Ion projection microlithography is a technique employing a high-resolution demagnifying ion-optical imaging system in connection with a precision step-and-repeat stage. Design patterns are contained in a self-supporting metal foil of 10× (or 20×) chip size, and are imaged in parallel, chip by chip. A tensile stress is induced in the mask foil such that the mask remains flat and undistorted, when heated by exposure to the ion beam. Different design layers are aligned to better than ±0.1 μm by a system that detects ions backscattered from registration marks.
When the surface of a solid sample is irradiated under vacuum by x-rays an electron emission, owing to photoabsorption, can be measured. As the electrons are detected under neglection of their kinetic energies the total electron yield (TEY) is determined. With a tuneable x-ray monochromator the TEY is measured below and above of one of the absorption edges of a given element. A jumplike increase of the TEY signal, due to the additional photoabsorptions in the corresponding atomic level, can be observed - qualitative analysis. The height of this jump can be correlateted to the concentration - quantitative analysis. It can be shown by a fundamental parameter approach for primary and secondary excitations how to use TEY for a quantitative analysis. The information depth lambda of this new method is approximately 2-400 nm depending on the chemical elements and on the original kinetic energies of Auger and photoelectrons. Thus, TEY is located between photoelectron spectrometry and x-ray fluorescence analysis.
We propose a description of the sampling depth (I.) of total electron yield experiments (TEY) in terms of kinetic Auger electron energies. This empirical response results from literature data'-6 on low energy ( < 2 keV) and from our own experiments performed on thin layers of Cu on Fe substrates and on thin layers of AI,Ga, _,As on GaAs substrates at energies of approximately 5 to 8 keV. From these investigations we estimate a sampling depth of 74 nm for Ga KLL Auger electrons in AI,Ga, -,As. For comparison, the sampling depth of x-ray fluorescence analysis (XRF) for AI Ka radiation in AI,Ga, -,As is 400 nm.Both methods (XRF and TEY) were joined for quantitative determination of the thickness t and the Al content x in thin AI,Ga, ,As layers on GaAs substrates. AI Ka fluorescence radiation excited by polychromatic x-radiation and the jump of the total electron yield in the vicinity of the GaK-edge were used in our analytical model. The validity of this model is verified by a comparison of our results with the expected values (known from preparation of the layers).
An ion projection system suitable for production of IC’s is described. Self-supporting metal masks are imaged with a demagnification of 10 : 1 onto a wafer. The resolution of the system is below 1 μm. Direct structuring of oxide and metal layers without any resist, pattern transposition with thin inorganic resists (40 nm) into semiconductor layers and pattern generation in organic resists is described. Exposure times per chip in the order of magnitude of seconds for all these materials are achieved.
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