Electron microscopy
  
Critical Dimension Uniformity (CDU)
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Wafer critical dimension uniformity (CDU) is a key parameter to characterize the performance of lithography process control.

In an example of splitting-type pitch doubling through dual patterning in page2284, as shown in Figure 2282a, during Step C, the 2nd patterning takes place on the wafer with topography created by the patterned hardmask with most of hardmask layer being etched away. In this case, the FI CDU populations #1 and #2 from the full lot are obtained as shown in Figure 2282b.

Schematic flows of basic double patterning process options

Figure 2282a. Difference in Litho 1 and 2, recurring different lith setup and different etch I and II bias. [1]

 

Schematic flows of basic double patterning process options

Figure 2282b. FI CDU populations #1 and #22 from the full lot. [1]

To obtain good CDU, the factors below are adjusted:
          i) Etch bias fingerprint.
          ii) Dose interfiled corrections.

For ASML's TWINSCAN NXE:3400B EUV scanner (ASML, 2017), the CDU specification is 1.1 nm.

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[1] Mircea Dusa, John Quaedackers, Olaf F. A. Larsen, Jeroen Meessen, Eddy van der Heijden, Gerald Dicker, Onno Wismans, Paul de Haas, Koen van Ingen Schenau, Jo Finders, Bert Vleemingb, Geert Storms, Patrick Jaenen, Shaunee Cheng, Mireille Maenhoudt, Pitch Doubling Through Dual Patterning Lithography Challenges in Integration and Litho Budgets, Proceedings of SPIE - The International Society for Optical Engineering 6520, DOI: 10.1117/12.714278, 2007.

 

 

 
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