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This paper reports the relationship between oxygen concentration and dislocation multiplication in silicon crystals during directional solidification using numerical analysis. Based on the Alexander&ndash, Haasen&ndash, Sumino model, this analysis involved oxygen diffusion from the bulk to dislocation cores during crystal growth and annealing processes in a furnace. The results showed that the dislocation density mainly increased during cooling process, rather than crystal growth, when the effect of oxygen diffusion to dislocation cores was ignored. On the contrary, the dislocation density increased during both crystal growth and cooling processes when the effect of interstitial oxygen diffusion was considered. At a dislocation density larger than 1.0 &times, 105 cm&minus, 2, the interstitial oxygen concentration in bulk decreased due to the diffusion process, if interstitial oxygen atoms were between dislocations, whereas the concentration at dislocation cores increases.

In order to establish the epitaxial wafer as the main substrate for semiconductor devices produced on large diameter wafers over 300 mm, the epitaxial wafer must satisfy stringent requirements in terms of both quality and costs. Before proceeding with 400 mm diameter epitaxial wafer development, we reviewed all technical issues for larger diameter epitaxial wafer development, and then determined an approach that adequately addressed the major technical hurdles. Our first technical accomplishment was the development of a low-temperature SiH 4 gas epitaxial growth process, followed by the design, manufacture, and installation of a single-wafer spin cleaner and original epitaxial furnace for 400 mm diameter wafers. We were successful in growing the entire surface of a 400 mm diameter wafer by a series of processes that were conducted with an appropriate combination of this equipment. Our challenge has opened the way to high-quality and low-cost epitaxial wafer manufacturing.

エピタキシャル成長炉投入前処理として, オゾン超純水による保護酸化膜形成, または希弗酸による水素終端をシリコンウェーハに施した. エピタキシャル成長炉投入前処理前後で酸化膜厚さ (XPSによる酸素分析), 清浄度 (XPSによるO, C分析) とマイクロラフネス (AFM) を評価した. その後, エピタキシャル成長炉に投入し, 水素中加熱処理を行った. 保護酸化膜を形成したウェーハでは950℃, 5min, 水素終端ウェーハでは950℃, 1min程度の水素中加熱で清浄かつ平滑な表面が得られた. さらに, モノシランガスにより, シリコンエピタキシャル成長を行った. 950℃, 1.01×105Paおよび4.00×104Paにおいて, 高品質エピタキシャル成長を得る低温成長プロセスを開発した.

A small angle incident X-ray photoelectron spectroscopy (XPS) instrument was developed to perform high sensitivity analyses on silicon surfaces by reducing background noise. Silicon surfaces were treated by a new wet cleaning process based on ultra clean technology. Cleaning effectiveness for this process was determined by small angle incident XPS measurements and spectra analyses. At each cleaning step, no elements other than silicon, oxygen, and carbon atoms were detected. The thickness of the SiO 2 film formed during each step was evaluated. Based on the relative O 1s and Si 2p intensities, too much oxygen was found on the surface to attribute only to SiO 2 .

Silicon single crystals with uniformity along the growth direction were grown using a new continuous Czochralski (CCZ) method. Polycrystalline silicon rods used as charge materials are melted by carbon heaters over a crucible without contact between the raw material and other substances. Using this method, silicon crystals with diameters as large as 6 or 8 inch and good uniformity along the growth direction were grown.

Optically active processes of the higher-order bands (HOB) are investigated at different temperatures in fast neutron irradiated silicon using Fourier transform infrared absorption measurement. It is shown that the optically active process is nearly temperature independent below 80 K, the slow decay process remains up to a heating temperature of 180 K. The observations are analyzed in terms of the relaxation behavior of photoexcited carriers governed by fast neutron radiation induced defect clusters.

The structure of separation by implanted oxygen (SIMOX) wafers oxidized at temperatures from 1000 to 1350°C has been investigated using cross-sectional transmission electron microscopy and spectroscopic ellipsometry. By high-temperature oxidation at 1350°C, a 43 nm thick internal thermal oxide (ITOX) layer is grown between the top Si layer and the buried oxide layer formed by oxygen implantation and subsequent annealing. The resulting buried-oxide thickness is one and one-half times the original. The thickness of ITOX increases with increasing oxidation temperature. In addition, the superficial thermal oxide layer formed on the SIMOX wafers during the oxidation is somewhat thinner than that on the bulk Si wafers. A mechanism to account for both superficial thermal oxidation and internal thermal oxidation is proposed. The top Si-buried oxide interface, where some oxygen atoms react with Si during high-temperature oxidation, acts as a sink for them and causes them to diffuse more easily through the thin top Si layer to the interface.

