Elektrokaplanmış nikel ince filmlerdeki stress gradyanlarının karakterizasyonu

Nickel is a widely employed and thus well-studied material in the MEMS field due to its superior mechanical properties such as its high modulus of elasticity and corrosion resistance and magnetic properties. Among different deposition techniques of nickel, electroplating, as a well-studied and commercialized technique used in the fabrication process of macro- and as well as micro-devices, has various advantages including the ability to manipulate mechanical properties such as the modulus of elasticity and residual stress simply with deposition parameters.Determination of residual stresses in thin films is necessary to optimize device performance and to lower fabrication costs. In addition to well-studied uniform residual stresses in thin films that control in-plane displacements, stress gradients that determine out-of-plane deflections of components need to be characterized to obtain straight microstructures designed as a moving part in a MEMS application.The main contribution of this study to the literature is the systematic characterization of residual stress gradients of electroplated 1-µm-thick nickel films using microcantilevers as a measurement tool. This is achieved by varying electroplating parameters of applied current density and solution temperature in the range of 1 ? 20 mA/cm2 and 30 ? 60 °C, respectively. Determination of cantilever tip deflections together with modulus of elastic measurements is performed to evaluate the residual stress gradients in nickel films. The modulus of elasticity of nickel is found to be in the range of 128,2 ? 175,9 GPa, which is smaller than that of bulk nickel, approximately 200 GPa. Then the stress gradient of DC plated cantilevers is calculated to vary from 129.95 to -67.91 MPa/µm. Measurements indicate zero residual stress gradient, i.e. straight cantilevers, can be achieved at approximately 8 and 14 mA/cm2 for the electroplating temperatures of 30 and 45 °C, respectively. However, there is no available current density within the investigated current density range leading to straight cantilevers at 60 °C electroplating temperature.Microstructural analyses, consisting of XRD measurements of samples having different nickel film thicknesses and SEM morphology analysis of film surface and cross section are also employed to explore growing film characteristics.