Low Energy Ion Beam Modification of High Performance Polymer
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LOW ENERGY ION BEAM MODIFICATION OF HIGH PERFORMANCE POLYMER
HYO-SOO JEONG AND R. C. WHITE Department of Electrical Engineering and Microelectronics Sciences Laboratories Columbia University, New York, N.Y., 10027 ABSTRACT Ion beam modification of polyimide (PI) by low energy and surface analysis were performed using XPS. The surface chemistry was monitored as a function of ion dose. The results indicate that even low energy ion beam (LEIB) induces a drastic change in chemical compositions on the PI surface, and the modification begins to occur at the onset of beam treatment, contrary to previous observations. Damage level is severely restricted to surface region. It is also proven that LEIB modification is a direct way to control interface chemistry. 1. INTRODUCTION Ion beam processing has been well established for creating strong, stable adhesion between materials having no bulk chemical affinity [1, 2]. Both interface chemistry and fracture mechanisms can be adjusted by ion beam treatment. By far the most successful and promising ion beam technique for adhesion enhancement has been that of pre-treatment of the substrate surface with a low energy Ar* ion beam in situ prior to deposition [3] . Such an inert LEIB may produce the following effects: (1) removing contaminant layers, (2) leaving active "dangling" bonds, (3) producing a roughened surface, and (4) altering the surface atomic composition. The effects have been observed to induce an electronically strong chemical bonding and to greatly enhance interface adhesion [3, 4]. Therefore, surface modification seems to be an efficient way of producing such interface chemical bonding upon thin film deposition. To date, the majority of the ion beam studies on polymers has been done by the use of HEIB (from several KeV to Mev) . However, little is known about the specific chemistry induced by ion beam treatment. This is because determination of chemical modification via surface sensitive probes is severely restricted for ion beam treated polymers due to the deep penetration of energetic ions into the polymer substrates. Thus, we have limited our study to low ion energy and low ion doses, where the depth sampled will not be disrupted completely by the ion bombardment. 2.
EXPERIMENTAL
XPS was used to follow the effects of Ar ion beam treatment of PMDA-ODA PI (DuPont PI-2545, thickness of -200 A spun on Si wafer). This thin PI film allows for characterization by XPS with shifts due to charging minimized to a few tenths of an eV or less [4] . We considered all PI core levels at both normal and grazing (30 degree from surface) emission. Mat. Res. Soc. Symp. Proc. Vol. 236. 01992 Materials Research Society
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a for 10 minutes in situ The sample was annealed in 8 torr) at 300"C prior to each chamber (
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