Particle-in-cell simulation of multi-frequency capacitively-coupled plasmas at low pressure: a 2D perspective in Ar and O2

Multi-frequency capacitively coupled plasmas (MFCCPs) are one of the key technologies enabling forefront of current etching process in 3D NAND and FinFET manufacturing.  These processes rely crucially on the precise control of plasma density profile, uniformity of ion/radical fluxes and ion energy distribution (IED) in MFCCPs.  Varying plasma chemistries in those processes also creates plasmas with different behaviors and scaling properties, e.g., highly electro-negative ion-ion plasmas in oxygen containing gases. In such a rapidly expanding process space, computational modeling has become an important tool in conjunction with experimental diagnostics in understanding the intricate physical mechanisms in MFCCPs.  In this paper, a 2D particle-in-cell (PIC) plasma model is used to study the kinetic behavior of low pressure (1 – 10’s mTorr) MFCCPs in two different representative chemistries: Ar and O2.  The low frequency RF source is at 100’s kHz while 10’s MHz is used for the high frequency.  Simulation shows a shift of the plasma density profile from center-peak to edge-peak over pressure ranging from 2 – 20 mTorr.  Results are compared with experimental measurements of plasma density, fluxes and IED over a range of pressure, frequency and RF voltages.  Comparison between electro-positive and electro-negative plasmas will also be discussed.