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From the SAL newsletter, "One Step Ahead", Vol. 2, No. 6, 1997:
X-RAY LITHOGRAPHY SAVES $$
A recently updated ASET study of cost of ownership compares x-ray lithography (XRL) with 193 nm DUV(ArF) and e-beam lithography methods. It includes i-line and 248 nm (KrF) lithographies as baselines for comparison purposes.
Device yield, which could increase XRL's advantage, was assumed to be equal for all technologies. The study also uses the same estimated mask/reticle costs for all lithography methods which understates the
advantage of XRL. Since the current plan is to introduce 193 nm lithography with full reticle enhancement techniques (RET) , the DUV reticle costs could be much higher, perhaps 2-3 times the cost of an x-ray mask, especially if 9" base reticles are required
Interestingly, this chart shows that the use of KrF lithography (248 mm) has a lower $cle (cost per chip level exposure) for 1 Gb devices than for 256 Mb devices! At first glance, this is counter-intuitive, since additional RET will be required for the 1 Gb devices. The assumptions are different, however; 200 mm wafers were assumed for 256 Mb production while 300 mm wafers were used in the calculation for 1 Gb devices. The additional cost of RET is apparently more than
offset by the economics of switching to 300 mm wafers.
According to the chart, x-ray lithography is clearly the most cost-effective choice for high-volume manufacturing of 1 Gb and 4 Gb devices. For 1 Gb manufacturing, XRL has a cost advantage for volumes which expose more than 500 wafers per mask.
This study by Gomei, et al updates a cost-of-ownership analysis done earlier which also found that x-ray lithography had a real advantage for both 1 Gb and 4 Gb volume manufacturing.
[Chart not reproducable here.]
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