Chemistry: electrical and wave energy – Apparatus – Coating – forming or etching by sputtering
Reexamination Certificate
2001-11-29
2004-09-07
McDonald, Rodney G. (Department: 1753)
Chemistry: electrical and wave energy
Apparatus
Coating, forming or etching by sputtering
C204S298060, C204S298090, C204S298110, C204S298160, C204S298190, C118S7230MP, C118S715000, C156S345330, C156S345370, C156S345380
Reexamination Certificate
active
06787010
ABSTRACT:
TECHNICAL FIELD
The present invention is generally directed to deposition of thin films and growth of bulk materials. In particular, the present invention is directed to non-thermionic, plasma-enhanced sputtering techniques.
BACKGROUND ART
A wide variety of techniques exist for depositing thin films onto substrates in order to achieve desirable properties which are either different from, similar to, or superior to the properties of the substrates themselves. Thin films are employed in many kinds of optical, electrical, magnetic, chemical, mechanical and thermal applications. Optical applications include reflective/anti-reflective coatings, interference filters, memory storage in compact disc form, and waveguides. Electrical applications include insulating, conducting and semiconductor devices, as well as piezoelectric drivers. Magnetic applications include memory discs. Chemical applications include barriers to diffusion or alloying (e.g., galling), protection against oxidation or corrosion, and gas or liquid sensors. Mechanical applications include tribological (wear-resistant) coatings, materials having desirable hardness or adhesion properties, and micromechanics. Thermal applications include barrier layers and heat sinks. Bulk materials can be used as substrates upon which thin films can be deposited and microelectronic and optical devices can be fabricated.
Thin-film techniques typically entail several sequential process steps. Generally, a source of film-forming material is supplied, the material is transported to the substrate, and deposition occurs on the substrate surface. The material transport step occurs in a contained environment such as a chamber containing a vacuum, one or more gaseous fluids, and/or a plasma medium. Deposition behavior is determined not only by the source and transport factors but also by deposition surface factors. Such surface factors include the substrate surface condition (e.g., surface roughness, contamination, degree of chemical bonding between the surface and the arriving material, and crystallographic or epitaxial parameters); the reactivity of the arriving material (e.g., the sticking coefficient, which provides an indication of the probability of arriving molecules reacting with the surface and becoming incorporated into the film); and the energy input (e.g., substrate temperature, positive-ion bombardment, and chemical reactions). The results of the deposition can be analyzed, and one or more process conditions can be modified as appropriate in order to obtain the specific film properties desired. Process control and monitoring steps are usually carried out at all key points along the process. Post-deposition annealing procedures can also be employed to activate grain growth, alter stoichiometry, introduce dopants, or deliberately cause oxidation.
Deposition processes are broadly delineated into “physical” vapor deposition (PVD) processes and “chemical” vapor deposition (CVD) processes, although some processes might better be characterized as being hybrids of PVD and CVD processes. The source of material supplied to the deposition system can be a solid, liquid, vapor, or gas. Solid materials must be vaporized in a PVD process in order to transport them to the substrate. Vaporization is accomplished either by employing a thermal technique (e.g., evaporation) or by providing an energetic beam of electrons, photons (e.g., laser ablation), or positive ions (e.g., sputtering). On the other hand, CVD techniques utilize gases, evaporated liquids, or chemically gasified solids as source materials. In both PVD and CVD processes, contamination is a critical factor during the source supply step, as well as in the transport and deposition steps. The source supply rate is also a critical factor, as film properties can vary with deposition rate and, in the case of compound films, with the ratio of elements supplied.
One common PVD process entails thermal evaporation, which is often accomplished by using a twisted-wire coil, a dimpled sheet-metal “evaporation boat,” or a heat-shielded crucible. In thermal evaporation, thermal energy alone (i.e., joule heating) is utilized to drive the evaporation, reaction and film structure development. On the other hand, several known deposition processes exist in which the primary source of energy can be characterized as being essentially “nonthermal.” In these “energy-beam” techniques, energy is delivered by electrons, photons or ions (usually positive ions) to vaporize the source material, activate the source material during transport, or modify film structure during deposition. Common energy-beam techniques used to carry out vaporization can be broadly categorized as electron-beam, cathodic-arc, anodic-arc, pulsed-laser, ion-beam sputtering, and glow-discharge sputtering processes. Clear differences exist between the first four techniques and the two sputtering techniques. In the first four techniques, electrons (via an electron beam), ions (via an arc) or photons (via a pulsed laser) are directed at the source material in a narrow beam having a diameter of approximately a few millimeters. Conversely, the ion beams and glow discharges employed in the sputtering techniques cover a much broader area. Additionally, the use of narrow beams leads to intense heating of the source material at the point of impact, so that the vaporization mechanism is thermal even though the energy input is non-thermal. By contrast, vaporization by sputtering involves direct momentum transfer from bombarding ions to the surface atoms of a relatively cool source material.
There are several advantages to using energy beams for vaporization as compared to joule-heated sources. First, virtually any material, no matter how refractory, can be vaporized. In the narrow-beam processes, this is a result of the very high energy density and surface temperature that is achieved. In sputtering, the advantage results from the fact that the bombarding ions have energies far exceeding chemical-bond strengths which typically are only a few electron volts (one electron volt, or 1 eV, will be understood as constituting the energy gain of a particle having one electronic charge upon passing through a potential drop of one volt). Second, in the cases of pulsed-laser evaporation and sputtering, the activated depth of source material can be in the range of only tens of nanometers, which results in stoichiometric (congruent) vaporization of multi-element materials, thereby assisting (albeit not necessarily guaranteeing) a stoichiometric deposit. Third, in all of the energy-beam processes, much of the vapor acquires energy well above the thermal energy of the surface of the source material, and this energy can greatly assist the deposition process. Atoms thermally evaporated by narrow energy beams acquire most of their energy by interaction with the beam in the vapor phase, while sputtered atoms have high energies at the time they leave the surface of the source material. In the case of ionized vapor, this energy can be further increased by accelerating ions toward the surface of the depositing film, which is accomplished by applying a negative bias to the substrate. Energy can also be directed at the deposition surface through the mechanism of either energetic-atom condensation or ion bombardment, which can result in significant improvement in film adherence and structure.
FIG. 1
illustrates the widely used parallel-plate plasma configuration, commonly known as a planar diode and generally designated
10
. Two electrodes, a cathode
12
and an anode
14
, are parallel to each other and spaced apart from each other by a distance or electrode gap L. Anode
14
can be at ground or alternatively driven with an RF bias source
16
and associated capacitor
16
A (shown in phantom), and cathode
12
is driven negative by a power supply
18
. A glow-discharge plasma
20
is generated between the two electrodes and confined by a grounded metal vacuum containment wall
22
. The bulk of plasma
20
floats above ground by the plasma potential, and has little voltage d
Cuomo Jerome J.
Williams N. Mark
Jenkins & Wilson & Taylor, P.A.
McDonald Rodney G.
North Carolina State University
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