Characterization of Low and Intermediate Molecular Weight Hydrogen Silsesquioxanes by Mass Spectrometry

Hydrogen silsesquioxanes (HSQ or H-resin), represented by (HSiO3/2)2n or TH2n, are an important class of polymers that have gained popularity as spin-on dielectrics by the electronic industry. Previously in the literature, small oligomeric species such as (HSiO3/2)2n, where n = 4–16, have been identified by GC-MS. However, nondestructive mass spectral results for larger H-resin molecules have not been reported, likely due to the nonpolar nature of these molecules. We have utilized a number of “soft” ionization techniques such as field desorption (FD), desorption chemical ionization (DCI), and matrix-assisted laser desorption/ionization (MALDI), and demonstrated that they are amenable to hydrogen silsesquioxanes. The [TH2n − H]+· ions were observed by FD-MS while [TH2n + NH4]+ and [TH2n + Na]+ ions were found utilizing DCI and MALDI, respectively. Based upon the MS results, the polymer compositions as well as molecular weight information can be easily obtained. The detailed structures of H-resin components, however, remain a difficult issue, which cannot be answered by MS data alone. With these preliminary MS results, we have clearly demonstrated that mass spectrometry with the above-mentioned ionization techniques is an invaluable tool that can be utilized when attempting to solve the challenge set forth by the complexity of hydrogen silsesquioxane materials.