We have developed a short beamline with high brightness for x-ray lithography. The beamline contains a single, a scanning toroidal mirror and a vacuum-protection system with an acoustic delay line. The practical exposure intensity on a wafer was approximately 50 mW/cm 2 at stored electron current of 500 mA. Dose uniformity of Ϯ2.8% was achieved in a 26 mmϫ26 mm exposure area by optimizing the scan speed. Minimum resolution of 80 nm was obtained with a 15 m gap. The optimum dose for TDUR-N908 ͑Tokyo Ohka͒ was 1300 mA s, which corresponds to exposure time of 2.6 s when the stored electron current is 500 mA. Since the sensitivity of TDUR-N908 is 110 mJ/cm 2 , the beam intensity in our beamline is estimated to be 43 mW/cm 2 . By reducing the exposure field, a beam intensity of more than 50 mW/cm 2 can be achieved.
Previously we described a video-based scattered-light alignment (SLA) system, capable of nanometer-scale alignment accuracy. In order to meet highly accurate alignment with low optical transparency in x-ray masks, we performed the modifications of alignment marks and an optical microscope imaging system on the conventional SLA system. The advanced SLA system has achieved a high alignment accuracy of 10.2–15.7 nm (|mean|+3σ) using a silicon carbide (SiC) x-ray mask of 18% optical transparency, coated with 5 nm thick chrome (Cr) film as an etching stop, with four different processed wafers: nitride, oxide, poly-Si, and aluminum. The different SiC membranes of 2–5 μm in thickness did not have an effect on the alignment accuracy in the nitride wafer.
The degradation of overlay accuracy due to metallization (i.e., aluminum copper physical
vapor deposition (PVD) process) on electronics devices is reported. In a video-based scattered-light alignment (SLA) system for X-ray lithography, the metal layer on the alignment mark
structure affects the alignment signal quality. In this paper, we specifically focus on the
significant effects of aluminum (AL) metallization on the performance of the scattered-light
alignment (SLA) system. The SLA system demonstrated an overlay accuracy of 10.1 nm or less smaller (mean + 3σ) for Al films of 0.1, 0.2, 0.3 and 0.4 µm thickness. Only the 1-µm-thick
Al-sputtered wafer showed a significantly poor performance of 44.4 nm error (mean + 3σ). The
SLA system employs two different types of alignment marks: one type uses narrow edges,
while the other types uses wide edges. We estimated the mark-related alignment error using the
two different types of alignment marks. The results showed that the narrow edges of the
alignment marks had the advantage of smaller mean shift error compared to the wide edges of
the alignment marks. Furthermore, we discuss an asymmetry-induced error in thick Al
metallization.
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