Design and characterization of a low defect density Mo/Si deposition system
for the fabrication of EUVL reticle blanks

D.R. Kania, S.P. Vernon, P.A. Kearney, R.A. Levesque

University of California
Lawrence Livermore National Laboratory
PO Box 808, Livermore CA 94551

A.V. Hayes, V. Kanarov, B. Vidinsky

Veeco Instuments Inc.
Microtech, Ion Beam Systems
Terminal Drive, Plainview NY 11803
	
	
Reticles for extreme ultraviolet lithography (EUVL) consist of  a high
reflectance multilayer (ML) coated substrate (the reticle blank) that is
overcoated with a patterned absorber layer to form a reflective mask.  Any
reflectance variation in the reticle constitutes a potential reticle defect. 
At present there are no strategies for repairing defective regions of the ML
coating. Consequently there is considerable interest in developing a
deposition technology capable of producing virtually defect free high
reflectance Mo/Si MLs.  Specifications for the reticle blank require a defect
density of less than 0.06/cm2 at 0.05 mm diameter or greater over reticle
dimensions of 13x22 cm at a magnification M=1/51.  In many respects, reticle
fabrication requires merging highly developed, disparate technologies - the
fabrication of a high reflectance low defect density ML optical coating to
standards normally associated with semiconductor manufacture.

The design and characterization of a low defect density Mo/Si ML deposition
system commissioned specifically for EUVL reticle blank fabrication is
reported. A filamentless, inductively coupled, low frequency rf ion source
with focusing optics2 is used to sequentially sputter elemental Mo and Si
targets  to form the ML.  Ar is used as the sputtering gas.  System features
include fully load-locked operation, single wafer transfer from cassette to
the deposition chamber and standard mechanical interface (SMIF) handling of
the cassette. Sample introduction and transfer occurs in a class 1
minienvironment.  150 mm diameter Si wafers are employed as substrates, a
concession to the ready availability of appropriately clean substrates and
compatibility with standard semiconductor diagnostic tools.  Defect
characterization is undertaken with a Surfscan 6420 which can detect 0.13mm
diameter particulates on the ML coated wafer surface at greater than 90%
efficiency3.  This instrument is also configured for SMIF handling of 
cassettes and is housed in its own class 1 minienvironment, adjacent to the
deposition system.                     


1 The National Technology Roadmap for Semiconductors, Semiconductor Industry
Association (1994).
2 Veeco Instruments RIM 210 ion source
3 Tencor Instruments, Santa Clara, Ca