Ion beam enhanced thermal depolymerization of poly(methyl methacrylate)
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Ion beam enhanced thermal depolymerization of poly(methyl methacrylate) M. E. Fragal`a, G. Compagnini, and O. Puglisi Dipartimento di Scienze Chimiche dell’ Universit`a di Catania, Viale A.Doria, 6-95125 Catania, Italy (Received 7 July 1997; accepted 16 March 1998)
Ion beam enhanced thermal depolymerization of poly(methyl methacrylate) thin films, 1–2 mm thick, has been studied in the temperature range 100–400 ±C using a 300 keV He1 beam at very low fluence (5 3 1010 –5 3 1011 ions cm22 ). A relevant monomer evolution (mass signal myz 100) at temperature (150 ±C) well below the conventional degradation temperature (360 ±C) has been detected during irradiation. The observed phenomenon is discussed in terms of activation energies and diffusion processes within the investigated films. The possibility offered by this phenomenon of performing a microlithography process in only one step is discussed.
I. INTRODUCTION
Ion beam induced modification of chemical and physical properties of polymers has been the main goal of a large number of publications in the last twenty years. The aim of these studies is twofold. There is the need to search for the correlation between the modifications induced by the ion beam and the various stages of the energy deposition process and the following mechanisms of energy dissipation in time and space.1,2 Moreover, the technological use of these modified polymers is appealing for many applications. In particular, poly(methyl methacrylate) (PMMA) is extensively used as photoresist in many microelectronics devices built-up procedures3,4 and in other technological fields, like wave guides5 and coatings. In all these applications radiation and thermal resistance must be well understood. For this reason, in the past, thermal degradation and radiation resistance of PMMA and other polymers have been studied with particular effort in a wide range of temperatures and conditions.6–8 It is generally understood that there are two different mechanisms of polymer thermal degradation. The first is a random process that produces fragments, which are usually larger than a monomer unit. In fact, during this reaction the chain scission occurs at random points along the chain. The second mechanism is a chain depolymerization that involves the release of monomer units in an unzipping reaction. This can be seen as the reverse process of the chain polymerization. The activation energy of depolymerization is higher than that of polymerization, but at elevated temperature the rates of the two reactions become equal and the temperature at which the equilibrium between them is reached is called ceiling temperature sTc d.9 In this respect PMMA belongs to the second class of polymers because it degrades thermally by a depoly228
http://journals.cambridge.org
J. Mater. Res., Vol. 14, No. 1, Jan 1999
Downloaded: 14 Mar 2015
merization process, as already reported.6 Moreover, it is known that vinyl-terminated PMMA thermally decomposes at lower temperature than saturated PM
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