|
Mitigation of pit-type defects proves to be a major hurdle facing the production of a defect-free mask blank for EUV
lithography. Recent efforts have been directed toward substrate smoothing methods during deposition. The angle of
incidence of the substrate is known to have a significant effect on the growth of defects during deposition. It has been
shown that shadowing effects for bump-type defects are reduced when depositing Mo/Si films at near-normal incidence,
resulting in a Gaussian growth profile in which the height and volume of the defect are minimized. Conversely,
operating at off-normal incidence reduces shadowing of pit-type defects. When altering the angle of incidence of the
substrate, the target angle must be changed to maintain uniformity. The resulting mask blank must also meet surface
roughness specifications post-deposition while maintaining a low defect density. In this study, various substrate angle
and target angle combinations were investigated within the Veeco Nexus Low Defect Density tool at SEMATECH to
find optimum in situ pit smoothing conditions using ion beam deposition on both quartz and low thermal expansion
material (LTEM) substrates. The possible substrate-target angle combinations are limited by the design of the current
deposition tool; therefore, a phase space has been mapped out to determine uniform and non-uniform regions. Other
deposition parameters including operating pressure and working gas composition were also explored. After deposition,
EUV reflectrometry measurements were taken to evaluate uniformity in the wavelength; surface roughness, change in pit
depth, change in full width at half maximum, and pit smoothing power were determined using atomic force microscopy
(AFM); transmission electron microscopy (TEM) was used to study the effect of film disruption through the multilayer;
and the printability of smoothed pits will be measure actinically using SEMATECH's AIT tool.
Preliminary results show that positive values for substrate angles in the uniform region tend to give a high surface
roughness after multilayer deposition; however, the combinations with negative substrate angles show promising results.
Substrate angles with lower values resulted in better smoothing than the higher substrate angles. AFM results confirmed
that pit smoothing power at lower substrate angles is greater than under the standard deposition conditions employed by
the tool. Lower chamber pressure was proven to increase the smoothing power of pit-type defects during deposition.
Preliminary TEM cross-section data confirmed the smoothing results obtained by AFM analysis. The use of Ne and Xe
as working gases is also under review. Extensive AFM analysis, TEM cross-sections, and printability data will be
presented.
|
