Kenneth S. Collins

Inductively Coupled Pulsed Plasmas in the Presence of Synchronous Pulsed Substrate Bias for Robust, Reliable, and Fine Conductor Etching

Inductively coupled pulsed plasmas in the presence of synchronous pulsed substrate bias are characterized in a commercial plasma etching reactor for conductor etching. The synchronous pulsed plasma characteristics are evaluated through the following: 1) Ar-based Langmuir probe diagnostics; 2) Ar/Cl2 plasma modeling utilizing the hybrid plasma equipment model and the Monte Carlo feature model for the investigation of feature profile evolutions; 3) basic etching characteristics such as average etch rate and uniformity; 4) sub-50-nm Dynamic Random Access Memory (DRAM) basic etching performance and profile control; and 5) charge damage evaluation. It is demonstrated that one can control the etching uniformity and profile in advanced gate etching, and reduce the leakage current by varying the synchronous pulsed plasma parameters. Moreover, it is shown that synchronous pulsing has the promise of significantly reducing the electron shading effects compared with source pulsing mode and continuous-wave mode. The synchronous pulsed plasma paves the way to a wider window of operating conditions, which allows new plasma etching processes to address the large number of challenges emerging in the 45-nm and below technologies.

Self-consistent simulation of very high frequency capacitively coupled plasmas

A two-dimensional plasma model that includes the full set of Maxwell equations is used to understand the physics of very high frequency capacitively coupled plasmas. The effect of radio frequency (RF) source power, inter-electrode gap and gas mixture (Ar, Ar/SF6, Ar/CF4) on the plasma characteristics is investigated. The computational results show that the plasma spatial profile is influenced by both electrostatic and electromagnetic effects. The electrostatic power deposition is stronger at the electrode edges due to electric field enhancement at corners. Therefore, when the electrostatic effects are dominant, the plasma density peaks off-axis. Due to a standing electromagnetic wave in the chamber, the electron density peak moves to the chamber center under conditions where electromagnetic effects become strong. Inductive heating due to the radial electromagnetic electric field can also influence the plasma spatial profile. The relative importance of electromagnetic and electrostatic effects is found to be a function of the RF source power, the inter-electrode gap and the plasma electronegativity. While the electron density peaks on-axis at a low source power, inductive power deposition at higher source powers shifts the electron density peak towards the electrode edge. Electrostatic power deposition makes the plasma more uniform at smaller inter-electrode gaps. Due to a lower electron density and a larger applied RF potential, electrostatic effects become more dominant in electronegative discharges.

Effect of simultaneous source and bias pulsing in inductively coupled plasma etching

Pulsed rf plasmas show promise to overcome challenges for plasma etching at future technological nodes. In pulsed plasmas, it is important to characterize the transient phenomena to optimize plasma processing of materials. In particular, it is important to evaluate the effect of the ion energy and angular distribution (IEAD) functions during pulsing on etching of nanoscale features. In this work, the impact of simultaneous pulsing of both source and bias in an inductively coupled plasma on plasma characteristics and feature profile evolution is discussed using results from a two-dimensional reactor scale plasma model coupled to a Monte Carlo based feature profile model. Results are discussed for an Ar∕Cl2 gas mixture which is typically used for poly-Si etching. The consequences of duty cycle, pulse shape, and the phase lag between source and bias power pulses on discharge characteristics, IEADs to the wafer, and feature profile evolution are discussed. The low plasma density during the initial period of t...

Self-consistent electrodynamics of large-area high-frequency capacitive plasma discharge

Capacitively coupled plasmas (CCPs) generated using high frequency (3–30 MHz) and very high frequency (30–300 MHz) radio-frequency (rf) sources are used for many plasma processing applications including thin film etching and deposition. When chamber dimensions become commensurate with the effective rf wavelength in the plasma, electromagnetic wave effects impose a significant influence on plasma behavior. Because the effective rf wavelength in plasma depends upon both rf and plasma process conditions (e.g., rf power and gas pressure), a self-consistent model including both the rf power delivery system and the plasma discharge is highly desirable to capture a more complete physical picture of the plasma behavior. A three-dimensional model for self-consistently studying both electrodynamic and plasma dynamic behavior of large-area (Gen 10, >8 m2) CCP is described in this paper. This model includes Maxwell’s equations and transport equations for charged and neutral species, which are coupled and solved in th...

Control of plasma uniformity in a capacitive discharge using two very high frequency power sources

Very high frequency (VHF) capacitively coupled plasma (CCP) discharges are being employed for dielectric etching due to VHF’s various benefits including low plasma potential, high electron density, and controllable dissociation. If the plasma is generated using multiple VHF sources, one can expect that the interaction between the sources can be important in determining the plasma characteristics. The effects of VHF mixing on plasma characteristics, especially its spatial profile, are investigated using both computational modeling and diagnostic experiments. The two-dimensional plasma model includes the full set of Maxwell equations in their potential formulation. The plasma simulation results show that electron density peaks at the center of the chamber at 180 MHz due to the standing electromagnetic wave. Electrostatic effects at the electrode edges tend to get stronger at lower VHFs such as 60 MHz. When the two rf sources are used simultaneously and power at 60 MHz is gradually increased, the ion flux be...

