Patent Application
20050178653
This invention relates to a method for elimination of sputtering into the backing plate of a sputter target/backing assembly in a sputtering apparatus using a novel backing plate with a groove disposed on an area compatible to and superimposed on the intended erosion groove of the sputter target.
Cathodic sputtering is widely used for the deposition of thin layers of material onto desired substrates. Basically, this process requires a gas ion bombardment of a target having a face formed of a desired material that is to be deposited as a thin film or layer on a substrate. Ion bombardment of the target not only causes atoms or molecules of the target materials to be sputtered, but imparts considerable thermal energy to the target. This heat is dissipated beneath or around a backing plate that is positioned in a heat exchange relationship with the target. The target forms a part of a cathode assembly that, together with an anode, is placed in a vacuum chamber filled with an inert gas, preferably argon. A high voltage electrical field is applied across the cathode and the anode. The inert gas is ionized by collision with electrons ejected from the cathode. Positively charged gas ions are attracted to the cathode and, upon impingement with the target surface, these ions dislodge the target material. The dislodged target material traverses the evacuated enclosure and deposits as a thin film on the desired substrate, which is normally located close to the anode.
In addition to the use of an electrical field, increasing sputtering rates have been achieved by the concurrent use of an arch-shaped magnetic field that is superimposed over the electrical field and formed in a closed loop configuration over the surface of the target. These methods are known as magnetron sputtering methods. The arch-shaped magnetic field traps electrons in an annular region adjacent to the target surface, thereby increasing the number of electron-gas atom collisions in the area to produce an increase in the number of positive gas ions in the regions that strike the target to dislodge the target material. Accordingly, the target material becomes eroded in a generally annular section of the target face, known as the erosion groove.
In a conventional target cathode assembly, the target is attached at a single bonding surface to a nonmagnetic backing plate to form a parallel interface in the assembly. The backing plate is used to provide a means for holding the target assembly in the sputtering chamber and to provide structural stability to the target assembly. Also, the backing plate is normally water-cooled to carry away the heat generated by the ion bombardment of the target. Magnets are typically arranged beneath the backing plate in well-defined positions to form the above-noted magnetic field in the form of a loop or tunnel extending around the exposed face of the target.
However, a localized erosion groove is generally generated in the sputter target. The rotation of a magnet assembly can cause the erosion over a wider area of the target. There is a risk that the entire thickness of the target can be exhausted at the bottom of the groove and thus contaminate the substrate, e.g., wafer, with the material of the backing plate. It has been suggested that wax is placed in a groove but the sputtering of the wax would contaminate the substrate. To prevent this target blow out, it was suggested that it would be better to only use about forty percent of the sputter target in order to avoid the contamination problem.
It is an object of the present invention to provide a method for eliminating the sputtering onto the backing plate of a sputter target/backing plate assembly using a novel backing plate design.
It is another object of the present invention to provide a sputtering apparatus with a novel backing plate that will eliminate sputtering into the backing plate when operating.
It is another object of the present invention to provide a novel design for a backing plate for a sputter target/backing plate assembly.
One embodiment of the present invention provides a method for preventing the sputtering into the backing plate of a sputter target/backing plate assembly in a sputtering apparatus comprising the steps:
When an opening or hole is formed in the erosion groove of the sputter target, the tubular channel connecting the backing plate groove to the atmosphere will allow air to enter the chamber and cause the sputtering apparatus to fault out or shut down. Thus upon the initial opening in the erosion groove, the sputtering apparatus will shut down, permitting maximum use of the sputter target material. Various sensing means can be employed to sense the opening in the erosion groove such as a cryo pump that will heat up and close a gate valve as soon as atmosphere enters the chamber. Upon shut down, the chamber can vent slowly while a new sputter target is installed and then the process can quickly be restored.
Preferably the groove would be an annular shape with a radial width between about 1 and about 2 inches, most preferably between about 1 and about 1½ inches; and a depth of the groove could be between about ⅛ and about 3/4 inch, preferably between about ¼ and about 1/2 inch; and more preferably between about ⅜ and about 1/2 inch. Preferably the area of the opening in the tubular channel is about 0.00019 and about 0.0123 square inch and more preferably between about 0.00019 and about 0.00077 square inch.
Another embodiment of the invention is a sputter target/backing plate assembly having a novel backing plate with at least one groove disposed in an area on its bonding surface that is compatible to and superimposed on the intended erosion groove of the sputter target and at least one tubular channel connecting the groove to the atmosphere.
Another embodiment of the invention is a magnetron apparatus comprising:
As used herein, groove could be a complete annular groove, any segment of an annular groove or any shaped groove.
To achieve good thermal and electrical contact between the sputter target and the backing plate, these members are commonly attached to each other by use of soldering, brazing, diffusion bonding, mechanical fastening or epoxy bonding.
The metals used for the sputter target and backing plate may be any of a number of different metals, either in pure or alloy form. For example, the sputter target may be made of titanium, aluminum, copper, molybdenum, cobalt, chromium, ruthenium, rhodium, palladium, silver, osmium, iridium, platinum, gold, tungsten, silicon, tantalum, vanadium, nickel, iron, manganese, germanium, or an alloy thereof. The backing plate could be made of copper, aluminum, titanium, or alloys thereof. Preferred sputter target/backing plate metal pairings include a titanium target bonded to an aluminum backing plate; a titanium target bonded to an copper backing plate; a titanium target bonded to a titanium backing plate; a molybdenum target bonded to a copper backing plate; a cobalt target bonded to a copper backing plate; a chromium target bonded to copper backing plate; and a target formed of a precious metal such as ruthenium, rhodium, palladium, silver, osmium, iridium, platinum or gold, bonded to a copper backing plate. If a titanium-tungsten alloy is used, the alloy preferably includes about 10% to 15% titanium by weight.
Although the drawings have been described in conjunction with a disc-shaped sputter target/backing plate assembly, it will be readily apparent to one of ordinary skill that the method may be used to bond sputter targets and backing plates having any of a number of different shapes and sizes.
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While the present invention has been illustrated by the description of an embodiment thereof, and while the embodiment has been described in considerable detail, it is not intended to restrict or in any way limit the scope of the appended claims to such detail. Additional advantages and modifications will readily appear to those skilled in the art. The invention in its broader aspects is therefore not limited to the specific details, representative assembly and method shown and described. Accordingly, departures may be made from such details without departing from the scope or spirit of applicant's general inventive concept.
