Material Characterization and the Formation of Nanoporous PMSSQ Low-K Dielectrics (original) (raw)
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Surface and Interface Analysis, 2004
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.
2005
The thermal transformation of spin-cast thin films to produce nanoporous low-k dielectric layers has been investigated using polymethysilsesquioxane ͑PMSSQ͒ for the low-k matrix and polymethylmethacrylate-co-dimethylaminoethylacrylate ͑PMMA-co-DMAEMA͒ as the porogen which is volatilized to leave nanopores in the matrix. Surface analysis methods, including time of flight-secondary ion mass spectrometry and x-ray photoelectron spectroscopy, and thin film analysis by small-angle neutron scattering revealed the kinetics of matrix crosslinking, while thermal desorption mass spectrometry showed the evolution of gaseous reaction products from porogen and matrix during the complex chemical transformations which occur with thermal cycling from 100°C to 450°C. Matrix crosslinking occurs primarily at lower temperatures ͑100-225°C͒, while porogen diffusion and decomposition begins somewhat above 200°C, leading to phase separation which creates the final nanoporous structure. Since matrix and porogen reaction kinetics have some overlap, relative kinetics can be important: e.g., matrix crosslinking proceeds more rapidly for PMSSQ precursors with high Si-OH content cf. low SiOH content, with implications for the morphology of porogen-derived nanostructure. As surface species transform ͑matrix crosslinking͒ and disappear ͑porogen volatilization͒, their complements are seen in the gas phase as reaction and decomposition products. Porogen decomposition is ligand selective, in that the N-containing ligand of DMAEMA is volatilized at considerably lower temperatures ͑ϳ200°C͒ than that ͑ϳ400°C͒ for the remaining species ͑the PMMA ligand and the common backbone for both PMMA and DMAEMA͒.
Journal of Vacuum Science & Technology B: Microelectronics and Nanometer Structures
The thermal transformation of spin-cast thin films to produce nanoporous low-k dielectric layers has been investigated using polymethysilsesquioxane ͑PMSSQ͒ for the low-k matrix and polymethylmethacrylate-co-dimethylaminoethylacrylate ͑PMMA-co-DMAEMA͒ as the porogen which is volatilized to leave nanopores in the matrix. Surface analysis methods, including time of flight-secondary ion mass spectrometry and x-ray photoelectron spectroscopy, and thin film analysis by small-angle neutron scattering revealed the kinetics of matrix crosslinking, while thermal desorption mass spectrometry showed the evolution of gaseous reaction products from porogen and matrix during the complex chemical transformations which occur with thermal cycling from 100°C to 450°C. Matrix crosslinking occurs primarily at lower temperatures ͑100-225°C͒, while porogen diffusion and decomposition begins somewhat above 200°C, leading to phase separation which creates the final nanoporous structure. Since matrix and porogen reaction kinetics have some overlap, relative kinetics can be important: e.g., matrix crosslinking proceeds more rapidly for PMSSQ precursors with high Si-OH content cf. low SiOH content, with implications for the morphology of porogen-derived nanostructure. As surface species transform ͑matrix crosslinking͒ and disappear ͑porogen volatilization͒, their complements are seen in the gas phase as reaction and decomposition products. Porogen decomposition is ligand selective, in that the N-containing ligand of DMAEMA is volatilized at considerably lower temperatures ͑ϳ200°C͒ than that ͑ϳ400°C͒ for the remaining species ͑the PMMA ligand and the common backbone for both PMMA and DMAEMA͒.
ECS Transactions, 2011
A high-temperature reactive porogen, triethoxy(polystyrene)silane (TEPSS) (Mw=3,500 g/mole), suitable for late-porogen removal integration scheme has been synthesized in p-xylene via atom transfer radical polymerization. TEPSS was then grafted onto poly(methyl-silsesquioxane) (MSQ) matrix (k=2.9) to circumvent possible phase separation between matrix and porogen in the hybrid approach and porogen aggregation. Our results shows porous low-k MSQ films possess uniform pore size, 24 nm for porosity up to 40%, primarily due to low PDI and reactive porogen, and the dielectric constant is decreased to 2.37 at 40% porosity. In addition, less porogen aggregation was observed at porogen loading ~40 v%.
