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The next generation in the optical media family which follows Compact Disc and DVD formats, will be a high density format that contains up to 25 GB of information on a surface area similar to that of a Compact Disc. The information is recorded as a spiral track of pits on a master disc by applying a lithographic process where a focused and modulated laser spot exposes a positive photoresist (`mastering' process). Compact Disc and DVD formats can typically be mastered with 413nm Kr-laser and conventional broadband novolak/DNQ-photoresists. When striving for higher densities, a reduction in exposure wavelength is needed to obtain a smaller laser spot and thus to create smaller pits. A frequency-doubled Ar laser is therefore chosen as recording laser, (lambda) = 257nm. The design of a DUV exposure tool will be outlined. The wavelength reduction is insufficient to obtain the required reduction in feature size. Consequently, a higher contrast photoresist process is necessary. Different types of broadband, I-line and chemically amplified photoresists were evaluated for this specific application. The main target was to obtain maximum resist contrast ((gamma) ) and minimal feature size. The maximum resist contrast obtained was 3 with I-line resist and 8 using a chemically amplified type. Features of 120 nm wide and 85 nm high were mastered. The photoresist layer thickness varies between 40nm and 85nm. The I-line photoresist with the highest contrast is Shipley Ultra-i-123. With this type of photoresist an optical disc with a capacity of 20.7GB of information has been produced. The quality of such a disc is indicated by the time resolution in the read-out signal, expressed as the so-called jitter (=time error/clock time). For the optical disc with 20.7GB of information the measured jitter equals 7.5% which is regarded as acceptable in optical read-out signals. For these results the process has been optimized by varying developer concentration, developer type and the exposure dose. Decreasing the concentration of hydroxide in metal ion containing developer (sodium and potassium based) increases the contrast and decreases the surface roughness. Due to the limits of I-line photoresist at 257nm wavelength further experiments with chemically amplified (3.2) and 257nm photoresists (3.3) have been carried out. Airborne molecular contamination causes some problems with the use of chemically amplified photoresist.
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