In-Situ Grazing Incidence Small-Angle X-ray Scattering Studies on Nanopore Evolution in Low-k Organosilicate Dielectric Thin Films

Abstract

The first in-situ two-dimensional grazing incidence small-angle X-ray scattering (2D GISAXS) study on the evolution of nanopores during the thin film formation of porous dielectrics from composite films is reported. A soluble poly(methylsilsesquioxane) (PMSSQ) precursor and a four-armed poly( -caprolactone) (PCL4) were chosen as the model matrix and porogen components within the composite film. The measured 2D GISAXS data were analyzed quantitatively using a GISAXS formula derived under the distorted wave Born approximation. It is shown that in-situ GISAXS is a powerful tool for monitoring the evolution of nanopores in dielectric thin films, providing structural characteristics such as size, size distribution, shape, electron density, and porosity, all as a function of temperature and time. In addition, the mechanism for forming imprinted nanopores in the dielectric films by sacrificial thermal degradation of the porogen was determined by in-situ GISAXS analysis. Phase separation of the PCL4 porogen was induced below 200 °C by cross-linking of the PMSSQ precursor matrix during thermal curing. This process generated porogen aggregates, each individually imprinted pore in the film through thermal degradation; the shape, size, and size distribution of the porogen aggregates are directly reflected in the dimensions of the imprinted pores. Moreover, it was found that higher porogen loadings caused larger porogen aggregates with a greater size distribution. The present results thus show that the structural characteristics of nanopores imprinted within PMSSQ dielectric films are governed by the PCL4 porogen aggregates formed through curing of the PMSSQ precursor matrix.

Waveguide-enhanced grazing-incidence small-angle x-ray scattering of buried nanostructures in thin films

“…A comprehensive review of the GISAXS technique for studying surface structures was recently done by Renaud et al 8 Given the high beam brilliance and intensity from synchrotron x-ray sources, it is feasible to investigate the kinetics and dynamics in thin films and at surfaces when GISAXS is integrated with time-resolved techniques. With these advantages, GISAXS has been applied to a variety of systems, such as nanostructured polymer thin films, [9][10][11][12][13][14][15][16][17][18] nanoparticle-polymer composites, 5,6,[19][20][21] and supported nanoislands. [22][23][24][25][26][27][28] Due to the complex data processing involving the distorted-wave Born approximation (DWBA), GISAXS analyses in early days were often performed in a qualitative manner, where only scattering peak positions and widths are identified.…”

Refractive Indexes of Porous Thin Films Prepared From Organic-templated Polymethylsilsesquioxanes

“…Star-shaped poly(ε-caprolactone)s (PCLs) are widely applied as pore generators (organic templates) in nanoporous material research [3][4][5][6][7][8][9][10]17]. These templates used in this work bear aliphatic ether cores, and four (or six) polyester arms.…”

“…The nanopore structures could be made and evenly distributed in the resulting PMSSQ film, via curing and calcination. The smaller sizes and uniform distribution of the pores significantly improve the structural stability of the film [3][4][5][6][7][8][9][10].…”

“…The refractive indexes of the porous films decreased with the increase of initial m-PCL loadings, resulting in increasing porosities of the films. The organic templates added to the PMSSQ composite films completely decomposed at elevated temperature, and remained voids in the films [3][4][5][6][7][8][9][10][11][12][13]16]. In addition, there are many previous studies for the size and structure of the pores generated in PMSSQ films [3][4][5][6][7][8][9][10].…”

“…Nanoporous silicate thin films are considered as important materials for advanced electronics. The formation of air-filled nanopores is a key technology for preparing insulating materials [3][4][5][6][7][8][9][10][11][12]. Polymethylsilsesquioxane (PMSSQ), with the empirical formula of (CH 3 -SiO 1.5 )n, is a potential candidate for low dielectric spin-on glass [13].…”