Stress Changes of Nanocrystalline CoNi Thin Films Electrodeposited from Chloride Baths

Abstract

Magnetic CoNi alloys were electrodeposited from chloride baths to investigate the influence of saccharin on thin film stress. As the Co 2ϩ concentration in the plating solution was increased, the stresses in the CoNi thin films increased. CoNi thin films electrodeposited from chloride baths without saccharin exhibited increased tensile stresses ͑from 145 to 270 MPa͒ with increasing Co concentration in the plating baths, whereas CoNi thin films electrodeposited with saccharin showed decreased stress. Notably, CoNi thin films deposited with saccharin showed the transition from compressive to tensile stress modes ͑Ϫ85 to 120 MPa͒ with increasing Co 2ϩ concentrations.Numerous studies of electrodeposited iron group thin films ͑Fe, Co, and Ni͒ have been carried out because of potential applications in computer read/write heads, 1,2 microelectromechanical systems ͑MEMS͒, 3-5 and ultralarge scale integration ͑ULSI͒ devices. 6,7 Electrochemical processes ͑electrodeposition and electroless deposition͒ have many advantages over vacuum processes because of roomtemperature operation, various deposition parameters, easy scale up and maintenance, low production cost, relatively rapid deposition rate, the capability of handling complex geometries, and the ability to ''tailor'' deposit structure and properties. Electroless deposits are less porous, more uniform, and more resistant to corrosion than electrodeposits. 8 However, electroless deposition processes are more expensive, and have slower deposition rates and less stable baths than electrodeposition processes. Therefore, electrodeposition processes may be more suitable for integration of magnetic materials into MEMS devices.Magnetic materials have recently been incorporated into MEMS devices such as sensors, microactuators, micromotors, and frictionless microgears because electromagnetic-actuated MEMS are more durable for force applications in severe environments compared to electrostatic-actuated MEMS. 9,10 To incorporate magnetic materials into MEMS devices, magnetic thin films must have good adhesion, low-stress, good corrosion resistance, and be thermally stable with excellent magnetic properties. Magnetic layer thicknesses in MEMS can range from a few tenths to hundreds of micrometers, depending on the applications. In particular, stress of the deposited films plays an important role in incorporation of magnetic materials into MEMS devices. High stress in magnetic thin/thick films may result in malfunction of MEMS devices because of deformation or detachment of the deposited films from the substrate ͑e.g., Si substrate͒. Although numerous studies have been carried out to investigate binary and ternary iron group magnetic thin films, there is a lack of systematic studies about the stress issue. In this study, we focused on stress changes of magnetic CoNi thin film alloys electrodeposited from chloride baths as a function of composition ratio in the films. The effects of an additive ͑saccharin͒ on the film stress were also studied. ExperimentalThe solution compositions fo...

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