Effects of a chirped bias voltage on ion energy distributions in inductively coupled plasma reactors

Abstract

The metrics for controlling reactive fluxes to wafers for microelectronics processing are becoming more stringent as feature sizes continue to shrink. Recent strategies for controlling ion energy distributions to the wafer involve using several different frequencies and/or pulsed powers. Although effective, these strategies are often costly or present challenges in impedance matching. With the advent of matching schemes for wide band amplifiers, other strategies to customize ion energy distributions become available. In this paper, we discuss results from a computational investigation of biasing substrates using chirped frequencies in high density, electronegative inductively coupled plasmas. Depending on the frequency range and chirp duration, the resulting ion energy distributions exhibit components sampled from the entire frequency range. However, the chirping process also produces transient shifts in the self-generated dc bias due to the reapportionment of displacement and conduction with frequency to balance the current in the system. The dynamics of the dc bias can also be leveraged towards customizing ion energy distributions.

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“…For low bias frequencies, ions transiting through the sheath in a small fraction of an RF period arrive with energy dependent on the phase and voltage of the bias when the ion enters the sheath. 131) For high bias frequencies, ions transiting through the sheath over many RF periods arrive at the substrate with a narrower distribution centered about the average sheath potential. 131) This motivated the use of multiple bias frequencies to customize the IEDs using a chirp, whose frequency was varied over time with an arbitrary waveform.…”

“…131) For high bias frequencies, ions transiting through the sheath over many RF periods arrive at the substrate with a narrower distribution centered about the average sheath potential. 131) This motivated the use of multiple bias frequencies to customize the IEDs using a chirp, whose frequency was varied over time with an arbitrary waveform. 131) Lamham and Kushner reported the computational results for biasing substrates using chirped frequencies in high-density, electronegative ICPs.…”

“…131) This motivated the use of multiple bias frequencies to customize the IEDs using a chirp, whose frequency was varied over time with an arbitrary waveform. 131) Lamham and Kushner reported the computational results for biasing substrates using chirped frequencies in high-density, electronegative ICPs. 131) The IED depended on the frequency range and chirp duration owing to transient shifts in the self-generated dc bias.…”

“…131) Lamham and Kushner reported the computational results for biasing substrates using chirped frequencies in high-density, electronegative ICPs. 131) The IED depended on the frequency range and chirp duration owing to transient shifts in the self-generated dc bias. 131) In addition, ions are transported from the plasma through the sheath to the surface.…”

“…131) The IED depended on the frequency range and chirp duration owing to transient shifts in the self-generated dc bias. 131) In addition, ions are transported from the plasma through the sheath to the surface. The IAD is actually spread over 5-10°around the essentially normal incidence angle.…”