Magnification errors arising from wafer processing cause significant overlay errors in lithography. We have devised a new, simple method that involves changing the wafer temperature to correct magnification errors on an x-ray stepper. A wafer is first heated in the wafer orientation unit, and then it is allowed to cool as it is transferred to the wafer stage due to the temperature difference between the wafer and the air in the chamber. For a given cooling time, the reproducibility of the wafer temperature is less than 0.3 °C; and the maximum available temperature change is 1.5 °C. The key point is that the placement of patterns on a wafer immediately after the chucking remains fixed regardless of further changes in the wafer temperature, provided that the force holding the wafer to the stage is strong enough. The maximum magnification error that can be corrected by this method is about 4 ppm. This is determined by the maximum available temperature change (1.5 °C) and the coefficient of linear expansion for Si. The results of overlay tests revealed the correction controllability to be below 0.2 ppm. When this correction method was used, the total overlay accuracy was found to be 38 nm (3σ), which includes mask placement error, etching process error, and so on.

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Optical lithography is facing resolution limit. To overcome this issue, highly complicated patterns with high data volume are being adopted for optical mask fabrications. With this background, new electron beam mask writing system, EBM-7000 is developed to satisfy requirements of hp 32nm generation. Electron optical system with low aberrations is developed to resolve finer patterns like 30nm L/S. In addition, high current density of 200 A/cm 2 is realized to avoid writing time increase. In data path, distributed processing system is newly built to handle large amounts of data efficiently. The data processing speed of 500MB/s, fast enough to process all the necessary data within exposure time in parallel for hp32nm generation, is achieved. And this also makes it possible to handle such large volume dense data as 2G shots/mm 2 local pattern density.In this paper, system configuration of EBM-7000 with accuracy data obtained are presented.

The scattering properties of the equatorial electrojet at a frequency of 21 Mc/s has been investigated. The results obtained suggest these nregularitles first occur when the electrojet current density is about 6.4 x A m-2. The corresponding drift velocity of the electrons is less than the mean thermal velocity of the ions. Thls situation does not favour the spontaneous formation of plasma waves, which is the mechanism suggested by Cohen and Bowles to account for the irregularities in the electrojet. The rapid and deep fading of the received signal suggest there are only a few scattering centres present which are moving at velocities of about 300 m sec-1. It is suggested that these scattering centres might be plasma waves with cylindrical wave fronts originating in the region of the electrojet which have been disturbed by the passage of meteors.

The exposure performance has been evaluated for the new x-ray stepper, the XRA, which is equipped with global alignment and magnification correction systems. Dose uniformity in the exposure field of 3.9%, stage accuracy of less than 20 nm, and good linearity and stability between the magnification change and applied force were obtained. For the 100 nm node, both critical dimension (CD) control of 10 nm and overlay accuracy of less than 30 nm were obtained using two 4 Gbit masks of the gate and contact hole by the double exposure method. Possible improvements of the dose uniformity and mask pattern CD will result in more accurate CD control. By compensating for the alignment offset, overlay accuracy of 23 nm for the 70 nm node is also expected.