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Title: Method for the manufacture of phase shifting masks for EUV lithography

Abstract

A method for fabricating an EUV phase shift mask is provided that includes a substrate upon which is deposited a thin film multilayer coating that has a complex-valued reflectance. An absorber layer or a buffer layer is attached onto the thin film multilayer, and the thickness of the thin film multilayer coating is altered to introduce a direct modulation in the complex-valued reflectance to produce phase shifting features.

Inventors:
; ; ;
Publication Date:
Research Org.:
EUV Limited Liability Corporation, Santa Clara, CA (United States)
Sponsoring Org.:
USDOE
OSTI Identifier:
1175687
Patent Number(s):
7,022,435
Application Number:
10/256,454
Assignee:
EUV Limited Liability Corporation (Santa Clara, CA) OSTI
DOE Contract Number:
W-7405-ENG-48
Resource Type:
Patent
Country of Publication:
United States
Language:
English
Subject:
42 ENGINEERING

Citation Formats

Stearns, Daniel G., Sweeney, Donald W., Mirkarimi, Paul B., and Barty, Anton. Method for the manufacture of phase shifting masks for EUV lithography. United States: N. p., 2006. Web.
Stearns, Daniel G., Sweeney, Donald W., Mirkarimi, Paul B., & Barty, Anton. Method for the manufacture of phase shifting masks for EUV lithography. United States.
Stearns, Daniel G., Sweeney, Donald W., Mirkarimi, Paul B., and Barty, Anton. Tue . "Method for the manufacture of phase shifting masks for EUV lithography". United States. doi:. https://www.osti.gov/servlets/purl/1175687.
@article{osti_1175687,
title = {Method for the manufacture of phase shifting masks for EUV lithography},
author = {Stearns, Daniel G. and Sweeney, Donald W. and Mirkarimi, Paul B. and Barty, Anton},
abstractNote = {A method for fabricating an EUV phase shift mask is provided that includes a substrate upon which is deposited a thin film multilayer coating that has a complex-valued reflectance. An absorber layer or a buffer layer is attached onto the thin film multilayer, and the thickness of the thin film multilayer coating is altered to introduce a direct modulation in the complex-valued reflectance to produce phase shifting features.},
doi = {},
journal = {},
number = ,
volume = ,
place = {United States},
year = {Tue Apr 04 00:00:00 EDT 2006},
month = {Tue Apr 04 00:00:00 EDT 2006}
}

Patent:

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  • A method is disclosed for the implementation of phase shifting masks for EUV lithography. The method involves directly etching material away from the multilayer coating of the mask, to cause a refractive phase shift in the mask. By etching into the multilayer (for example, by reactive ion etching), rather than depositing extra material on the top of the multilayer, there will be minimal absorption loss associated with the phase shift.
  • The authors describe the implementation of a phase-retrieval algorithm to reconstruct phase and complex amplitude of structures on EUV lithography masks. Many native defects commonly found on EUV reticles are difficult to detect and review accurately because they have a strong phase component. Understanding the complex amplitude of mask features is essential for predictive modeling of defect printability and defect repair. Besides printing in a stepper, the most accurate way to characterize such defects is with actinic inspection, performed at the design, EUV wavelength. Phase defect and phase structures show a distinct through-focus behavior that enables qualitative evaluation of themore » object phase from two or more high-resolution intensity measurements. For the first time, phase of structures and defects on EUV masks were quantitatively reconstructed based on aerial image measurements, using a modified version of a phase-retrieval algorithm developed to test optical phase shifting reticles.« less
  • An analysis is presented of a method to protect the reticle (mask) in an extreme ultraviolet (EUV) mask inspection tool using a showerhead plenum to provide a continuous flow of clean gas over the surface of a reticle. The reticle is suspended in an inverted fashion (face down) within a stage/holder that moves back and forth over the showerhead plenum as the reticle is inspected. It is essential that no particles of 10-nm diameter or larger be deposited on the reticle during inspection. Particles can originate from multiple sources in the system, and mask protection from each source is explicitlymore » analyzed. The showerhead plate has an internal plenum with a solid conical wall isolating the aperture. The upper and lower surfaces of the plate are thin flat sheets of porous-metal material. These porous sheets form the top and bottom showerheads that supply the region between the showerhead plate and the reticle and the region between the conical aperture and the Optics Zone box with continuous flows of clean gas. The model studies show that the top showerhead provides robust reticle protection from particles of 10-nm diameter or larger originating from the Reticle Zone and from plenum surfaces contaminated by exposure to the Reticle Zone. Protection is achieved with negligible effect on EUV transmission. Furthermore, the bottom showerhead efficiently protects the reticle from nanoscale particles originating from the Optics Zone.« less
  • Absorber material used in conventional EUVL reticles is eliminated by introducing a direct modulation in the complex-valued reflectance of the multilayer. A spatially localized energy source such as a focused electron or ion beam directly writes a reticle pattern onto the reflective multilayer coating. Interdiffusion is activated within the film by an energy source that causes the multilayer period to contract in the exposed regions. The contraction is accurately determined by the energy dose. A controllable variation in the phase and amplitude of the reflected field in the reticle plane is produced by the spatial modulation of the multilayer period.more » This method for patterning an EUVL reticle has the advantages of (1) avoiding the process steps associated with depositing and patterning an absorber layer and (2) providing control of the phase and amplitude of the reflected field with high spatial resolution.« less
  • A method and apparatus are provided for the repair of an amplitude defect in a multilayer coating. A significant number of layers underneath the amplitude defect are undamaged. The repair technique restores the local reflectivity of the coating by physically removing the defect and leaving a wide, shallow crater that exposes the underlying intact layers. The particle, pit or scratch is first removed the remaining damaged region is etched away without disturbing the intact underlying layers.