Availability of defect-free masks is one of the most critical issues for enabling EUV lithography. Among others,
multilayer phase defects embedded in EUV blanks are primary concern because multilayer defects as low as 2nm are
expected to be printable. Therefore, thorough understanding of defect printability through experiments is anticipated
to derive critical sizes of multilayer defects. A test mask with programmed multilayer defects has been fabricated for
this purpose with various sizes of defects as well as various protrusion sizes of defects from the absorber lines. As the
first step toward rigorous printability prediction that can comprehend any arbitrary-shaped multilayer defects, line
defects parallel to absorber lines have been selected for printability experiments using micro exposure tool (MET) in
Lawrence Berkeley National Lab. for direct comparison with 2D simulation. The simulation of electro-magnetic field
with multilayer defects has been carried out using finite-element-method with triangular cells that well match the needs
for incorporation of minute change in multilayer profile as observed in a TEM photograph. The experiments have
proved that there is systematic correlation between the sizes of defect protrusion from beneath the absorber line with
printed line CD. The defect with protrusion size of 33nm on mask, however, did not show any evidence of defects
while aerial image simulation indicated there should be detectable difference in print results. Root cause investigation
for this gap indicated that the multilayer bump affected the absorber width and profile above and hence generated the
gap between experiments and simulation that assumed identical absorbers. Simulation with exact absorber shape input
well matched experimental results.
To reduce the surface roughness of a substrate for mask blanks for extreme ultraviolet (EUV) lithography, the layers of
a Mo-Si multilayer structure being deposited by magnetron sputtering were treated with an assisted ion beam. The
effectiveness was analyzed by atomic force microscopy, X-ray reflection diffraction, and EUV reflectivity
measurements, which revealed a large improvement in the interface and surface roughness, resulting in a multilayer
with better EUV performance than one formed without such treatment.
Mask substrate defects continue to be one of the critical issues for EUV technology development. Current
specifications call for allowable defects in the 25nm height range for production masks blanks. Simulations seem to
indicate that defects as small as 3nm high will cause printable defects on the wafer. To study the effects of small aspect defects on the printed image we undertook a study to look at 10nm height (mask
substrate size) defects. A mask was fabricated with 12nm height defects in arrays based on area. Defects of 110nm,
190nm, 300nm, and 1000nm were fabricated. Multi-layers were then deposited and the mask was patterned with
line/space patterns with pitches (mask size) of 600nm, 800nm, and 1000nm. Wafers were then exposed using a well characterized resist and the results were analyzed. All sizes of defects printed at
least once. The largest defect size (1000nm mask) caused multiple bridges to form while even the smallest defect size
(110nm mask) could cause a bridge on the 600nm (mask size) pitch.
Ion beam sputtering and magnetron sputtering were used to grow Mo-Si multilayer structures to investigate which is more suitable for the fabrication of mask blanks for extreme ultraviolet (EUV) lithography. For ion beam sputtering, the difference between using Ar and Xe as the sputtering gas was also examined. For ion beam sputtering, the peak EUV reflectivity of 40 Mo-Si bilayers was measured to be about 62% at wavelengths in the range of 12-15 nm; while for magnetron sputtering, the value was 65%. A transmission electron microscopy analysis of multilayers deposited by ion beam sputtering revealed an interface layer between the two materials: It had a thickness of 1.5 ± 0.2 nm when Mo was deposited on Si, and a thickness of 0.7 ± 0.2 nm when Si was deposited on Mo. These interface layers were 30-50% thicker than those formed during magnetron sputtering. The mechanism by which interface layers form is discussed based on an ion implantation model.
This paper is a summary of the work to date done by the ASET consortia to look at the impact of deposition method on defects. The study includes scratch and bump type defects coated with EUVL quality multi-layers using Magnetron Sputtering, Ion Beam Sputtering, or Ion Beam Sputtering with a secondary ion etch. After the deposition TEM samples were taken of the individual defects and the impact of the deposition method on the multi-layers was examined.
Photomask handling is significantly more challenging for 157 nm lithography than for any previous generation of optical lithography. First, pellicle materials are not currently available which meet all the requirements for 157 nm lithography. Polymeric materials used at 193 nm higher wavelengths are not sufficiently transmissive at 157 nm, while modified fused silica materials have adequate transmission properties but introduce optical distortion. Second, the problem of molecular level contamination on the reticle must be solved. This contamination is due to the presence of oxygen, carbon dioxide, water, and other attenuators of 157 nm radiation on the mask surface. It must be removed using something other than the lithography laser due to throughput and cost of ownership considerations. Third, there is the issue of removing attenuators from under the pellicle after a material becomes available. Both the ambient atmosphere and other introduced contaminants must be removed from the space between the reticle and pellicle after cleaning but before exposure. Fourth are the potential issues for storage of reticles both during transportation from the mask shop and after it is in the wafer fab. Finally, the problems associated with operating in an optically inert dry environment must be addressed. The lack of moisture in the environment removes one of the key electrical discharge paths off of the reticle, which greatly increases the risk of electrostatic damage to the pattern (ESD). In order to address these and related issues in a timeframe consistent with the aggressive implementation plan for 157 nm lithography, International Sematech (ISMT) formed the 157 nm Reticle Handling Team in November of 1999. This paper details the most critical results to date of this industry-wide team, and gives a prognosis for successful completion of the team's primary goal: a demonstration of a feasible 157 nm reticle handling strategy by December of 2000.
Photomask handling is significantly more challenging for 157nm lithography than for any previous generation of optical lithography. First, pellicle materials are not currently available which meet all the requirements for 157nm lithography. Polymeric materials used at 193nm higher wavelengths are not transmissive at 157nm, while modified fused silica materials have adequate transmission and durability but have mechanical issues that need to be resolved. Second, the problem of molecular level contamination on the reticle must be solved. This contamination is due to the presence of oxygen, carbon dioxide, water, and other attenuators of 157nm radiation on the mask surface. It must be removed using something other than the lithography laser due to throughput and cost of ownership considerations. Third, there is the issue of removing attenuators from under the pellicle after a material becomes available. Both the ambient atmosphere and other introduced contaminants must be removed from the space between the reticle and pellicle after cleaning but before exposure. Forth are the potential issues for storage of reticles both during transportation from the mask shop and after it is in the wafer fab. Finally, the problems associated with operating in an optically inert dry environment must be addressed. The lack of moisture in the environment removes one of the key electrical discharge paths off of the reticle, which greatly increases the risk of electro-static damage to the pattern (ESD).
Photomask handling is significantly more challenging for 157nm lithography than for any previous generation of optical lithography. First, pellicle materials are not currently available which meet the requirements for 157nm lithography. Polymeric materials used at 193nm and above are not sufficiently transmissive at 157nm, while modified fused silica materials have adequate transmission properties but introduce optical distortion.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.