Kathleen R. Early

Cost of ownership for x-ray proximity lithography

We present an analysis of the cost of ownership for a synchrotron-based x-ray proximity printing system. We consider the total number of lithography tools that would be needed for a 0.25-micron manufacturing plant with 5000 200-mm wafer starts per week. We compare the cost of x ray with that of deep ultraviolet lithography for patterning critical levels. For reference, we calculate costs for the noncritical levels as well. We examine x ray costs as functions of synchrotron under-utilization, of reticle cost and usage, and of throughput. Our analysis indicates that, under the assumptions of identical process yield and throughput, x-ray system costs with a fully utilized synchrotron are competitive with deep ultraviolet costs if the manufacturing product has high volume. For low or moderate volume products deep ultraviolet lithography is cheaper, predominantly because of lower reticle costs. The lack of a strong economic driver for x ray suggests that it is unlikely to be introduced into manufacturing until it is clear that no optical technology can adequately meet production needs.

Cost of Ownership for Soft-X-Ray Projection Lithography*

We present a general analysis of cost of ownership for an integrated circuit production lithography system. We illustrate the method with examples from i-line and deep ultraviolet lithography, as well as soft x-ray projection lithography. Tool utilization is emphasized as well as system throughput. Our analysis suggests that with 20 wafer per hour throughput, which may be attainable with soft x-ray projection lithography, lithography costs will rise to four times todays i-line costs, or higher. In addition to throughput, reticles and photoresist will be cost drivers for this technology.

Resolution and components of critical dimension variation in x-ray lithography

We report on an IC lithographic resolution study in which APEX-E resist on polysilicon coated wafers was exposed to synchrotron x radiation through a high-resolution mask that contained Au-electroplated features ranging in size from 0.5 down to 0.15-micrometers . Exposures were made at mask-to-substrate gaps ranging from 20 to 35 micrometers and at doses from 100 to 134 mJ/cm2. We probed the wafers with an SEM, both before and after etch, and electrically. From the electrical linewidth probing, we found that for isolated lines and 1:2 L:S patterns the feature widths were linear down to 0.18-micrometers . For the 1:1 and 2:1 L:S arrays, the widths were linear down to 0.25-micrometers . Dense and isolated lines down to 0.25-micrometers exhibited +/- 15% dose latitude over a 10-micrometers gap range. Contact holes were examined only by SEM. The smallest size that printed was nominally 0.225 micrometers , but was measured to be 0.20-micrometers after etch. Critical dimension uniformity, calculated with each feature type allowed its own mean value, was approximately equals 40 nm (3(sigma) ), including intrafield and across wafer variation. The mask CD uniformity was approximately equals 30 nm (mean + 3(sigma) ). The wafer-to-wafer CD variation was found to be 6 nm (3(sigma) ) and the electrical test-to-test CD variation was 3 nm (3(sigma) ). We use regression analysis to separate the component of CD variation that is assignable to intrafield form that assignable to interfield. The regression analysis to separate the component of CD variation that is assignable to intrafield from that assignable to interfield. The regression analysis indicates that these components of CD variation are systematic rather than random. The main contributor to the interfield component may be polysilicon etch. The intrafield error is believed to be caused predominantly by beamline nonuniformity and not by errors on the 1x mask.