| AVS 61st International Symposium & Exhibition | |
| Tribology Focus Topic | Friday Sessions |
| Session TR-FrM |
| Session: | Applications of Novel Materials in Tribology |
| Presenter: | Yijie Jiang, University of Pennsylvania |
| Authors: | Y. Jiang, University of Pennsylvania Z.B. Milne, University of Pennsylvania M. Fallet, United States Naval Academy J.A. Harrison, United States Naval Academy R.W. Carpick, University of Pennsylvania K.T. Turner, University of Pennsylvania |
| Correspondent: | Click to Email |
Atomic force microscopy (AFM) is increasingly used for probe-based metrology and tip-based nanomanufacturing (TBN) processes. In these processes, a sharp silicon- or carbon-based tip often interacts with the surface of a polymer film on a substrate. During this mechanical interaction, the polymer film can wear and contaminate the tip. To improve the reliability and control of these processes, a fundamental understanding of the tribological properties of nanoscale tip-polymer contacts is required.
Polymethyl methacrylate (PMMA), a common polymer used in nanofabrication, is studied here. PMMA is used as a resist in electron-beam (e-beam) lithography and also employed in TBN processes to realize 2D patterns and 3D structures. The tribological properties of PMMA are important in the optimization and selection of operating parameters in TBN processes and AFM-based metrology. Studies of PMMA wear have been performed from the millimeter- to nano-scale. The reported wear rates of PMMA vary over a wide range, likely due to differences in PMMA compositions tested, varied experimental conditions, and lack of control for the effect of debris. The debris can contaminate both the surface and the tip, and this often makes it difficult to accurately assess wear in experiments at the small scale.
In this work, nanoscale wear of PMMA is investigated using systematic AFM-based nanomechanical wear experiments. The experiments are performed on thin PMMA layers (131±4 nm thick) on silicon substrates. To allow for precise quantification of the evolution of the PMMA, the film is patterned via e-beam lithography into structured patterns. The gaps between the patterns minimize debris and also facilitate tip cleaning. The structures primarily consist of long rectangular and square structures of PMMA. The exposed Si surface in the gaps serves as a reference surface, which allows for accurate measurements of film height to be obtained throughout the test. The use of AFM for applying the mechanical load and scanning as well as for imaging the structures allows for in-situ observation of the wear process. Different volume loss rates of the polymer are measured under varying loads and scanning speeds. The tip geometry and contamination are assessed by scanning over a reference sample and by imaging using transmission electron microscopy. The load and tip geometry data are used to determine contact stresses during the test. This talk will discuss the experimental method and results, and the development of models to describe the relationship between wear volume, applied load, and scanning speed.