Cu/Co多层膜表面粗糙度及织构演化机制

Evolution of Surface Roughness and Texture in Cu/Co Multilayers

薄膜材料中的微观结构和织构特征对其性能有重要的影响作用,但目前薄膜中微观结构和织构的关系尚未清楚。以Cu/Co多层膜为对象,研究薄膜中的表面粗糙度和织构。采用磁控溅射法在单晶Si基底上制备Cu/Co多层膜,通过扫描电子显微镜和原子力显微镜对多层膜的表面粗糙度进行逐层表征,结合薄膜外延生长模型分析薄膜表面自由能的层间差异对薄膜生长模式和表面粗糙度的影响。结果表明,在Si基底上沉积的Cu薄膜呈岛状模式生长,表面粗糙度较小;继续在Cu薄膜上沉积的Co薄膜亦呈岛状模式生长,表面粗糙度增加;最后在Co薄膜上沉积的Cu薄膜,趋向于层状模式生长,表面粗糙度下降。此外,利用XRD与EBSD分析Cu/Co多层膜的织构演变行为,发现在Cu和Co层交替沉积的过程中,织构类型由{111}变为{0001}再变为{111},织构强度逐渐变弱。分析表明,薄膜的织构强度与其表面粗糙度存在一定关系,Cu薄膜中{111}织构强度越高,薄膜的表面粗糙度越小。通过明确Cu/Co薄膜生长过程中的织构演化规律以及织构与微观结构的相互作用,可为薄膜制备技术和性能调控的研究提供一定启示及参考意义。

The giant magnetoresistance(GMR) effect refers to the phenomenon in which the resistivity of a magnetic material changes significantly in the presence of an external magnetic field compared with when there is no external magnetic field.Thus,when the GMR film is applied to an external magnetic field,there is a large variation in resistance.In light of this special property,the GMR film can be applied as a sensor,high-density magnetic recording read-head,giant magnetoresistance random access memory,magnetic spin transistors,and other electronic components.In recent years,the structures and properties of GMR multilayers have been extensively studied.In multitudinous GMR multilayer systems,Cu/Co multilayers have attracted significant attention owing to their good thermal stability and high magnetoresistance change rate.Previous studies have shown that the reduction in the interface roughness of Cu/Co multilayers increased the electron spin correlation scattering at the interface,which could enhance the GMR effect.The microstructure and texture of the multilayers also affect the oscillating exchange coupling and electron spin correlation scattering between the magnetic layers of the GMR films.However,the relationships between the thin film preparation and the formation and evolution of the texture,as well as the change in microstructure,have yet to be thoroughly and systematically studied.The microstructure and texture of thin-film materials significantly influence their properties,but the relationship between them remains unclear.In this paper,the surface roughness and texture of Cu/Co multilayers were studied in detail.First,Cu/Co multilayers were prepared on single-crystal Si substrates by magnetron sputtering.The purity of the sputtering target was99.9%.The substrate was a single-crystal(001) Si;the system background vacuum during sputtering was better than 0.10 mPa;the working pressure was controlled at 0.5 Pa;and the sputtering gas was high-purity argon.During the sputtering process,the power was set at 250 W and the layer thickness was controlled at 100 nm.Based on the above parameters,Cu(100 nm),Cu(100 nm)/Co(100 nm),and Cu(100 nm)/Co(100 nm)/Cu(100 nm) films were prepared.Second,the surface roughness of the multilayer films was characterized by scanning electron microscopy and atomic force microscopy.Combined with the film epitaxial growth model,the effects of the difference between the layer surface energies on the film growth mode and surface roughness were analyzed.By calculating the surface energy in different crystal plane of the Co/Cu film,it was found that surface energy minimization was the main driving force of {111} preferred orientation.The Cu layer deposited on the Si substrate was grown in the island mode with a low surface roughness.The Co layer deposited on the Cu layer was also grown in the island mode with increased surface roughness.The Cu layer deposited on the Co layer tended to grow in the layered mode with reduced surface roughness.The texture evolution of the Cu/Co multilayers was analyzed by X-ray diffraction and electron backscattering diffraction.It was found that during the deposition process,the texture types changed from {111} to {0001},and then to {111},and the texture strength gradually weakened.In Cu/Co multilayers,a relationship exists between the texture and surface roughness:the higher the {111} texture strength in the Cu film,the lower the surface roughness of the multilayers.Clarifying the texture evolution during the growth of Cu/Co films and establishing the interaction between the texture and microstructure provides insight and serves as a reference for film preparation and performance control.