Resist trimming in high-density CF4/O2 plasmas for sub-0.1 μm device fabrication

Abstract

Resist trimming using a CF 4 /O 2 plasma generated by an inductively coupled high-density plasma source is investigated. Results show that the resist trimming process is applicable for the fabrication of a sub-0.1 m polysilicon gate electrode with conventional 248 nm lithography. The trim rate depends strongly on gas composition, temperature, rf source power, bias voltage, reactor pressure and total gas flow. The trim rate increases with increasing temperature, rf source power and reactor pressure but decreases with higher bias voltage. For a typical trimming condition at gas composition of CF 4 and O 2 with a ratio of 3.3:1, the resist trim rates are 1.0 and 1.2 nm/s for dense and isolated lines, respectively. By examining the effect of various process parameters, it is found that the trimming process is dominated by the neutral reactant species. Angle-resolved x-ray photoelectron spectroscopy shows that a fluorinated carbon oxyfluoride polymer is deposited on the sidewall of photoresist. The degree of carbon fluorination of the film is influenced by the process parameters. A more fluorinated film, obtained at lower bias voltage and higher source power, gives more trimming.

Effect of halogen in high‐density oxygen plasmas on photoresist trimming

“…Our previous study showed that the change in resist length is a linear function of trim time (Sin et al, 2002). Lateral trim rates of about 1.02 and 1.23 nm/s are observed for dense and isolated lines, respectively, at 100 sccm CF 4 and 30 sccm O 2 .…”

“…Without breaking the vacuum in the same etcher, the subsequent etching process of the polysilicon gate electrode is then performed using the trimmed resist/BARC as an etch mask. Our previous study successfully illustrated the fabrication of the 80-nm gate length transistors using the 248-nm lithography (Sin et al, 2002(Sin et al, , 2003 In this study, the characteristics of resist trimming-the trim rate and the resist profile-are examined for the two-component halogen-O 2 mixtures (HBr/O 2 , Cl 2 /O 2 , and CF 4 /O 2 ). The activation energy of trimming in different gas chemistry is also determined.…”

“…Sometimes the second constituent is also added to the plasma to slow down the spontaneous reaction between the oxygen and the photoresist. Commonly, fluorocarbons are added to form passivation layers on the feature to maintain the vertical profiles (Doemling et al, 1998;Hsu et al, 2000;Li et al, 2002;Sin et al, 2002).…”

“…Process optimization requires an understanding of the trimming mechanisms of the organic resist (Sin et al, 2002(Sin et al, , 2003 as well as the effect of different chemistry on the trimming performance. Thus, the aim of this work is to investigate the effects of different gas chemistry in plasmas on the characteristic of the resist trimming.…”

“…The new strategy proposed to make gate transistors less than the resolution allowed is to reduce the critical dimension (CD) of the photoresist feature, to be used as the etch mask, before the subsequent procedures of the polysilicon gate etching. The final critical dimension of the polysilicon gate is thus determined by the trimmed amount of the photoresist (Sin et al, 2002).…”