Microscopy and Microanalysis, 2005
Ultramicrotomy, the technique of cutting nanometers-thin slices of material using a diamond knife, was applied to prepare transmission electron microscope (TEM) specimens of nanoporous poly(methylsilsesquioxane) (PMSSQ) thin films. This technique was compared to focused ion beam (FIB) cross-section preparation to address possible artifacts resulting from deformation of nanoporous microstructure during the sample preparation. It was found that ultramicrotomy is a successful TEM specimen preparation method for nanoporous PMSSQ thin films when combined with low-energy ion milling as a final step. A thick, sacrificial carbon coating was identified as a method of reducing defects from the FIB process which included film shrinkage and pore deformation.
Chemistry of Materials, 2002
Nanoporous methyl silsesquioxane (MSSQ), which is an important and promising candidate for spin-on ultralow dielectric constant applications, has been produced via the thermosetting of MSSQ, templated by a nanodispersed, thermally decomposable pore generator (porogen)poly(methyl methacrylate-co-dimethylaminoethyl methacrylate) [P(MMA-co-DMAEMA)]. Fourier transform infrared spectroscopy is used to study the interaction and structural changes of MSSQ/P(MMA-co-DMAEMA) nanocomposites as a function of curing temperature (ranging from 25 to 450°C) and porogen loading (ranging from 0 to 70 wt %). We find that strong hydrogen-bonding interactions occur between the -OH end groups in MSSQ and the tertiary amino groups in P(MMA-co-DMAEMA) in films at 25°C. An increase in cure temperature from 25 to 250°C and finally to 450°C transforms MSSQ from a material with many reactive end groups to a highly cross-linked structure. In addition, the amino substituent in P(MMA-co-DMAEMA) can act as a catalyst for the condensation and crosslinking of MSSQ. An increase of porogen loading to 70 wt % and a decrease in the silanol group concentration in MSSQ both hinder the formation of the -Si-O-Si-network. Finally, small-angle X-ray scattering (SAXS) results indicate that MSSQ resins initially having higher -OH end group concentrations ultimately generate smaller pores after the removal of porogens. Castillo, D.; DeVries, R.; Buske, G.; Rondan, N.; Froelicher, S.; Marshall, J.; Shaffer, E. O.; Im, J.-H.; Mater. Res. Soc.
Proceedings of the IEEE 2003 International Interconnect Technology Conference (Cat. No.03TH8695), 2003
Methylsilsesquioxane based porous low-k dielectric films with different porogen loading have been characterized using X-ray porosimetry to determine their pore size distribution, average density, wall density and porosity. By varying the porogen content from 1 % to 30 %, the porosity and the average pore size changed from 12 % to 34 % and from I O A to 15 A in radius, respectively. The wall density was found to he indeprndent of the porogen content and it appeared that the porogen is not 100% effective in generating pores. Pore size of these samples was also obtained from small angle neutron scattering measurements and the results were found to be consistent with that from XRP.
Surface and Interface Analysis, 2014
Ultra-low-k thin films are largely used as a dielectric in microelectronic interconnections; the most advanced ones are based on a porous organosilicate SiOCH skeleton where the porosity is obtained by removing a sacrificial porogen. During integrated circuits fabrication, low-k materials are exposed to various processes (e.g. lithography, etching, and cleaning), which modify the physical and chemical properties of these layers. A depth-resolved chemical characterization is therefore required to understand these changes and improve the fabrication process. In this work, an industrial porous low-k material, exposed to typical integration processes (specifically plasma etching, wet cleaning, and surface restoration) is studied. Results show that the treatments made on the samples produce small changes in the data collected by time-of-flight secondary ion mass spectrometry. These slight modifications have been interpreted and de-convoluted using principal component analysis. Principal component analysis was applied to a large set of ions from mass spectra relative to a specific depth zone, i.e. the top surface, in order to characterize the near-surface composition changing between the samples. This investigation led us to find a reduced set of ions discriminating the slight chemical differences between samples.
Integration challenges of porous ultra low-k spin-on dielectrics
Microelectronic Engineering, 2002
In the latest edition of the International Technology Roadmap for Semiconductors (ITRS), the predicted time for the introduction of porous ultra low-k materials with a dielectric constant of 2.2 has slipped significantly against earlier predictions. This is largely due to greater-than-expected problems with the integration of these fragile materials, which generally exhibit weak mechanical properties and low resistance against chemical attack, requiring great care during the integration process. This paper discusses some of the challenges encountered and improvements made at International Sematech and elsewhere regarding the integration of spin-on porous ultra low-k dielectrics into a copper dual damascene process.