Sean W. King

Defect structure and electronic properties of SiOC:H films used for back end of line dielectrics

Back end of the line dielectrics (BEOL) with low dielectric constants, so called low-k dielectrics, are needed for current and future integrated circuit technology nodes. However, an understanding of the defects which limit reliability and cause leakage currents for these films is not yet developed. We primarily utilize conventional electron paramagnetic resonance (EPR) and leakage current measurements to investigate amorphous hydrogenated carbon doped oxide (a-SiOC:H) dielectrics, the most important in current BEOL technology. The resonance measurements were complemented by transmission Fourier-transform infra-red spectroscopy, x-ray reflectivity, and Rutherford backscattering measurements. Various compositions of a-SiOC:H films were deposited on 300u2009mm diameter Si (100) wafers. They exhibit a wide range of dielectric constant, composition, and porosity. Variations in deposition method, process chemistry, and post deposition curing were also investigated. We observe a remarkable range of paramagnetic def...

Mechanical properties of high porosity low-k dielectric nano-films determined by Brillouin light scattering

Integrating nanometre sized pores into hybrid organic-inorganic interconnect layers is one of the key approaches being undertaken by the semiconductor industry to sustain the continued scale down of micro-electronic devices. While increasing porosity of the layers achieves the desirable lowering of the dielectric constant (k), it also has the potential to reduce mechanical and thermal stability and degrade device functionality. We report on Brillouin light scattering to measure the independent elastic constants, and thus the mechanical properties, of ultrathin dielectric films with porosity levels up to 45%, the highest in the industry. Longitudinal and transverse acoustic standing mode type excitations were observed from sub 200nm thick low-k thin films, and their frequency dispersion and associated light scattering intensities were utilized to determine Poisson’s ratio (ν)and Young’s modulus (E). In comparison with SiO2 and non-porous low-k materials, significant modifications were found in ν and E of these highly porous carbon-doped SiO2 (Si‐O‐C‐H) and amorphous carbon (a-C:H) low-k interlayer dielectrics.

Elastic properties of porous low-k dielectric nano-films

Low-k dielectrics have predominantly replaced silicon dioxide as the interlayer dielectric for interconnects in state of the art integrated circuits. In order to further reduce interconnect RC delays, additional reductions in k for these low-k materials are being pursued via the introduction of controlled levels of porosity. The main challenge for such dielectrics is the substantial reduction in elastic properties that accompanies the increased pore volume. We report on Brillouin light scattering measurements used to determine the elastic properties of these films at thicknesses well below 200 nm, which are pertinent to their introduction into present ultralarge scale integrated technology. The observation of longitudinal and transverse standing wave acoustic resonances and their transformation into traveling waves with finite in-plane wave vectors provides for a direct non-destructive measure of the principal elastic constants that characterize the elastic properties of these porous nano-scale films. The...

A method to extract absorption coefficient of thin films from transmission spectra of the films on thick substrates

In this paper we present a method that allows extraction of the absorption coefficient of a thin film from transmittance spectrum of the film on a silicon substrate. The method essentially removes all “optical effects,” such as interference fringes, reflectance losses, substrate absorption, etc. The method requires that the refractive index of the film is known at one wavelength and that the thickness of the film is approximately known, both of which are generally available from ellipsometric measurements. As a by-product of the procedure, the method also extracts optical constants of the film over the entire spectral range of interest and provides improved values of thickness and refractive index over those provided by ellipsometry.

Validation of a correction procedure for removing the optical effects from transmission spectra of thin films on substrates

Transmission spectra of thin films on double side polished substrates feature a quasi sinusoidal baseline superimposed onto the true absorption spectra of the thin film. The quasi sinusoidal baseline is due to strong interference from multiple reflections within the film and can directly affect the relative degree of the measured absorption in the film. In a previous article [S. W. King and M. Milosevic, J. Appl. Phys. 111, 073109 (2012)], we described a method for the removal of these optical effects from infrared transmission spectra. This method renormalizes the spectrum and removes modulations imprinted onto the absorption by interference fringes. Here, we use simulated spectra for a model material to explicitly validate that the proposed correction procedure accurately extracts the pure absorption coefficient of the thin film and is not an ad hoc baseline correction procedure.

Mechanical properties of low- and high-k dielectric thin films: A surface Brillouin light scattering study

Surface Brillouin light scattering measurements are used to determine the elastic constants of nano-porous low-k SiOC:H (165u2009nm) and high-k HfO2 (25u2009nm) as well as BN:H (100u2009nm) films grown on Si substrates. In addition, the study investigates the mechanical properties of ultra-thin (25u2009nm) blanket TiN cap layers often used as hard masks for patterning, and their effects on the underlying low-k dielectrics that support a high level of interconnected porosity. Depending on the relative material properties of individual component layers, the acoustic modes manifest as confined, propagating, or damped resonances in the light scattering spectra, thereby enabling the mechanical properties of the ultra-thin films to be determined.

Picosecond ultrasonic study of surface acoustic waves on titanium nitride nanostructures

We have measured surface acoustic waves on nanostructured TiN wires overlaid on multiple thin films on a silicon substrate using the ultrafast pump-probe technique known as picosecond ultrasonics. We find a prominent oscillation in the range of 11–54u2009GHz for samples with varying pitch ranging from 420u2009nm down to 168u2009nm. We find that the observed oscillation increases monotonically in frequency with decrease in pitch, but that the increase is not linear. By comparing our data to two-dimensional mechanical simulations of the nanostructures, we find that the type of surface oscillation to which we are sensitive changes depending on the pitch of the sample. Surface waves on substrates that are loaded by thin films can take multiple forms, including Rayleigh-like waves, Sezawa waves, and radiative (leaky) surface waves. We describe evidence for detection of modes that display characteristics of these three surface wave types.

Acoustic Phonons and Mechanical Properties of Ultra-Thin Porous Low- k Films: A Surface Brillouin Scattering Study

To reduce the RC (resistance–capacitance) time delay of interconnects, a key development of the past 20xa0years has been the introduction of porous low-k dielectrics to replace the traditional use of SiO2. Moreover, in keeping pace with concomitant reduction in technology nodes, these low-k materials have reached thicknesses below 100xa0nm wherein the porosity becomes a significant fraction of the film volume. The large degree of porosity not only reduces mechanical strength of the dielectric layer but also renders a need for non-destructive approaches to measure the mechanical properties of such ultra-thin films within device configurations. In this study, surface Brillouin scattering (SBS) is utilized to determine the elastic constants, Poisson’s ratio, and Young’s modulus of these porous low-k SiOC:H films (∼u200925–250xa0nm thick) grown on Si substrates by probing surface acoustic phonons and their dispersions.