tailieunhanh - The Materials Science of Thin Films 2011 Part 10

Tham khảo tài liệu 'the materials science of thin films 2011 part 10', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | 428 Mechanical Properties of Thin Films is too simplistic a view. Sputtered films display a rich variety of effects including tensile-to-compressive stress transitions as a function of process variables. For example in rf-diode-sputtered tungsten films a stress reversal from tension to compression was achieved in no less than three ways Ref. 15 a. By raising the power level about 30 w at zero substrate bias b. By reversing the de bias from positive to negative c. By reducing the argon pressure Oxygen incorporation in the film favored tension whereas argon was apparently responsible for the observed compression. The results of extensive studies by Hoffman and Thornton Ref. 16 on magnetron-sputtered metal films are particularly instructive since the internal stress correlates directly with microstructural features and physical properties. Magnetron sputtering sources have made it possible to deposit films over a wide range of pressures and deposition rates in the absence of plasma bombardment and substrate heating. It was found that two distinct regimes INCREMENTAL FILM STRESS GPa COMPRESSION TENSION MAGNETRON a ARGON PRESSURE Pa 11. a Biaxial internal stresses as ATOMIC MASS function of Ar pressure for Cr Mo Ta and Pt films sputtered onto glass substrates parallel and perpendicular to long axis of planar cathode. From Ref. 16 . b Ar transition pressure vs. atomic mass of sputtered metals for tensile to compressive stress reversal. From Ref. 16 . . Stress in Thin Films 429 separated by a relatively sharp boundary exist where the change in film properties is almost discontinuous. The transition boundary can be thought of as a multidimensional space of the materials and processing variables involved. On one side of the boundary the films contain compressive intrinsic stresses and entrapped gases but exhibit near-bulklike values of electrical resistivity and optical reflectance. This side of the boundary occurs at low sputtering pressures with light sputtering gases