Effect of elastic modulus of PMMA films on its machinability by AFM-based nanoscratching method

In the present study, elastic modulus is used to estimate the machinability of Polymethylmethacrylate (PMMA) films using an atomic force microscope (AFM). PMMA is widely used in microsystem field as coatings and packaging materials. A better understanding of its mechanical properties is essential to optimize its application. By spinning coating PMMA solution on a silicon substrate, the influences of the spin-coating speed and concentration of the PMMA solution on the thickness of the PMMA films are studied. Results show that the film thickness decreases with the increase of spin-coating speed and the decrease of solution concentration, respectively. Finally PMMA films with dimensions of the thickness spanning from dozens to hundreds nanometers are obtained. The atomic force microscope has been demonstrated to be a useful tool for fabricating and imaging materials at nanometer scale. Elastic moduli of the PMMA films spin coated with different parameters are evaluated using the PeakForce Quantitative NanoMechanics (QNM) module of the AFM system. Experimental results show that smaller elastic moduli are measured on thicker PMMA films. Meanwhile, several V-shape grooves are scratched with the same normal load by AFM probes on different PMMA film specimens. The relationship between elastic moduli and machinability of the PMMA films is obtained by contrasting the depth of the grooves.