Chemistry: electrical and wave energy – Processes and products – Coating – forming or etching by sputtering
Reexamination Certificate
2000-06-15
2003-04-22
McDonald, Rodney G. (Department: 1753)
Chemistry: electrical and wave energy
Processes and products
Coating, forming or etching by sputtering
C204S192130, C204S298120, C204S298130
Reexamination Certificate
active
06551470
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention (Technical Field)
The present invention relates to targets and clamps for physical vapor deposition and similar processes.
2. Background Art
Information on physical vapor deposition and other similar processes are available from a wide variety of sources. For example, the Institute of Advanced Manufacturing Sciences (1111 Edison Drive Cincinnati, Ohio 45216-2265) provides such information to the public, for example, through its Web site (www.iams.org). The goal of most PVD and similar processes is to form a layer of material on a substrate. The formed layer is often referred to as a coating. In general, PVD coatings are between approximately 2 microns and approximately 5 microns. PVD processes encompass several different types of deposition processes in which atoms are removed by physical means from a source and deposited on a substrate. For example, processes that use thermal energy and/or ion bombardment are PVD processes that convert a source material into a vapor, which can later condense on a substrate. Thus, PVD processes typically involve evaporation of a first condensed phase to form a gas or vapor phase. The gas or vapor phase is then transported to or otherwise brought into contact with a substrate. The gas or vapor phase then condenses on the substrate to form a second condensed phase. It is important to note that the first and/or second condensed phases optionally comprise a solid phase and/or a liquid phase.
In a typical PVD process a substrate or “workpiece” is placed in a vacuum chamber and a very high vacuum is drawn. The vacuum chamber space is heated to between approximately 400° F. and approximately 900° F., depending on the specific process. Where plasma etching is used, plasma is created from an inert gas such as argon to further clean the surface of the workpiece. Next, the source or coating metal is forced into a gas or vapor phase.
Three methods of forcing a source metal, alloy or compound thereof are commonly used: evaporation, sputtering, and ion plating. Evaporation comprises use of a high-current electron beam or resistive heaters to evaporate source material from, for example, a crucible. The evaporated material forms a cloud that fills the deposition chamber and then condenses onto the substrate to produce the desired film. In such a process, atoms take on a relatively low energy state (0.2 to 0.6 eV) and the deposited films, as a result, are not excessively adherent or dense. In some instances, deposition of a substantially uniform coating may require complex rotation of the substrate since the vapor flux may be localized and directional.
Sputtering is another method wherein the surface of the source material is bombarded with energetic ions, usually in an ionized inert gas environment comprising, for example, argon. The physical erosion of atoms from the coating material that results from this bombardment is known as sputtering. The substrate is positioned as to intercept the flux of displaced or sputtered atoms from the target. Sputtering deposits atoms with energies in the range of 4.0 to 10.0 eV onto a substrate. While sputtering is, in general, more controllable than evaporation it can be a rather inefficient way to produce vapor. For example, energy costs for sputtering processes are typically 3 to 10 times that of evaporation processes.
Another method is ion plating, which can produce superior coating adhesion by bombarding the substrate with energy and during deposition process. In ion plating processes, particles accelerate towards the substrate and arrive with energy levels up to hundreds of electron volts. These atoms sputter off some of the substrate material resulting in a cleaner, more adherent deposit. This “cleaning” process continues as the substrate is coated. The film growth is assured when the deposition rate is faster than the sputtering or cleaning rate. In general, high gas pressure results in greater scattering of the vapor and a more uniform deposit on the substrate.
An important variation on these processes involves the introduction of a gas such as oxygen or nitrogen into the chamber to form oxide or nitride deposits, respectively. These reactive deposition processes are used to deposit films of material such as titanium nitride, silicon dioxide, and aluminum oxide.
Overall, PVD processes results in a thin, uniform coating that is much less likely to require machining after application. The specifics of the aforementioned three variations of PVD processes are by no means exclusive. For example, some PVD processes use laser ablation or pulsed laser deposition to release a controlled amount of target material in the form of a gas. Also consider that accelerated plasma can be used in the PVD process to deliver a heat pulse to a target to release a controlled amount of gaseous target material.
Physical vapor deposition, and similar deposition processes are used, for example, in the fabrication of thin film materials, such as, but not limited to, fabrication of thin films for “compact discs” (CDs). For example, sputtering processes are often involved in the coating of a semiconductor wafer or other substrate mounted within a processing chamber. In a typical semiconductor manufacturing, sputtering process, an inert gas is introduced into a processing chamber containing a target and an electric field is applied to ionize the inert gas. Positive ions of the inert gas bombard the target material and dislodge atoms from the target, which are subsequently deposited onto the wafer or other substrate in the form of a thin film. In many instances, the target is held within the deposition chamber by a device called a sputter-coating source. Often, the sputter-coating source has an electrical circuit for biasing the target material structure with a negative voltage, either DC for conductive targets, or AC having a radio frequency for non-conductive targets, so the target will attract positive ions from the plasma of an inert gas. To cool the sputter-coating source, a cooling circuit is often provided for the target structure. In addition, magnetic fields are useful for containing and enhancing the plasma.
In a semiconductor manufacturing, sputtering process, positive ions extracted from the plasma are accelerated to a high kinetic energy. These high kinetic energy ions strike the surface of the target structure whereby a portion of the kinetic energy is transferred to the target atoms of the target or source material. Target atoms that obtain sufficient energy to overcome their respective binding energy escape from the target surface and are ejected into the vacuum chamber. Objects, such as a substrate or a semiconductor wafer, placed in the line-of-sight of the target source are then coated by the atoms ejected from the target surface. Of course, it may be possible to “bend” the line-of-sight through application of electromagnetic and/or other energy.
In the prior art it is common to bond the metal or metal alloy target to a copper backing plate. An indium-based bonding technology is generally used to attach the target to the backing plate. The backing plate is required in order to support the target in the chamber in which the sputtering takes place. Often, materials used to bond the target to the backing plate contribute to contamination during the deposition process. In addition, bonding materials can interfere with the maintenance of electrical and/or thermal conductivity of the backing plate and the target. The deficiencies are dependent on the type of bonding material used; however, to date no single bonding material has emerged that does not introduce some process limitation. For example, some bonding agents have operating temperature restrictions. If the temperature of the bonded source exceeds a temperature restriction, then the bond may break and/or bonding material may enter the gas or vapor phase and consequently deposit onto a substrate. Therefore, a need exists for better bonding technology and/or altogether elimination or drastic minimization of the need for bonding
Academy Precision Materials
Fain Katy C.
McDonald Rodney G.
Peacock Deborah A.
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