In the subquarter-micron range, X-ray lithography and demagnifying ion projection are promising printing techniques. For both methods special designed masks are needed which have to fulfil strong requirements including flatness, stabiltiy, defect density, transparency, and surface properties. In this paper we would like to demonstrate that silicon membrane based mask blanks are well suited to meet most of these demands. Furthermore, silicon as membrane material offers the advantage to make use of the experience in semiconductor process technology. A fabrication sequence has been developed, based on silicon epitaxial growing, clean-room compatible wet etching and anodic bonding techniques. Highly boron doped silicon layers with germanium as counter-dopant offer the possibility of stress engineering. An etching process on the base of KOH/IPA is applied in a clean-room environment to decrease the particle density during etching. A very comfortable bonding process for fixing silicon membranes on glass ring carriers was optimized and yieds super flat mask blanks. The application of this process and the results of the blank characterization are presented and discussed.
The impact of statistical fluctuations due to the finite number of quanta absorbed during the exposure of highspeed X-ray photoresists on photoresist development and lithographic structure transfer is examined. Evidence for percolation processes during photoresist development is provided, and theoretical models are presented in the form of a Monte -Carlo type computer experiment, and a statistical analysis of surface clusters by means of a simple continuous -space percolation model. Finally achievable structure transfer is analyzed in terms of the optical and statistical components of the normalized process parameter NPL.
Statistically designed experiments for optimization in processing the high sensitive negative tone Hoechst resist RAY-PN (AZ PN 100) were used to establish robust processes for two different applications of the resist: (1) pattern replication on a wafer and (2) during the mask copy process under 40-mbar He environment via x-ray lithography. Minimization of linewidth change with respect to a 1:1 pattern transfer was achieved through manipulation of the following variables: exposure dose, post-exposure bake (PEB) time and temperature, and development time. A two-stage sequential strategy was employed. After specifying the response and the primary variables, the first stage of the sequential approach was based on a full factorial design. In the second stage, the influence of PEB parameters for wafers as well as for x-ray mask blanks were studied using a central composite design. Finally, the response surfaces for the pattern replication on x-ray mask blanks are demonstrated and the optimal process parameter set for a linewidth control within 50 nm for 0.5- to 3.0-μm feature size values are given.
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