Erik A. Edelberg

Modeling of SiO2 deposition in high density plasma reactors and comparisons of model predictions with experimental measurements

High-density-plasma deposition of SiO2 is an important process in integrated circuit manufacturing. A list of gas-phase and surface reactions has been compiled for modeling plasma-enhanced chemical vapor deposition of SiO2 from SiH4, O2, and Ar gas mixtures in high-density-plasma reactors. The gas-phase reactions include electron impact, neutral–neutral, ion–ion, and ion–neutral reactions. The surface reactions and deposition mechanism is based on insights gained from attenuated total reflection Fourier transform infrared spectroscopy experiments and includes radical adsorption onto the SiO2 surface, ion-enhanced desorption from the surface layer, radical abstractions, as well as direct ion-energy-dependent sputtering of the oxide film. A well-mixed reactor model that consists of mass and energy conservation equations averaged across the reactor volume was used to model three different kinds of high-density plasma deposition chambers. Experimental measurements of total ion densities, relative radical dens...

Silicon hydride composition of plasma-deposited hydrogenated amorphous and nanocrystalline silicon films and surfaces

In situ attenuated total reflection Fourier transform infrared spectroscopy was used to study the H bonding on the surfaces of a-Si:H and nc-Si:H during plasma enhanced chemical vapor deposition from SiH4/H2/Ar containing discharges. Well-resolved SiHx (1⩽x⩽3) absorption lines that correspond to the vibrational frequencies commonly associated with surface silicon hydrides were detected. During deposition of a-Si:H films using SiH4 without H2 dilution, the surface coverage was primarily di- and trihydrides, and there are very few dangling bonds on the surface. In contrast, during deposition of nc-Si:H using SiH4 diluted with H2, the amount of di- and trihydrides on the surface is drastically reduced and monohydrides dominate the surface. Furthermore, the vibrational frequencies of the monohydrides on nc-Si:H film surfaces match well with the resonant frequencies of monohydrides on H terminated Si (111) and Si (100) surfaces. The decrease of higher hydrides on the surface upon H2 dilution is attributed to i...

Effect of chamber wall conditions on Cl and Cl2 concentrations in an inductively coupled plasma reactor

The effect of chamber wall conditions on the Cl and Cl2 concentrations in a Cl2 discharge was studied in an inductively coupled plasma reactor. Cl and Cl2 mole fractions were determined using optical emission spectroscopy in conjunction with actinometry, while the state of the reactor walls was monitored using a surface probe that enables detection of films and adsorbates that deposit on these walls. Prolonged exposure of the chamber walls to a Cl2 plasma increases the Cl concentration in the discharge. This increase is due to the decreasing recombination probability of Cl atoms on the walls which with time are covered with a thin SiO2 film. The source of the SiO2 is the quartz dielectric window which is sputtered by ion bombardment. A SF6/O2 plasma etches the SiO2 film from the chamber walls and restores the chamber walls to a “clean” state. The Cl concentration in the reactor with these two different states of the wall conditions, under otherwise identical plasma operating conditions, was dramatically d...

Modeling of the sheath and the energy distribution of ions bombarding rf-biased substrates in high density plasma reactors and comparison to experimental measurements

In plasma etching and deposition processes, the energy distribution of ions incident onto the substrate strongly affects the surface reactions and the film deposition and etching rates. The magnitude and frequency of the rf-bias power applied to the substrate electrode determines the spatiotemporal variations of the sheath potentials and hence the energy distribution of the ions impinging upon the substrate. A self-consistent dynamic model of the sheath, capable of predicting ion energy distributions impinging on a rf-biased electrode, was developed. The model consists of equations describing the charge transport in the sheath coupled to an equivalent circuit model of the sheath to predict the spatiotemporal charge and potential distributions near the surface. Experimental measurements of the energy distributions of ions impinging on a rf-biased electrostatic chuck have also been made in a high density transformer coupled plasma reactor through Ar and Ne plasmas. The predicted ion energy distributions and sheath profiles are in very good agreement with the experimental measurements.

LUMINESCENCE FROM PLASMA DEPOSITED SILICON FILMS

We report the observation of room-temperature and low-temperature visible photoluminescence from nanocrystalline silicon (nc-Si) thin films produced by plasma-enhanced chemical vapor deposition (PECVD) through a gas discharge containing SiH4 diluted in Ar and H2. The nanocrystalline silicon films were characterized using transmission electron microscopy, spectroscopic ellipsometry, infrared and Raman spectroscopy, and were examined for photoluminescence. Luminescent films consisted of dense silicon nanocrystals that grew in a columnar structure with approximately 20%–30% void space dispersed inside the film. Aside from having small crystalline silicon regions, the structure of the nc-Si films is different than that of porous Si, another luminescent Si material generally produced by electrochemical anodization. Yet, the photoluminescence spectra of the thin nc-Si films were found to be similar to those observed from porous silicon. This similarity suggests that the same mechanism responsible for light emis...

