BY VIVEK BAKSHI, EUV Litho, Inc.

IBM’s NXE3300B scanner, at the EUV Center of Excellence in Albany, recently completed a “40W” EUV light source upgrade. The upgrade resulted in better than projected performance with 44W of EUV light being measured at intermediate focus and confirmed in resist at the wafer level. In the first 24 hours of operation after the upgrade, 637 wafer exposures were completed in normal production lot mode with: 20 mJ dose; 83 image fields/ wafer (full wafer coverage, including partial die); conventional illumination.

Dan Corliss, the EUV Development Program Manager for IBM

In the process of benchmarking leading edge tools, the performance of the tool is divided into several sections and each part is validated separately. One can divide an EUVL scanner into the major components of optics, source, mask and resist. All parts, except higher power for EUV light source, have been validated for a long time – with challenges remaining but no showstopper. High source power has remained the #1 issue and a potential showstopper. The ~40 W EUV light sources were deployed but have been working at the lower level of 20 W. The validation at 43 W is a ~100% improvement in source power. The previously reported throughput for an EUVL scanner was 200 wafers per day (WPD), so 637 WPD is over three times improvement and exceeds ASML’ s own expectation of 500 WPD for 2014.

The imaging performance of EUV scanners (CD, CDU, pitch, LER) are a function of scanner design, optics, mask, source and resist. The performance of these parts, except source, has been confirmed for some time now and needs no new validation. The source stability has some effect as well on imaging; hence, the power has to be stable and it is one reason for lower power results from the field. However, the #1 issue for EUV has been the throughput of the EUV scanner, which is directly related to the power of the source, as I mentioned above. Although one will eventually test the imaging performance at higher power levels, it does not make sense to be doing that imaging test (and when you know that part works fine) when you are testing for source power upgrade verification – your main challenge. This is how one benchmarks complex machines. As IBM pointed out, it was an unintended but very exciting result of their benchmark, as the focus was to validate higher source power. Other parts of the scanner and the overall imaging performance have been verified by several chip makers for some time.

The next version of the NXE3300B EUV scanner will be potentially used for patterning at the 7 nm and 5nm nodes. The resolution of printed images will be increased by either multiple patterning (EUV MP), which has been already demonstrated, or via high NA optics (projects are in progress but no demonstration of a high NA EUV tool has occurred yet). 20 mJ of dose for a chemically amplified (CAR) resist, to test the throughput of a EUV scanner, is a very decent dose choice and it is backed by ample data. If this benchmark was done for a 5 mJ CAR resist dose, I will question the test as well, as final images will not meet LER requirements. The good news is that due to recent developments in the high sensitivity resists, now 2-5 mJ dose can give us the same resolution and LER, as from 20 mJ or higher dose CAR resists. In the 2014 SPIE AL meeting, there were many papers confirming the performance of these new types of resists. Hence, the triangle of death (sensitivity, LER and resolution) for CAR resists is no longer valid for these new types of resists. The implications of these new resists are very striking – if we can use these new 5 mJ resists – the throughput will be 3-4 x larger than what is reported for 20 mJ resists. I am hoping that these new high sensitivity resists will mature in another year for HVM use.