High-Resolution Thermal Wave Imaging of Surface and Subsurface Defects in IC Metal Lines

Using a thermal wave imaging system we have been able to detect and identify a variety of microscopic defects commonly found in fine metal Al connector lines used in the IC industry. The defects of interest are hillocks, surface and subsurface Si and Cu precipitates and subsurface voids and notches. Defects as small as 0.1 μm have been detected. This thermal wave imaging system has also been used to detect subsurface defects in Al and W metal contact plugs

Thermal Wave Characterization of Semiconductors and Superconductors

Thermal wave technology has proven to be a very effective means for investigating the near surface region of several different materials. Although there are many methods for generating and detecting thermal waves the most desirable for quantitative NDE are the noncontact and nondamaging laser methods. When a material is excited with an intensity-modulated laser pump beam a thermal wave is generated within the near surface of the sample. Since the complex refractive index of most materials depends on temperature, the laser pump induced modulations in the local temperature of the sample will induce a corresponding modulation in the local refractive index. This variation in refractive index can in turn be detected through the modulation in the reflectance of a laser probe beam from the surface of the material [1,2]. This method is not only a highly effective method for generating and detecting thermal waves, but also permits thermal wave measurements to be performed with micron scale spatial resolution by utilizing highly focused pump and probe laser beams

Beam profile reflectometry: a new technique for thin film measurements

In the manufacture of semiconductor devices, it is of critical importance to know the thickness and material properties of various dielectric and semiconducting thin films. Although there are many techniques for measuring these films, the most commonly used are reflection spectrophotometry [1,2] and ellipsometry [3]. In the former method, the normal- incidence reflectivity is measured as a function of wavelength. The shape of the reflectivity spectrum is then analyzed using the Fresnel equations to determine the thickness of the film. In some cases, the refractive index can also be determined provided that the dispersion of the optical constants are well known. The latter method consists of reflecting a beam of known polarization off the sample surface at an oblique angle. The film thickness, and in some cases the refractive index, can be determined from the change in polarization experienced upon reflection

Process Control in IC Manufacturing with Thermal Waves

In today’s semiconductor market, manufacturers face a daunting challenge. Product concepts evolve rapidly in response to rapidly changing markets while design rules, i.e., device geometries, become increasingly smaller and wafers become larger. Devices must run faster, reliability must improve and the resultant increasing complexity in IC design and fabrication technology intensifies the need for tighter controls of process variables. To compete effectively in this market, manufacturers must improve both product development and product manufacturing processes.</p

Thermal Wave Physics in NDE

There has been considerable interest lately in imaging techniques that employ thermal waves [1–4]. In thermal-wave imaging, a beam of energy, usually a laser or electron beam, is focused and scanned across the surface of a sample. This beam is generally intensity-modulated at a frequency in the range of 10kHz to 10MHz. As the beam scans across the sample it is absorbed at or near the surface, and periodic surface heating results at the beam modulation frequency. This periodic heating is the source of thermal waves, which propagate from the heated region. The thermal waves are diffusive waves similar to eddy current waves, evanescent waves, and other critically damped phenomena that travel only one to two wavelengths before their intensity becomes negligibly small. Nevertheless, within their range, the thermal waves interact with thermal features in a manner that is mathematically similar to the scattering and reflection processes of conventional propagating waves [5], Thus any features on or beneath the surface of the sample that are within the range of these thermal waves and that have thermal characteristics different from their surroundings will reflect and scatter the waves and thus become visible.</p

STRATUM CORNEUM STUDIES WITH PHOTOACOUSTIC SPECTROSCOPY

Conventional spectroscopic studies on opaque membranes are difficult to pursue because of excessive light scattering and complications arising from the specimen's surface. Recently, a new spectroscopic technique, photoacoustic spectroscopy, unlike conventional optical spectroscopy, has been demonstrated to be an informative technique amenable to spectroscopic studies of solids and membrane-like samples. We have applied photoacoustic spectroscopy to the study of hydration and maturation of newborn rat stratum corneum, and have obtained clean spectra in the 220 to 450nm region indicative of a change in thermal diffusivity with increased hydration, and biochemical changes associated with the initial maturation period