Chemistry: electrical and wave energy – Processes and products – Coating – forming or etching by sputtering
Reexamination Certificate
1999-09-29
2001-07-10
Huff, Mark F. (Department: 1756)
Chemistry: electrical and wave energy
Processes and products
Coating, forming or etching by sputtering
C204S298200, C204S298190, C204S298070, C204S298120, C204S298130
Reexamination Certificate
active
06258217
ABSTRACT:
FIELD OF THE INVENTION
The present invention is directed to a method and apparatus for depositing metal and metal-reactive gas coatings onto a substrate.
BACKGROUND OF THE INVENTION
The sputter deposition of insulating films, particularly Aluminum Oxide (Al
2
O
3
), is conventionally accomplished by radio frequency (“RF”) diode sputtering from a ceramic target. While somewhat effective, the RF diode sputtering process is quite slow with deposition rates of approximately 500 Angstroms/Minute. With such low deposition rates batch loading is required for economic machine throughput.
Batch processing involves coating multiple substrates in a single deposition run. However, batch processing has long been recognized by the semiconductor industry as less than optimum because of several factors. First, batch processing requires the use of larger targets, and thus much greater (and more expensive) power supplies are required. Second, there is an increased risk that wafer-to-wafer deposition uniformity will vary. Third, if there is a problem during a deposition run, multiple wafers will be lost. Thus, with batch processing, greater compromises must be made to distribute process results over the batch.
Single substrate processing, on the other hand, offers the benefits of better wafer-to-wafer deposition control and reduced losses in non-useable wafers due to deposition run problems. However, a commercially viable deposition rate would have to be increased by a substantial amount over the rate achievable in conventional RF diode sputtering systems. For example, a three times increase in deposition rate over the conventional RF diode approach would yield an acceptable rate for commercial applications. This increased rate can be achievable by utilizing a reactive sputtering process. In one reactive sputtering technique, an Aluminum target is placed in proximity to the presence of Oxygen to create an Al
2
O
3
film as it is being deposited. The rate increase is realized because the sputter rate for metallic Aluminum is many times faster than for Aluminum Oxide and more conventional DC type power supplies can be used.
In addition to deposition rate, another important processing parameter is the deposition uniformity, which directly impacts the number of usable devices yielded from each substrate. An acceptable commercial deposition full range uniformity (of the coating layer thickness over the entire substrate) is <2% and is thus a major parameter in the source design. To achieve this kind of uniformity a large area sputter target would be needed.
To realize increased deposition rates for depositing metal films, conventional “magnetron” designs have been developed. These magnetron systems typically include a source, a metal target (typically Aluminum (Al) acting as a cathode), an electrode, and a substrate in close proximity to the electrode. A sputter gas medium, such as Argon (Ar) is introduced in the vacuum chamber and is ionized. The Ar
+
ions accelerate towards the negatively charged target and collide with the target to release Al atoms that are deposited on the substrate.
One conventional magnetron design utilizes a stationary magnet to generate a magnetic field that is used to keep electrons from escaping the target vicinity before ionizing a number of Ar atoms which sputter the target. However, use of stationary magnets creates a “trenching” of the target which results in a non-uniform erosion of the target. This is disadvantageous because utilizing a non-uniform erosion pattern increases the risk that the deposited film will be non-uniform.
Other conventional sputter source designs include a rotating magnet to provide both high rate and large area coverage. These rotating magnet designs are typically offset (and are thus asymmetrical) with respect to the rotating axis and come in a variety of shapes, such as heart-shaped (cartioid) and apple-shaped rotating magnets. Examples of such magnet designs are provided in U.S. Pat. Nos. 4,995,958; 5,194,131; and 5,248,402. However, these conventional rotating magnet designs were developed almost exclusively for metal film deposition, and as such were not ideally suited for reactive sputtering.
Thus, what is needed is a magnet design, sputtering source and process that provides an acceptable quality film (in terms of film uniformity) on a substrate, where the deposition rate is sufficiently fast to allow single substrate processing (as opposed to batch processing) in order to eliminate the time and control problems stemming from the repeated venting of the substrate chamber under the conventional batch processing technique. Automated handling with a single substrate processing technique is desirable for its reduction in processing time, as well as providing for process control benefits.
SUMMARY OF THE INVENTION
In view of the foregoing, it would be desirable to provide a magnet array for a rotating magnetron sputtering system. A plurality of magnets are disposed on a plate. The plurality of magnets is arranged such that a magnetic path is formed. The shape of the magnetic path is a double-lobe structure that includes first and second lobes that are symmetrical about an axis in the plane of the plate that intersects a center of rotation of the plate. In one embodiment, the magnets are arranged in several rows. A first row of magnets has a double-lobe structure that corresponds to the first and second lobes of the magnetic path. Second and third rows of magnets are arranged in the shape of a rings inside the first and second lobes of the magnetic path magnetic path. The lobe structure is designed to maximize the erosion of the perimeter region of a sputtering target. For example, the lobe structure can be circular or elliptical in shape.
In view of the foregoing it is also desirable to provide a sputtering system for depositing a coating on a substrate. The sputtering system includes a metal sputtering target that is coupled to a power source, where the sputtering target shaped as an annulus.
The sputtering system also includes a rotatable magnet array disposed over the sputtering target. The magnet array can be shaped as in the embodiments described above. With this magnet array, the resulting magnetic path generates a substantially uniform erosion of the sputtering target.
In view of the foregoing, it is further desirable to provide a method for the high rate deposition of a metal-reactive gas material onto a substrate. To achieve a high deposition rate, a magnet array, such as the magnet arrays described in the preceding embodiments, is rotated in proximity to a metal sputtering target. The rotation of the magnetic path thereby generates a substantially uniform erosion of the sputtering target. A reactive gas is introduced proximate to a surface of the substrate to react with sputtered metal atoms released from the sputtering plate. The resulting metal-reactive gas coating deposits on the surface of the substrate at a high rate.
Further features and advantages of the invention, as well as the structure and operation of various embodiments of the invention, are described in detail below with reference to the accompanying drawings.
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Fournier Paul R.
Johnson David
Kenney Mark D.
Lateef Abdul
Lishan David G.
Chacko-Davis Daborah
Huff Mark F.
Plasma-Therm, Inc.
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