ASML’s Latest Immersion Tool Enables 38 nm Memory

ASML Holding NV (Veldhoven, Netherlands) announced its latest immersion lithography tool, the Twinscan XT:1950i, at SEMICON West today. Although the system uses a lens with the same 1.35 numerical aperture (NA) as its predecessor, resolution with the new system is improved from 40 nm to 38 nm, which effectively provides a 10% gain in wafer area available for chips.

Aaron Hand, Executive Editor, Electronic Media -- Semiconductor International, 7/15/2008 12:14:00 AM

ASML Holding NV (Veldhoven, Netherlands) announced its latest immersion lithography tool, the Twinscan XT:1950i, at SEMICON West today. Although the system uses a lens with the same 1.35 numerical aperture (NA) as its predecessor, resolution with the new system is improved from 40 nm to 38 nm, which effectively provides a 10% gain in wafer area available for chips.

ASML’s Twinscan XT:1950i improves image resolution over its previous system from 40 to 38 nm, and also provides higher throughput and tighter overlay.

A system performance gain of 25% overall includes improvements in overlay, resolution, critical dimension uniformity (CDU) and throughput. In addition to 38 nm capability for memory and 32 nm logic (which ranges upwards from 45 nm), throughput has increased from the 131 wph specified on ASML’s XT:1900i to 148 wph on the XT:1950i. Throughput improvements come as the result of new immersion techniques and enhanced stages, including a faster chuck swap and faster measure cycles. A new immersion hood layout and design enables higher meniscus stability, which means that the machines can be run at higher-acceleration scan speeds, providing better productivity control, noted Skip Miller, director of strategic marketing for ASML.

Single-machine overlay has also improved, from 6 nm to 4 nm. Dedicated chuck overlay is 3.5 nm; and matched-machine overlay is 7 nm. The 30% tighter overlay accuracy is achieved through improved stage control, as well as improved thermal control. The wafer table has moved from a single-zone to multi-zone thermal control, Miller explained, which enables an optimized temperature profile. The tighter overlay is important for chipmakers not only to improve the quality of the chips produced, but overlay is a key parameter in achieving effective double patterning, which is considered a necessary bridge between 193 nm water immersion and extreme ultraviolet (EUV) lithography.

The ~5% improvement in resolution over the 1900i comes through advanced image stability, according to Miller. What ASML calls its advanced lens controller adds new manipulators in the lens that provide capability for additional Zernike control — specifically Z6, Z10 and Z17, he said.

The XT:1950i brings 193 nm water immersion lithography to its resolution limits, according to Miller. Beyond 38 nm imaging, immersion lithography will likely need to move to a double patterning scheme.

With an NA=1.35, ASML has taken its latest immersion scanner to what it says is the resolution limit for single-exposure patterning.

ASML has also introduced a couple optional features on the 1950i that are geared toward cleanliness. A liquid particle monitor option, for example, provides feedback on the immersion water quality, making sure it’s particle-free. The other option is called iClean, and it provides an in situ ability to clean the immersion hood.

ASML expects to begin shipping the XT:1950i by the first quarter of 2009. “Early systems are going to both memory as well as logic houses,” Miller said.

The lithography tool manufacturer will also introduce a comprehensive package of upgrades to increase the performance of its existing immersion systems XT:1700i and XT:1900i. The upgrade packages, also available beginning in 1Q09, will improve overlay by 14 and 17%, and productivity by 4 and 7%, respectively.