A digitally controlled solid-state microwave generator allowing variable frequency operation and precise phase control is adopted for plasma generation. In this study, a resonant cylindrical cavity is used as a microwave applicator in place of conventional waveguides. In order to improve the plasma uniformity, the TE111 mode is agitated by injecting microwaves into the cavity from two spatially orthogonal directions, with a temporal phase difference ϕ. Theoretical analyses and finite-difference time-domain simulations derive the following effects of the phase control. In the case of ϕ = ±π/2, fast rotation of the cavity field takes place with a rotational frequency of ω/2π (= 2.4–2.5 GHz), where ω denotes the microwave angular frequency. On the other hand, when ϕ is linearly modulated in time with a low frequency of Ω/2π (= 0.1–1000 Hz), slow pulsation takes place, in which the cavity field alternately excites a circular rotation and a standing oscillation at the modulation frequency. These effects are experimentally confirmed in microwave discharges in argon at 0.1–20 Torr with total injection powers from 50 to 800 W. Two-dimensional images of the optical emission from the generated plasma show that both the fast rotation and slow pulsation improve azimuthal plasma uniformity.

Slow rotation of microwave plasma at a rotational frequency of Ω/2π = 0.1–1000 Hz is realized to improve plasma uniformity by using a resonant cylindrical cavity and a solid-state microwave generator at a frequency of ω/2π = 2.4–2.5 GHz. The microwave at ω/2π is modulated in amplitude at Ω/2π and injected into the cavity from two orthogonal positions, exciting the TE111 mode. The cavity fields rotate either clockwise or anticlockwise at a frequency of Ω/2π when the phase differences, Δϕ at ω and ΔΦ at Ω, between the input microwaves are properly set as calculated by a theoretical analysis and finite-difference time-domain simulation. Rotating plasmas are experimentally measured in the microwave discharges of argon at 0.1–20 Torr. When the rotational frequency is low (Ω/2π < 30 Hz), a plasma rotation is visible in the optical emission image; the azimuthal rotation of a local ion density is also confirmed by a rotatable Langmuir probe array. Conversely, when Ω/2π > 1000 Hz, the electron density measurement by a curling probe reveals that the plasma rotation disappears in the downstream region. This observation is supported by a simplified analysis based on the diffusion equation, proving a characteristic distance of plasma rotation disappearance to be (Da: ambipolar diffusion coefficient).

Cone-shaped hollow cathode electrode configuration for a damage free remote plasma removal process has been optimized for given pressures based on Paschen characteristic curves, voltage-current characteristics and time-resolved discharge observations as well as oxide film removal performances. Remote plasmas have been generated in two types of cone-shaped electrodes with mixtures of He, NF3, and NH3 for pressure range of 1-30 Torr. Paschen characteristic curves and voltage-current (V-I) characteristics define an operating pressure for low breakdown voltage and the hollow cathode effect to minimize the particles. Sinusoidal voltage waveform and asymmetry electrode configuration alternate the glow discharge and hollow cathode discharge modes in a cycle. The current and infrared emission intensity from the glow discharge increases together for both cone-shaped electrodes with increasing pressure, whereas the hollow cathode discharge plasma emits strong infrared only when pD condition is satisfied. For the wide cone electrode configuration, high voltage operation at higher pressure results in particle contamination on the processed wafer by high energy ion bombardment. Operating at optimum pressure for a given electrode configuration shows faster oxide etch rate with better uniformity over a whole 300mm wafer. (C) 2016 The Japan Society of Applied Physics

Summary form only given. Applied Materials' funnel-shaped electrode configuration for remote plasma process is being used for oxide removals in semiconductor manufacturing process. Remote plasma removal process actively uses chemically activated species from plasma rather than charged particles that could possibly damage the structures fabricated on the wafer.Electrical and optical characteristics by using probe technique and optical emission spectroscopy (actinometry) has been investigated to optimize the funnel-shaped electrode structure which is hollow cathode concept design. Plasma generations inside the electrode has been studied with various type of driving methods of pulsed DC, low frequency (<;1MHz) and radio frequency (>1MHz). Spatiotemporal plasma diagnostics by using ICCD (intensified chargecoupled device) camera confirms that low frequency driving enables dual discharge modes operation - glow and hollow cathode discharges while pulsed-DC driving gives only single mode operation. Also, time-resolved images by ICCD camera reveal that radio frequency driving has different discharge mode with different electron heating mechanism than low frequency driving. The oxide etch rates and 300mm in-wafer uniformities have been compared with various driving methods. To maximize the hollow cathode effect in the funnel-shaped electrode configuration, the pulsed-DC has been investigated. Pulsed-DC operation with funnel-shaped electrode configuration enables strong hollow cathode effect at the center of the electrode improving electron impact ionization as well as radical generation. Wafer process performances of pulsed-DC driving, such as etch rate, uniformity and cleanness has been compared to the process performance of other driving techniques.

Summary form only given. A remote plasma source for selective removal process in semiconductor device fabrication has been investigated. Plasma has been generated between the cone-shaped electrode powered by commercial electronic ballast and the grounded plane electrode with noble gases of argon, helium or a mixture gas of He+NF3+NH3 for the pressure range from 1 Torr to 30 Torr. Sinusoidal voltage waveform and asymmetry electrode configuration alternate the glow discharge and the hollow cathode discharge modes in a cycle - two different discharge modes in a cycle. It is noted that the operating pressure windows of the hollow cathode discharge mode was wider than the glow discharge mode. The glow discharge started to extinguish at relatively higher pressure while the hollow cathode discharge mode kept growing. These results show that the stable operation window of the system could be limited by the glow discharge mode rather than the hollow cathode discharge mode and could be improved by optimizing the applied voltage waveform and electrode configuration.

An argon plasma generated between the cone-shaped electrode powered by commercial electronic ballast and grounded plane electrode has been investigated. Since the electronic ballast has positive and negative cycle in a period, two different discharge modes of remote plasma-the normal glow discharge mode and the hollow cathode discharge mode-have been observed. It is noted that the hollow cathode discharge mode has wider operation window in gas pressure than the glow discharge one. The glow discharge started to be extinguished at pressure higher than 4.1 torr and turned to the hollow cathode discharge mode in the holes on ground plate, while the hollow cathode discharge mode kept growing until 10 torr. These results show that the stable operation window of the system could be defined by the glow discharge mode rather than the hollow cathode discharge mode and could be improved by optimizing the applied voltage waveform and electrode configuration.