The gettering of Cu and Ni impurities in intentionally contaminated SIMOX wafers have been studied by means of cross-sectional transmission electron microscopy, nanoprobe energy dispersive x-ray spectroscopy, secondary ion mass spectrometry, and selective etching. The wafers with Cu or Ni surface concentrations ranged from about 10 12 up to 10 17 atom/cm 2 were annealed at various temperatures followed by slow cooling to room temperature. Single and multistep thermal treatments were applied. It has been found that the buried oxide does not prevent the diffusion of both Cu and Ni contaminants from the top silicon layer into the bulk substrate at the whole investigated temperature range from 600 to 950°C. Moreover the effective gettering of Cu and Ni in the thin silicon substrate layer located just beneath the buried oxide has been observed and explained as being due to the heterogeneous impurity precipitation at stacking fault tetrahedra formed there during the SIMOX manufacturing. The gettering process has remained stable during the thermal simulation of CMOS device process of new generation ICs with 0.25 μm feature size.

Using Fourier transform infrared absorption measurement with excitation at low temperatures, we have investigated the optical active process involving higher order bands (HOB) in fast neutron irradiated float-zone silicon. It is found experimentally that the photoexcitation and decay process of the HOB as well as the saturation value of the absorption intensity are in good agreement with the predictions of the macroscopic barrier model for the slow relaxation of photoexcited carriers caused mainly by defect clusters.

Using Fourier transform infrared absorption spectroscopy and Hall effect measurements mainly the infrared active electronic defects in fast neutron irradiated float-zone silicon and Czochralski silicon after annealing at 450 °C are investigated. Introducing thermal donors (TD) to alter the Fermi level, the defect associated with the higher-order bands (HOB) is analyzed, which is proposed to have at least three charge states within the band gap. The defect level giving rise to the HOB is located slightly below Ec −0.15 eV, and another level possibly exists near the bottom of the conduction band. Moreover, the measurement results indicate that the characteristic of photoexcitation and decay of the HOB is associated with the slow relaxation process of photoexcited carriers.

Synchrotron X-radiation plane-wave topography for thinned silicon crystals is shown to be effective and sensitive for imaging minute strains around microdefects. Visibility of microdefects in crystals thinned down to a thickness (about 100 μm) smaller than several times the extinction distance is compared with that in crystals as thick (0.6 mm for Mo Kα 1 ) as μ -1 (μ: linear absorption coefficient). Various kinds of microdefects reveal themselves much more in the thinned crystals. Observed microdefects are classified into five morphological categories. One of the observed microdefects has an image extinction rule suggesting a specified strain field around it. The morphology of microdefects is described in detail.

Optically active behaviors of the infrared active defect, so‐called higher order bands, have been investigated at different temperatures in fast neutron irradiated silicon. It is found that the optically active decay follows logarithmic time dependence with a decay time of about 105 s, which is nearly temperature independent below 80 K. The residual absorption remains up to heating temperatures of 180 K. The experimental findings are discussed in terms of the relaxation characteristic of photoexcited carriers governed by neutron irradiation induced defect clusters.

Using Fourier transform infrared absorption spectroscopy and Hall‐effect measurements we have investigated the higher order bands (HOB) in the fast neutron irradiated Czochralski silicon. Introducing the thermal donors (TD) to alter the Fermi level, the defect level giving rise to the HOB is analyzed, which is proposed to be located slightly below the TD(+/++) level. Furthermore, the observation for the characteristics of the photoexcitation and decay of both the HOB and the TD+ supports the assumption that this characteristic of the HOB is associated with a slow relaxation of photoexcited carriers.

