Abstract

The progressive transition from Excimer to extreme ultraviolet (EUV) lithography is driving a need for flatter and smoother photomask blanks. It is, however, proving difficult to meet the next-generation specification with the conventional chemical mechanical polishing technology commonly used for finishing photomask blanks. This paper reports on the application of subaperture computer numerical control precessed bonnet polishing technology to the corrective finishing of photomask substrates for EUV lithography. Full-factorial analysis was used to identify process parameters capable of delivering microroughness below 0.5 nm rms while retaining relatively high removal rates. Experimental results show that masks prepolished to 300–600 nm peak-to-valley (P-V) flatness by chemical/mechanical polishing can then be improved down to 50–100 nm P-V flatness using the automated technology described in this paper. A series of edge polishing experiments also hints at the possibility of increasing the quality area beyond the 142 mm square defined in the official EUV photomask specification.

© 2014 Optical Society of America

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References

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  1. The Global Micropatterning Committee, “Specification for extreme ultraviolet lithography mask substrates,” (2010), pp. 1–10.
  2. T. Shoki, M. Mitsui, M. Sakamoto, N. Sakaya, M. Ootsuka, T. Asakawa, and H. Mitsui, “Improvement of total quality on EUV mask blanks toward volume production,” Proc. SPIE 7636, 76360U (2010).
    [CrossRef]
  3. Y. Hirabayashi, “Development status of EUVL mask blank and substrate,” Proc. SPIE 8166, 81663T (2011).
    [CrossRef]
  4. A. Beaucamp, Y. Namba, I. Inasaki, and R. Freeman, “Finishing of optical molds to λ/20 by automated corrective polishing,” Ann. CIRP 60, 375–378 (2011).
    [CrossRef]
  5. D. Walker, R. Freeman, and A. Beaucamp, “Use of the precessions process for prepolishing and correcting form,” Opt. Express 14, 11787–11795 (2006).
    [CrossRef]
  6. A. Beaucamp and Y. Namba, “Super-smooth finishing of diamond turned hard X-ray molding dies by combined fluid jet and bonnet polishing,” Ann. CIRP 62, 315–318 (2013).
    [CrossRef]
  7. C. King, “New approach to stitching optical metrology data,” Ph.D dissertation (University College London, 2008).
  8. W. Wang, M. Xu, G. Yu, D. Walker, and H. Zhu, “Research on edge control in the process of polishing using ultra precise bonnet on optical elements,” Proc. SPIE 7654, 76540N (2010).
    [CrossRef]
  9. D. Walker, G. Yu, A. Beaucamp, and W. Messelink, “Edges in CNC polishing: from mirror segments towards semiconductors,” Opt. Express 20, 19787–19798 (2012).
    [CrossRef]
  10. H. Li, D. Walker, G. Yu, A. Sayle, W. Messelink, R. Evans, and A. Beaucamp, “Edge control in CNC polishing: simulation and validation of tool influence functions on edges,” Opt. Express 21, 370–381 (2013).
    [CrossRef]
  11. L. Cook, “Chemical processes in glass polishing,” J. Non-Cryst. Solids 120, 152–171 (1990).
    [CrossRef]

2013 (2)

A. Beaucamp and Y. Namba, “Super-smooth finishing of diamond turned hard X-ray molding dies by combined fluid jet and bonnet polishing,” Ann. CIRP 62, 315–318 (2013).
[CrossRef]

H. Li, D. Walker, G. Yu, A. Sayle, W. Messelink, R. Evans, and A. Beaucamp, “Edge control in CNC polishing: simulation and validation of tool influence functions on edges,” Opt. Express 21, 370–381 (2013).
[CrossRef]

2012 (1)

2011 (2)

Y. Hirabayashi, “Development status of EUVL mask blank and substrate,” Proc. SPIE 8166, 81663T (2011).
[CrossRef]

A. Beaucamp, Y. Namba, I. Inasaki, and R. Freeman, “Finishing of optical molds to λ/20 by automated corrective polishing,” Ann. CIRP 60, 375–378 (2011).
[CrossRef]

2010 (2)

W. Wang, M. Xu, G. Yu, D. Walker, and H. Zhu, “Research on edge control in the process of polishing using ultra precise bonnet on optical elements,” Proc. SPIE 7654, 76540N (2010).
[CrossRef]

T. Shoki, M. Mitsui, M. Sakamoto, N. Sakaya, M. Ootsuka, T. Asakawa, and H. Mitsui, “Improvement of total quality on EUV mask blanks toward volume production,” Proc. SPIE 7636, 76360U (2010).
[CrossRef]

2006 (1)

1990 (1)

L. Cook, “Chemical processes in glass polishing,” J. Non-Cryst. Solids 120, 152–171 (1990).
[CrossRef]

Asakawa, T.

