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Hollow Cathode-Enhanced RF Sputtering System

IP.com Disclosure Number: IPCOM000060165D
Original Publication Date: 1986-Mar-01
Included in the Prior Art Database: 2005-Mar-08
Document File: 3 page(s) / 41K

Publishing Venue

IBM

Related People

Bumble, B: AUTHOR [+5]

Abstract

The present system consists of an existing RF sputtering system which has been modified by the addition of a critically placed hollow cathode. Hollow cathode operation has been described in detail in the literature [*]. The function of the hollow cathode is to emit energetic electrons into the plasma of the RF device. Those emitted electrons are energetic enough to cause additional ionization of the background gas, and hence form a denser plasma than was possible with simply the applied RF voltage alone. This denser plasma formed by the hollow cathode electrons causes additional ion bombardment of the RF target cathode and increased sputtering and deposition rates. The system consists of a primary electrode 11 which is sometimes called the cathode. A counter electrode 12 is usually present, but not absolutely necessary.

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Hollow Cathode-Enhanced RF Sputtering System

The present system consists of an existing RF sputtering system which has been modified by the addition of a critically placed hollow cathode. Hollow cathode operation has been described in detail in the literature [*]. The function of the hollow cathode is to emit energetic electrons into the plasma of the RF device. Those emitted electrons are energetic enough to cause additional ionization of the background gas, and hence form a denser plasma than was possible with simply the applied RF voltage alone. This denser plasma formed by the hollow cathode electrons causes additional ion bombardment of the RF target cathode and increased sputtering and deposition rates. The system consists of a primary electrode 11 which is sometimes called the cathode. A counter electrode 12 is usually present, but not absolutely necessary. The primary electrode is driven by an RF generator 13 of 13.56 megahertz. Power from this generator is coupled into the primary electrode 11 through a matching network 14, which balances the impedances in the circuit for maximum power. The electrodes are enclosed in a vacuum system 15, which is grounded, and has sufficient pumping capability to produce a vacuum below 0.1 millitorr and operating pressure for the RF system in the 10 - 100 millitorr range. All other power supplies and gauges necessary for operation of the vacuum system have been deleted for clarity. The placement or position of the hollow cathode 19 in the hollow cathode-enhanced RF system is critical. A diagram of one configuration is shown in the figure. The hollow cathode 19 in this case is located in the center of the upper electrode 12, and protrudes through a small hole into the plasma region between the two plates. The hollow cathode is biased negative of the walls of the grounded chamber, which in this case serve as anodes for the hollow cathode discharge. Electrons are emitted from the hollow cathode due to the attractive positive potential of the walls, which forms a sheath near the surface of the hollow cathode. There is a net electron current radially from the hollow cathode to the walls. This current serves to provide a relatively uniform discharge in the region between the plates. This net radial component to the electron current flow from the hollow cathode to the surrounding walls is the critical aspect to the hollow cathode position within the RF system. The hollow cathode requires a gas source for operation 18. If the magnitude of this flow is small compared with the background gas pressure, then there will be no pressure gradients across the target surface, and no gradient in the plasma density. Experimentally, this constraint is easy to satisfy as the hollow cathode can operate at <1 millitorr and typical discharges will be 5 - 100 millitorr. Other positions of the hollow cathode or multiple cathodes are possible. For example, the hollow cathode electrons need not enter through the upper...