Smoothing of substrate pits using ion beam deposition for EUV lithography

Abstract

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.

Advances in lithographic techniques for precision nanostructure fabrication in biomedical applications

“…These defects include soft particles bonded to the surface via van der Waals forces, and hard particles which can be embedded in the substrate and leave a pit when removed [ 100 ]. Various pit smoothing techniques have been devised [ 101 ], however, these methods are limited by the ability to analyse the substrate to identify the defects which must be removed [ 102 , 103 ]. Furthermore, the compound effect of multiple mirrors results in low efficiency, with approximately 1–5% of the photons produced from the UV source interacting with the wafer.…”

Evaluating printability of buried native extreme ultraviolet mask phase defects through a modeling and simulation approach

“…The net phase change adds to the intrinsic effect of the core defect and its influence on the growth of the multilayer stack during deposition. Therefore, identifying this influence is critical and would help in determining strategies to mitigate the printability of such defects by employing various techniques like defect smoothing, 7 multilayer defect compensation technique, 8 or using an additional buffer layer, 9 to name a few.…”