Chirped pulsed bias power in inductively coupled plasma reactors

Summary form only given. Fine control over ion energy distributions (IEDs) in plasma material processing reactors is critical to producing the features required for next generation microelectronics. One promising way of increasing control is through the use of pulsed power. Methods such as inductively coupled power (ICP) pulsing, radio frequency (RF) biased substrate pulsing, and synchronously pulsed bias and ICP power have previously been investigated [1]. Additional control over the IED can be gained by applying a frequency chirped bias power over a pulsed cycle. Chirped power is where the frequency is modulated in a predictable way, such as through a linear or exponential increase in frequency with time. Applied frequency greatly affects the IED, where close bimodal peaks are observed at high frequency and wide asymmetric peaks are observed for lower frequencies [2]. When averaged over the pulsed cycle, varied applied frequency can, therefore, be used to create a customized IED.In addition to increasing IED control, chirped power can be used to enhance power matching with pulsed plasmas. When pulsing an ICP power source, plasma impedance rapidly varies over the pulse cycle due to variations in electron density and impedance of the discharge. Applied chirped power enables the frequency to be pre-emptively adjusted to match these variations and minimize the amount of reflected power. Chirped power can therefore be an effective tool to ensure optimal power transfer for pulsed plasma operation. The behavior of chirped pulsed bias power for an Ar/Cl2 inductively coupled plasma was investigated using the Hybrid Plasma Equipment Model (HPEM) - a 2D fluid hydrodynamics plasma simulation [3]. IEDs will be discussed with the ICP power operating in continuous wave mode with a chirped RF bias. Similarly, the effect of chirped power on power transfer efficiency will be discussed while pulsing the ICP power with the RF bias operating in chirped mode.