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In this paper we present methods for generating bounds on interconnection delays in a combinational network having specified timing requirements at its input and output terminals. An automatic placement program which uses wirability as its primary objective could use these delay bounds to generate length or capacitance bounds for interconnection nets as secondary objectives. Thus, unlike previous timing-driven placement algorithms described in the literature, the desired performance of the circuit is guaranteed when a wirable placement meeting these objectives is found. We also provide fast algorithms which maximize the delay range, and hence the margin for error in layout, for various types of timing constraints. * * Ellen J. Yoffa (M'86) received the B.S. and Ph.D. degrees in physics from the Massachusetts Institute of Technology, where her area of study was theoretical solid-state physics. In 1978, she joined the IBM Thomas J. Watson Research Center for postdoctoral work in the Semiconductor Science and Technology Depanment, where she investigated ballistic conduction in semiconductor devices and the physics of the laser annealing process. Since 1980, she has been a member of the research staff in the Computer Science Department and is currently senior manager of the System Design and Verification Department, where she is responsible for managing research in tools for computer-aided design of VLSI chips, including system description and early design tools, logic synthesis, and hardware and software logic simulation. She is a member of the editorial board of lEEE Design and Tesf of Computers. Her research has involved the development of tools for VLSI physical design automation. Dr. Yoffa is a member of Phi Beta Kappa and Sigma Xi.

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The design and operational features arc described for a computer-assisted ellipsometer (called ETA for Ellipsometric Thickness Analyzer), developed to provide reliable, real-time measurement of field-effect transistor gate insulator thickness in a manufacturing environment, ETA illuminates the sample with light of fixed polarization and uses' a rotating analyzer to measure the polarization of the reflected light Sample alignment is done automatically by ETA, so that usually no operator adjustments are required. Fourier analysis of the light transmitted by the analyzer is used to reduce noise and enhance measurement precision.In its normal mode of operation (incident light linearly polarized at 45°) , ETA can measure single and double-layer films of Si0 2 and Si 3N, in the thickness range of 300 to 800 A with precision comparable to that of conventional ellipsometers, Other modes of operation, which make use of a fixed-position compensator in the incident light path, allow precise measurement of thin films (0 to 300 A)and permit use of ETA as a general-purpose ellipsometer. The typical time interval required for wafer alignment, data acquisition, analysis and recorded output of film thickness is about five seconds, and the measurement reproducibility is typically about I A.472