Patent Application
20080110752
A portion of the disclosure of this patent document contains material that is subject to copyright protection. The copyright owner has no objection to the facsimile reproduction by anyone of the patent disclosure, as it appears in the Patent and Trademark Office patent files or records, but otherwise reserves all copyright rights whatsoever.
The present invention relates to sputtering systems and methods. In particular, but not by way of limitation, the present invention relates to systems and methods for high-energy sputtering using highly-conductive return conductors.
Sputtering is used in several industries to deposit and adhere material to substrates. For example, sputtering is used extensively in semiconductor, glass, and display manufacturing. Sputtering is well-known in the art and is only described briefly herein. Those of skill in the art are very familiar with this process.
In basic sputtering, a target material is placed inside a process chamber. This target material is often referred to as the “cathode,” and the two terms are used interchangeable in this document. A power supply applies a negative potential to the target, which causes the target to emit electrons. These electrons move toward a return path—called an “anode.” The anode typically includes any grounded surface, including the inner walls of the process chamber.
As the electrons move from the target toward the anode, they pass through an inert gas introduced into the process chamber. The electrons energize the inert gas, thereby forming a plasma. Ions from the plasma are attracted to the negatively charged target and when they impact the target, small particles of the target are ejected (sputtered). Most of these sputtered particles are deposited on and adhere to a nearby substrate. Some of the particles also adhere to the anode surfaces.
To complete the electrical circuit, the electrons must move from the target through the gas to the anode and back to the power supply. This return path includes two portions: inside the chamber and outside the chamber. The path inside the chamber typically includes the electrons returning along the anode surfaces internal to the process chamber, then along the process chamber walls, and then back through the shortest path of resistance. This shortest path of resistance is typically the path around the insulator of the cathode and/or the dark space shielding. The path outside the chamber typically includes the outer walls of the chamber (or a cathode box attached to the outer walls of the chamber) and a connection to the power supply.
For the purposes of this document, the term “power supply” is used broadly. It encompasses stand-alone power supplies, power supplies integrated with impedance matching networks, power supplies operated in conjunction with impedance matching networks, AC, DC, pulsed DC, RF power supplies, switching power supplies, etc.
These typical return paths inside the process chamber are problematic for high-power/high-frequency power supplies because the return paths are too resistant to electron flow. First, skin effects force the electrons to flow along the surface of the inside of the process chamber, thereby reducing the effectiveness of the return path. And as the frequency of the power supply increases, this skin effect becomes more pronounced and reduces the effectiveness of the return path to unacceptable levels. Moreover, the resistance of the inner portions of the process chamber are further increased by the manufacturing process for the process chamber. These chambers are generally stainless steel and are roughed by the use of a bead blast. Rough surfaces present far more resistance to electron flow than do smooth surfaces, and stainless steel is a poor conductor.
The primary problem with high resistance is that it causes a voltage differential to develop at certain points in the process chamber. This voltage differential can cause arcing and localized plasma formation. These localized plasmas cause sputtering of internal components of the process chamber and even the process chamber itself. These unwanted sputtered particles are deposited as impurities on the substrate. Further, the unwanted sputtering can become so extreme that it destroys the process chamber.
One solution to the resistance problem is to form the process chamber out of a highly-conductive material such as gold or silver. But given the large size of most commercially-used sputtering systems, it is impractical to use these expensive materials on a large scale.
Present sputtering technology does not work adequately with all power supplies and in particular not with high-energy/high-frequency power supplies. Accordingly, a system and method are needed to address the shortfalls of present technology and to provide other new and innovative features.
Exemplary embodiments of the present invention that are shown in the drawings are summarized below. These and other embodiments are more fully described in the Detailed Description section. It is to be understood, however, that there is no intention to limit the invention to the forms described in this Summary of the Invention or in the Detailed Description. One skilled in the art can recognize that there are numerous modifications, equivalents and alternative constructions that fall within the spirit and scope of the invention as expressed in the claims.
The present invention can provide a system and method for sputtering. In one exemplary embodiment, the present invention can include a vacuum chamber; a gas box secured to the inner surface of the vacuum chamber; a plurality of return conductors engaged with the gas box, the plurality of return conductors extending through the vacuum chamber; and a plurality of seals configured to engage corresponding ones of the plurality of return conductors, the plurality of seal configured to maintain the vacuum inside the vacuum chamber.
Various objects and advantages and a more complete understanding of the present invention are apparent and more readily appreciated by reference to the following Detailed Description and to the appended claims when taken in conjunction with the accompanying Drawings wherein:
Referring now to the drawings, where like or similar elements are designated with identical reference numerals throughout the several views, and referring in particular to
The power supply 105 is connected to the target 110, which is located inside the process chamber 115. During operation, an inert gas is release around the target 110, preferably through the use of a gas box 120 that helps distribute the gas evenly. The gas box 120 typically partially encloses the target 110. The portion of the gas box 120 between the target 110 and the substrate 125 is open so that sputtered particles can be deposited on the substrate.
When power is applied to the target 110, electrons escape and excite the surrounding gas, thereby forming the plasma 130. These electrons seek a return path 135, which as previously described, generally involves the inner portions of the process chamber 115.
The return conductors 145 are typically formed of highly conductive materials such as copper. They can be mechanically attached to a flat-bottomed gas box or they can be integrally formed with the gas box. Moreover, the number, shape, and location of the return conductors can be varied. For example, the return conductor could be rectangular, square, cylindrical, etc. And in one embodiment, two or more return conductors are connected to a plate. This plate can then be attached to the gas box.
During operation, electrons from the target 110 pass through the inert gas and return to the power supply 105 using the return conductors 145. By increasing the amount of surface area in the return path, the return conductors 145 significantly reduce the resistance, thereby preventing arcing and unintended sputtering. These return conductors 145 provide such an improvement in the return path that full scale commercial sputtering systems can be developed and operated with RF power sources.
This embodiment also includes conductive strips 170 placed on the outside of the process chamber. Typically, the process chamber is manufactured from stainless steel, which is a poor conductor. The conductive strips can be formed of highly conductive material such as copper and provide a mechanism for moving electrons from the return conductors 160 to the power supply. Alternatively (or in addition), the return conductors can be connected directly to the power supply by highly-conductive strips or wires.
This embodiment also includes a fastener 175 for mechanically attaching the return conductor 160 to the process chamber 155. For illustration purposes, only one fastener 175 is illustrated. But those of skill in the art understand that more fasteners can be used. Fasteners are known in the art and not discussed in detail herein.
Referring now to
In conclusion, the present invention provides, among other things, a system and method for improved operation of sputtering devices. Those skilled in the art can readily recognize that numerous variations and substitutions may be made in the invention, its use and its configuration to achieve substantially the same results as achieved by the embodiments described herein. Accordingly, there is no intention to limit the invention to the disclosed exemplary forms. Many variations, modifications and alternative constructions fall within the scope and spirit of the disclosed invention as expressed in the claims.
