Kallol Bera

Effects of design and operating variables on process characteristics in a methane discharge: a numerical study

A self-consistent two-dimensional radio frequency capacitively coupled glow discharge model has been developed in cylindrical coordinates for a methane discharge using a fluid model. The objective of the study is to identify the effects of design and operating variables of the reactor on the process characteristics such as the deposition rate, uniformity and the quality of the diamond-like-carbon film. The simulations provide insights to charged species dynamics and investigate their effects on the plasma process for a depositing methane discharge. The model includes continuity equations for electrons and positive and negative ions, and energy equation for electrons. Swarm data as a function of electron energy are provided as input to the model. The model predicts the electron density, ion density, and their fluxes and energies to the cathode. The roles of electrons, dominating ions and radicals in a capacitively coupled discharge are investigated. The radical and neutral densities in the discharge are calculated using a gas phase chemistry model. The diamond-like-carbon thin-film deposition rate is predicted using surface chemistry model. The gas phase chemistry model considers diffusion of radicals and neutrals along with creation and loss terms. The surface deposition/etching process involves adsorption-desorption, adsorption layer reaction, ion stitching, direct ion incorporation, etching and carbon sputtering. A systematic parametric study of plasma processing has been performed to identify process parameters to obtain better film deposition/etching on a wafer. The present work shows how plasma equipment simulation can be used for the practical investigation and optimization of a plasma-assisted chemical vapour deposition process. The simultaneous treatment of plasma dynamics and surface processes enables a very precise prediction of the process characteristics in terms of the film deposition rate, uniformity and the quality as functions of discharge control parameters and the reactor geometry.

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...

Inductively coupled radio frequency methane plasma simulation

A self-consistent two-dimensional radio frequency inductively coupled glow discharge model has been developed in cylindrical coordinates using a fluid model. The objective of the study is to provide insight into charged species dynamics and investigate their effects on plasma process for a methane discharge. The model includes continuity and energy equations for electrons and continuity, momentum and energy equations for positive and negative ions. An electromagnetic model that considers the electric field due to the space charge within the plasma and due to inductive power coupling is also incorporated. For an inductively coupled methane discharge we expect to find higher fluxes of ions and radicals to the cathode, and hence a higher deposition/etch rate for a high-density plasma. The independent control of ion energy to the cathode in an inductively coupled discharge will facilitate control on film deposition/etch rate and uniformity on the wafer. Swarm data as a function of the electron energy are provided as input to the model. The model predicts the electron density, ion density and their fluxes and energies to the cathode. The radical and neutral densities in the discharge are calculated using a gas phase chemistry model. The diamond-like-carbon thin-film deposition/etch rate is predicted using a surface chemistry model. The gas phase chemistry model considers the diffusion of radicals and neutrals along with creation and loss terms. The surface deposition/etching process involves adsorption-desorption, adsorption layer reaction, ion stitching, direct ion incorporation and carbon sputtering.

Control of Plasma Uniformity Using Phase Difference in a VHF Plasma Process Chamber

Very high frequency (VHF) capacitively coupled plasma sources are widely used for semiconductor manufacturing processes. Uniform plasma can be difficult to achieve at VHF for different load conditions (pressure, power, gas mixture electronegativity, etc.). This paper discusses how voltage phase difference between top and bottom electrodes can be used to control plasma uniformity above the wafer.

Effects of reactor pressure on two-dimensional radio-frequency methane plasma: a numerical study

A self-consistent two-dimensional radio-frequency glow discharge model has been developed for methane gas using a fluid model. The objective of the study is to provide insights into charged-species dynamics and investigate their effects on deposition in a polyatomic gas discharge. Swarm data as a function of electron energy are provided as input to the model. The necessary dc bias for the discharge is also predicted consistently such that the cycle-averaged current to the powered electrode becomes zero. The predictions provide a comprehensive understanding of the various processes in methane discharges found in plasma-assisted chemical vapour deposition (PACVD) reactors for the deposition of carbon films. The effects of discharge pressure on discharge variables are identified and presented in the paper.