Newly developed SIMOX wafers have high thickness uniformity of top silicon and buried oxide layers. The top silicon layer is nearly defect-free. It is virtually free from heavy metal contamination caused by implanting and annealing procedures. However, the wide application of SIMOX wafers for advanced circuit production requires further improvement of wafer quality. It has been reported that the gate oxide voltage breakdown of MOSFET's on SIMOX wafers have a higher incidence of low-voltage breakdown than on bulk CZ wafers. This effect has been explained as due to the increased surface microroughness of SIMOX wafers, which leads to a higher thermal oxide defect density than that of the bulk wafers. Therefore, the surface morphology of SIMOX wafers must be improved. In this paper a method for improving the surface morphology is proposed. The method is based on the result that the surface microroughness of SIMOX wafers can be significantly reduced by high-temperature oxidation. The experimental results demonstrate that the surface morphology of SIMOX wafers is improved and the proposed method will allow further improvement of the surface morphology by optimization of the oxidation conditions.

In order to develop the low-temperature silicon epitaxial growth process, the change in the surface morphology of the silicon dioxide film and the silicon surface is studied in a transient state, for the first time, at 1223 K at a pressure of 40–101 kPa in a hydrogen ambient. A very smooth and clear silicon substrate surface is achieved using a uniform silicon dioxide film formed using ozonated ultrapure water and a very low flow rate of hydrogen gas. The surface morphology of the silicon substrate finally becomes smooth and the pit formation is suppressed, although the surface shows a nonuniform island appearance during the removal of the silicon dioxide film. The microroughness of the silicon substrate surface is improved by heating in a hydrogen ambient and by the silicon epitaxial film growth after complete removal of the ozone oxide film.

The epitaxial wafer is expected to become the industry standard for super large-diameter wafers over 300 mm. The demand for reductions in production cost along with stringent quality improvements are driving diameters upward. The super silicon project has developed an epitaxial process, for 400 mm epitaxial wafers, using SiH 4 gas at a low temperature just under 1000°C. This process promises to decrease contamination, to prevent slip generation, and to improve productivity. Since the epitaxial layer quality is tightly correlated with the growth process, we also characterized the microdefects and microroughness on the surface of epitaxial wafers that were grown with the SiH 4 process. Comparing the results of this experiment with those of a conventional SiHCl 3 process, we conclude that the SiH 4 process presents no problems when applied to super large-diameter epitaxial wafer production.

Oxygen concentration in the top silicon layer of silicon-on-insulator materials formed by low-dose implantation of oxygen has been measured by means of secondary ion mass spectroscopy. A value of less than 1×1017 atoms/cm3 has been obtained. We propose that the oxygen concentration in the top silicon layer is controlled by oxygen out-diffusion during the wafer cooling process.

The enhancement effect of Fe impurities on the generation of surface and bulk microdefects, such as oxidation-induced stacking faults, oxide precipitates, precipitate-dislocation complexes and bulk stacking faults, has been observed in annealed silicon wafers prepared from Czochralski grown crystals intentionally contaminated with iron. The effect remains significant even for an Fe concentration as low as 1012 atoms/cm3. It has been found that Fe facilitates the nucleation of oxide precipitates in silicon. The mechanism of Fe-assisted nucleation of oxide precipitates is discussed. The effect of Fe on the generation of oxidation-induced stacking faults is explained, assuming that both oxide precipitates and Fe:Si precipitates formed near the wafer surface serve as active nucleation sites of these microdefects.

X-ray plane-wave topography in a Laue-transmission case has been widely used to observe microdefects in otherwise perfect silicon crystals. To show the experimental effect of specimen thickness, plane-wave topographic observations were conducted before and after the stepwise chemical etching of the specimen crystal. The observations showed a heightening of the strain sensitivity when reducing the specimen thickness to less than several times the extinction distance of the relevant diffraction. The thickness effect was interpreted through X-ray dynamical diffraction theory for distorted crystals (Takagi-Taupin theory). The computer simulations of the diffraction theory proved that correlations exist amongst the divergence of the incident X-ray beams, the crystal thickness, and the quantity of the minute strain.

In order to reveal more minute microdefects in as-grown CZ silicon crystals, thinned crystals as thin as the order of the extinction distance have been successfully observed by ultra plane-wave topography using synchrotron X-radiation. Various kinds of microdefects reveal themselves only in the thinned region. Using thinned crystals for plane-wave topography is essential for the present experiment. Observed morphologies of microdefects are classified into five categories. One of the observed microdefects has an image extinction rule suggesting a specified strain field around it. The morphology of microdefects has been described in detail.

