AZ-1518 Photoresist analysis with synchrotron radiation using high-resolution time-of-flight mass spectrometry L.A.V. Mendes a , R.R. Pinho b , L.F.  Avila c , C.R.A. Lima b , M.L.M. Rocco a, * a Departamento de Fı ´sico-Quı ´mica, Instituto de Quı ´mica, Universidade Federal do Rio de Janeiro, Cidade Universita ´ria, Ilha do Fund~ ao, 21941-590 Rio de Janeiro, RJ, Brazil b Departamento de Fı ´sica-ICE, Universidade Federal de Juiz de Fora, Campus Universita ´rio, 36036-330 Juiz de Fora, MG, Brazil c Instituto de Fı ´sica, Universidade Estadual de Campinas (UNICAMP), Caixa Postal 6165, 13083-97 Campinas, SP, Brazil Received 22 December 2006; received in revised form 9 March 2007; accepted 19 March 2007 Available online 21 March 2007 Abstract With the aim of identifying molecular modifications among photoresists unexposed and previously exposed to the ultraviolet light the photon stimulated ion desorption (PSID) technique was employed in the study of the AZ-1518 photoresist. Data acquisition was performed at the Brazilian Synchrotron Light Source (LNLS), during a single-bunch operation mode of the storage ring and using high-resolution time-of-flight mass spectrometry (TOF-MS) for ion analysis. PSID mass spectra on both photoresists (unexposed and exposed) were obtained following the S K-shell photoexcitation and desorption ion yield curves have been determined for the main fragments as a function of the photon energy. The AZ-1518 photoresists presented different PSID spectra, showing characteristic fragments. Most of the analyzed ions showed larger relative yields for the exposed photoresist. Fragments related to the photochemical decomposition of the photoresist could be clearly identified. These results showed that the PSID technique is adequate to investigate structural changes in molecular level in unexposed and exposed photoresists. Ó 2007 Elsevier Ltd. All rights reserved. Keywords: Photoresist; Photodegradation; Photon stimulated ion desorption; Positive ions; Time-of-flight mass spectrometry 1. Introduction Positive photoresists are widely used in lithographic pro- cess in microelectronics and in optics for the fabrication of relief components. In microelectronics, they are used as masks to transfer geometric patterns by manufactures of the integrated circuits. In optics, the photoresists are used to construct periodic structures with diffractive optics proper- ties [1]. The most popular positive photoresist is composed of the photoactive compound (PAC) denominated diazonaph- thoquinone (DNQ) and the matrix material that is a thick resin called novolak, which are shown in Fig. 1(a) and (b), respectively. The novolak is a phenoleformaldehyde con- densation polymer of moderate molecular weight, which is used to supply a mechanical support for the photoresist, be- ing very strong to chemical attacks. In unexposed areas the novolak þ DNQ films are essentially invariable during the development process. When positive photoresists are exposed to UV light, changes in their physical and chemical properties occur which is traduced by some alterations in the complex refractive index of the material. The changes during the exposure process de- pend on the absorbed energy by the material. Fig. 2 shows the chemical processes suffered by the photoactive compound when exposed to the UV light. The nitrogen molecule in the PAC is weakly bonded and is liberated of the aromatic ring when exposed to the light, turning the unoccupied orbital highly reagent. To stabilize the structure, one of the carbon atoms moves outside of the ring and the oxygen atom is then covalently bonded to it. This process is denominated as Wolff rearrangement and the resulting molecule is denomi- nated as ketene [2]. In the presence of water, a final * Corresponding author. Tel.: þ55 21 25627786; fax: þ55 21 25627265. E-mail address: luiza@iq.ufrj.br (M.L.M. Rocco). 0141-3910/$ - see front matter Ó 2007 Elsevier Ltd. All rights reserved. doi:10.1016/j.polymdegradstab.2007.03.011 Polymer Degradation and Stability 92 (2007) 933e938 www.elsevier.com/locate/polydegstab