T. Shoki, M. Mitsui, M. Sakamoto, N. Sakaya, M. Ootsuka, T. Asakawa, and H. Mitsui, “Improvement of total quality on EUV mask blanks toward volume production,” Proc. SPIE 7636, 76360U (2010).
[CrossRef]

Beaucamp, A.

Cook, L.

L. Cook, “Chemical processes in glass polishing,” J. Non-Cryst. Solids 120, 152–171 (1990).
[CrossRef]

Evans, R.

Freeman, R.

A. Beaucamp, Y. Namba, I. Inasaki, and R. Freeman, “Finishing of optical molds to λ/20 by automated corrective polishing,” Ann. CIRP 60, 375–378 (2011).
[CrossRef]

D. Walker, R. Freeman, and A. Beaucamp, “Use of the precessions process for prepolishing and correcting form,” Opt. Express 14, 11787–11795 (2006).
[CrossRef]

Hirabayashi, Y.

Y. Hirabayashi, “Development status of EUVL mask blank and substrate,” Proc. SPIE 8166, 81663T (2011).
[CrossRef]

Inasaki, I.

A. Beaucamp, Y. Namba, I. Inasaki, and R. Freeman, “Finishing of optical molds to λ/20 by automated corrective polishing,” Ann. CIRP 60, 375–378 (2011).
[CrossRef]

King, C.

C. King, “New approach to stitching optical metrology data,” Ph.D dissertation (University College London, 2008).

Li, H.

Messelink, W.

Mitsui, H.

T. Shoki, M. Mitsui, M. Sakamoto, N. Sakaya, M. Ootsuka, T. Asakawa, and H. Mitsui, “Improvement of total quality on EUV mask blanks toward volume production,” Proc. SPIE 7636, 76360U (2010).
[CrossRef]

Mitsui, M.

T. Shoki, M. Mitsui, M. Sakamoto, N. Sakaya, M. Ootsuka, T. Asakawa, and H. Mitsui, “Improvement of total quality on EUV mask blanks toward volume production,” Proc. SPIE 7636, 76360U (2010).
[CrossRef]

Namba, Y.

A. Beaucamp and Y. Namba, “Super-smooth finishing of diamond turned hard X-ray molding dies by combined fluid jet and bonnet polishing,” Ann. CIRP 62, 315–318 (2013).
[CrossRef]

A. Beaucamp, Y. Namba, I. Inasaki, and R. Freeman, “Finishing of optical molds to λ/20 by automated corrective polishing,” Ann. CIRP 60, 375–378 (2011).
[CrossRef]

Ootsuka, M.

T. Shoki, M. Mitsui, M. Sakamoto, N. Sakaya, M. Ootsuka, T. Asakawa, and H. Mitsui, “Improvement of total quality on EUV mask blanks toward volume production,” Proc. SPIE 7636, 76360U (2010).
[CrossRef]

Sakamoto, M.

T. Shoki, M. Mitsui, M. Sakamoto, N. Sakaya, M. Ootsuka, T. Asakawa, and H. Mitsui, “Improvement of total quality on EUV mask blanks toward volume production,” Proc. SPIE 7636, 76360U (2010).
[CrossRef]

Sakaya, N.

T. Shoki, M. Mitsui, M. Sakamoto, N. Sakaya, M. Ootsuka, T. Asakawa, and H. Mitsui, “Improvement of total quality on EUV mask blanks toward volume production,” Proc. SPIE 7636, 76360U (2010).
[CrossRef]

Sayle, A.

Shoki, T.

