ToF‐SIMS studies of nanoporous PMSSQ materials: kinetics and reactions in the processing of low‐K dielectrics for ULSI applications

Abstract

Detailed investigations of spin-on polymethylsilsesquioxane (PMSSQ)-based low-K materials were carried out by means of time-of-flight secondary ion mass spectrometry (ToF-SIMS) to identify the reaction kinetics and mechanisms occurring during the manufacturing of nanoporous dielectrics for ULSI applications. Analysis of the static SIMS fingerprints led to the identification of key species related to the PMSSQ oligomers, as well to the observation of features related to the initial functionality of the precursor materials. The intensity variations of the key species with thermal curing reveal the polymerization kinetics of the dielectric precursors. In addition, thermal decomposition and volatilization of the polymethylmethacrylate-dimethylaminoethylmethacrylate copolymer (PMMA-co-DMAEMA) porogen was established based on the detection of fragments related to the different moieties of the copolymer molecule. Porogen degradation takes place via cleavage of the DMAEMA co-monomer at low temperature, followed by volatilization of the residual PMMA-enriched polymer upon annealing at higher temperature. Several complementary phenomena occurring during the formation of these complex systems can be evaluated by ToF-SIMS, revealing major features crucial to materials development and the manufacturing of novel low-dielectric-constant (K) dielectrics.

Thin-film transformations and volatile products in the formation of nanoporous low-k polymethylsilsesquioxane-based dielectric

“…4͑a͔͒ and positive ͓Fig. 7 These key species in the figures show characteristic patterns as a function of temperature, roughly similar in shape for all fragments. These data are normalized to the intensities obtained from the sample cured at 50°C.…”

“…7 TDMS was performed at the University of Maryland to analyze volatile products of the curing process in the gas phase. TOF-SIMS was performed in both static and dynamic modes.…”

“…Even though there are still thermal decomposition problems for some of the materials at an elevated temperature, 5 these materials usually show better thermal and mechanical performance than purely organic materials at the processing temperatures near 450°C which are required for interconnect technology. [6][7][8] While these materials offer dielectric constants in the range of 2 Ͻ k Ͻ 3, ultra low-k materials ͑k Ͻ 2.0͒ are required for sub-65 nm technology. Some would argue that thermal processing of spin-cast materials is an approach more extendible to highly porous low-k structures, so that lower effective k values can be obtained.…”

In-Situ Metrology: the Path to Real-Time Advanced Process Control

“…[32,43] But the general notion of sensing chemical reaction signatures for chemical processes is much broader. For example, we have begun investigations of the curing process used to create nanoporous low-K dielectrics by spin-casting, using time-of-flight secondary ion mass spectrometry (ToF-SIMS) [44]. The properties of the material depend sensitively on the details of how the sacrificial porogen species are volatilized (they are the placeholders for the nanopores that will remain in the low-K matrix).…”

Characterisation of poly(methyl methacrylate) film deposited on iron powder particles by electropolymerization

“…TOF-SIMS has made it possible to analyse of polymers and oligomers not only to determine the structure but also to propose a mechanism of the fragmentation for these complex systems. Detailed investigations of spinon polymethylsilsesquioxane based low-K materials were carried out by means of TOF-SIMS to identify the reaction kinetics and mechanisms occurring during the manufacturing of nanoporous dielectrics for applications [2]. Characteristic fragments formed from PMMA in TOF-SIMS analyses were declared with m/z values 15, 41, 59, 69, 81 and 101, in a positive ion region, and m/z 13, 16, 25, 31, 41, 55, 85 amu in a negative ion range [3].…”