Novel Clean Concept of Advanced Patterning Film (Amorphous Carbon) for Beyond 2xnm Generation Self-Aligned Double-Patterning (SADP) Process

AbstractAdvanced Patterning Film (APF, Amorphous Carbon) is newly developed hard mask material by APPLY MATERIALS, Inc. for fine pattern definition, especially used in ArF immersion process. However, amorphous carbon is one candidate of core materials of self align double pattering (SADP) process, usually suggested not to use wet clean process after patter definition due to moisture absorption of APF. We successfully demonstrate better amorphous carbon surface clean performance without any film damaged and line edge roughness (LER) improve 18.2% CD variation, 1.1nm in space even-odd bias beyond 28nm generation.

           APF of APPLY MATERIALS, Inc. is chemical vapor deposition (CVD) amorphous carbon (a-C) which precursors are normally acetylene (C₂H₂) and propane (C₃H₆). Traditional post clean SPM chemical consists of sulfuric acid (H₂SO₄) and hydro peroxide (H₂O₂). Hydro peroxide will oxidize amorphous carbon into CO or CO₂and result in pattern damaged. We surveyed some post clean candidates in semiconductor fabrication common used, as table 1 shows. Only APM and DHF showed miner or no etching rate to amorphous carbon film.

           APM is first chosen chemical for amorphous carbon core post etching clean. In Figure 1-a, 3nm/side etching polymer is found on a-C sidewall, and Figure 1-b shows that dry etching polymer are totally removed after APM 10 minutes treatment. However, in SADP process, core material should be with higher removal rate than spacer material, which is usually selected by high temperature deposition film to achieve the high selectivity to core material in core removal process.

As Figure 2 shows, amorphous carbon with C₂H₂precursor is porous structure. 10 minutes APM process will induce moisture absorption by porous amorphous carbon film and line twist in following high temperature spacer material deposition, 450C atomic layer deposition silicon nitride, shows as Figure 3-a. Figure 3-b shows worse even-odd spacer bias after SADP spacer defined.

           Shorter clean process time and high clean efficiency become the keys of a-C core post clean step. Two chemicals A and B, A is higher fluorine concentration contained and B is lower fluorine concentration contained, a-C core post clean efficiency were investigated and both process times are confined within 90 seconds, including rinse and drying steps. Figure 4-a., 4-b. and 4-c show chemical A has better polymer removal capability than chemical B. Line edge roughness (LER) is reduced from 3.03nm to 2.48nm, 18.2% improvement, shows as Figure 5. In Figure 6 good LER and even-odd space performance of SADP gate definition after adopting chemical A for a-C post etching clean.

           Long time clean process will result in water absorption of amorphous carbon film due to its porous structure, and will cause worse line edge roughness (LER) in the following high temperature spacer material deposition process. Shorten clean process time to avoid water absorption and improve clean efficiency are the major criteria to achieve successful amorphous carbon clean. Novel a-C clean method by raising F concentration to achieve higher clean efficiency and successfully improve LER 18.2% after core etching and post clean in positive tone SADP process beyond 2xnm generation.