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Estimates of the average technical efficiency on the 2-digit industry-level for France (1962) are obtained by means of a maximum likelihood estimation of the Cobb-Douglas frontier production model with composed error. The theoretical and statistical implications of a possible relationship between technical efficiency and firm-size are discussed. The computations are carried out for each industry as a whole and the results are compared with the respective results for separate size-classes.

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Currently, most silicon microstructures used in microsystems are produced by photolithographic methods. The reason for this is the well-developed etching technology, used in microelectronics, that has been transferred to the microsystem domain. But since the making of an arbitrary shape or angle on silicon mainly depends on the crystal orientation, some severe limits exist in the production of three-dimensional structures.Electro-Discharge Machining (EDM) is basically a thermal process. During the 11DM process material is removed by electric sparking. It is therefore completely different from etching. In this work, micro-EDM is introduced as a potential approach for solving the above mentioned drawbacks. First, this work presents several testing experiments with different process parameters to investigate the influence of the micro-EDM process on the silicon structure. Main emphasis is put on the surface roughness and on avoiding microcracks generated by the sparking process. It is found that microstructures with a sufficiently low surface roughness and with small microcracks can be produced. The remainder of the work concentrates on making small beam structures, which is a common structure in many microsensor designs. It is found that for a wafer thickness of 650 pm, the thinnest beam that can be produced is about 30 .tm wide. This means that micro-EDM can offer an aspect ratio of 20 in combination with a good dimensional control.

The micro-EDM silicon machining performances have been studied on a highly doped P-type { 100) silicon wafer. To demonstrate and to emphasis the special performances of silicon micro-EDM, one kind of stainless steel is machined as a reference material. Both materials are sparked with specific sparking energy in micro-Joule energy range and machining characteristics such as material removal mechanism, cutting rate, relative electrode wear ratio and surface quality are examined and analyzed. The thermally induced microcracks are also examined and analyzed using an optical and a Scanning Electron Microscope (SEM). It is found that for silicon, the micro-EDM material removal mechanism is not completely similar to conventional metal micro-EDM; besides melting and evaporation there is a significant contribution from thermal spallation, which is a kind of direct mechanical material damage without melting. This paper also presents that microcrack generation is not only related to the sparking energy but also has a close relationship with the silicon crystal lattice. In order to get microcrack free silicon surfaces, the sparking energy should be controlled to low levels, which are much lower than the voltage levels used in metal micro-EDM. All in all, thermal spalling should be reduced as much as possible, to obtain smooth and crack free machined surfaces.