The effect of heavy boron doping on oxygen precipitation in Czochralski silicon substrates of epitaxial wafers has been studied with transmission electron microscopy observations and a preferential etching method. Prolonged isothermal annealing between 700 and 1000ЊC for up to 700 h was performed on p/pϩ (5-20 m⍀ cm) and p/pϪ (10 ⍀ cm) wafers. It was found that, with an increase in boron concentration, (i) the precipitate density increased, and (ii) the precipitates could nucleate at a higher temperature. The growth process of platelet precipitates was also investigated and compared with the process in polished pϪ wafers. It was confirmed that (i) precipitate growth rate in p/pϩ wafers was higher than that in pϪ wafers, and (ii) precipitate nucleation in p/pϪ wafers was delayed compared with p/pϩ wafers. The precipitate growth in p/p+ wafers was determined to be reaction-limited, which differed from the diffusion-limited growth in pϪ wafers.
A theoretical model, based on the bond-polarizability concept, js presented for the calculation of the Raman scattering intensities for crystals. The bonds in a unit cell are classified into groups in which the individual bond Raman polarizabihties are equivalent. The Raman polarizability of the crystals is expressed as the sum of the product of the bond Raman polarizability and the relative displacement of the end atoms linked by the bond. The theory is applied to the SiC polytypes. The calculated Raman intensity profiles reproduce qualitatively the observed Raman spectra of the folded modes which arise from TAand TO-phonon branches along the c direction.
Dependence of mechanical strength of Czochralski silicon (CZ‐Si) wafers on the temperature of oxygen precipitation annealing has been studied both experimentally and theoretically. Thermal stress was applied to CZ‐Si wafers after oxygen precipitation annealing at 1100°C or 1000°C after preannealing at 800°C. The warpages and the densities of slip dislocations in the wafers annealed at 1100°C are much higher than those in the wafers annealed at 1000°C, nevertheless each precipitate density is almost equal. Transmission electron microscopy observations of the 1100°C samples showed that both platelet and polyhedral precipitates were generated, but very few of these precipitates actually generated punched‐out dislocations. In contrast, in the 1000°C samples, only platelet precipitates were generated, many of which generated punched‐out dislocations. Further studies showed that slip dislocations formed only from platelets which did not punch out dislocations, i.e., slip dislocations formed only in the 1100°C samples. The mechanism of the generation of slip dislocation by oxide precipitates is discussed with calculated results of the system energy change due to slip dislocation generation.
It is widely recognized that heavy metal impurities such as Fe, Ni, and Cu degrade silicon device performance and yield. Gettering techniques of internal gettering (IG) by oxide precipitates, 1-10 boron gettering, [5][6][7][9][10][11] and various external gettering (EG) [5][6][7][8]12,13 are used for the removal of metal contaminants from surface active regions to ensure high device performance. Further advances in device processing will probably require double-side polishing of wafers in order to achieve higher flatness. For such wafers, implementation of EG at the wafer back surface is obviously difficult to realize. Furthermore, it is known that boron gettering cannot be expected for Ni contamination. 7 Therefore, IG is crucial for Ni contamination in the next generation of device processes. However, IG behavior for Ni contamination is not fully understood. Shabani et al. 8 and Kageyama et al. 9 emphasized that Ni was very difficult element to be gettered by IG. On the other hand, Falster and Bergholz 3 found that Ni was easily gettered by IG when the oxide precipitates were not visible by the etching method or X-ray topography. To control IG for Ni contamination, it is important to investigate the IG effect as a function of precipitate density and size.The main process for future device fabrication is a low temperature process using high-energy ion implantation whose maximum temperatures are below 1050ЊC. In some cases, the precipitate size becomes less than the detection limit of the preferential etching method. This brings about the difficulty in the prediction of the IG effect in the target wafers.In this paper, we have studied the IG behavior for Ni contamination. On the basis of the experimental and calculated results, the critical size of the oxide precipitate for the IG effect was determined. We have also developed the method of IG prediction for Ni contamination in actual device processes by comparing the calculated precipitate size with determined critical size. Experimental and ResultsThe samples used were lightly boron doped (4.5-6.5 ⍀ cm) p-type, 6 in., Czochralski silicon (100) wafers. Oxygen concentration of the as-received wafers was (16.25 Ϯ 0.25) ϫ 10 17 atom/cm 3 (old ASTM). These wafers were initially contaminated with Ni of 5 ϫ 10 11 atom/cm 2 by a spin-coating method. 14 Ni concentration was determined with total reflection X-ray fluorescence. This contamination level should be far higher than that in actual device processes. The contaminated wafers were subjected to isothermal annealing at 800, 900, 950, and 1000ЊC for up to 16 h in a N 2 ambient. This isothermal annealing plays the roles of Ni drive-in annealing and oxide precipitate generation with certain density and size at the same time. After isothermal annealing, the wafers were pulled from the horizontal furnace at a rate of 10 cm/min. In the pulling process, the wafers were cooled from annealing temperature to room temperature at an average rate of Յ40ЊC/min. This cooling rate supplies enough time for Ni atoms to diffuse from t...
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