The use of sputtering in order to depositing coatings on substrates is known in the art. For example, and without limitation, see U.S. Pat. Nos. 5,403,458; 5,317,006; 5,527,439; 5,591,314; 5,262,032; and 5,284,564, the disclosures of which are hereby incorporated herein by reference.
Sputter coating is typically known as an electric discharge type process which is conducted in a vacuum chamber in the presence of at least one gas. Typically, a sputtering apparatus includes a vacuum chamber(s), a power source, an anode, and one or more cathode targets which include a material used to create a layer in the coating system. When an electrical potential is applied to the cathode target, the gas forms a plasma which bombards the target causing particles of the material from the target to leave the target itself. This material, which has left the target, typically falls onto the substrate in order to help form the coating. When sputtering is conducted in the presence of a reactive gas, a reactive product of the target material and the gas forms on the substrate in order to help form the coating. Different types of sputtering targets may be used (e.g., planar targets, rotational cylindrical targets, etc.). Magnetron type sputtering is one such example of a sputtering which is commonly used in the art. In certain instances, rotatable sputtering targets may be used in C-MAG type magnetron sputtering systems.
FIG. 1 illustrates a conventional magnetron sputtering apparatus. The apparatus includes metallic walls 1 of the vacuum chamber in which sputtering is performed; and a cylindrical rotating target 3 that is supported by supports 5 so that the target is rotatable about axis 7. Gas is supplied into the sputtering chamber via gas supply 8, and the chamber is evacuated to a pressure less than atmospheric via vacuum pump(s) 10. Substrate (e.g., glass substrate) 9 is moved beneath the target 3 (via rollers or the like) as the target rotates. A plasma is created within the vacuum chamber by applying a voltage from power supply 12 to the sputtering target 3 which is negative relative to the walls 1 or the like which may be grounded. The plasma is positioned adjacent a sputtering zone of the target, such position being controlled by magnet(s) which is/are located in the target or at any other suitable location. As material is sputtered from the target 3, it falls onto substrate 9 there under in order to form the coating as is known in the art.
The material of a sputtering target to be sputtered onto a substrate is typically homogenous (i.e., only one type of sputtering material is provided per target). However, occasionally targets included multiple sputtering materials have been mentioned.
For example, U.S. Pat. No. 5,427,665 to Hartig et al. discloses a sputtering target including alternating strips on different sputtering materials around the target. These different materials each extend all the way around the periphery of the target, but are axially segmented from one another along the length of the target. The first material (e.g., Si) located in the center of the target has a high affinity for reactive gas, while the second material (e.g., Sn) located only at the axial ends of the cylindrical target have a low affinity for the reactive gas. However, the purpose of this target is not to deposit different materials on a substrate. In fact, given a single gas in the sputtering device, this target would be incapable of depositing an alternating layer stack on a substrate. Instead, the purpose of the different materials of the target in the '665 Patent is to cause the first material (Si) to be sputtered onto the substrate while the second material (Sn) is sputtered onto a diaphragm shield so that it does not reach the substrate (e.g., see the '665 Patent at col. 2, lines 17-23; and col. 5, lines 40-44).
U.S. Pat. No. 5,403,458, also to Hartig et al., is similar to the aforesaid '665 Patent in that it briefly mentions that strips of different materials may be provided (see col. 10, lines 18-21). However, these different strips of the '458 Patent are not for depositing alternating layers on a substrate. Instead, these different materials of the '458 Patent are a) target material, and b) dopant, respectively. Moreover, Hartig '458 does not disclose how the dopant strips are oriented on the target.
Repetitive multi-layer/superlattice coating structures have been reported in the art to exhibit desirable properties. For example, metallic superlattices may be used in x-ray optics and semiconductor devices. Ceramic nanoscale multi-layer structures such as TiN/VN, TiN/WN, TiN/AlN, TiN/NbN, TiAlN/CrN, etc. are characterized by desirable hardness, wear resistance, oxidation resistance and/or corrosion resistance. In addition, many optical band filters such as Rugate filters use repeated high/low index layers (e.g., titanium oxide (e.g., TiO2)/silicon dioxide) in the layer stack.
Conventionally, the aforesaid superlattice structures and/or alternating high/low index layer stacks have been sputter deposited where a single cathode target is used for each layer. Thus, the number of layers to be deposited dictates the number of sputter targets required. For example, if a repeating high/low index layer stack requires 30 layers (15 of the high index of refraction material, and 15 of the low index of refraction material), then at least 30 sputtering targets are required (at least 15 targets of the high index material, and at least 15 targets of the low index material). The high/low index targets are arranged in alternating fashion along the sputtering line. The use of such a large number of sputtering targets is not practical given the layer stack to be deposited, as it requires a very long sputter coater with many chambers/targets.
Thus, it will be apparent to those skilled in the art that there exists a need for a more efficient way in which to sputter deposit layers stacks that use repeated alternating high/low index layers, and/or multi-layer/superlattice coating structures.