On the Origin of Charging Damage during Etching of Antenna Structures

Abstract

Monte Carlo simulations of charging and profile evolution in patterned antenna structures during etching in high-density plasmas reveal a rapid change in the potential of the lines at end point, which causes a surge in electron tunneling through thin gate oxides and possibly charging damage. The condition of the substrate (grounded vs. floating) determines the magnitude of the surge and whether it will be followed by a steady-state current until all lines of the pattern become disconnected. A reduction in damage is possible by controlling the substrate condition, which may be assessed through notching experiments.When plasma-etching patterned wafers, the directionality difference between ions and electrons at the wafer causes differential microstructure charging,' which affects the in-trench etch rate,2 can lead to profile distortion (notching),34 and may induce electron tunneling through thin gate oxides.'5 Large tunneling currents are believed to cause electrical degradation or even breakdown of the oxide.6 Termed the "electron shading" effect,' this form of damage is particularly aggravating because of its latent nature and is feared to become a showstopper in the quest for smaller critical dimensions. Despite tremendous effort by researchers worldwide to fight the problem,7 a solution has yet to be found. The physics of the electron shading damage has been elusive, in part because of the experimental hurdles in measuring tunneling currents in situ under realistic processing conditions. Numerical simulations could provide insight into the origin of the tunneling currents and improve understanding of the limitations of existing etch tools and device layout rules. To be sure, such simulations are complex; the charging and etching processes are coupled, requiring the simultaneous handling of phenomena that occur over disparate time scales such as electron tunneling (<1 0' s), microstructure charging (10 5), and profile evolution (102 5), on patterned surfaces consisting of dissimilar materials. Results from such comprehensive calculations for gate electrode etching suggest that the period from open area clearing (end point) to trench bottom clearing is critical for damage.58 Tunneling current tran-

Foundations of low-temperature plasma enhanced materials synthesis and etching

“…Part of the observed damage effects are electrical in nature, e.g. charging-induced damage due to electron or ioninduced charging of insulators [192][193][194][195]. Damage effects are also very important for compound semiconductor etching [196,197].…”

Modeling of charging damage during interlevel oxide deposition in high-density plasmas

“…10͑b͒, matches the metal line potential and demonstrates the significant increase in charging damage that is expected to accompany the change in the aspect ratio. The calculated tunneling currents for damage during plasma etching 18,19 pale next to these currents. The results suggest that charging damage may become a problem more serious in HDP chemical vapor deposition than in HDP etching of future generations of devices.…”

Charging damage during residual metal overetching

“…Charging damage in patterned structures exposed to a uniform plasma may occur by means of ͑a͒ tunneling current surges at the onset of overetching, 6 and ͑b͒ steady-state tunneling currents during overetching. 5,6 Overetching is needed due to reactive ion etching lag ͑RIE-lag͒, a phenomenon that describes a decrease in etch rate with aspect ratio of the pattern.…”

“…3 Electron shading describes the imbalance of ion and electron currents to the bottom of narrow trenches due to differences in their angular distributions. 4 Although the physics of charging damage due to electron shading has been proposed, 5,6 the influence of critical plasma parameters is not understood.…”

“…5,6 Overetching is needed due to reactive ion etching lag ͑RIE-lag͒, a phenomenon that describes a decrease in etch rate with aspect ratio of the pattern. 7 Overetching begins when open areas between patterns clear and ends when the narrow trenches between lines are also thoroughly etched.…”