Chrome mask blanks find extensive use in the fabrication of masks for various lithographic processes
used in solid-state device fabrication. The masks fabricated on these blanks have various advantages
like fine resolution, edge acuty and longer shelf-life in repeated process of lithography. Further, where
sub- micron geometries are encountered, the use of a mask fabricated on these chrome blanks by
E-beam writing is the only solution. Chrome blanks are therefore the basic material for directly
writing masks by E-beam process.
Chrome blanks are basically glass plates with specific optical transmission (85 per cent at l = 0.35
m), mechanical flatness (2 mm), and parallelism on which a controlled film of chromium (800-1000 Å) is
deposited maintaining excellent adhesion and uniformity of thickness (+ 5 per cent) over its extended
Further, since these blanks are to be used for fabrication of masks by E-beam process, film resistivity
(20 ohm/sq) is an essential requirement. In addition, deposited chromium film should have pinhole
density of 0.05 Pcs/cm2.
DRDO has been regularly importing these chrome glass blanks for writing the masks of micron and
sub-micron geometries. Appreciating the strategic technological importance of chrome glass blanks,
DRDO planned a crash programme to indigenously develop these chrome blanks using existing
facilities and expertise in collaboration with the Department of Electronics.
DRDO has now successfully developed and demonstrated the technology for fabrication of chrome
mask blanks for 2.5 and 3.5 in. size. The blanks meet all the required specifications. The performance
evaluation of fabricated blanks has also been carried out by Bharat Electronics Ltd, Bangalore and
SAC, Ahmedabad, in addition to DRDO.
The following specifications have been achieved:
Film thickness 900 + 70 Å
Film thickness + 5 per cent uniformity
Sheet resistance 20 ohm/sq
Optical density 2.8
at 4000 Å
Pinhole density 0.05 Pcs/
(1-4 mm) cm2
Pattern roughness ~ 0.2 mm