T. Shoki, M. Mitsui, M. Sakamoto, N. Sakaya, M. Ootsuka, T. Asakawa, and H. Mitsui, “Improvement of total quality on EUV mask blanks toward volume production,” Proc. SPIE 7636, 76360U (2010).
[CrossRef]

Walker, D.

Wang, W.

W. Wang, M. Xu, G. Yu, D. Walker, and H. Zhu, “Research on edge control in the process of polishing using ultra precise bonnet on optical elements,” Proc. SPIE 7654, 76540N (2010).
[CrossRef]

Xu, M.

W. Wang, M. Xu, G. Yu, D. Walker, and H. Zhu, “Research on edge control in the process of polishing using ultra precise bonnet on optical elements,” Proc. SPIE 7654, 76540N (2010).
[CrossRef]

Yu, G.

Zhu, H.

W. Wang, M. Xu, G. Yu, D. Walker, and H. Zhu, “Research on edge control in the process of polishing using ultra precise bonnet on optical elements,” Proc. SPIE 7654, 76540N (2010).
[CrossRef]

Ann. CIRP (2)

A. Beaucamp, Y. Namba, I. Inasaki, and R. Freeman, “Finishing of optical molds to λ/20 by automated corrective polishing,” Ann. CIRP 60, 375–378 (2011).
[CrossRef]

A. Beaucamp and Y. Namba, “Super-smooth finishing of diamond turned hard X-ray molding dies by combined fluid jet and bonnet polishing,” Ann. CIRP 62, 315–318 (2013).
[CrossRef]

J. Non-Cryst. Solids (1)

L. Cook, “Chemical processes in glass polishing,” J. Non-Cryst. Solids 120, 152–171 (1990).
[CrossRef]

Opt. Express (3)

Proc. SPIE (3)

T. Shoki, M. Mitsui, M. Sakamoto, N. Sakaya, M. Ootsuka, T. Asakawa, and H. Mitsui, “Improvement of total quality on EUV mask blanks toward volume production,” Proc. SPIE 7636, 76360U (2010).
[CrossRef]

Y. Hirabayashi, “Development status of EUVL mask blank and substrate,” Proc. SPIE 8166, 81663T (2011).
[CrossRef]

W. Wang, M. Xu, G. Yu, D. Walker, and H. Zhu, “Research on edge control in the process of polishing using ultra precise bonnet on optical elements,” Proc. SPIE 7654, 76540N (2010).
[CrossRef]

Other (2)

The Global Micropatterning Committee, “Specification for extreme ultraviolet lithography mask substrates,” (2010), pp. 1–10.

C. King, “New approach to stitching optical metrology data,” Ph.D dissertation (University College London, 2008).

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Figures (12)

Fig. 1.
Fig. 1.

EUV photomask on seven-axis CNC bonnet polisher.

Fig. 2.
Fig. 2.

Principle of precessed polishing tool and seven-axis CNC machine [4].

Fig. 3.
Fig. 3.

Quadrants measured for input into stitching software.

Fig. 4.
Fig. 4.

Edge control parameters.

Fig. 5.
Fig. 5.

Edge polishing experiments (subtracting measurements before and after polishing).

Fig. 6.
Fig. 6.

RMS of microroughness (λspatial<10μm) as function of spindle speed, air pressure, and precess angle (0.5 μm CeO2 abrasives).

Fig. 7.
Fig. 7.

RMS of microroughness (λspatial<10μm) as function of spindle speed, air pressure, and precess angle (1.5 μm CeO2 abrasives).

Fig. 8.
Fig. 8.

Microroughness of finished surface (λspatial<10μm) as measured by WLI.

Fig. 9.
Fig. 9.

Micrograph of finished surface, as measured by AFM.

Fig. 10.
Fig. 10.

Flatness of photomask before and after corrective bonnet polishing.

Fig. 11.
Fig. 11.

Edge profile as function of TO.

Fig. 12.
Fig. 12.

Edge profile as function of EZ.

Tables (4)

Tables Icon

Table 1. Specification for EUV Photomask Blanks [1]

Tables Icon

Table 2. Parameters of Full-Factorial Analysis

Tables Icon

Table 3. Parameters of Edge Control Experiments

Equations (1)

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TL:0.6mm,TO:2mm,EZ:4mm,EF:50%.

Metrics