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Fig 1.) Visualization of the ECR plasma diffusing into the Cirrus reactor. Magnets at the walls confine the plasma to the field-free central volume of the chamber. The result is a plasma of exceptional uniformity.
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ECR Plasma Applications
The ECR effect occurs when magnetized electrons are excited with an electric field at resonance with the electron cyclotron frequency. This resonant absorption of microwave energy produces an efficient, high density plasma at pressures below 10 mtorr. In the Cirrus systems, the ECR plasma diffuses into a multipolar confinement volume, a field-free region where it achieves exceptional uniformity. This is in contrast with other high density plasmas that attempt to achieve uniformity by physical or magnetic shaping, resulting in narrow operating windows.
The Cirrus is the pre-eminent workhorse for process applications where precise control of ions and chemistry is required. Based on the technology of ECR, the Cirrus provides unparalleled results in three main areas:
- Low temperature CVD processes for SiO2, Si3N4, and DLC below 150
°C;
- Low damage etch processes for silicon and compound semiconductors; and
- High current, high bias etch processes for materials such as ceramics and platinum.
In each case, the independent control of ion generation, ion energy, and plasma chemistry provides flexibility for difficult applications.
Compound Semiconductors
Electro-optics and telecommunications technologies are driving the requirements for advanced III-V processing. These processes increasingly rely on the unique design of the Cirrus reactor for the independent control of ions and chemistry. The remote discharge of the ECR reactor generates an etching environment that produces volatile etch products without redeposition and with minimal ion damage to the wafer. The result is a gentle, controllable anisotropic etch process with profile control for materials such as GaAs, AlGaAs, InP, and InGaP.
Magnetic Disk Heads
Applications involving magnetic disk heads are growing rapidly with the increasing demands for high density storage in computers. Higher bit densities on hard disks are driving advanced read/write heads. These advances require the etching of aerodynamic features in Al2O3/TiC ceramic.
Combining a chlorine or fluorine chemistry with high ion current and high RF-induced DC self bias, the Cirrus produces a smooth, residue-free etch. High etch rates and a large processing area are achievable with NEXX Systems' unique multipolar plasma confinement chamber, ensuring increased productivity for manufacturing. The Cirrus can also be used to deposit the hard, uniform films required for lubrication and protection of disk heads.
Low Temperature PECVD
PECVD is a plasma initiated and thermally activated process. Free radicals formed in the plasma react with each other to form gas phase precursors of the film. These precursors then condense on the surface, where the heat of the substrate and/or energy imparted by impinging ions finish the reaction, densifying the film and driving off gaseous byproducts.
In conventional RFPECVD processes, temperatures up to 450 °C are required to achieve the desired film properties. The Cirrus is an enabling technology for deposition on temperature sensitive substrates where temperatures must be kept below 150 °C. The ECR plasma is highly efficient at dissociating the precursors, and the high ion current to the wafer densifies the film. The result is a film deposited below 150 °C, superior in properties to films deposited in conventional reactors at temperatures several hundred degrees higher.
Following are two application notes of interest:
“Silicon nitride films deposited at substrate temperatures <100° C in a permanent magnet electron cyclotron resonance plasma” by C. Doughty et al., JVSTA 17(5) Sep/Oct 1999. [108k]
“Low stress SiN films deposited by low temperature ECR PECVD” by R. DeVito and K. O’Donnell, Oct 2002 [948k]
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