Chemistry: electrical and wave energy – Processes and products – Coating – forming or etching by sputtering
Reexamination Certificate
2000-07-14
2002-12-03
VerSteeg, Steven H. (Department: 1753)
Chemistry: electrical and wave energy
Processes and products
Coating, forming or etching by sputtering
C204S192120, C204S298070, C204S298110, C204S298120, C204S298200, C204S298220, C204S298260, C204S298280
Reexamination Certificate
active
06488824
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates generally to physical vapor deposition (PVD) coating systems and processes, and more particularly to sputtering machines utilizing magnetrons operated in a manner which produces high deposition rates with excellent process control and long term operating stability. The design of such machines and processes is intended to make it useful for depositing metallic, electrically insulating (dielectric) and semiconducting films on a variety of substrates. Products benefiting from this technology include but are not limited to computer recording heads, flat panel displays, integrated circuits, computer memory disks, and a variety of coated glass products.
2. Brief Description of the Prior Art
The methods commonly used for depositing thin film coatings in vacuum generally can be classified as physical vapor deposition (PVD) or chemical vapor deposition (CVD) processes. PVD methods can be divided into evaporation (thermal energy source) and sputtering (plasma energy source). Both evaporation and sputtering have enjoyed successful application in various product lines. Evaporation has been used mostly for coating relatively small substrates. Some examples of high tech products include eyeglasses, filters, optical windows of many types, lenses, and laser optics. These products rely heavily on dielectric coatings for their functionality. Large evaporative coating machines are used for less sophisticated metallic coatings on rolls of substrate. Typical products include food packaging, decorative coatings, and the surface coating (corrosion treatment) of rolls of steel.
The sputtering phenomenon was recognized before evaporation, but evaporation technology was developed first because sputtering deposition rates were initially so low that it was not considered useful. A familiar example of low sputtering rate is the slow erosion of the tungsten filaments of ordinary incandescent light bulbs. They are very slowly sputtered by the argon gas used to fill the bulb to protect the hot filament from oxidation. The material removal rate is so slow that only a slight discoloration is noticed on the inside of the glass envelope after many hours of use. The early development of sputtering technology used a simple cathode and anode (diode) placed in a vacuum system with the cathode formed from the metal to be sputtered. Direct current (DC) in the range of 1,000 to 20,000 volts was the most commonly used power source. The process was able to produce an opaque metal coating on glass (a mirror) in about an hour to several hours depending upon the metal used. A description of the early sputtering process is given by J. Strong in “
Procedures in Experimental Physics
” copyrighted in 1938.
Sputtering became a more commercially viable process with the invention of the planar magnetron, U.S. Pat. No. 4,166,018 issued to Chapin and entitled “Sputtering Process and Apparatus”. This patent described a sputtering apparatus in which a magnetic field is formed adjacent to a planar sputtering surface with the field comprising arching lines of magnetic flux over a closed loop erosion region on the sputtering surface. A key enabling feature of the device was that the magnetic field lines penetrated the target material. The erosion region took the form of an annular erosion zone over the target material. The annular erosion zone is referred to, among those skilled in the art, as the “racetrack” because of its elongated shape on a rectangular planar magnetron. On round planar magnetrons, the “racetrack” usually has a circular shape, but it can have other shapes as dictated by the design of the magnet array so long as the racetrack is a closed loop. The magnetrons were almost always operated with DC power, and the phrase “DC Magnetron Sputtering” became the way the process was usually referred to. The erosion process caused heating in the annular erosion zone, which had to be removed by cooling the target material either directly or indirectly with water.
Industrial use of DC magnetron sputtering for the deposition of metallic films increased during the late 1970's and early 1980's. Large sputtering machines were built to coat solar heat reducing reflective films on windows for large commercial buildings and for other applications. For large substrates, it was superior to evaporation for controllability and uniformity. And, although the deposition rates were not as high as for evaporation, sputtering had become an economically useful process. Initially, in the erosion zone, early magnet arrays created a relatively sharp cross-section in the target material. A large metal target plate would quickly “burn through,” resulting in very poor utilization of the material. Increased target life was achieved (i) by improving the design of the magnet array to widen the erosion zone on the surface of the target, (ii) by increasing the magnetic field strength to operate with thicker targets, and (iii) by mechanisms which moved the arrays to widen the erosion zone during operation. U.S. Pat. No. 5,262,028 issued to Manley and entitled “Planar Magnetron Sputtering Magnet Assembly” is an example of an improved design for the magnet array to widen the erosion zone. U.S. Pat. No. 5,417,833 issued to Harra et al and entitled “Sputtering Apparatus Having a Rotating Magnet Array and Fixed Electromagnets” is an example a circular planar magnetron with a rotating magnet array to improve target utilization.
Another approach to improving the utilization of the target material was taught in U.S. Pat. No. 4,356,073 issued to McKelvey. The target material was formed into a straight (constant diameter) tube, which was rotated around its cylindrical axis with internal racetrack magnets that were held fixed with respect to the substrate. In this embodiment the target material (the tube) becomes thinner as the process proceeded and no “burn through” in the erosion zone occurs. Its initial use was for the large scale coating of metal films on architectural glass by DC magnetron sputtering. The magnetron coated only one side of the glass substrate in the horizontal position. Later U.S. Pat. No. 4,445,997 again issued to McKelvey disclosed another rotatable sputtering magnetron in which the target tube was contoured longitudinally to match the geometry of a substrate with the shape of an automobile windshield. This magnetron was also designed for use in the horizontal position. In U.S. Pat. No. 4,466,877 McKelvey describes a pair of rotatable cylindrical magnetrons mounted horizontally and spaced in a parallel relationship to each other such that the sputtered flux directed inwardly and downwardly from each is focused on the same region of the substrate. Further details of this dual embodiment are given in an article by Shatterproof Glass Corporation entitled “Rotatable Magnetron Sputtering Source”,
Solid State Technology
, April 1986. Two important points from the article are first, the magnetrons are rotated at speeds from 1 to 12 RPM, and second, the horizontal mounting for sputtering downward on glass causes the target cooling water to be fed through two rotating seals in vacuum, causing reliability problems and limiting rotation speeds.
In addition to the sputtering of metal films, DC reactive magnetron sputtering has been developed for the deposition of insulating (dielectric) and semiconducting coatings; in particular, for the deposition of the oxides and nitrides of metals. In reactive sputtering, the inert working gas is usually argon and the added reactive gas is often oxygen and/or nitrogen. The coating of dielectric materials can be accomplished by RF sputtering of the dielectric material itself used as the target. However, in both RF diode and RF magnetron modes the deposition rates are very low. Despite the low rates, this form of sputtering is still used in the production of thin film recording heads and integrated circuits. DC reactive magnetron sputtering of insulating films has the potential advantages of higher deposition rates and lower costs, but good
Hollars Dennis R.
Petersen Carl T.
Rosenblum Martin P.
Hamrick Claude A. S.
Oppenheimer Wolff & Donnelly LLP
Raycom Technologies, Inc.
VerSteeg Steven H.
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