Effects of interelectrode gap on high frequency and very high frequency capacitively coupled plasmas

Capacitively coupled plasma (CCP) discharges using high frequency (HF) and very high frequency (VHF) sources are widely used for dielectric etching in the semiconductor industry. A two-dimensional fluid plasma model is used to investigate the effects of interelectrode gap on plasma spatial characteristics of both HF and VHF CCPs. The plasma model includes the full set of Maxwell’s equations in their potential formulation. The peak in plasma density is close to the electrode edge at 13.5MHz for a small interelectrode gap. This is due to electric field enhancement at the electrode edge. As the gap is increased, the plasma produced at the electrode edge diffuses to the chamber center and the plasma becomes more uniform. At 180MHz, where electromagnetic standing wave effects are strong, the plasma density peaks at the chamber center at large interelectrode gap. As the interelectrode gap is decreased, the electron density increases near the electrode edge due to inductive heating and electrostatic electron heating, which makes the plasma more uniform in the interelectrode region.Capacitively coupled plasma (CCP) discharges using high frequency (HF) and very high frequency (VHF) sources are widely used for dielectric etching in the semiconductor industry. A two-dimensional fluid plasma model is used to investigate the effects of interelectrode gap on plasma spatial characteristics of both HF and VHF CCPs. The plasma model includes the full set of Maxwell’s equations in their potential formulation. The peak in plasma density is close to the electrode edge at 13.5MHz for a small interelectrode gap. This is due to electric field enhancement at the electrode edge. As the gap is increased, the plasma produced at the electrode edge diffuses to the chamber center and the plasma becomes more uniform. At 180MHz, where electromagnetic standing wave effects are strong, the plasma density peaks at the chamber center at large interelectrode gap. As the interelectrode gap is decreased, the electron density increases near the electrode edge due to inductive heating and electrostatic electron hea...

Gas heating mechanisms in capacitively coupled plasmas

Capacitively coupled plasma (CCP) tools utilized for plasma etching of dielectric features utilize large amounts of power for processing. As a result, neutral gas heats up significantly during processing. The resulting gas density variations across the reactor can affect reaction rates, radical densities, plasma characteristics and uniformity within the reactor. In this paper, results from a two-dimensional computational investigation of an Ar/CF4 CCP discharge incorporating an energy equation solution for all ions and neutrals are discussed. The dominant neutral gas heating process is identified to be elastic collisions with ions while conduction is found to be the major mechanism of heat transport. Some species such as F and CF3 demonstrate higher temperatures than the feedstock gases owing to additional heating via charge-exchange reactions and/or Franck–Condon heating. Typical process parameters such as pressure, frequency of excitation, power and gas composition are varied to investigate their impact on gas temperature. At higher excitation frequency and/or pressure, increased elastic collisions with ions lead to greater heat generation. The heat generated per molecule of the radicals, however, decreases with increase in pressure leading to a decrease in gas temperature. The increase in neutral collision frequencies with pressure also results in the decrease in temperature difference between species in the plasma. As CF4 fraction increases, both the elastic collision cross-section and Franck–Condon heating sources increase, leading to higher gas temperatures.

Power dynamics in a low pressure capacitively coupled plasma discharge

A one-dimensional coupled particle-in-cell and fluid model is used to understand power dynamics at low gas pressures in a capacitively coupled Ar discharge. For the range of gas pressure (5?500?mTorr) and excitation frequency (30?120?MHz) examined, the electrons absorb power at the sheath edge during sheath expansion. Energetic electron beams are generated at the edge of the expanding sheath, which are responsible for plasma production and sustenance. These energetic electrons are able to reach the opposite sheath at low gas pressures and return some of their energy during deceleration in the sheath. As a result, peak electron density decreases significantly below 10?mTorr. Above 50?mTorr, peak electron density is relatively insensitive to pressure as beam electrons deposit most of their energy in the plasma bulk. Secondary electron emission is found critical for plasma sustenance at 30?MHz, while sheath electron heating is the dominant electron heating mechanism at higher frequencies.

Effect of resonance in external radio-frequency circuit on very high frequency plasma discharge

A fully electromagnetic plasma model for an asymmetric capacitively coupled plasma discharge is used to understand the interaction between the external radio-frequency (rf) distributed circuit and the plasma. The plasma is excited using a 150 MHz rf source connected to the top electrode, the bottom electrode is connected to a shorted transmission line, and the electrodes are separated from the chamber walls through dielectric rings. Under typical conditions, the electron density peaks in the center of the plasma chamber due to the standing electromagnetic wave and the rf current from the top electrode primarily returns through the bottom electrode. When the electrical length of the bottom transmission line is adjusted such that it presents a large (open-circuit) impedance at the plasma chamber interface, the rf return current shifts from the bottom electrode to the chamber wall. As a consequence, the peak in electron density also moves from the center of the chamber toward its outer periphery.

Recouping etch rates in pulsed inductively coupled plasmas

Pulsed rf plasmas are increasingly being employed for plasma etching at future technological nodes. Although the plasma uniformity usually improves with pulsing, the lower time-averaged power decreases the etch rate and the lower throughput is undesirable. It is therefore important to evaluate different strategies to restore higher etch rates while retaining the advantages of pulsed plasmas. In this work, the impact of varying pulsing modes in an inductively coupled plasma on plasma characteristics and feature profile evolution are discussed using the results from a two-dimensional reactor scale plasma model coupled to a Monte Carlo based feature profile model. Results are discussed for poly-Si etching in an Ar/Cl2 gas mixture. The consequences of source-only and bias-only pulsing modes on discharge characteristics, ion energy distributions (IEDs) to the wafer, and feature profile evolution are discussed. Although the etch depth rates were found to be higher for source-only pulsing compared to the synchro...