Visible luminescence from nanocrystalline silicon films produced by plasma enhanced chemical vapor deposition

Thin nanocrystalline silicon (nc‐Si) films deposited by plasma enhanced chemical vapor deposition (PECVD) exhibited room‐temperature photoluminescence in the visible range of the electromagnetic spectrum. High resolution transmission electron microscopy revealed that the films are made of Si crystals with dimensions 2–15 nm. The photoluminescence spectra of the nc‐Si films were similar to the spectra observed from porous silicon produced by anodization and electrochemical dissolution of crystalline Si. This similarity suggests that the luminescence mechanism of nc‐Si films is similar to the mechanism of light emission from porous silicon. The ability to manufacture luminescent Si films by methods which are compatible with the current Si based technology, such as PECVD, can provide new possibilities in the realization of optoelectronic devices.

ENERGY DISTRIBUTION OF IONS BOMBARDING BIASED ELECTRODES IN HIGH DENSITY PLASMA REACTORS

A compact retarding field ion energy analyzer has been designed and built to measure the energy distribution of ions bombarding the wafer surfaces placed on radio frequency (rf) biased electrodes in high-density plasma reactors. The analyzer was used to measure the energy distribution of ions impinging on the rf-biased electrostatic chuck in a high-density transformer coupled plasma (TCP) reactor. The effects of TCP power, rf bias, gas composition, and ion mass on the ion energy distributions (IEDs) were demonstrated through Ar, Ne, Ar/Ne, O2 and CF4/O2 discharges. In the operating range studied, the average ion energy increased linearly with increasing rf bias while the ion flux remained constant indicating that independent control of ion flux and energy was achieved in the TCP reactor. Bimodal ion energy distributions resulting from ion energy modulation in the sheath were observed and multiple peaks in the IEDs measured in gas mixtures were identified as ions with different masses falling through the sheath.A compact retarding field ion energy analyzer has been designed and built to measure the energy distribution of ions bombarding the wafer surfaces placed on radio frequency (rf) biased electrodes in high-density plasma reactors. The analyzer was used to measure the energy distribution of ions impinging on the rf-biased electrostatic chuck in a high-density transformer coupled plasma (TCP) reactor. The effects of TCP power, rf bias, gas composition, and ion mass on the ion energy distributions (IEDs) were demonstrated through Ar, Ne, Ar/Ne, O2 and CF4/O2 discharges. In the operating range studied, the average ion energy increased linearly with increasing rf bias while the ion flux remained constant indicating that independent control of ion flux and energy was achieved in the TCP reactor. Bimodal ion energy distributions resulting from ion energy modulation in the sheath were observed and multiple peaks in the IEDs measured in gas mixtures were identified as ions with different masses falling through the s...

New diagnostic method for monitoring plasma reactor walls: Multiple total internal reflection Fourier transform infrared surface probe

Films and adsorbates that deposit on reactor walls during plasma etching and deposition affect the discharge properties such as the charged particle and reactive radical concentrations. A systematic study of this plasma–wall interaction is made difficult by a lack of diagnostic methods that enable one to monitor the chemical nature of the reactor wall surface. A new diagnostic technique based on multiple total internal reflection Fourier transform infrared (MTIR-FTIR) spectroscopy was developed to monitor films and adsorbates on plasma etching and deposition reactor walls with monolayer sensitivity. Applications of this MTIR-FTIR probe are demonstrated. Specifically, we use this probe to (i) detect etch products and films that deposit on the reactor walls during Cl2 plasma etching of Si, (ii) determine the efficacy of a SF6 plasma to clean films deposited on reactor walls during Cl2/O2 etching of Si, and (iii) monitor wafer-to-wafer etching reproducibility.

Compact floating ion energy analyzer for measuring energy distributions of ions bombarding radio-frequency biased electrode surfaces

A compact floating retarding-field ion energy analyzer and the accompanying electronics have been designed and built to measure the energy distribution of ions bombarding radio-frequency (rf) biased electrodes in high-density plasma reactors. The design consists of two main components, a compact retarding field vacuum probe and an integrated stack of floating electronics for providing output voltages, measuring currents and voltages and transmitting data to a computer. The operation and capabilities of the energy analyzer are demonstrated through ion energy distribution measurements conducted on a 4 MHz rf-biased electrostatic chuck in a 13.56 MHz high-density transformer coupled plasma (TCP) reactor. The analyzer is capable of operating while floating on several hundreds of volts of rf bias and at pressures up to 30 mTorr without differential pumping. The effects of pressure (2–30 mTorr), TCP power (500–1500 W), rf-bias power (0–800 W), gas composition, and ion mass on the ion energy distributions are de...

Effect of H2 dilution on the surface composition of plasma-deposited silicon films from SiH4

Abstract The surface composition of silicon films deposited from SiH 4 , Ar, and H 2 plasmas was studied using in situ attenuated total reflection Fourier transform infrared spectroscopy with emphasis on the effects of H 2 dilution. In the absence of H 2 , the surface is primarily covered with SiH 3 and SiH 2 . With heavy H 2 dilution, the surface is predominantly monohydride terminated with infrared absorption frequencies consistent with the presence of SiH on Si (100) and Si (111) surfaces.