Paper PS1-MoA11
Impact of Plasma and Annealing Treatments on 193nm Photoresist Line Width Roughness and Profile

Monday, October 18, 2010, 5:20 pm, Room Aztec

As the Critical Dimension (CD) of gate transistors scales down to the nanometer range, line width roughness (LWR) becomes a serious issue, which directly impacts the electrical performance of CMOS devices. It has previously been shown that the photoresist (PR) sidewall roughness present after lithography (6nm, 3σ) is transferred during the subsequent plasma etching processes into the gate, resulting in a final LWR far above the ITRS requirements for the 32nm technological node (1.7nm, 3σ). The key to decrease the final gate LWR is to minimize the photoresist LWR before the plasma etching steps involved in the gate patterning process. The best and simplest way is to expose the photoresist patterns to plasma treatments prior to gate patterning. Indeed, it was observed that Vacuum Ultra Violet (VUV) light emitted by plasmas plays a key role in the photoresist LWR decrease. In the present study, we have used CD-SEM and CD-AFM techniques to investigate the impact of plasma treatment on the photoresist LWR and profiles. Several plasmas (HBr, Ar, He, H₂) emitting strongly in the VUV region (100-200nm) have been investigated. LiF windows placed between the plasma and the photoresist patterns have been used to evaluate the role of the plasma VUV light only on the LWR evolution. The role of the substrate temperature has also been studied. Many characterization techniques have been used to characterize the physico-chemical modifications of photoresist films exposed to the same plasma treatments (Multiple Internal Reflection infrared spectroscopy (MIR), Raman, gas chromatography (GC)).

The results obtained indicate that all plasma treatments lead to a LWR decrease. We have observed that for all plasma investigated, VUV light only seems to induce a slight reflow of the resist which is probably correlated with the LWR decrease. On the other hand, in HBr and Ar plasmas, resist patterns remain square indicating that no reflow occurs. Heating resist patterns up to 200°C without plasma exposure also leads to a LWR decrease, resist reflow being only observed above 200°C . All treatments generate the cleavage of the side groups (lactone group for plasma treatment and protecting group for annealing treatment) and the decrease of the glass transition temperature which is potentially correlated to the LWR decrease. GC analysis also reveals that under Ar and HBr plasma exposure, cleaved side groups can be trapped in the resist polymer matrix because of the presence of a denser surface layer. This dense layer could prevent the resist reflow leading in final to the square profiles observed in HBr plasmas.