| An optical strain gauge was custom built to measure substrate strain in-situ for ultra high vacuum conditions. The gauge is completely integrated with a computer for control and data acquisition and has the novel feature of feedback to remove drift. This gauge is used to observe surface stress in cobalt and titanium ultrathin film silicides on both the silicon(111) and silicon(100) surfaces during room temperature deposition and subsequent anneal.;For cobalt on silicon(111), room temperature growth shows a stress of -(0.91 +/- 0.02) Nm-1/ML for film thickness of about 2 to 8 ML, suggestive of epitaxial dicobalt silicide (Co2Si). This compares remarkably well with the value of -0.90 Nm-1/ML predicted for this phase. For films annealed to 800°C and less than 10 ML thick, a stress of +1.1 Nm-1/ML is measured, closely agreeing with the calculated stress of +1.2 Nm-1/ML for a fully coherent cobalt disilicide (COSi2) phase. Annealed films greater than 10 ML show reduced stress, presumably due to strain relief by dislocations. This break in stress at 10 ML Co coverage is suggestive of a critical thickness.;For cobalt on silicon(100), a tensile stress is observed upon both deposition at room temperature and subsequent anneal to 800°C. For titanium on silicon(100), a tensile stress is observed upon room temperature deposition up to about 3 ML, and further deposition shows a compressive film stress through 40 ML. Subsequent anneal of the film to 850°C produces a large tensile stress probably due to the volume contraction of the film during reaction. This volume change would indicate formation of titanium disilicide (TiSi2). |
