SiO 2 buffer-etch processes with a TaN absorber for EUV mask fabrication

Abstract

Extreme Ultraviolet Lithography (EUVL) is the favourite next generation lithography candidate for IC device manufacturing with feature sizes beyond 32nm. The SiO 2 buffer dry etching is a crucial step in the manufacture of the EUV mask due to stringent CD-and reflectance requirements. In contrast to conventional chromium absorber layers new absorber materials e.g. TaN require an adjustment of the SiO 2 buffer etch chemistry and process parameters to avoid a strong influence on the initial absorber profile and thickness. We have developed a SiO 2 buffer dry etch process that uses the structured TaN absorber as masking layer. A laser reflectometer was used during the SiO 2 dry etch process for process control and endpoint detection. Different dry etch processes with SF 6 /He, CF 4 and CHF 3 /O 2 etch chemistry have been evaluated and compared with regard to TaN-and SiO 2 -etch rate, TaN-and SiO 2 etch profile and Si capping layer selectivity. We focused our work on minimum feature sizes and simultaneous etching of different line (e.g. dense-and isolated lines) and hole patterns. Line and contact hole structures with feature sizes down to 100nm have been realized and characterized in a SEM LEO 1560. The whole mask patterning process was executed on an advanced tool set comprising of a Leica SB 350 variable shaped e-beam writer, a blank coater Steag HamaTech ASR5000, a developer Steag HamaTech ASP5000 and a two chamber UNAXIS mask etcher III.

Absorber stack optimization toward EUV lithography mask blank pilot production

“…This makes clearly dry etching of TaN the easiest part of mask process. Dry etch process for buffer layer is still by optimization and current etch selectivity to TaN and to Si capping material can fluctuate with the settings of etch chemistry [10]. We are currently observing a residual etch rate of TaN during SiO 2 process around 0.8nm/min.…”

Lithography for the 32-nm Node and Beyond

“…IMS Chips in Stuttgart was taking care of the development of a complete patterning process with tight CD uniformity and linearity specs for final EUV test masks. This included the e-beam lithography of complex mask pattern in the 100 nm feature size range with chemically amplified resists [21], dry etching of new Ta based absorbers [22] and etching of different buffer materials like SiO 2 or Cr [23]. The developed single processes have been integrated into a full mask flow process and finally applied for the [24] and the first full field setup mask for the ASML α-tool [25,26].…”