The effect of internal gettering on circuit performance has been studied for I2L and linear logic bipolar circuits. The gettering has been introduced by controlled precipitation of oxygen in silicon wafers during processing, and its effect has been measured as reduction of circuit leakage current, which has been reflected in yield improvement. The efficiency of internal gettering has been found to be a strong function of the amount of precipitated oxygen and precipitate's morphology. It has also been found that the same factors affect the mechanical strength (warpage) of silicon wafers. The best gettering and yield improvement was obtained for relatively low amounts of precipitated oxygen (about 10 ppm), which resulted in the desired precipitate's morphology. An increase in the amount of precipitated oxygen decreased the gettering efficiency and also reduced the mechanical strength of the silicon wafers. The present work showed that, in addition to well‐known factors, such as the interstitial oxygen concentration in virgin wafers, oxygen‐precipitation kinetics during bipolar processing is strongly affected by other factors, such as concentration of nucleation centers for oxygen precipitation. They control the rate of oxygen precipitation and precipitate's morphology. Since the concentration of these centers is related to the crystal‐growth conditions, differences in precipitation kinetics are found in the wafers provided by various commercial suppliers. This can lead to unusual results. For instance, lower amounts of precipitated oxygen have been found in wafers with an initial oxygen concentration of 40 ppm than in wafers with 28 or 31 ppm coming from different suppliers. We believe that our results clearly demonstrate that internal gettering after optimization can be used to improve circuit yield in bipolar processing lines.
The growth rate of selective epitaxial silicon is a function of the nucleation site seed area and the ratio of the area of the SiO2 mask to silicon area exposed. Therefore, with commonly employed IC circuit patterns, it is difficult to achieve, using conventional epitaxial growth conditions, silicon deposit thickness uniformity needed for IC processing. This constitutes one of the main obstacles to utilizing CVD selective epitaxy as an SOI process or as a replacement of LOCOS for oxide isolation. Reported in this publication is a method of growing uniformly thick selective epitaxial silicon on a silicon wafer with SiO2 mask openings to the substrate of various dimensions, and with various Si/SiO2 area ratios. The desired control of the deposit thickness is achieved at reduced pressures (below 50 torr) and relatively low deposition temperatures (850 ~ _+ 10~
003ChemInform Abstract has been investigated by introducing different amounts of nitrogen (9•1014-7•1015 cm-3) into silicon wafers during the float zone process. The effect of nitrogen on the mechanical properties of silicon is complex and is similar to the behavior of oxygen in silicon. The nitrogen state and concentration must be carefully controlled to achieve beneficial effects. The mechanical strength of the N-doped wafers is improved only in a certain state of nitrogen and for concentrations very close to the solubility limit. The improvement of the mechanical properties is reflected in the reduction in the amount of process-induced defects, and in the improvement of CCD imager yield.
A manganese sheet was phosphidized at 400~176 in phosphorus vapor at 1 atm by a sealed-tube method. The following conclusions were drawn:1. All the phosphidization reactions were parabolic and therefore rate apparently limited by a diffusion process.2. A marker experiment indicated that the component which diffused was not phosphorus, but was manganese.3. The parabolic rate constant K, was given as a function of the absolute temperature by the following expression K, = 4.55 exp (-24.1 x 103 cal -mol-1/RT)g 2 cm -4 h -I, (1 atm, 673-873 K) 4. X-ray diffraction patterns and an electron probe microanalysis of the product phosphide films showed that at 400~ a thin single layer composed of MnP alone was formed, but at 450~176 double layers composed of outer MnP and inner Mn2P were formed.
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