Tailored waveform biasing in atomic and molecular plasmas for atomic scale processing

Atomic scale processes such as plasma-enhanced atomic layer deposition (ALD) and atomic layer etching (ALE) are vital to fabricate critical features in semiconductor devices that require excellent thickness control. Inert atomic plasmas are typically used for material removal by plasma ALE, whereas reactive molecular plasmas are used for synthesizing thin films by plasma ALD. To achieve accurate thickness control, high etch selectivity, and desirable material properties, accurate control of the ion energy is often important for these plasmas. However, controlling the ion energy by conventional radio-frequency sinusoidal waveform biasing results in a broad ion energy distribution. In this work, we investigate more precise ion energy control with tailored waveform biasing in atomic and molecular plasmas. A commercial remote plasma reactor was equipped with a prototype tailored voltage waveform generator for applying tailored bias waveforms, consisting of a positive voltage pulse and a negative linear voltage ramp. Various aspects of tailored bias waveforms including the voltage ramp rate, voltage pulse amplitude, voltage pulse duty cycle, and waveform repetition frequency were thoroughly investigated in terms of their influence on the ion flux-energy distribution functions of an inert atomic plasma (Ar). Moreover, it is demonstrated that this accurate ion energy control can be applied to reactive molecular plasmas (O2, Ar–H2, and N2) as well. This work serves as a guideline for the implementation of tailored waveform biasing in plasma-enhanced atomic scale processing.