Advanced AI systems require more exotic packaging solutions to increase performance and manage power loads. Packaging designers not only need increased interconnect density through pitch scaling, but also seek to print this advantage over areas beyond the capability of standard lithography. These demands call for innovations in materials, processes, integrations, and tools for packaging. In a bid to find solutions for finer L/S pattern in redistribution layers, photo-imageable polyimides (PIDs) from different vendors were tested for performance properties (resolution, dose to size, sidewall quality) using direct write exposure methods, and then assessed for compatibility in a dual damascene (DD) integration for FOWLP packaging.
Defect characterization of epitaxial silicon films grown on lightly boron-doped Si (100) substrates by low temperature photo-enhanced chemical vapor deposition (PCVD) using 193 nm ArF excimer laser dissociation of Si2H6 in an ultra-high-vacuum (3 X 10-9 Torr) chamber is discussed. A factorial design of experiments was used to investigate the dependence of crystallinity and growth rate on laser intensity, Si2H6 partial pressure, substrate temperature, and substrate-to-laser-beam distance. PCVD of Si was achieved in two ways: with the laser passing parallel to the substrate or directly incident on it. For parallel laser incidence, epitaxial films were achieved at temperatures as low as 250 degree(s)C with controllable deposition rates of 0.5 approximately equals 4 angstroms/min. using photon flux densities of 1015 photons/pulse.cm2, and Si2H6 partial pressure of 20 mTorr. The growth rates were observed to be linearly dependent on laser power. For direct laser incidence, single crystal films with a growth rate of approximately equals 20 angstroms/min. were obtained at a photon flux density of 7 X 1014 photons/pulse.cm2 at 300 degree(s)C and 20 mTorr Si2H6 partial pressure. The growth rate were found to be linearly dependent on photon flux density also. The crystallinity was studied by in situ reflection high energy electron diffraction (RHEED), and selected area electron diffraction in a transmission electron microscope (TEM), and defects such as stacking faults and dislocation loops were investigated by TEM and dilute Schimmel etching/Nomarski microscopy.
Low temperature silicon epitaxy has been achieved at substrate temperatures ranging from 250 degree(s)C to 350 degree(s)C using the 193 nm output of ArF excimer laser to generate reactive growth precursors by photolytic decomposition of Si2H6. Growth rate dependencies on substrate temperature, Si2H6 partial pressure, laser photon flux density, and beam-to-substrate distance are presented. A simple expression for the growth rate as a function of process parameters can be obtained by considering the single-photon absorption rate of Si2H6 at the ArF excimer laser wavelength of 193 nm, and the gas kinetic transport of the resulting photofragments to the substrate surface. With the beam tangentially positioned approximately 1 mm from the substrate, a large percentage (7 +/- 1%) of the silicon available from the excited Si2H6 contributes to film formation. As the beam is moved away from the substrate, the chemical reaction rate of the growth precursors becomes significant with respect to the diffusion rate and the growth rate is observed to decrease. By tilting the laser beam to provide a normally incident component striking the substrate surface, the dangling bond density of the surface can be increased by photon assisted H desorption and growth rates are observed to increase. At substrate temperatures less than 400 degree(s)C, the growth rate is weakly dependent on temperatures with an activation energy of approximately equals 0.05 eV, whereas for temperatures above 400 degree(s)C, film deposition becomes dominated by pyrolytic decomposition of Si2H6 with an activation energy of approximately equals 1.2 eV.
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