Abstract
AbstractWe use two kinds of specimen, the soft film / hard substrate system ( low-k film deposited on silicon ) and the hard film / soft substrate system ( gold film deposited on polycarbonate ), to investigate the mechanical properties of thin film. From the nanoindentation test, it is observed that the hardness and Young’s modulus varied with D/t ratio and film thickness. However, the hardness is independent of D/t ratio when film thickness exceeds 1 μm and the value is approximately about 1875.2 MPa. Through the observations of indentation impressions by optical microscope and atomic force microscope (AFM), it is suggested to restrict the applied load of nanoindenter to avoid the fractures, which cause errors during measuring.The hardness of bulk polycarbonate obtained from microhardness (144MPa) is employed to calibrate the calculation and determination of Young’s modulus obtained from nanoindenter (2.8GPa). Through this calibration method, it is obtained with much higher accuracy. A fitting equation that predict the hardness and the Young’s modulus when the parameter a and the D/t ratio are given in the hard film / soft substrate system is also constructed. The parameters a to the hardness and Young’s modulus are 6.84537 and 7.4543, respectively.Microscratch test, four-point bending test and modified edge lifted-off test are effective techniques adopted to evaluate the adhesion of thin film. The results of the strength of the coating / substrate interfaces evaluated through these techniques are compared and discussed in terms of film thickness. It is found that the critical stress to peel thin film decreases with increasing film thickness in microscratch test and four-point bending test. Similarly, the adhesion of low-k film decreases with film thickness in the four-point bending test and modified edge lift-off test. But it has an opposite result in meauring adhesion in microscratch test.In addition, the analytical method using curvature to measure the stress and strain in thin film and the substrate is studied. In gold film / polycarbonate substrate specimen, it is found that the differential strain and residual stress increase with increasing film thickness. However, as the thickness exceeded 700 nm, the differential strain and the maximum stress of thin film become independent of film thickness, and approximately equal to 0.0036 and 239.3 MPa.