Deformation state of 49BF-implanted Si wafers after high-temperature thermal annealing

The bending of ⁴⁹BF-implanted Si wafers due to high-temperature annealing (T = 900 to 1100 °C) is investigated by means of X-ray topographic techniques. The results are comperatively considered with those for low-temperature annealing (T ≦ 800 °C) obtained earlier by the authors. It is shown that the most essential differences in low- and high-temperature intervals occur for implantation dose below the amorphization one.     

Numerical investigation of carbon and silicon carbide contamination during the melting process of the Czochralski silicon crystal growth

Carbon contamination in single crystalline silicon is detrimental to the minority carrier lifetime, one of the critical parameters for electronic wafers. In order to study the generation and accumulation of carbon contamination, transient global modeling of heat and mass transport was performed for the melting process of the Czochralski silicon crystal growth. Carbon contamination, caused by the presence of carbon monoxide in argon gas and silicon carbide in the silicon feedstock, was predicted by the fully coupled chemical model; the model included six reactions taking place in the chamber. A simplified model for silicon carbide generation by the reaction between carbon monoxide and solid silicon was proposed using the closest packing assumption for the blocky silicon feedstock. The accumulation of carbon in the melted silicon feedstock during the melting and stabilization stages was predicted. Owing to this initial carbon content in the melt, controlling carbon contamination before the growth stage becomes crucial for reducing the carbon incorporation in a growing crystal.     

Effect of generated defects during plastic deformation on electron properties of silicon

Conductivity, photoconductivity and SDP of n-type silicon deformed and annealed under different thermal conditions were investigated. The conductivity was found to be dependent on the temperature of deformation and additional annealing. Recombination in deformed samples is fully controlled by paramagnetic centers localized within the charge space region around the dislocations.     

Generation of dislocations on polished surfaces of dislocation free silicon wafers

This paper describes investigations into the influence of wafer defects (surface defects) on the generation of process induced crystal defects in dislocation-free n-type silicon material of both Czochralski and zone-floating techniques. The surface defects are artificial defects, which were produced by scratching with definite forces. The behaviour of scratched silicon surfaces as well as that of scratched and polished silicon surfaces was studied at room temperature and after heat treatment. The experimental results are discussed.     

Systematic studies of Si and Ge hemispherical concave wafers prepared by plastic deformation

Si and Ge hemispherical concave wafers can be prepared by plastic deformation using Si and Ge single- and polycrystal wafers. Deformation regions in which such Si and Ge hemispherical wafers can be obtained by high-temperature plastic deformation were systematically studied. The deformation regions in which well-shaped Si concave wafers can be obtained were studied for (1 0 0), (1 1 1), and polycrystal Si. It was found that Si (1 1 1) crystal wafers can be more easily deformed to a perfect hemispherical shape than (1 0 0) wafers because of the crystallographic symmetry. Si hemispherical wafers with a small radius of 25 mm can be perfectly deformed when 0.5-mm-thick Si (1 1 1) crystal wafers are used. Ge hemispherical wafers with a radius of 100 mm can be perfectly deformed when 0.5-mm-thick Ge crystal wafers are used. Ge hemispherical concave wafers with a perfect shape can be more easily obtained using Ge (1 1 1) wafers than (1 0 0) wafers. According to these results, the deformation behavior of Ge wafers is very similar to that of Si wafers at a normalized pressing temperature. As both the radius and the load on Si and Ge hemispherical wafers increase, thicker Si and Ge wafers can be used to obtain hemispherical wafers with a perfect shape. The dislocation density in the shaped wafers markedly decreases as the pressing temperature and hemisphere radius increase. Thus, it is suggested that Si and Ge shaped wafers are of sufficient quality and have the high potential for use as several types of lens such as those in Si and Ge X-ray monochromators.     

Enhancement effect of nitrogen co-doping on oxygen precipitation in heavily phosphorus-doped Czochralski silicon during high-temperature annealing

Oxygen precipitation in conventional and nitrogen co-doped heavily phosphorus (P)-doped Czochralski silicon (CZ-Si) crystal subjected to various high-temperature annealing in the range of 1000–1150 °C was comparatively investigated. It was revealed that oxygen precipitates hardly generated in conventional heavily P-doped CZ-Si; while they remarkably generated in the nitrogen co-doped one. Moreover, nitrogen doping could enhance oxygen precipitation during the prolonged annealing with a rapid thermal process (RTP) pre-treatment, but it has neglectable influence on oxygen precipitation for short-time annealing. It was believed that nitrogen co-doped heavily P-doped CZ-Si possesses nitrogen-related complexes that act as heterogeneous nuclei for super-saturated interstitial oxygen and then enhanced oxygen precipitation. Finally, it was found that nitrogen doping could hardly enhance oxygen precipitation in heavily P-doped CZ-Si at 1200 °C.     

Slip band formation during bending of gap wafers

{001} LEC-GaP:S wafers were deformed between 470 °C and 640 °C. {111} slip planes of maximum resolved shear stress were activated. Heights and densities of slip steps have been measured by optical and electron microscopy. At lower temperatures deformation proceeds mainly by growth of step heights whereas at higher temperatures bending is accomplished by the increase of slip band density rather than of height.     

Influence of impurity atmosphere on the deformation of silicon crystals

The Alexander–Haasen theory, which describes the deformation kinetics of silicon crystals, has been generalized for impurity crystals. The deformation kinetics of an impurity sample is calculated in a wide range of parameters, including the cases of partial and complete entrainment of impurities by moving dislocations. The developed model, despite its simplicity, adequately describes the qualitative transformation of the stress–strain curves of impurity silicon crystals in dependence of the impurity concentration and other material parameters. The manifestation of negative velocity dependence of the yield stress, observed in natural experiments, is analyzed.     

