Studies of plasma surface interactions during short time plasma etching of 193 and 248nm photoresist materials

Abstract

As the device dimensions scale to 100nm, the use of photoresist materials is suitable for lithographic patterning at 193nm. The molecular structure of 193nm photoresist materials is significantly different from that of 248nm photoresist materials [H. Ito, IBM J. Res. Deu. 45, 683 (2001), T. Kajita et al., Proc. SPIE 4345, 712 (2001)], which leads to a number of undesirable consequences, including pronounced surface and line edge roughness during plasma etching [H. Ito, IBM J. Res. Deu. 41, 69 (1997), [E. Reichmanis et al., J. Vac. Sci. Technol. B 15, 2528 (1997), [L. Ling et al., ibid. 22, 2594 (2004)]. In this article, we present an investigation of the mechanisms for the surface/line edge roughening of photoresist materials during plasma etching using C4F8∕90%Ar discharges. We emphasized in our study short exposure times (the first few seconds) of the photoresist materials and structures to the plasma, a time regime that has not been well studied. Rapid modifications were observed for both 193 and 248nm photoresists during short time exposure. During the first seconds of plasma exposure, photoresist material densification and hydrogen depletion are important processes. It is also found that rough surfaces develop within a few seconds of exposure to the C4F8∕90%Ar discharges. Plasma exposure leads to the formation of rough edges on the top of trench sidewalls in photoresist trench and line structures. During prolonged exposure to the plasma, the roughness is transferred to produce striations on the sidewalls. After an initial stage, the roughening rate remains constant for 193nm photoresist, whereas for 248nm photoresist the roughening rate is negligible. This difference is possibly related to the preferential removal of carbonyl groups for the 193nm photoresist material, which has been revealed by x-ray photoelectron spectroscopy and seconday ion mass spectroscopy.

Benefits of plasma treatments on critical dimension control and line width roughness transfer during gate patterning

“…But, as reference resist is etched faster, it develops higher roughness for a given processing time. This is consistent with other studies 13,14,35,36 that show that polymers with greater plasma induced material loss present increased surface roughness. The reason is that during steady state etching, the existing surface roughness can be amplified by an ion induced transfer mechanism where locally nonuniform removal rates lead to enhanced surface roughness since low and high surface features will not be etched at the same rate.…”

“…This is consistent with previous works. 3,5,13,14,36 Hua et al 13 observed that rough surfaces develop within few seconds of exposure of 193 nm PR to FC plasma, and that the transfer of surface roughness produces rough sidewalls that exhibit vertical aligned features. Similar observations were made on 248 nm photoresist.…”

“…[3][4][5][6][7][8][9][10] Moreover, 193 nm photoresist polymers show poor etch resistance and develop important surface roughness when exposed to fluorocarboned plasma processes typically used to open hard mask layers. [11][12][13][14] The consequence is that the photoresist LWR tends to be degraded during hard mask opening steps and the degradation is transferred into the final gate. Some authors have shown the benefit of introducing plasma treatment prior plasma transfer in order to decrease the resist LWR and also to limit the resist degradation during the plasma process.…”

Dependence of photoresist surface modifications during plasma-based pattern transfer on choice of feedgas composition: Comparison of C4F8- and CF4-based discharges

“…While studies addressing issues of either photoresist ͑PR͒ materials [1][2][3] or discharge conditions 4,5 on PR degradation have been published, a combined study of both PR material and plasma conditions has been missing.…”

Novel ArF photoresist polymer to suppress the roughness formation in plasma etching processes

“…Since several studies have suggested that the surface roughness of ArF photoresist films is linearly proportional to the LER in patterned ArF photoresist films and the formation mechanisms of surface roughness and LER are identical. [10,11] Therefore, the discussion on surface roughness can also be applied to LER in this paper. Figure 3 shows the etching rate of the ArF photoresist films.…”