Molecular weight and processing effects on the dissolution properties of thin poly(methyl methacrylate) films A. Kokkinis a , E.S. Valamontes b,c , D. Goustouridis a , Th. Ganetsos d , K. Beltsios e , I. Raptis a, * a Institute of Microelectronics, NCSR ‘‘Demokritos’’, 15310 Ag. Paraskevi, Greece b Department of Telecommunications, University of Peloponnese, GR-22100 Tripoli, Greece c Department of Electronics, TEI of Athens, 12210 Aegaleo, Greece d TEI of Lamia, Department of Electronics, 35100 Lamia, Greece e Materials Science and Engineering Department, University of Ioannina, Ioannina 45110, Greece Received 10 August 2006; received in revised form 26 March 2007; accepted 9 April 2007 Available online 29 April 2007 Abstract An experimental set-up based on multiwavelength interferometry, is applied in order to study in-situ the dissolution process of thin resist films. The interference function was the basis for a fitting algorithm, which analyses the experimental data and evaluates the pro- gress of the resist thickness with time. The dissolution of various PMMA molecular weights (15 K, 350 K, 996 K) and resist thicknesses (20–300 nm), in various developers, consisting of mixtures of methyl iso butyl ketone (MIBK), iso propanol (IPA), H 2 O at various rel- ative concentrations, was studied. Surface dissolution inhibition was shown in unexposed resists with high molecular weights and increased thickness in the case of MIBK–IPA 1-1 and IPA–H 2 O 7-3 developers. After that the whole dissolution process evolved at a steady rate. Dissolution of thick films proved to be unpredictable showing complex dissolution curves. Low molecular weight resists pre- sented a smooth dissolution curve without dissolution inhibition. Samples exposed with small DUV doses, exhibited dissolution behavior similar to the unexposed cases, whereas high exposure doses, within the lithographically useful range, led to smooth dissolution behavior. In the case of MIBK–IPA 1-3 developer significant swelling was observed. Ó 2007 Elsevier B.V. All rights reserved. Keywords: Poly(methyl methacrylate); Thin film; Lithography; Dissolution; Multiwavelength interferometry 1. Introduction During the last 10–15 years significant research effort has been devoted worldwide, to the understanding of thin polymeric film properties (e.g.[1–5]). In such thin polymeric films, several parameters appear totally different from the ones at thicker films. From the point of view of patterning the two most important properties that undergo significant change from the transition of relatively thick to thin films are physicochemical properties such as the glass transition temperature ðT film g Þ (e.g. [6–8]) and the dissolution rate (e.g. [9,10]). A polymeric film supported on a substrate could be considered as a 3-layer stack; the top layer (resist/environ- ment interface) and the bottom layer (resist/substrate inter- face) having a thickness of a few radii of gyration and the middle layer having the properties of the bulk film. As total film thickness decreases below a certain value, the contribu- tion of the interfacial layers increase and thus the physico- chemical properties start to deviate from the bulk ones. The established methods for the characterization of poly- meric films and in particular resists, provide information attributed to the average properties, and sometimes are not applicable to thin films. For example the differential scanning calorimetry (DSC) tools, which are used for the measurement of glass transition temperature of bulk poly- 0167-9317/$ - see front matter Ó 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.mee.2007.04.141 * Corresponding author. E-mail address: raptis@imel.demokritos.gr (I. Raptis). www.elsevier.com/locate/mee Available online at www.sciencedirect.com Microelectronic Engineering 85 (2008) 93–99