Characteristics of an Electron Cyclotron Resonance Plasma Source for the Production of Active Nitrogen Species in III-V
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Internet Journal o f
Nitride S emiconductor Research
Volume 2, Article 46
Characteristics of an Electron Cyclotron Resonance Plasma Source for the Production of Active Nitrogen Species in III-V Nitride Epitaxy M. Meyyappan NASA Ames Research Center This article was received on November 25, 1997 and accepted on December 11, 1997.
Abstract A simple analysis is provided to determine the characteristics of an electron cyclotron resonance (ECR) plasma source for the generation of active nitrogen species in the molecular beam epitaxy of III-V nitrides. The effects of reactor geometry, pressure, power, and flow rate on the dissociation efficiency and ion flux are presented. Pulsing the input power is proposed to reduce the ion flux.
1. Introduction The nitride family of materials cover an energy gap range of 1.9 - 6.2 eV and exhibit high surface acoustic velocity, thermal conductivity, and high temperature stability. A wide variety of applications for the nitrides has been advocated: UV detectors, UV and visible LEDs, laser diodes for read-write applications, Bragg reflectors and wave guides, negative electron affinity cold cathodes, and transistors for high temperature operation. Potential also exists for miniaturization of on-board data storage for future generation unmanned space crafts, detection of chemical species with absorption bands in the blue/UV range, and cockpit displays. Molecular beam epitaxy (MBE) is one of the techniques to grow nitride layers with desirable electrical, structural and luminescent characteristics. This approach needs a source of active nitrogen species, and electron cyclotron resonance (ECR) plasma source has been popular in the nitride community [1] [2] [3] [4] [5] [6]. ECR source is widely used in silicon integrated circuit fabrication to deposit or etch semiconductor and insulating materials. It provides plasma densities of the order of 10 11 cm-3 which is two orders of magnitude higher than that possible with radio frequency (rf) capacitive plasma sources. Such a high plasma density enables high rates of generation of active neutral species for materials processing applications. However, a large flux of ions may not be desirable for some applications, particularly for the growth of GaN [1], [2]. Hence, the nitride community is interested in large fluxes of active nitrogen species while keeping the flux of ions low. In this article, a model for the ECR nitrogen source is used to investigate the effects of various system parameters on the dissociation efficiency and ion densities.
2. Analysis The operation of an ECR source is extremely complex and characterized by a strong coupling of various features: power coupling, magnetic field-microwave interaction, plasma generation, plasma heating, rarefied gas flow, generation and transport of active species, and interaction of various species with walls and wafers. Kinetic models such as particle-in-cell techniques to study the physics of plasma sources are complex. Recently, simple zero-dimensional models have been used to analyze high d
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