D. Keith Bowen

X-Ray Metrology by Diffraction and Reflectivity

X-ray methods can provide measurements that, for certain parameters of great technological importance, are the most accurate and sensitive available. High-resolution X-ray Diffraction (HRXRD) has become a vital tool in the silicon industry with the use of silicon-germanium epitaxial layers in the construction of HBT devices. Compositions and thicknesses of both uniform and compositionally-graded Si-Ge and Si cap layers may be rapidly and accurately derived from HRXRD. X-ray Reflectivity (XRR) is an important method for the metrology of thin films in the range 1 nm to 1000 nm. It measures film thickness, roughness and electron density, and it is routinely applied to both high-k and low-k dielectrics, hetereoepitaxial layers and amorphous metallic films. It is of particular importance in the process development of thin gate oxides (and oxynitrides) for which optical constants are very uncertain. A metrological measurement should be traceable to a national standards laboratory, and be readily standardizable ...

X-Ray Reflectometry from Semiconductor Surfaces and Interfaces

X-ray reflectance measurements at grazing incidence provide non-destructively a measure of the thickness of thin layers, the electron density as a function of depth, and interface and surface roughness. We show that the effect of roughness at a buried interface is only to reduce the visibility of the interference fringes, whereas roughness at the top surface leads also to an overall increase in the rate of fall of intensity with angle (or energy). These two contributions can then be readily distinguished. Most work has been performed in monochromatic angular dispersive mode. We present here a preliminary study of the application of the high-energy, fixed-angle, energy dispersive mode for the study of thin epitaxial layers, Langmuir-Blodgett films, surface damage on silicon chemi-sol polished wafers and ion implanted silicon and aluminium. Data has been analysed using the theory of Parratt, which we have adapted for use in the energy dispersive method.

Accuracy and Repeatability of X‐Ray Metrology

All metrology tools must make a trade‐off between data quality and wafer throughput. Moreover, most X‐ray metrology may be performed on regions inside the scribe lines. This paper discusses the appropriate choices of trade‐offs for throughput, repeatability and spot size, choosing examples from silicon‐germanium composition and thickness metrology. The repeatability varies from 0.7% to 0.1% 1σ with data collection cycles between 20 s and 1000 s. We show that for most of the parameters determined by X‐rays the metrology is absolute, and that both accuracy and tool matching is achieved by traceable calibration of the X‐ray wavelength and the angle encoders on the tools. Tool matching achieved by this absolute approach to metrology is typically 0.2% in thickness and 0.05% in composition for Si‐20%Ge layers ∼ 50 nm thick. For 30 nm metal or dielectric layers measured within a 100 mm scribe line, 0.65% 1σ repeatability is achieved at 150 measurement points/hr and 0.33% at 75 sites/hr.

Calibration of height-measuring probes

Many industries now require control of surface heights to sub-micrometre precision. The systems that calibrate quality control instruments for such applications must have capability at the nanometre level, or better, and excellent traceability. Xray interferometry is currently the strongest candidate for this task. As this paper demonstrates, it is quite feasibly used in a normal standards room yet provides accuracies of better than 0.1 nm. Following a description of the preferred meirological configuration, which uses silicon monolithic devices, some features that have improved its accessibility are discussed. Particular attention is paid to sensors and actuators that may t as transfer standards to provide convenient routine calibrations. Finally, a design for a stand-alone, desk-sized instrument is presented.

Application of a Desk-Side Double-Axis X-Ray Diffractometer for Very Large Area Epilayer Characterization

A new desk-side double-axis X-ray diffractometer capable of rapid, automatic measurement of lattice mismatch between epitaxial thin films and substrate in a two dimensional grid 150 mm square has been built. The design principles behind the five independent axis systems, specimen loading, and the fail-to-safety X-ray shutter are elucidated, and examples of typical data from substrate material and thin epitaxial films of III-V compounds are presented.

Application of Differential Evolution to the Analysis of X-Ray Reflectivity Data

X-ray reflectivity (XRR) is a technique for characterizing the structure of thin, multi-layer devices. This section describes the application of the differential evolution (DE) algorithm to automatically and reliably analyze XRR data. A data-fitting method is presented that is conceptually simple, easy to implement and is capable of converging to a global minimum in the parameter space even when there are many additional local minima. The method is quite general and could be applied to many problems in science and engineering.

Full‐Wafer Defect Identification using X‐ray Topography

The timely identification of defects can lead to increased yields and significant cost savings in wafer production. X‐ray topography (XRT) is recognized as being a powerful tool for directly imaging defects in single crystals, such as semiconductor substrates and epitaxial thin‐films. In XRT, defects are imaged by measuring changes in the diffracted X‐ray intensity across a wafer due to strain and/or tilt that the defects introduce into the crystal lattice. We have developed a novel, high‐speed digital XRT method for non‐destructive defect characterization of up to 300mm diameter wafers. This method, called BedeScan™, offers substantial advantages to conventional topography, especially for rapid, convenient defect identification in a wafer manufacturing/processing environment. X‐rays from a microfocus source are diffracted from a wafer, which is translated with fast, high‐precision motions in front of a fixed CCD camera and a sequence of images is recorded. A virtual scan of the camera in the computer is ...