The authors report on phase resolved optical emission spectroscopy (PROES) measurements of pulsed capacitive coupled plasmas (CCPs) through argon. The PROES results indicate that under some conditions, the electron heating mechanism can be changed substantially from that dominant in continuous CCPs. The normally dominant α heating mode of electropositive plasmas can be aided by a drift-ambipolar (DA) heating mode during the early portion of the reignition. The DA heating mode is ordinarily only found in electronegative discharges. The authors found that Ar discharges pulsed at 10 kHz only exhibited the α heating mode throughout the reignition process, while those pulsed at 0.1 kHz exhibited a mixed α and DA heating mode during the reignition. The differences in the two heating modes cause substantial differences in the spatial pattern of the light emission from the plasma in addition to an overshoot in the light emission intensity.
Phase resolved optical emission spectroscopy (PROES) measurements were combined with measurements of the optical emission intensity (OEI) and electrical characteristics (RF current and voltage, power, and DC bias voltage) as a function of time during the re-ignition of Ar plasmas pulsed at 100 Hz and 10 kHz. The OEI exhibits a large overshoot at the 100 Hz pulsing rate even though no such overshoot is present in any of the electrical characteristics. The OEI overshoot occurs at a point in time when the RF power, voltage, DC bias voltage, and electron density are all smaller than they become later in the glow. PROES measurements in combination with the time resolved electrical characteristics indicate that the heating mechanism for the electrons changes during the time of the overshoot in the OEI from stochastic heating to a combination of stochastic and ohmic heating. This combination appears to enable a more efficient transfer of the electrical energy into the electrons.
Pitch subdivision of tantalum nitride (TaN) lines is demonstrated across a 200 mm wafer using a cyclic quasi‐atomic layer etch process in an inductively coupled plasma reactor. Chlorine (Cl2) and hydrogen (H
2) chemistries are introduced sequentially to an argon plasma in discrete steps to etch the TaN film. The starting lithographic pattern with critical dimension (CD) of approximately 82 nm and pitch of 200 nm thus yields lines of approximately 40 nm CD and 100 nm pitch with minimal line edge roughness increase. We identify a synergistic effect between H
2‐exposed TaN and Cl
2 plasma as contributing to this result, as well as a potential link to surface oxidation. Optical emission spectroscopy analysis of the plasma discharge is used to characterize reactive species densities and explain the observed changes in profile.
Front Cover: The ability to control individual step parameters in cyclic plasma etch processes provides novel capabilities for nanofabrication. In this example, the pitch of a line/space array is halved as the pattern is transferred into a tantalum nitride (TaN) film. The redeposition of a partially oxidized surface layer creates a self‐aligned mask, and line edge roughness (LER) is maintained by the highly selective nature of the etch.
Further details can be found in the article by Nathan Marchack, Keith Hernandez, Benjamin Walusiak, Jon‐l Innocent‐Dolor, Sebastian Engelmann (https://doi.org/10.1002/ppap.201900008).
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