Simulation of Thin Carbon Film Deposition in a Radio‐Frequency Methane Plasma Reactor

Two‐dimensional radio‐frequency methane plasma simulations have been carried out. The simulations consider discharge physics, gas phase chemistry, and surface deposition. The objectives of the study are to provide insights to species dynamics and investigate their effects on the deposition process for a polyatomic depositing gas discharge under the operating conditions of an experimental reactor. The model predictions of the electron density profile and self‐generated dc bias compare well with the experimental results. The temporal and spatial variations of plasma variables are also obtained for real reactor operating condition. The gas phase chemistry and surface deposition model predictions of the axial variations of and radical densities are also compared with experimental data. The and radicals and positive ion fluxes to the cathode are used for the prediction of the carbon thin film deposition rate on the wafer.

Frequency optimization for capacitively coupled plasma source

Design of an all-in-one (main etch, PR ash and clean) dielectric etch chamber requires independent control of plasma generation from ion energy. Plasma simulation has been performed for a capacitively coupled discharge to study frequency effect on electron density, power deposition, and dissociation fraction. Simulation results demonstrate that plasma production efficiency enhances with increase in frequency while energy of the bombarding ions diminishes. A very high frequency source has been developed to generate high density plasma while radio frequency bias has been used to control ion energy. As illustrated, the etch rate for a dual damascene trench etch process increases, while damage due to ion bombardment is reduced. The dissociation fraction is well behaved to provide necessary corner protection. High-frequency source was used to achieve better performance for dual damascene trench etch process.

Two-dimensional radio-frequency methane plasma simulation: comparison with experiments

Plasma variables are predicted using a glow discharge physics model and compared with experimental data obtained from plasma assisted chemical vapor deposition (PACVD) reactors. The present study provides insights to charged species dynamics and their effects on deposition in a polyatomic gas (methane) discharge. Swarm data as a function of electron energy are provided as input to the model. The necessary DC bias for the discharge is also predicted such that the cycle-averaged current to the powered electrode becomes zero. The simulations are performed for the operating conditions of two different experimental reactors. The model predictions of electron density, self-generated DC bias, and power requirement compare very well with the experimental results. The model predictions of axial and radial variations of plasma density also compare well with the experimental data. The radial and axial variations of plasma variables in the reactors are also presented.

Plasma-Profile Control Using External Circuit in a Capacitively Coupled Plasma Reactor

Very high frequency (VHF) capacitively coupled plasma (CCP) sources offer several benefits, including low plasma potential, high electron density, and controllable dissociation. However, standing electromagnetic waves can make the spatial structure of VHF plasmas a sensitive function of operating conditions and reactor geometry. This paper discusses how the profile of VHF CCPs can be controlled using an external circuit that modifies the electrical boundary conditions. A 2-D plasma model with external circuit has been used for this study, where networks of passive circuit elements can be connected to different electrodes in the reactor. Plasma simulations have been performed for several combinations of capacitors and inductors. It is found that the external circuit can be used to change the radio-frequency current return path, thereby modifying the plasma profile. In general, the plasma is pulled toward the electrode with an inductive impedance and pushed away from the electrode with a capacitive impedance. These changes in plasma profile are related to the relative voltage and their phase on different electrodes.

Plasma impedance in a narrow gap capacitively coupled RF discharge

Capacitively coupled reactors with narrow gap spacings are extensively used for plasma enhanced chemical vapor deposition (PECVD) processes in the semiconductor industry. An understanding of the plasma impedance is important for efficient coupling of the source power to the plasma. The plasma impedance can change based on operating conditions as the structure of the discharge changes. The plasma impedance and power requirement are calculated for different RF potential. Images of the electron density distribution, and the electron and ion density profiles in the well-resolved sheath are also presented to provide better insight of the plasma behavior.