In this work, experimental measurements of the electronic band gap of low-k organosilicate dielectrics will be presented and discussed. The measurement of bandgap energies of organosilicates will be made by examining the onset of inelastic energy loss in core-level atomic spectra using X-ray photoelectron spectroscopy. This energy serves as a reference point from which many other facets of the material can be understood, such as the location and presence of defect states in the bulk or at the interface. A comparison with other measurement techniques reported in the literature is presented. V C 2014 AIP Publishing LLC.

We report experiments in which a subpicosecond pump light pulse is used to excite vibrations in a nanostructure consisting of a periodic array of copper wires embedded in a glass matrix on a silicon substrate. The motion of the wires after excitation is detected using a time-delayed probe light pulse. From the measured data, it is possible to determine the frequencies νn and damping rates Γn of a number of the normal modes of the structure. These modes have frequencies lying in the range 1–30 GHz. By comparison of the measured νn and Γn with the frequencies and damping rates calculated from a computer simulation of the vibrations of the nanostructure, we have been able to deduce the vibration patterns of six of the normal modes.

Ultrafast lasers have long been used to study the dynamics of fast optical, electronic, and chemical processes in materials. These tools can also be used in a variety of optical pump and probe spectroscopies to generate and detect acoustic signals with frequencies on the order of 100 GHz, and to generate and detect thermal waves with penetration depths on the scale of nanometers. The short wavelengths of these probes make them ideal for the study of the mechanical and thermal properties of thin films, their interfaces, and nanostructures. We describe the picosecond-laser acoustics technique and demonstrate how it can be used to extract the elastic constants and the adhesion of thin films and probe the normal modes of vibration of nanostructures. The thermal properties of thin films are also accessible through time-domain thermoreflectance. Since the mechanical and thermal properties can be obtained quickly on micrometer-scale regions of a sample, spatial mapping of the properties is also possible.

Fourier transform infrared (FTIR) analyses of low-k materials exposed to either oxygen radicals or to capacitively coupled O2 plasma indicate that carbon depletion from these materials is dominated by O radical diffusion. FTIR measurements of changes in absorbance related to silanol formation (3500 cm−1) and carbon depletion (2980 cm−1, 900–700 cm−1) exhibit a linear dependence on the square root of the exposure time. Diffusion is faster for a sample of higher porosity and interconnectedness (k=2.54) than for a sample with lower porosity (k=3.0). However, a sample with high porosity (k=2.57) but low interconnectedness (as measured by liquid diffusion) exhibits a high initial rate of carbon loss, followed by no further carbon loss at longer times. Further, pretreatment of k=3.0 material by 500 eV noble gas ions results in a sharp decrease in the rate of carbon loss upon subsequent exposure to oxygen radicals. The data indicate that the main mechanism of carbon depletion in organosilicate glass (OSG) materials during oxygen plasma exposure is loss due to a reaction front created by oxygen radicals diffusing through interconnected pores. Further, carbon depletion can be minimized for low-k OSG materials either by formation of high porosity/low interconnectedness samples, or by pretreatment by noble gas ion bombardment, which seals surface pores.

Vacuum ultraviolet ͑VUV͒ spectroscopy is used to determine the valence-band structure and location of defect states within the bandgap of porous organosilicate ͑SiCOH͒ dielectrics both before and after VUV and UV irradiation. SiCOH dielectrics have bandgap energies of about 9 eV. In addition, positive charge is trapped by defect states located 1 eV above the top of the SiCOH valence-band edge. These defect states can be populated or depopulated with electrons during UV and VUV irradiation, respectively. This is verified by measuring the magnitude and polarity of the trapped charge after VUV irradiation using two techniques: ͑i͒ capacitance vs voltage characteristics obtained with a mercury probe and ͑ii͒ surface-potential measurements obtained with a Kelvin probe. Both techniques show that the defect states are uncharged when occupied with electrons and positively charged when depleted of electrons.

Articles you may be interested inTime-dependent dielectric breakdown measurements of porous organosilicate glass using mercury and solid metal probes

Plasmas, known to emit high levels of vacuum ultraviolet (VUV) radiation, are used in the semiconductor industry for processing of low-k organosilicate glass (SiCOH) dielectric device structures. VUV irradiation induces photoconduction, photoemission, and photoinjection. These effects generate trapped charges within the dielectric film, which can degrade electrical properties of the dielectric. The amount of charge accumulation in low-k dielectrics depends on factors that affect photoconduction, photoemission, and photoinjection. Changes in the photo and intrinsic conductivities of SiCOH are also ascribed to the changes in the numbers of charged traps generated during VUV irradiation. The dielectric-substrate interface controls charge trapping by affecting photoinjection of charged carriers into the dielectric from the substrate. The number of trapped charges increases with increasing porosity of SiCOH because of charge trapping sites in the nanopores. Modifications to these three parameters, i.e., (1) VUV induced charge generation, (2) dielectric-substrate interface, and (3) porosity of dielectrics, can be used to reduce trappedcharge accumulation during processing of low-j SiCOH dielectrics. Photons from the plasma are responsible for trapped-charge accumulation within the dielectric, while ions stick primarily to the surface of the dielectrics. In addition, as the dielectric constant was decreased by adding porosity, the defect concentrations increased. V

The propagation of ultrashort sound pulses in water has been studied by using the picosecond ultrasonic technique and a pulse time-of-flight technique for measuring the depths of deep channels in Si-based nanostructure was demonstrated. The sound pulses were generated when light was absorbed in a metal transducer film and detected by a time-delayed probe light pulse. First, the attenuation and velocity of sound of frequency 4.8 GHz in water were measured through an analysis of the Brillouin frequency oscillations in the reflectivity of the probe light. Measurements at frequencies up to about 11 GHz were made by sending a sound pulse across a thin layer of water and measuring the change in shape of the returning echo due to the attenuation of the different Fourier components. Second, we also report on proof-of-concept ultrasonic experiments to acquire spatial profile information from nanostructures, where sound pulses propagate down narrow channels in patterned nanostructures. We have been able to detect acoustic echoes for sound propagating along a channel as narrow as 35 nm.