Lozes Technology Consulting

Specializing in nanolithography engineering & related topics

BACUS 2014: Mask data preparation

In an engaging talk, Fujimura-san (D2S) reviewed the trajectory of MDP over the years. He pointed out the inexorable trend from rule-based, context-independent methods to simulation-based, context-sensitive processing. Ohara-san (Nippon Control Systems) reviewed the trials and tribulations faced by MDP software providers in actually delivering software following this trend.

Abboud (Intel) made the claim that multi-beam will relieve the pressure on MDP throughput. At the same time, it is evident that such relief (should it appear) will quickly be swallowed up by yet more demanding corrections. In the panel discussion, TSMC warned that MDP is near to becoming the greatest cost in the mask production pipeline, assuming multi-beam writers enter production on time. For the VSB writers to date, the speaker reported the worst case MDP time for TSMC as 500k CPU hours.

References:

Fujimura, et al., Trends in mask data preparation, doi:10.1117/12.2073368
Ohara, MDP challenges from a software provider’s perspective, doi:10.1117/12.2070163
Abboud, et al., Mask data processing in the era of multibeam writers, doi:10.1117/12.2072135

BACUS 2014: Scanning Microscopies

In order to help with the conference costs and attendance, SPIE adjoined the Scanning Microscopies conference with BACUS this year. One of the more interesting papers, given in a joint session between SEM and BACUS, concerned 3D SEM metrology at the 10 nm scale. The speaker pointed out that three operational steps are required to obtain sub-nm resolution:

  • First, the obvious, tune up the SEM (focus, stigmation, …).
  • Second, eliminate all contamination (H2 plasma) to prevent (hydro)carbon coating. This stabilizes the image and prevents it washing out during the observation.
  • Third, acquire the image not with slow scans, but with many, very rapid scans. These scans must be aligned digitally, thereby eliminating effects of drift, vibration, and stray magnetic fields. In regard to this third step, NIST recommends heavier algorithm development for SEM metrology. Further details may be found in a NIST paper from the SEM conference.

Under these conditions, one sees excellent 3D images. In fact, the speaker passed around 3D glasses so that one could view 3D images on the conference room screen.

Given that SEM and BACUS ran in mostly parallel sessions, it was difficult to get much of the hoped-for mixing between disciplines. No doubt SPIE realized better space utilization at the conference center.

BACUS 2014: E-beam mask writing

NuFlare announced the EBM-9000, which incorporates a brighter thermionic gun, three-stage shape deflection, and “immersion” objective optics. By increasing brightness and increasing the beam semi-angle, NuFlare achieves J = 800 A/cm2 current density. According to the published paper, the brightness increase is obtained by lowering the work-function. While this would be easy if one substituted CeB6 for LaB6, NuFlare claims the cathode is LaB6. So how the brightness is achieved (without increasing temperature) is not clear.

The increased semi-angle would increase aberrations (objective, deflection, and stochastic), but NuFlare has countered this by “deep immersion optics”. Details are lacking, but it appears to me to involve in-lens deflection. NuFlare has taken a page from the old Etec RSB design to include a microvectoring deflector, which they call “tertiary”. (Shape type selection and shape size deflectors are also separate.) The advantage of deflection with a range of only 600 nm is that it can be made very fast, so that shape size selection and shape placement settle in 10 ns.

Main deflection and subfield deflection have both been reduced to keep the deflection aberrations under control. The main field reduction has been the more drastic. While the EBM-8000 had 120 X 180 microns, the EBM-9000 has 90 X 81 microns main field.

Maximum shape size has been reduced to 250 nm in order to control stochastic blur.

Overall, the EBM-9000 looks like a solid advance for mask writing.

Reference: H Takekoshi, EB-9000: EB mask writer for product mask fabrication of 16nm half-pitch generation and beyond, Proc. SPIE 9235, Photomask Technology 2014, 92350X; doi:10.1117/12.2065551.

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I was disappointed that the IMS/JEOL collaboration did not have a paper for us. The only information we received was a rather hurried look at a recent monthly timeline of progress by Dan Chalom of IMS. He claimed that the team is now integrating “corrections”, without being too specific. I for one certainly would like to see a full paper at SPIE in late winter.

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