The effect of thin film stress on the formation of Cr texture and on the coercivity of CoCrX(X=Pt, Ta)/Cr magnetic thin film was investigated by controlling the thin stress developing during the film formation through the variation of applied bias and of deposition temperature. The coercivity of CoCrX/Cr magnetic thin film was dependent on the grain size of the Cr underlayer, increasing with the grain size for grain size smaller than about 20nm. This was closely related to the change of Cr texture from the (110) to the (200) orientations. The (200) Cr texture was preponderant over the (110) Cr texture in a deposition condition that the ad-atoms are highly energetic and mobile. The (200) texture of Cr thin film tended to suddenly appear at the average film stresses smaller than a critical stress. This sudden change of Cr texture is however not directly determined by this change of average film stress. The stress that is critical is instead the surface stress and attains a sufficiently large compressive stress at this average film stress to energetically favor the (200) over the (110) Cr orientation. The coherency between the film substrate is not a necessary condition for the formation of the (200) Cr texture. The only requirement is to achieve a dynamic surface structure containing a high density of compressive ledge. This can be achieved not only by controlling the energy of ad-atoms but also by controlling the average film stress.
Stress control of Cr underlayer and CoCrPtX magnetic layer was possible by the mean of introducing a new amorphous FeTi seed layer and by controlling the applied bias. Amorphous FeTi seed layer induced the stress in Cr underlayer with same sense, and the stress in CoCrPtX magnetic layer with opposite one. Deposition condition obtaining maximum coercivity was to remove the applied negative bias in bottom layer. The optimum stress condition was the one that is small tensile stresses in FeTi seed layer and Cr underlayer. Because of the heteroepitaxial relationship between Cr underlayer and CoCrPtX magnetic layer, the stress in CoCrPtX magnetic layer was compressive. At the case, a promotion of Cr segregation in CoCrPtX grain boundary was observed by EFTEM. ΔM measurement also ascertained the result. The condition removing the applied bias in bottom layer allowed large coercivity and appropriate coercive squareness by the reducing the intergranular coupling between magnetic grains through inducing large compressive stress in magnetic layer.
Evolution of grain structure of as-deposited Cr thin film by DC-magnetron sputter deposition was investigated by experimentally measuring the evolution of grain size distribution and by computing the film growth using Monte Carlo simulation. The variation of grain size distribution with the deposition temperature was discussed in terms of the film growth mechanisms. A stagnant columnar grain structure develops at comparatively small film thickness (67nm) and at the deposition temperatures 200-300℃ far lower than the $0.3T_m$. This is believed to arise from the fact the mobility of ad-atoms greatly increases as a result of the application of negative bias and that the Ar+ ion tends to pin the grain boundary. The film growth at 400℃ significantly deviates from the columnar grain growth and indicates the occurrence of significant amount bulk diffusion despite too low a temperature for the formation of equiaxed grain structure. This discrepancy is also believed to arise from the significant contribution of biasing effect to the grain growth by DC-magnetron sputter deposition.