An in situ X-ray topographic technique using a high-power X-ray generator has been used to study the dislocation mobility at elevated temperatures in the stress range 1·2-40 MN m−2 for pure and impurity-doped silicon crystals. The variation of velocity with stress for both 60° and screw dislocations in high-purity crystal is linear throughout the whole stress range investigated, the activation energies for motion being independent of stress. No previously published theoretical models are able to account for the measured velocities quantitatively. Effects of impurities, such as oxygen, carbon, nitrogen, phosphorus and boron, are investigated in detail. Generally, the impurities bring about a deviation from linearity of the variation of velocity with stress under low stresses. Dislocations originally moving in impure crystals are immobilized when the stress becomes lower than a critical value. These phenomena are interpreted in terms of the development of an impurity atmosphere around slowly moving...

The characteristics of dislocation behavior and mechanical strength in tensile tests are investigated on the silicon crystals that are doped with nitrogen at the time of crystal growth by the floating‐zone technique. These are compared with those in the usual floating‐zone‐grown silicon crystals. Nitrogen atoms dispersed in a silicon crystal are shown to have no influence on the velocities of dislocations in motion in the temperature range above 600 °C. Dislocations in the nitrogen‐doped crystal are, however, immobilized while the crystal is kept under a low or zero applied stress at elevated temperatures. Like Czochralski‐grown silicon, nitrogen‐doped silicon shows a much higher yield strength than usual floating‐zone‐grown silicon when crystals are dislocated. It is concluded that interstitial nitrogen atoms bring about the hardening of silicon crystals through locking of dislocations upon congregating on the latter.

Par mesure de l'intensite diffractee on peut etudier les phenomenes de precipitation de l'oxygene dans un cristal de Si obtenu par la methode Czochralski

The characteristics of dislocation locking due to the development of an impurity atmosphere have been investigated by the in situ X-ray topographic technique for silicon crystals doped with various types of impurities. Oxygen, nitrogen and phosphorus atoms are found to be effective in locking dislocations while carbon atoms are not. The dependence of the locking behaviour on the impurity concentration is investigated in detail for oxygen-doped crystals. It is known that the magnitude of the locking force is determined uniquely by the number of impurity atoms congregated on a unit length of dislocations if the species and concentration of the impurity atoms in the crystal are specified. Individual nitrogen atoms exhibit the strongest locking effect among the impurity atoms investigated. However, locking proceeds most pronouncedly in oxygen-doped crystals owing to a high diffusion rate and a higher solubility of oxygen atoms in silicon. The origins of the strong locking effects of various impurity ...

Growth striations in Czochralski‐grown Si wafers have been observed by a scanning x‐ray double‐crystal method. We confirmed that the striations on the topographs relate to the variation of oxygen concentration.

Effects of interstitial oxygen atoms and substitutional phosphor atoms on the dislocation mobility and the mechanical behaviour in silicon crystals are investigated. Dissolved oxygen atoms do not affect the velocities of dislocations in the temperature range investigated, but develop atmospheres around slowly moving and static dislocations and lock them firmly. The locked dislocations lose the function of the multiplication centers and the mechanical behaviour of the crystals becomes similar to that of nearly dislocation-free crystals. Phosphor atoms increase the mobility of dislocations but have no appreciable locking effect. The behaviour of the effective stress, and, thus, the state of the collective motion of dislocations in the steady state of deformation both with and without the presence of the solute atoms are correctly described by the hypothesis of Sumino.

In order to observe microdefects in silicon crystals, plane-wave topography using synchrotron X-radiation has been successfully applied to thin silicon crystals. We have aimed increasing a ratio of a diffraction signal from microdefects to diffracted intensity from the matrix crystal by taking advantage of an extinction effect of X-ray dynamical intensity. Our plane-wave topography revealed that microdefects for such thin crystals always show a distinct contrast, though we have not obtained zero intensity at the background because of a long-range elastic strain. It is proposed that when silicon wafers are thinned, stress relief at the specimen surface allows a strain field to apread around microdefects to an extent which is detectable using plane-wave topography.