Surface energy is one of the most fundamental parameters of a solid since it depends directly on the binding forces of the material. Indeed, it is a measure of the work necessary to separate a material into two parts along a plane. Very few measurements have been made of this quantity and these by indirect means, because of difficulties of measurement and interpretation. This report deals with a direct measurement of specific surface energy of Ge and Si made by the cleavage technique. By measuring the force just necessary to move a crack “in reversible fashion” the surface energy can be obtained. The measured value for the {111} planes of Ge and Si are 1060 ergs/cm2 and 1230 ergs/cm2. From these measured values the energy of the planes {100} and {110}can be estimated. They are: 100110Ge1835 ergs/normalcm21300ergs/normalcm2Si2130 ergs/normalcm21510 ergs/normalcm2 Using the measured value of specific surface energy, assuming this is due to the appropriate number of broken normalbonds/cm2 , the bond strength of Ge and Si was obtained as normalGe‐normalGe=42.6 normalkcal/normalmole ; normalSi‐normalSi=45.5 normalkcal/normalmole .

When Si is thermally oxidized, the SiO2 resulting is in a state of compression on the surface. This paper reports an experimental determination of the magnitude of this stress and its dependence on the temperature of oxidation. Samples of (111)- and (100)-oriented Si were oxidized at several temperatures between 875°–1200°C to thicknesses of 2000 Å-20 000 Å. Stress determination was made by two techniques: (a) the thin Si sample was used as a beam, and the amount of bowing under the strain exerted by oxide left on one surface was measured; (b) the unsupported SiO2 window was used as a balloon, and strain was measured as a function of air pressure inflating the balloon. Results of these measurements are in agreement with the stress expected from thermal mismatch of Si and SiO2. For an oxidation carried out at 1200°C the measured stress is 3.1×109 dyn/cm2. The data from the SiO2 balloons showed that the strain grown in the oxide was greater than 10−3. In addition, determination was made of Young's modulus from the stress-strain curves of the unsupported films. The value of 6.6×1011 dyn/cm2 obtained compares favorably with the value 7±1.5 1011 dyn/cm2 found for silicate glasses. Some implications of this stress are briefly discussed. Dislocation generation at borders of holes cut into oxide, bowing and slip processes of slices, impurity segregation, and precipitation are all possible results of this mismatch between the two materials.

We have developed a kinetic model to describe the oxidation behavior of Si1−xGex alloys during Ge segregation, which compares the Deal–Grove flux of oxidant diffusing through the oxide to the maximum flux of Si diffusing through the Ge-rich layer. This is motivated by thermal oxidation experiments on Si1−xGex alloys (x<0.17) using a fluorine-containing ambient (O2 and 200 ppm of NF3). The fluorine is known to modify point defect generation during oxidation of pure Si toward vacancy production, which is also the case for Ge in Si. We demonstrate that fluorinated oxidation of Si1−xGex enhances the oxidation rate by 25%–40% in the temperature range of 700–800 °C. Oxides formed at these temperatures were SiO2, while those formed at 600 °C exhibited a transition from SiO2 to mixed oxide growth at some point during the very early phase of oxidation, depending on the alloy composition. Consideration of these data suggests that other factors in addition to oxidation temperature must be considered in predicting which oxide type will be produced, in contrast to most previous reports. Our model, indeed, shows that alloy composition, oxide thickness, and oxidant partial pressure are also important parameters. We believe that the model is very useful in predicting the oxide type that should result from a given set of growth conditions, and in particular, it suggests that a changeover from SiO2 to mixed oxide formation is likely at some point during the oxidation process, particularly if carried to larger thicknesses.

This paper offers a construction that gives the limiting or ``equilibrium'' shape of an etching crystal. The conditions for hillock and pit stability and face rounding are also obtained. Experimentally, germanium cylinders with different zone axes were etched to develop ``equilibrium cross sections.'' These were in good agreement with the construction. Other uses of the construction are discussed.

Enhancement of silicon oxidation rate due to tensile mechanical stress