals usually contain large octahedral vacancy agglomerates. These voids are known as D defects, which degrade the integrity of thin gate oxides by causing time zero dielectric breakdown. After annealing the wafers at temperatures above 1100 degrees C, the gate oxide integrity is clearly improved. We show by theor...

The formation of grown-in void-like defects was studied for vacancy-rich silicon crystals by experiments and simulation, by taking into account the thermal history of the crystals, the intrinsic point defect dynamics and the aggregation of vacancies. Radially non-uniform grown-in void distributions result from Radial varying vacancy concentrations....

This paper demonstrates a method that reveals the density versus stability temperature distribution of grown-in oxide precipitate nuclei. These so-called defect density spectra can be measured after each processing step in a device process. Thus, the process steps that are critical for defect generation can be analyzed. This was done for a thermall...

The size distribution of grown-in oxide precipitate nuclei in wafers with a transition from vacancy-rich to interstitial-rich is radially inhomogeneous because of the radially varying supersaturation of intrinsic point defects in the growing crystal. However, using a slow ramp all nuclei can be grown to form a radially homogeneous bulk defect zone....

It is well known that octahedral voids about 100 - 300 nm in size can be correlated with the substrate related gate oxide degradation in Czochralski silicon wafers. A convenient way of analyzing the density of voids which are grown in during crystal pulling is measuring the so called Crystal Originated Particles (COPs) with surface sensitive light...

Grown-in D-Defects in Czochralski silicon wafers were investigated by a combination of Brewster angle laser scattering tomography (LST) and transmission electron microscopy (TEM). We observed single and paired octahedral defects varying in size between 30 and 150nm. Diffraction contrast investigations and the application of the Ashby-Brown criterio...

Grown-in oxide precipitate nucleation during crystal cooling is strongly influenced by the residual vacancy concentration remaining after vacancy agglomeration. The lower the cooling rate of the crystal, the more vacancies are absorbed by D-defects before oxide precipitate nucleation. This results in smaller grown-in oxide precipitate nuclei becaus...

A review is given of new developments in quantitative understanding and modeling of the process of oxygen precipitation in Czochralski (Cz) grown silicon. Based on a well accepted expression for the critical radius of a silicon oxide precipitate, the various material parameters which have an important impact on precipitate nucleation are discussed...

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 mo...

Si wafers with boron concentrations up to 2 · 1019 cm-3 were characterized by delineating defects with SC1 solution and analyzing them with respect to crystal originated particles (COP). No oxidation induced stacking fault (OSF) ring appears, and the whole wafer displays a homogeneous COP density after SC1 treatment for low boron doped ingots in a...

Defects in as-grown and heat-treated 150 and 200 mm Czochralski silicon crystals are investigated for different crystal pulling conditions and thermal treatments. First results are presented using noncontact carrier recombination imaging for detection of electrically active defects. The defect densities and sizes are compared with the results of co...

The influence of the boron doping level in the range of 1 × 1015-2 × 1019cm−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 Ccrit defined by the ratio of t...

The formation of grown-in voids in Czochralski silicon crystals was simulated by taking into account thermal history and intrinsic point defect dynamics. Grown-in voids were considered as spherical clusters of vacancies that nucleate homogeneously and grow during cooling of the crystal. Nucleation of voids proceeds in the temperature range of 1100...

Grown-in defects are dominant in most substrate related defect generation processes in silicon. This is shown in detail for a thermally simulated CMOS process and for nucleation anneals of internal gettering procedures. The size distribution of grown-in oxide precipitate nuclei determines to a large extent if precipitation of oxygen is easy or diff...

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 CMOS device process. The first thermal step determines which parts of the grown-in defects grow to large stable defect formations an...

Grown-in D-defects in Czochralski silicon wafers were studied by light scattering tomography (LST), transmission electron microscopy (TEM), and Secco etching. Using Brewster angle LST, they can be studied nondestructively. Their average diameter as observed by TEM was 30-150 nm. This correlates very well with the size of the D-defects determined by...

Defects in as-grown and annealed Cz wafers have been investigated with a differential interference contrast microscope. The obtained defect densities are in agreement with Infrared Light Scattering Tomography (IR-LST) and Gate Oxide Integrity (GOI) data. Defect size distributions have been determined and a clear effect of thermal pre-treatments is...

The nature and stability of grown-in defects in Czochralski silicon is discussed as well as their dependence on crystal pulling conditions. It is shown that large voids are formed during crystal cooling by agglomeration of vacancies together with much smaller silicon oxide precipitates. During further thermal treatments the oxide precipitates becom...

Small point defect clusters grown-in during Czochralski (Cz) crystal pulling can have an important impact on gate oxide integrity (GOI) for present day high quality silicon substrates. A pronounced effect of the crystal pulling conditions on GOI is indeed observed for gate oxide thicknesses between 10 and 100 nm as was already reported more than 20...

Oxygen- and nitrogen-doped floating zone (FZ) crystals were investigated with regard to radial oxygen precipitation, D-defect formation and gate oxide integrity (GOI) behavior as a function of the nitrogen content. It is shown that the inactivation of the nitrogen-enhanced D-defect suppression and GOI improvement is not a result of the reduction of...

