Laser-induced reactions in a deep UV resist system: Studied with picosecond infrared spectroscopy Page: 2 of 7
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Laser-induced Reactions in a Deep UV Resist System: Studied with Picosecond Infrared
Spectroscopy
T. Lippert, A. Koskelo, P. O. Stoutland
Division of Chemical Science and Technology, Mail Stop J-567, Los Alamos National
Laboratory, Los Alamos, NM 87545, lippert@lanl.gov
ABSTRACT
One of the most technologically important uses of organic photochemistry is in the
imaging industry where radiation-sensitive organic monomers and polymers are used in
photoresists. A widely-used class of compounds for imaging applications are diazoketones; these
compounds undergo a photoinduced Wolff rearrangement to form a ketene intermediate which
subsequently hydrolyses to a base-soluble, carboxylic acid. Another use of organic molecules in
polymer matrices is for dopant induced ablation of polymers. As part of a program to develop
diagnostics for laser-driven. reactions in polymer matrices, we have investigated the photo-
induced decomposition of 5-diazo-2,2-dimiethyl-1,3-dioxane4,6-dione (5-diazo Meldrum's acid,
DM) in a PMMA matrix using picosecond infrared spectroscopy. In particular, irradiation of DM
with a 60 ps 266 nm laser pulse results in immediate bleaching of the diazo infrared band (v =
2172 cm-1). Similarly, a new band appears within our instrument response at 2161 cm-1 (FWHM
= 29 cm-1) and is stable to greater than 6 ns.; we assign- this band to the ketene photoproduct of
the Wolff rearrangement. Using deconvolution techniques we estimate a limit for its rate of
formation of ti < 20 ps. The linear dependence of the absorbance change with the pump power
(266 nm) even above the threshold of ablation suggest that material ejection take place after 6ns.
INTRODUCTION
One of the most technologically important uses of organic photochemistry is in the
imaging industry where radiation-sensitive organic monomers and polymers are used in
photoresists.1 Common examples include systems in which photochemically formed acids
become soluble in aqueous base (i.e. positive photoresists)2 and where organic dopants sensitize
a polymer towards ablation.3 The chemistry which occurs in these systems is the basis for the
manufacture of high-density electronic circuits, as well as for the production of printing plates.
One of the most widely-used class of compounds for imaging applications are
diazoketones.4 These compounds undergo a photoinduced Wolff5 rearrangement to form a
ketene intermediate which subsequently hydrolyses to a base-soluble carboxylic acid.6 As part of
a program to develop diagnostics for laser-driven reactions in, polymer matrices7, we have
investigated the photo-induced decomposition of 5-diazo-2,2-dimethyl-1;3-dioxane-4,6-dione (5-
diazo Meldrum~s:acid, :DM) i -aPMMA matrix. This particular didzoketone is sensitive to deep
UV (200-260 nmjmakking j.t suitableuf r high-sesoh io.lit.ographi-applications sIt -has
historically beend4ifficultto study therheisteofsuoh:resistsJnany .of the-intermediates are
short-lived and absorb only in .the UV.ic.ent advances. in ultrafast infrared spectroscopy,
however, now allow 'us to directly examine the initial steps occurring in UV photoresists with
infrared spectroscopy. Herein, we describe the first room temperature observation of
intermediates in the photochemistry of DM with ultrafast infrared spectroscopy.
Shown below is the generally accepted mechanism for the photodecomposition of diazo
Meldrum's acid.9
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Lippert, T.; Koskelo, A. & Stoutland, P.O. Laser-induced reactions in a deep UV resist system: Studied with picosecond infrared spectroscopy, article, December 31, 1995; New Mexico. (https://digital.library.unt.edu/ark:/67531/metadc671868/m1/2/: accessed March 29, 2024), University of North Texas Libraries, UNT Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.