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EUV Lithography at the SEMATECH-Berkeley Microfield Exposure Tool Facility (BMET)

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20 nm 22 nm 30 nm 30 nm
20nm 22nm 30nm 30nm

Addressing Critical Areas in EUV Lithography Research

The top three critical roadblocks on the path to realizing large-scale manufacturing use of EUV lithography, as identified by the 2008 International EUVL Steering Committee, are:

  1. A reliable high-power source and collector module.
  2. The availability of defect-free masks.
  3. Criteria for resist resolution, sensitivity, and Line Edge Roughness (LER) must be met simultaneously.

The BMET focuses on the second and third of these issues. Resolution and sensitivity are largely solved issues, though LER still remains a challenge (see The World's Highest Resolution Projection EUV Lithography Tool, and Resist Development). Progress has been made in making defect-free masks (see Mask Development; CXRO also contributes to this field using the the Actinic Inspection Tool).

Lithography is the process by which a circuit pattern is transferred into silicon to produce computer chips. Lithography tools can be thought of as Xerox machines for computer chips. Extreme ultraviolet (EUV) lithography [1] uses light of 13.5 nm and is the leading candidate for high volume manufacturing of nano-electronics at feature sizes of 22 nm and below. To make this a reality, advanced research tools operating with numerical apertures (NA) of 0.25 or greater are required today. To address this issue, CXRO has developed a 0.3-NA EUV microexposure tool. This tool uses the Advanced Light Source (ALS) as its source of EUV radiation. The CXRO exposure station is designed to be capable of 12-nm equal-line-space printing.

Figure 1 Figure 2
Figure 1: The MET system. Figure 2: The active scanning illuminator.

Figure 1 shows a CAD model of the exposure system depicting the major components as well as the EUV beam path [2]. Effectively coherent radiation from ALS undulator beamline 12 [3,4] impinges on the scanning illuminator. The light is directed to a reflective reticle. From there the light is re-imaged by the all-reflective 0.3-NA optic with 5´ demagnification to the wafer plane. A grazing incidence laser system is used to monitor the height of the wafer at the print site ensuring that it remains in focus. With the wafer removed, the light propagates to a scintillator plate sitting effectively in the far field. Pupil-fill monitoring is achieved by re-imaging the scintillator plate through a vacuum window to a visible-light CCD camera. A significant difficulty with using a synchrotron source for lithography, however, is the poor match between the intrinsically high coherence of the source as compared to the partial coherence requirements of a lithographic tool. Directly using synchrotron sources would typically limit one to coherence factors below 0.1. To overcome this issue, an active scanning illuminator has been developed (Fig. 2). The use of this scanning illuminator allows lossless variable illumination in patterns such as Fig. 3, as well as those presented on the next page ("The World's Highest Resolution Projection EUV Lithography Tool").

Lossless variable illumination (a) Lossless variable illumination (b)
a
b
Fig. 3: Illustrations of lossless variable illumination

using the scanning illuminator.

Select an image to view it full-size.

References This research was supported by International Sematech.

  1. R. Stulen and D. Sweeney, "Extreme ultraviolet lithography," IEEE J. Quantum Electron. 35, 694-699 (1999).
  2. P. Naulleau, K. Goldberg, E. Anderson, et al., Proc. SPIE Vol. 5374, 881-891 (2004).
  3. D. Attwood, G. Sommargren, R. Beguiristain, K. Nguyen, J. Bokor, N. Ceglio, K. Jackson, M. Koike, and J. Underwood, "Undulator radiation for at-wavelength interferometry of optics for extreme-ultraviolet lithography," Appl. Opt. 32, 7022-7031 (1993).
  4. C. Chang, P. Naulleau, E. Anderson, and D. Attwood, "Spatial coherence characterization of undulator radiation," Opt. Comm. 182, 24-34 (2000).
  5. P. Naulleau, K. Goldberg, E. Anderson, J. Cain, P. Denham, K. Jackson, A. Morlens, S. Rekawa, F. Salmassi, "EUV microexposures at the ALS using the 0.3-NA MET optic," J. Vac. Sci. & Technol. B, in review (2004).
  6. J. Cain, P. Naulleau, C. Spanos, "Advanced metrology for characterization of extreme ultraviolet lithography process effects," J. Vac. Sci. & Technol. B, in review (2004).
  7. R. Soufli et al., Appl. Opt. 46, 3736 (2007)