In this paper we discuss a laser focus drilling technique which has recently been developed for advanced
immersion lithography scanners to increase the depth of focus and therefore reduce process variability of contact-hole
patterns. Focus drilling is enabled by operating the lithography light-source at an increased spectral bandwidth, and has
been made possible by new actuators, metrology and control in advanced dual-chamber light-sources. We report wafer
experimental and simulation results, which demonstrate a process window enhancement for targeted device patterns.
The depth of focus can be increased by 50% or more in certain cases with only a modest reduction in exposure latitude,
or contrast, at best focus. Given this tradeoff, the optimum laser focus drilling setting needs to be carefully selected to
achieve the target depth of focus gain at an acceptable contrast, mask error factor and optical proximity behavior over
the range of critical patterning geometries. In this paper, we also discuss metrology and control requirements for the
light-source spectrum in focus drilling mode required for stable imaging and report initial trend monitoring results over
several weeks on a production exposure tool. We additionally simulate the effects of higher-order chromatic aberration
and show that cross-field and pattern-dependent image placement and critical dimension variation are minimally
impacted for a range of focus drilling laser spectra. Finally, we demonstrate the practical process window benefits and
tradeoffs required to select the target focus drilling laser bandwidth set-point and increase effectiveness of the sourcemask
solution for contact patterning.
Double Patterning (DP), Spacers and other advanced Litho technologies require an enormous amount of CD and tool
data collection and development time for Optical Proximity Correction (OPC) modeling. Unfortunately this process
could be started typically only when the Litho and Etch process development for the OPC'ed layer is done. This leads to
significant (a month and more) delays with the mask tape-outs and final chip readiness for production.
In this paper we discussed a way to reduce the overall OPC and MDP preparation and product-to-market time and
increase the OPC accuracy by early collection of the OPC measurements, automatic CD-SEM recipe generation and CD
data analysis and model calibration with Tachyon software.
We reviewed the design of the OPC test chip, OPC exposures, data analysis and OPC modeling on the advanced and
accurate Tachyon T2.0 OPC platform and ways to improve modeling cycle time.
Another critical parameter of the OPC modeling is accuracy as one of the main parts of the CD error budget. We
investigated approaches to OPC modeling accuracy and achieved RMS below 1nm for critical features by using module
data of the respective ASML TWINSCAN XT:1900i scanner and advanced Tachyon software.
The polarization properties of light become more and more important as numerical apertures of the projection lens increase. With unpolarized light the contrast of the image is degraded because of poor interference of the TM component of the light. By applying only TE linear polarized illumination light, the contrast loss can be minimized. The challenge will be to control the polarization variation throughout the imaged field. Besides contrast also the light incoupling in the resist depends on polarization. The different polarization directions (TE and TM) induce virtual dose differences. Immersion lithography reduces this effect due to reduced incident angles at a given lens NA. In the upcoming era beyond 0.9 NA, imaging enhancements by polarized illumination are needed. There are several components in a lithographic scanner which potentially influence polarization properties. Apart from illuminator and projection lens the reticle blank and the patterned mask absorber including 3D effects may impact the final intensity distribution in the resist. Last but not least the ability to measure the polarization state is a prerequisite to actively control polarization within the exposure system. The ability to assess the unpolarized and polarized projection lens performance with the on-scanner interferometer (ILIAS<sup>TM</sup>) allows us to do this. In order to verify the benefits and challenges of polarized illumination systems, we built a prototype illuminator and tested it on both a 0.85 NA ArF system as well as on a 0.93 NA ArF system. Next to the successful qualification of illuminator and projection lens we were able to verify the expected gain in imaging performance with polarized light. In this paper we present results of the experimental work and compare the data with our simulations.
For the near future generations of lithography we investigate the reticle measurements of contact holes with respect to their lithographic performance. The difficulty with the shrinking size of contact holes is that their X and/or Y measurement on reticle does not correlate with the lithographic results. The shape of the contact hole will have a large impact. This paper considers the several types of reticle SEM measurement on isolated contact holes, the simulations on asymmetric contact holes, reticle photo analysis of contact hole shape, and lithographic result of 115-nm contact holes. A set of contact holes has been measured with a CD SEM in several ways as x-size, y-size, area, diameter in various angles. Only area measurement will suffice to judge contact hole size and shape. A second step simulates the behaviour of asymmetric contact hole shapes. For attenuated phase shifted contact holes of 130nm (lx) and smaller, shape asymmetry can lead to small CD deviations. The third step correlates lithographic performance with the reticle measurements. Contact hole area or effective circular diameter correlates with wafer results. A better correlation results from reticle CD uniformity profile. The attenuated (6%) PSM that we used, has a large variety of sizes and pitches in contact holes. The reticle was exposed using the ASML Step and Scan PAS55OO/1100 system. The reticle was measured with a KLA SEM.
This study assesses the various approaches to printing contacts in the sub 100nm regime using 193nm. Traditional techniques are analyzed along with the use of tri-tone contacts and pupil filtering. Approaches using attPSM masks looks promising down to pitches of 300nm. Below this, assist features may be needed to prevent residual artifacts due to sidelobes. For pitches > 400nm the use of tri-tone masks show a significant improvement in process latitude and ease of overlapping process windows. The pupil filter solution does not seem provide any significant improvement as compared to other solutions with the exception that it provides the lower MEF. Realization of this solution will increase machine complexity and will possibly impact throughput, especially if using transmission filters. However, pupil filtering can be an option for isolated contact layers that are printed with binary masks. We find that the process and enhancement techniques to print a dense contacts and isolated contacts to be vastly different. This may require a split into two exposures if an extensive pitch range is needed.