Eckhard Wolfgang

Electron beam testing

Abstract This paper shows a simple approach to simulating the electron-beam lithography for sub-0.2 μm T-gate fabrication. Both the proximity parameters and the solubility rates of resists are experimentally determined. The simulation assumes that resists are removed at rates that are only governed by the local exposure doses. This simplified assumption produces a resist profile evolution that is quite consistent with scanning electron microscope (SEM) observation. Together with corrections from the SEM, the fabricated gate length can be predicted within an error of less than 15% for gate lengths from 0.1 through 0.5 μm. The successful development of high-yield process demonstrates the usefulness of this simulation tool.

Electron-beam testing of VLSI circuits

The voltages at the internal voltage nodes of an IC have to be measured if the device operates imperfectly or the quality of a device or computer simulation have to be checked. Whereas the mechanical probe conventionally used for this purpose usually imposes such a large capacitive load on the specimen that its performance undergoes a change, the electron probe is both nonloading and nondestructive and can be used not only for quantitative waveform measurements on an IC but also for obtaining images of the logical states of relatively large portions of its circuit configuration. Since each type of configuration calls for a separate measuring technique, six different techniques are treated and their application and equipment needs described. The state of the art of electron-beam testing is demonstrated with reference to three typical applications, viz., checking a decoding schema, measuring the sense signal (approximately 300 mV) of a 16-kbit MOS RAM, and checking the operation of the timing circuitry of a 4-bit microprocessor. The present applicational limitations and future perspectives of electron-beam testing are discussed.

Future trends in electron beam testing

Current trends in electron beam testing (EBT) are determined by those prevailing in microelectronics. This paper describes those aspects of microelectronics which have a particularly significant effect on EBT. Future trends in EBT are discussed against this background and on the basis of a description of state-of-the-art EBT systems. In its currently available, basic form, EBT can deal with the next two circuit generations, although interesting scopes still exist for improving the time resolution. A critical view must be taken of integration with computer-aided design (CAD) and computer-aided testing (CAT) where standardized interfaces are lacking.

Optimal Design of High Power Electronic Devices by Topology Optimization

High power electronic devices such as converter modules are frequently used as electric drives for high power electromotors. The efficient and reliable operating behaviour of such devices requires an optimal design with regard to a minimization of power losses due to parasitic inductivities caused by eddy currents. The mathematical modelling gives rise to a topology optimization problem where the state variables are required to satisfy the quasistationary limit of Maxwell’s equations and the design variables are subject to both equality and inequality constraints. Based on appropriate finite element approximations involving domain decomposition techniques, the discretized optimization problem is solved by a primaldual Newton interior-point method.

Advances in power electronic devices

The development of new silicon-based power devices will remain important for decades to come thanks to many significant applications. Silicon power semiconductors (thyristors, IGBTs, CoolMOS/sup TM/) will benefit immediately from advances in silicon microelectronics. These include: an improved understanding of and greater precision in individual fabrication processes; a continued reduction in defect density; larger wafer diameters; and a wide diversity of topologies, e.g., in trench IGBTs. These developments lead to ongoing improvements in quality and reliability and a continuous reduction in the cost of chip manufacture.

A New Method of Electron-Probe Microanalysis for Determining the Degree of Oxidation in Silicon Oxides

Silicon oxides arc used as isolating and passivating films in semiconductor devices and as protective and anti-reflection layers in optical systems. The electrical and optical parameters of such films and layers depend greatly on the chemical composition, i. e. the degree of oxidation.