News
Broadband MALDI-FT-ICRMS spectrum oo polyvinyl pyrrolidone with ununown wne group. (Adapted with permission on the American Society for Mass Spectrometry.)
Understanding the expansion and contraction dynamics of polymer films Although laser ablation is commonly used for material processing and fabrication, the mechanism of the resulting rapid morphological changes has not been eluciated. Hiroshi Masuhara and colleagues at Osaka University (Japan) have used nanosecond timeresolved interferometry to investigate the nanosecond transient expansion and contraction dynamics of poly(methyl methacrylate) (PMMA) and poly (methyl acrylate) (PMA) films
sion method, an averaging method of calculating the uncertainty in the end-group mass provides higher accuracy if the elemental composition of the monomer is known. The researchers tested the method using polyethylene glycol with known end groups. They then analyzed polyvinyl pyrrolidone with an unknown end group by the averaging method and determined it to have end groups of (CHg)2CHO- and H-, which were confirmed by the manufacturer. The averaging method allows end-group mass determinations with an accuracy within 3 mass units in the weight range 5-1400 u and within 20 mass units in the weight range 3400 5000u (J. Am. .oc. Mass Sbectrom. 1996 7 449-57)
doped with pyrene following excimer laser irradiation. A KrF excimer laser was used to induce expansion of thefilms,and a Q-switched Nd3+: YAG laser was used as a probe light source for the Michelson interferometer. Interference patterns were captured by a CCD camera, and time-resolved measurements were made by controlling the time delay between excitation and probe-laser pulse peaks. They found that at 150 mj/cm2 laser irradiation, polymer films with a thickness of ~ 2 urn rapidly expanded by ~ 250 nm, then slowly contracted with no permanent etching on the surface Contraction behavior depended on the thermal properties of the substrate and the maximum value of the transient expansion showed different fluen rlgnendence for PMMA and PMA films They inter preted thedif ference in expansion behaviors between 11.
Characterizing etching processes Investigating the surface of real structures to better understand processing and failure issues for very large-scale integrated (VLSI) devices requires the ability to analyze separately the bottom and sidewall surfaces of trenches. M. C. Peignon and colleagues at the Institut des Materiaux de Nantes (France) have shown that angleresolved X-ray photoelectron spectroscopy (XPS) can be used to characterize the surface chemistry and crystalline damage of patterned samples. They used the technique to study photoresist/Si02/Si structures after CHF3/ CF4/Ar plasma etching of contact holes in commercial parallel-plate reactive ionetching reactors and the etching of Si02 over Si with high-density plasmas. Si02/Si etch selectivity was achieved by depositing an involatile fluorocarbon film to protect the surface. After etching, the Si of the trench bottom of patterned samples showed the same modifications as unpatterned Si0 2 /Si samples that can
be described by a two-layer model involving? a fluorocarbon overlayer and interface layer. The researchers found that thickness and composition of the overlayer varies from 7 to 60 A. depending on the type of treatment and the relative composition of F-C and C-C bonds changed and that the interface layer was composed of Si-F Si-C and Si-0 bonds XPS analyses performed with a monnrhromatized X ray source revealed that damaged Si caused by t h e etchincr ten s removed hv each of three t t h i n c treatments (1 Ffo t rhe S IQQfi 74? 1^4.7-541
ill
the twofilmsin terms of the glass-rubber s re a e mo ecExpansion dynamics of PMMA (9) and PMA (O) films doped with pyrene at a fluence of 150 mj/cm2. The solid and broken lines represent an excimer laser pulse and the time integration of the laser pulse, respectively.
400 A
Analytical Chemistry News & &eatures, July 1, 1,96
u ar monons in tne polymer ains."' ^ Ltiem. iyyt) 100,6871-75)
Spectra from normal and angular XPS obtained from a patterned sample after etching. .Adapted with permission on The Electrochemical Society.)