High temperature annealing of Czochralski Si wafers in Ar or hydrogen ambients reduces as-grown crystal defects close to the surface of Si wafers. This results in improved electrical properties and an oxygen denuded zone. The depth profile of the defect density and the defect size distribution is investigated by removing successive Si layers by pol...

Wafers from silicon ingots grown in the vacancy rich regime with different crystal cooling rates have been used for investigations by infrared light scattering tomography (IR-LST), preferential defect etching and gate oxide integrity (GOI) tests. GOI evaluation was done for 6.4 nm and 15 nm gate oxides. A clear correlation is obtained between subst...

High-temperature annealing in hydrogen, argon, and oxygen ambients improves the electrical performance of Czochralski Si wafers considerably. The gate oxide integrity of such wafers can approach values close to 100% yield after annealing for 1 to 2 h at 1200°C in argon and hydrogen ambient which is related to a significant reduction of near-surface...

The influence of pyrolytic boron nitride (pBN) crucibles on the GaAs liquid encapsulated Crochralski (LEC) growth process and on the crystal properties was investigated. An increased boron concentration in the crystals is found to be caused by oxidation processes between B2O3 · xH2O, GaAs and impurity elements in GaAs as a function of water content...

Results are presented of a combined study using both surface and bulk characterisation tools to address the defects in Czochralski grown silicon substrates which are responsible for reduced gate oxide integrity (GOI). A clear correlation is observed between bulk defects observed with infrared light scattering tomography, crystal originated particle...

Bulk crystal defects are accessible for investigation when silicon crystals are sliced and the defects occur close to or at the surface of wafers. Such near-surface defects can then be delineated by modifying some processes used for preparing clean, polished wafers. The delineated defects usually occur as pits the shape of which depends on the deli...

Oxygen- and nitrogen-doped floating zone (FZ) crystals were investigated with regard to radial oxygen precipitation, D-defect formation and gate oxide integrity (GOI) behavior as a function of the nitrogen content. It is shown that the inactivation of the nitrogen-enhanced D-defect suppression and GOI improvement is not a result of the reduction of...

High temperatures annealing of Czochralski Si wafers in Ar or hydrogen ambients reduces as-grown crystal defects close to the surface of Si wafers. This results in improved electrical properties and an oxygen denuded zone. The depth profile of the defect density and the defect size distribution is investigated by removing successive Si layers by po...

The quality of arsenic and of GaAs polymaterial influences the substrate properties and their reproducibility. Interactions and correlations are investigated. The purification process of arsenic and the process parameters of the two-step synthesis were optimized. The impurity concentration and the stoichiometry variations in GaAs boules have been s...

Radiofrequency spark source mass spectrometry is a reliable and precise analytical method to measure the amount of oxygen in silicon grown by the Czochralski technique from SiO2 crucibles in the common range from 2ppm(atomic) to 20ppm(atomic) and in silicon grown by the floating zone technique below 0.1ppm(atomic). The technique is also excellent f...

A structural family of the summarizing formula M5-pT4+pO14 with p = 0 or p = 1 is described. It comprises three structure types I, II and III and a large number of compounds. The structure types of I (P321) and II (I2/a) are known. For the unknown monoclinic structure of III a partial structure proposal is developed. The basic unit of all structure...

Light-emitting diodes, high-speed transistors, laser diodes, and solar cells are just a few of the applications of gallium arsenide (GaAs), for which the availability of ultrapure materials or materials with closely controlled impurity profiles is of utmost importance. The development and optimization of one major method of GaAs crystal growth is d...

Numerous interactions in the multicomponent system of s.i. GaAs single crystals were studied in order to improve the reproducible adjustment of resistivity. The sources for the impurities Zn and C are the raw materials. The refining effect of synthesis and growth process with B2O3 of well-defined water content allows a reproducible adjustment of re...

Twenty seven new rare earth (Ln) compounds CuLn2 Ge2O8, CuLn2Ge4O12 and CuLn2Si4O12 have been synthesized. The powder diagrams were indexed and solid solutions of silicates and germanates were investigated. Structural variations with temperature, lanthanide contraction and Ge/Si substitution are described. Indications for second order phase transit...

Ternary systems CuO-M2O3-TO2 with T = Si, Ge and M3+ = Al, Ga, Fe, Cr, Bi and Y were investigated at 1000°C. Ternary compounds were found only for M3+ = Y. CuY2Ge2O8 is monoclinic with a = 9.477 Å, b = 15.005 Å, c = 8.030 Å and β = 147.50°; CuY2 Si4 O12 is monoclinic with a = 7.052 Å, b = 14.283 Å, c = 4.738 Å and β = 103.32°; CuY2Ge4O12 is triclin...

CRYSTAL CHEMISTRY OF OXYGEN COORDINATED Cu2+. By W. Eysel, K.-H. Breuer and U. Lambert The crystal chemistry of oxygen coordinated Cu2+ (including also OH- and H2O as ligands) is discussed with particular emphasis on silicates and germanates. For Cu2+ various coordination polyhedra are known: Elongated octahedron Cu4+2 , steep tetragonal pyramid C...