Production of low-thermal-expansion EUVL mask blanks with low-defect multilayer, buffer, and absorber

Abstract

Schott Lithotec has introduced all relevant technology steps to manufacture EUV mask blanks -ranging from Low Thermal Expansion Material (LTEM) via high quality substrate polishing to low defect blank manufacturing. New polishing and cleaning technologies, improved sputter technology and updated metrology enable us to routinely produce EUVL mask blanks meeting already many of the roadmap requirements. The goal is pilot production of EUV blanks for the 45 nm node end of 2005. There are several technology options for achieving the mechanical, optical and chemical specs for substrates and coatings. Some of them are already integrated in our processes. An important focus of this paper is the understanding of defect sources starting from the LTEM bulk material to the fully coated blanks with multilayer, buffer and absorber. We present details on some production steps controlling defect detection sensitivity dedicated to various layers and report on new results on defect reduction research after the different process steps.

Absorber stack optimization toward EUV lithography mask blank pilot production

“…After deposition process modifications we reached a very good surface roughness 0.22nm rms on a substrate surface roughness of 0.20nm rms. More detailed were given in a former publication [9]. Regarding thickness uniformity of this new process, Figure 1 shows the absolute measurement of the thickness of our 30nm SiO 2 buffer layer.…”

The first full-field EUV masks ready for printing

“…To avoid particle generation and to minimize clamping errors, an electrostatic clamp is used which requires the back-side of the mask blank to have a conductive layer. The resistance of the coating should be in the order of < 27Ω⋅cm [4]. The clamp area dimensions are defined in [3].…”