IEDF control using multifrequency harmonic drive

Summary form only given. Multi-frequency RF power delivery for IEDF control has become commonplace in semiconductor manufacturing, particularly in plasma etch applications.¹ Recently, two frequency drives where the higher drive frequency is a harmonic of the lower drive frequency have shown interesting influence on IEDF´s with phase acting as an additional tuning knob for control.² In this work, an RF sheath model that assumes a matrix sheath condition and known electron density is used to compare the influence of multiple frequencies over transient sheath parameters, specifically the time dependent potential across the powered sheath. Using this time dependent potential, ion energies incident on the plasma facing surface are calculated using an ion transit time dependent dampening term.³ Ion energy distribution functions are obtained for dual frequency conditions where the two frequencies are integer multiples of each other and compared to the more typical case where the frequencies are not integers of each other. Control of the distribution width is identical with respect to relative RF current from two sources for both the integer and non-integer case. The integer frequency drive produces (n-1) intermediate peaks in the distribution between the maximum and minimum energies whose energy and magnitude can be controlled with the relative phase of the two waveforms. Manipulation of the phase and amplitude of these two power sources can also produce some unique distribution functions, in some cases mimicking distributions that are normally achieved outside of the range of frequencies used to drive the sheath potential, and lend an additional level of IEDF control not achievable with comparable non-integer dual frequency drives. This work will present a brief review of dual frequency IEDF control and present a model that captures the effects of both frequency mixing and phase of integer multiple frequency drives.