Study of temperature distribution in high-temperature furnaces for silicon carbide monocrystal and epitaxial layer growing

A method to determine temperature gradient and distribution in high-temperature furnaces for silicon carbide monocrystal and epitaxial layer growing is suggested on the basis of the results obtained from the experiments on silicon carbide epitaxial layer growing kinetics in gas using 2 „sandwiches”︁.     

A SAXS study of the gelation process of silicon and titanium alkoxides

The gelation process of silicon ethoxide and titanium iso-propoxide solutions was studied as a function of water content and reaction time by small-angle X-ray scattering (SAXS). Approaching the gelation points, the SAXS intensities for titanium tetra-iso-propoxide solutions start to follow a power-law decay in the Porod region, except for a H₂O/Ti ratio greater than 4. For silicon ethoxide solutions, the fractal dimension, d_f, measured for aggregated clusters increases continually with the H₂O/Si ratio and can be related to the spinnability of the solutions. For solutions of both silicon and titanium alkoxides, a solution of fractal dimension d_f < 1.79 shows spinnability, whereas solutions having d_f > 1.79 and no fractal structures do not show spinnability.     

Investigation of nitrogen solubility process in silicon carbide

On the basis of the epitaxial layers of SiC (N) grown from vapour phase by the sublimation method in a temperature interval (1900–2200) °C and at nitrogen partial pressures from 4 to 760 Torr has been determined the dependence of the nitrogen content in the epitaxial layers of SiC(N) on the nitrogen partial pressure and the temperature of growing. A thermodynamics analysis of the nitrogen solubility process in silicon carbide has been developed taking account of the electron-hole interaction. The experimental and calculation results, we have obtained, allowed us to determine the partial mol solubility heat of nitrogen in SiC.     

Investigation of the thermal conditions during silicon carbide crystal growth

In the present work an analysis of the thermal conditions during silicon carbide crystal growth from the vapour phase by the sublimation method is carried out. On the basis of the obtained results from the calculation of the temperature distribution along the length of the growing crystal it was drawn a conclusion that in order to decrease the density of dislocations in the growing crystals it is necessary to decrease the temperature gradients in the crucible for growing.     

Three-dimensional global analysis of thermal stress and dislocations in a silicon ingot during a unidirectional solidification process with a square crucible

A three-dimensional global model was used to obtain the solution of a thermal field within the entire furnace during a unidirectional solidification process of multicrystalline silicon with a square crucible. Then the thermal stress distribution in the silicon ingot was solved. Based on the solution of thermal stress, relaxation of stress and multiplication of dislocations were performed by using the Haasen–Alexander–Sumino model (HAS model). The influence of crucible constraint on stress levels and dislocations was investigated. It was found that the crucible constraint had significant influence on the thermal stresses and dislocations in the ingot. The results indicated that it is important to reduce the crucible constraint in order to relax thermal stresses and reduce dislocations in a silicon ingot during the solidification process.     

Substrate holder biasing for improvement of microcrystalline silicon deposition process

Application of a dual frequency plasma source for the deposition of microcrystalline silicon thin films from highly diluted SiH₄/H₂ was investigated in this paper. A positively or negatively biased low frequency voltage was applied on the substrate holder while the conventional frequency of 13.56 MHz was used for the powered electrode. The results show a significant increase of the deposition rate and an improvement of the film crystallinity in the case of the positive biasing. Plasma diagnostics and modeling were used to understand the beneficial effect of positive biasing on the deposition process. The results revealed that the observed changes are not only due to the variation of ion flux and ion bombardment but also depend on the changes in the production and distribution of neutral species in the discharge space.     

Amorphous and nanocrystalline silicon made by varying deposition pressure in PECVD process

Silicon thin films are deposited using plasma enhanced chemical vapor deposition (PECVD) of silane, argon, hydrogen mixture at various pressures in the range of 2–8 Torr. Raman scattering shows these to be amorphous in the pressure range 6–8 Torr, and nanocrystalline in the range 2–4 Torr. The volume fraction of nanocrystals is estimated by fitting the Raman data to three peaks and is found to be ～75% for the films deposited at low pressure, density of states of these films was measured. It is observed that the electrical conduction in these films depends on the crystalline volume fraction (ρ), estimated from the laser Raman Spectroscopy. Temperature dependence electrical conductivity shows that at lower temperatures thermionic emission dominates for the films with lower ρ, whereas, hopping is the main conduction mechanism for the films having high ρ. The density of states is estimated from the space charge limited currents (SCLC) observed at high fields. Photoconductivity at room temperature is also measured. The amorphous films are found to be more photosensitive than the nanocrystalline one. In the context of these findings, changes in the properties of silicon from amorphous to nanocrystalline are described.     

The characteristics of solid phase crystallized (SPC) polycrystalline silicon thin film transistors employing amorphous silicon process

We investigated the electrical properties of polycrystalline silicon (poly-Si) thin film transistors (TFTs) employing field-enhanced solid phase crystallization (FESPC). An n+ amorphous silicon (n+ a-Si) layer was deposited to improve the contact resistance between the active Si and source/drain (S/D) metal instead of ion doping. By using C–V measurement method, we could explain the diffused phosphorous ions (P+ ions) on the channel surface caused a negatively shifted threshold voltage (V_TH) of ?7.81 V at a drain bias of 0.1 V, and stretched out a subthreshold swing (S) of 1.698 V/dec. This process was almost compatible with the widely used hydrogenated amorphous silicon (a-Si:H) TFT fabrication process and also offers a better uniformity when compared to the conventional laser-crystallized poly-Si TFT process because of non-laser crystallization.