Coating processes – Direct application of electrical – magnetic – wave – or... – Plasma
Reexamination Certificate
2000-02-01
2002-04-09
Dang, Thi (Department: 1763)
Coating processes
Direct application of electrical, magnetic, wave, or...
Plasma
C427S571000, C427S577000, C118S7230MP, C118S7230HC, C118S7230ER
Reexamination Certificate
active
06368678
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to systems and methods for processing electrically floating substrates, either single sided or two-sided, using plasmas created through generated ions and, more particularly, to processing systems and methods for controlled treatment of substrate surfaces.
BACKGROUND OF THE INVENTION
Commercial plasma sources are used for both controlled deposition onto and etching from surfaces for a wide variety of industrial applications, especially semiconductor, optical, and magnetic thin film processing. The plasma formed by such sources generates reactive neutral and ionic species which can chemically and/or physically interact with surfaces to deposit or remove material.
In many processes, the use of energetic ions from plasma sources can result in the deposition of materials with unique properties or allow the etching of surfaces under conditions which would not otherwise be effective. A method for processing substrates in a plasma generally includes an ion source mounted in a vacuum chamber in which the substrate is present. A gas with specific chemical properties is supplied to the ion source for ionization. The plasma generated is a mixture of selected reactive neutral and ionic chemical species as well as energetic electrons. The energy of the ionic species interacting with the surface depends upon plasma electrical properties, the electrical potential of the substrate and chamber pressure. In the prior art, the energy of ions bombarding the substrate is controlled by means of the bias applied to the substrate. In the present work there is disclosed an alternative wherein the substrate is electrically floating and acquires a net charge thereby establishing the potential of the substrate. The ion energy is determined by the difference between the plasma potential and the potential at the surface of the substrate for which there is zero net current. The floating potential of the substrate is controlled in accord with the present invention.
For a wide variety of plasma based processes a critical parameter for the treatment of a substrate is the kinetic energy of the ion(s) intercepting the substrate. The ion kinetic energy is a probabilistic function of several variables characterizing the plasma, such as the pressure, temperature, the specific plasma gas, ion source parameters and the like. The potential of the substrate is a major contributing variable to the kinetic energy. For the case of a conducting substrate, this potential may be controlled by direct connection to an appropriate power source, as commonly practiced in the prior art. In the extreme case of a dielectric substrate, such a procedure can not produce a uniform constant potential over the surface of the substrate. As described herein, the present invention is directed to any situation wherein direct coupling to a power source will not suffice to control the substrate potential or such electrical coupling to the substrate is otherwise undesirable. The present invention is not limited to a perfect dielectric substrate, nor is it limited to the specific processes which are disclosed herein as exemplary exploitation of the invention
In some applications, it is desirable to process both sides of a substrate simultaneously. This is typical in the deposition of thin layers of various materials in the manufacture of magnetic hard disks used in magnetic memory systems. In this case, ion sources are positioned on opposite sides of the disk. However, ion sources which utilize an anode for establishing a plasma potential tend to exhibit plasma instability and oscillation when two such sources are operated simultaneously in a processing chamber. Such unstable behavior does not permit predictable ion generation and process stability. Prior co-pending application Ser. No. 076,971 addressed this problem by a time division multiplex of depositions by the respective ion sources thereby obtaining symmetrical coatings of the respective surfaces of the substrate. Also, it has proven difficult to coat thin films to the specifications satisfying the requirements of a protective film on a hard disk, for example, for computer data storage applications. Thinner coatings permit the head to fly closer to the magnetic domains at the surface of the disk as to permit an increase in Arial density of recorded information. In depositing overcoatings of the magnetic surface, the coating should have sufficient hardness, density, and adhesion as well as practical qualities in the finished disk, including high deposition rates and low numbers of resulting macroscopic particles on the surface. Accordingly, there is a need for improved substrate processing systems and methods wherein ion sources may operate in a stable manner in a processing chamber and wherein the properties of the deposited layers may be improved for their intended purpose.
Co-pending applications referenced above, taught the advantage accruing from differential biasing of substrate and chamber walls whereby the deposits on the chamber walls were characterized by low internal stresses resulting from a lower ion energy whereas the thin film material concurrently deposited on the substrate possessed desirable characteristics of hardness, density and adhesion resulting from deposits from ions of higher kinetic energy relative to the substrate.
These same practical requirements noted above are appropriate to optical as well as magnetic media. For example if a protective coating is desired for an optical substrate, uses of the disk require that coatings that are deposited be deposited with the desired hardness, density and adhesion at a high rate while extremely thin and that variations through the presence of varying particles be minimized.
SUMMARY OF THE INVENTION
According to a first aspect of the invention, a novel substrate processing system is provided. The substrate processing system comprises a processing chamber, an electrically floating substrate holder positioned in the chamber, a gas source for supplying a process gas to the processing chamber, at least one ion source located in the processing chamber and a power source for applying various voltages to the ion source or sources (in the event more than one source is present), and to also energize other surfaces of the chamber and a controller for regulating the duty cycle of the time dependent electron source portion of each ion source. Each ion source ionizes the process gas to produce ions for processing a substrate disposed on the substrate holder. Each ion source has a cathode and an anode. Each ion source also produces sufficient electron flux of appropriate energy distribution to produce a net negative charge accumulation on the substrate in the presence of an active plasma, to further lower the substrate potential. The power source energizes the one or more cathodes of the ion source or sources as well as the one or more anodes. In the event that more than one ion source is being used, the power source energizes the ion sources in a time multiplexed manner such that only one of the ion sources is energized at any time.
The controller senses chamber pressure through a pressure sensor and also monitors such electrical parameters as electron source emission current and anode and cathode potentials (of each ion source). By controlling these parameters, a desired substrate potential can be maintained.
The energy and density of electrons emitted by the cathode determine the net charge accumulation on the substrate, thereby controlling the substrate potential. The energy spectra of the electrons emitted by the cathode is controlled by the voltage difference between the anode and cathode, while the density of electrons emitted by the cathode is determined by the emission current (rate of electrons leaving the cathode) and the transport of electrons to the wall. In order to obtain a significant range of substrate potentials, some form of electron confinement is required, either with the use of magnetic fields (such as multipole fields) or electrostatic fields (cathode potential equal to
Bluck Terry
Rogers James H.
Berkowitz Edward
Cole Stanley Z.
Dang Thi
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