Control of ion energy distributions using phase shifting in multi-frequency capacitively coupled plasmas

Summary form only given. Anisotropic etching for microelectronics fabrication is accomplished by energetic ion bombardment in chemically enhanced sputtering. One challenge is being able to control the ion energy-angular distributions (IEADs) onto the surface of the wafer to selectively activate desired processes, which is advantageous for maintaining the critical dimension (CD) of features. Capacitive coupled plasmas (CCPs) powered by non-sinusoidal waveforms and or using multiple frequencies are strategies employed to provide flexible control of IEADs which produce high selectivity and uniformity. Varying relative voltages, powers and phases between multiple frequencies that differ by integer multiples have demonstrated potential control mechanisms for the IEADs and optimization of etching profiles. In this paper, we report on computational and experimental investigations of lEAD control in a dual-frequency CCP where the phase between the frequencies is used as a control variable. The rf frequency and its harmonic frequencies are both applied to the wafer substrate. Both symmetric and asymmetric CCPs are studied. The Hybrid Plasma Equipment Model (HPEM) was employed to predict plasma properties and obtain the harmonic contributions to the power applied to the same electrode. The ion and radical fluxes incident onto the surface are used as input to the Monte Carlo Feature Profile Module (MCFPM) with which profiles are predicted. The operating conditions are 5-100 mTorr in Ar and Ar/CF₄/O₂ gas under different frequency mixing and phase of integer multiple frequency drives. We find that by changing the phase between the applied rf frequency and its second harmonic, the Electrical Asymmetric Effects (EAE) is significant and can shift the dc self-bias.[I] When changing phases between the rf and its higher harmonics, the EAE becomes less effective and ion energy distributions spike at specific energies. Computed results for lEADs are compared with - f phase locked harmonic experimental results measured by Radio Frequency Ion Energy Analyzer.