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We show that a combination of beam profile reflectometry, beam profile ellipsometry, and deep ultraviolet-visible spectroreflectometry can accurately characterize ultrathin oxide on nitride on oxide films with total thicknesses of less than 200 A. Beam profile ellipsometry establishes the total thickness, while beam profile reflectometry provides the key data to detect the multilayer structure. Optical absorption of the nitride layer at wavelengths shorter than 270 nm as measured by spectroreflectometry provides additional accuracy in determining the thicknesses of the individual layers. The fit to the data is improved by including a 12 A interlayer between the Si substrate and the bottom oxide. Determined thicknesses are in excellent agreement with those deduced by cross-sectional transmission electron microscopy.

A novel approach for monitoring the capacitance using optical data from the material characteristics of hemispherical grain (HSG) polycrystalline silicon film is reported. This noncontact optical method provides indirect measurement of electrical capacitance for advanced dynamic random access memory (DRAM) applications using HSG material. By a simple statistical analysis of the microscopic HSG structure, the actual electrical capacitance is estimated to better than 90% confidence level through correlation of the optically measured thickness and the void content of the HSG film. Data from broad band spectrop otometry (190-750 nm) with beam profile reflectometry are fitted in the context of the Bruggeman effective medium approximation (EMA) model to give HSG thickness and void content. The actual capacitance obtained from the electrical probe technique using an intrusive electrode on finished DRAM devices indicates good agreement with our approach.

Titanium nitride (TiN) films on various substrates (Si, 1000 A of oxide on Si, and Al) were characterized using spectrophotometry, beam-profile reflectometry (BPR), beam-profile ellipsometry (BPE) and spectroscopic beam-profile ellipsometry (SBPE). For the TiN film on Si or on oxide, the combination of BPR and BPE is found to be the most effective measurement recipe. However, for the TiN film on Al, spectrophotometry is recommended due to large scattering at the Al grain boundaries. Visible-range SBPE adds some information but not enough to warrant its use in production. Surface roughness on the TiN films was treated as a mixture of voids and TiN by using the Bruggeman effective medium approximation. A comparative study of cross-sectional transmission electron microscopy (XTEM) and optical characterization shows excellent agreement.

Visible-near-IR spectrophotometry was combined with single-wavelength beam profile reflectometry to measure all six layer thicknesses of a silicon on oxide film stack. The spectrometer or beam profile reflectometer alone is insufficient to solve such a complicated film stack. Development of a robust measurement recipe required a new global optimization method working in parameter spaces of up to 12 parameters. The recipe obtained was applied to a 50-site mapping of the wafer. We found excellent agreement between our optical measurement results and scanning electron micrograph (SEM) data for all thicknesses.

We performed simultaneous measurements of all the layer thicknesses in six layer silicon on oxide film structures. Visible-near-infrared spectrophotometry was combined with beam profile reflectometry to produce enough information to discriminate between potential solutions; the spectrometer or beam profile reflectometer alone is insufficient to solve such a complicated film stack. Development of a robust measurement recipe required a new global optimization method working in parameter spaces of up to 12 parameters. The recipe obtained was applied to a 50 site mapping of the wafer. We found excellent agreement between our optical measurement results and scanning electron micrograph data for all thicknesses.

As the design rule of devices decreases with shrinking gate width dimensions, the properties of sidewall layers are becoming increasingly important for controlling electrical properties, especially for processes in the nanometer-grade range. Poor control of the sidewall process can cause errors in both the implant area and length of the device channel. An optical technology has been developed and is shown here to monitor directly the width of the sidewall on the grating structure. In addition, this technology can obtain more information including the thickness of each film, optical properties, and CD's (critical dimensions) in the structure simultaneously. This nondestructive inspection technology provides accurate results with good precision, repeatability and high throughput on several user-selectable information outputs. In this study, the technology is used to measure a dual-sidewall structure on metal gate for DRAM. Good correlations are obtained when comparing the measurement results to X-SEM (cross-section SEM) and electrical property test, in particular, a 0.97 correlation with a resistance test. The technology can potentially replace traditional monitor method for dual-sidewall structure as seen in this study.

Thermal wave measurements and images are presented that illustrate the sensitivity to damage and defect resolution attainable in a laser-based thermal wave system.

Thermoacoustic imaging is a new technique that permits the detection and imaging of microscopic surface and subsurface fea- tures in a sample. We present a detailed theoretical treatment of the thermoacoustic process with particular emphasis on the roles of ther- mal and elastic parameters in both one and three dimensions. Exam- ples are presented of thermoacoustic images obtained with a scanning electron microscope. These include images of subsurface mechanical defects, metallic grains and grain boundaries, and of dislocation net- works and dopant regions in semiconductor crystals.

When a material is excited with an intensity-modulated energy source, or pump, its optical properties can be altered by the absorption of the incident energy. This results in the sample’s complex refractive index undergoing periodic variations at the modulation frequency of the pump intensity excitation. These periodic variations in the sample’s optical refractive index can be detected by measuring the modulated reflectance, scattering, transmittance or deflection of an optical probe that is reflected from or transmitted through the sample. Since the complex refractive index of most materials depends on temperature, a modulated temperature will induce a corresponding modulation in the refractive index and, consequently, a modulation in the optical reflectivity. In a semiconductor, the refractive index is also affected by the density of free carriers so that a modulated electron-hole plasma density will provide an additional modulation in the optical reflectivity.

In modulated reflectance experiments on silicon wafers the signal arises primarily from the Drude modulation of the silicon refractive index from the laser generated electron-hole plasma density [1,2]. We have recently found that both the magnitude and phase of the modulated reflectance signal, ΔR/R, are usually dependent on the duration of continuous pump and probe laser irradiation [1]. We attribute this temporal behavior of the ΔR/R signal to a laser induced modification of the defect-related electronic interface states at the Si/Si02 interface which act as trapping sites for the photogenerated carriers. Furthermore, there appear to be two broad categories of such interface states; stable and metastable. The stable states undergo temporal modification only under continuous high intensity laser irradiation, while the metastable states also exhibit spontaneous temporal evolution.