Control of electron velocity distributions at the wafer by tailored voltage waveforms in capacitively coupled plasmas to compensate surface charging in high-aspect ratio etch features

Abstract

Low pressure single- or dual-frequency capacitively coupled radio frequency (RF) plasmas are frequently used for high-aspect ratio (HAR) dielectric etching due to their capability to generate vertical ion bombardment of the wafer at high energies. Electrons typically reach the wafer at low energies and with a wide angular distribution during the local sheath collapse. Thus, in contrast to positive ions, electrons cannot propagate deeply into HAR etch features and the bottom as well as the sidewalls of such trenches can charge up positively, while the mask charges negatively. This causes etch stops and distortion of profile shapes. Here, we investigate low pressure, high voltage capacitively coupled RF argon gas discharges by Particle-In-Cell/Monte Carlo collisions simulations and demonstrate that this problem can be solved by Voltage Waveform Tailoring, i.e. the velocity and angular distribution of electrons impacting on the electrodes can be tuned towards high velocities and small angles to the surface-normal, while keeping the energies of the impacting ions high. The applied voltage waveforms consist of a base frequency of 400 kHz with 10 kV amplitude and a series of higher harmonics. A high frequency component at 40 or 60 MHz is used additionally. Square voltage waveforms with different rise-times are examined as well. We show that high fluxes of electrons towards the wafer at normal velocities of up to 2.2 × 107 m s−1 (corresponding to 1.4 keV energy) can be realized.

Current status and new insights about the capacitively coupled electronegative plasma source: injection of energetic beam-like electrons to electrode

“…Recently, a modeling to inject high energy electrons to the electrode was carried out in a pulsed 2f-CCP in electropositive Ar [55]. It is interesting to compare the difference in operating conditions with ours.…”

“…The LF source plays a role in accelerating positive ions in the sheath toward the electrode. The artificial voltage waveform at the biased electrode is numerically studied to control the energy distribution of electrons and ions to the electrode in a CCP [54][55][56][57][58].…”

Equivalent electric circuit model of accurate ion energy control with tailored waveform biasing

“…respectively. It should be pointed out that I i1 can also be calculated from (19) after finding C t . While theoretically the minimum of the effective capacitance and current should be achieved at the same uout , both methods should give the same result.…”

“…A better decoupled control of ion flux and ion energy in dual-frequency CCPs can be obtained by controlling the phase shift between two fixed-frequency RF sources utilizing the electrical asymmetry effect, as done in [14][15][16][17]. Moreover, other voltage waveform tailoring techniques, such as using a low-frequency square waveform with high-frequency harmonics [18,19], have also been developed for CCPs.…”

Characterization of SiO2 Etching Profiles in Pulse-Modulated Capacitively Coupled Plasmas

“…As the feature size of semiconductors continues to decrease, and the structure of semiconductors is altered from two to three dimensions, high-aspect-ratio contact (HARC) hole etching has emerged as one of the most important goals in the semiconductor manufacturing process. Achieving high-performance HARC hole etching requires high selectivity [1][2][3][4][5][6][7], anisotropic etching [8][9][10][11][12], and reduced charge damage [13][14][15][16]. As continuous wave (CW) plasma reacts with a consistent ion flux on a wafer surface, it is difficult to attain these aspects with CW plasma.…”