Double exposure technique for 45nm node and beyond

Abstract

The technical challenges in using F2 lithography for the 45nm node, along with the insurmountable difficulties in EUV lithography, has driven the semiconductor chipmaker into the low k 1 lithography era under the pressure of ever decreasing feature sizes. Extending lithography towards lower k 1 puts heavy demand on the resolution enhancement technique (RET), exposure tool, and the need for litho friendly design. Hyper numerical aperture (NA) exposure tools, immersion [1], and double exposure techniques (DET's) are the promising methods to extend lithography manufacturing to the 45nm node at k 1 factors below 0.3. Scattering bars (SB's) [2] have become an integral part of the lithography process as chipmakers move to production at ever lower k 1 factors. To achieve better critical dimension (CD) control, polarization is applied to enhance the image contrast in the preferential imaging orientation, which increases the risk of SB printability. The optimum SB width is approximately (0.20 ~ 0.25)*(λ/NA).[1] When the SB width becomes less than the exposure wavelength on the 4X mask, Kirchhoff's scalar theory under predicts the SB intensity. The optical weighting factor of the SB increases ( Figure 1b) and the SB's become more susceptible to printing. Meanwhile, under hyper NA condition's, the effectiveness of "sub-resolution" SB's is significantly diminished. A full-sized scattering bars (FSB) scheme becomes necessary. Double exposure methods, such as using ternary 6% attenuated PSM (attPSM) for DDL, are good imaging solutions that can reach and likely go beyond the 45nm node. Today DDL, using binary chrome masks, is capable of printing 65 nm device patterns. [3,4,5] In this work, we investigate the use of DET with 6% attPSM masks to target 45nm node device. The SB scalability and printability issues can be taken cared of by using "mutual trimming", i.e., with the combined energy from the two exposures. In this study, we share our findings of using DET to pattern a 45nm node device design with polarization and immersion. We also explore other double patterning methods which in addition to having two exposures, incorporates double coat/developing/etch processing to break the 0.25 k 1 barrier.

Dark field Double Dipole Lithography (DDL) for 45nm node and beyond

“…As discussed in section 2.2, the larger pitch the higher the 0 th order, so we need to add shielding for the critical features in the respective low contrast orientation. The sum of the total exposure can implicitly trim away the FSB without leaving the print residues [5]. This cannot be done in dark field DDL; however, in order to improve the depth of focus for a manufacturing-worthy process, "dark-field SB" slots, or sub-resolution assist slots [9] are added during the OPC process.…”

“…Double dipole lithography (DDL) is becoming a popular RET candidate for foundries and memory makers to pattern the poly gate active layer [2, 3, 4]. Double exposure method or double pattern technique (DPT), [5,6,7] using ternary 6% attenuated PSM (attPSM) is a good imaging solution that can reach and likely go beyond the 45nm node. In this work, back end of the line (BEOL) metal like test structures were used for developing a model-based dark field DDL method.…”

A SEM-based system for photomask placement metrology

“…With Immersion Lithography, k 1 is projected to reach 0.25. Beyond that, pitch doubling may further reduce the k 1 factor to 0.20 and below 3 .…”

Double-exposure mask synthesis using inverse lithography

“…Double-exposure lithography has gained a lot of importance recently and is tipped as one of the important technologies for enabling 45 nm and smaller technology nodes. 8,9 DEL uses two ͑same or different͒ masks and two ͑same or different͒ illumination settings to print the desired circuit pattern. There are many variants of DEL such as using a trim mask with alternating phase-shift masks ͑PSM͒, 10 double dipole lithography ͑DDL͒, innovative double-exposure by advanced lithography ͑IDEAL͒, 8 etc.…”

“…All DEL systems involve some sort of pattern decomposition targeted toward the individual exposures. A typical DDL scheme proposed by Hsu et al 9 starts by separating the target into horizontal and vertical geometries for use with Dy and Dx dipoles, respectively. The final image with the two exposures is the sum of the energies at the wafer plane.…”