All films were deposited by sputtering onto Si (100) substrates that were solvent cleaned in an ultrasonic bath. The surface stress evolution in Cr film and Co/Cr multilayer was measured by in situ stress measurement system during and after sputtering deposition, using a laser beam reflected from a cantilevered substrate and a photodiode array to measure the laser beam position.
At room temperature Cr thin film exhibits only tensile surface stress over the whole thickness range. F/w evolution of Ag thin film exhibits a brief initial compressive part, followed by a tensile maximum, and finally a constant compressive surface stress.
At elevated substrate temperatures and deposition rate for Cr film, compressive surface stress is found during the initial growth stage and compressive minimum value of F/w is lowered at higher film thickness. We think the atom mobility is so sufficiently high that islands instead of columnar mode are formed during the initial growth stage. The average grain size is increased at higher substrate temperature and thicker thickness.
It was found that by increasing the Ar gas pressure the surface tensile stress increases a little during deposition.
When the Cr film deposition is stopped, a change in F/w is always in the tensile direction. This occurs, even of the stress in the film is already tensile or compressive. Furthermore, upon resumption of the deposition, F/w returns to the value it had when the deposition was stopped and continues as if no interruption had occurred. When deposition of the same Cr is resumed, the time constant of the decrease back to the level of F/w at the end of the last deposition is considerably shorter than the time constant of the tensile increase after deposition ends. This indicates that the steady state dynamic surface structure is restored after deposition of just a few monolayers. The magnitude and duration of the change in F/w after deposition increases with the thickness of the top layer.
When a Co/Cr multilayer is deposited continuously, the evolution of F/w is depends on the thickness of the layer immediately beneath the layer being deposited. Interesting thing is that compressive-compressive and tensile-tensile trends are seen. This indicates that the epitaxial relationship between Cr and CoCrTaPt layers. Another interesting thing is no small compressive minimum associated with the beginning of each layer, as there is for deposition on a fresh substrate. This is because the surfaces are sufficiently rough that there can be coalescence between the new crystallites and the existing surface soon after nucleation occurs. so by tailoring the precise thickness of the individual layer, it is possible to produce multilayered films with any average stress between wide limits (compressive to tensile).
By applying higher deposition rate Co/Cr multilayer Co(10.1) peak intensity increase, transition from columnar to equiaxed structure and coercivity increase are found. And also we can confirm increasing coercivity with increasing compressive surface stress in CoCrTaPt.
