Patent Application
20080011601
So that the manner in which the above recited features of the present invention can be understood in detail, a more particular description of the invention, briefly summarized above, may be had by reference to embodiments, some of which are illustrated in the appended drawings. It is to be noted, however, that the appended drawings illustrate only typical embodiments of this invention and are therefore not to be considered limiting of its scope, for the invention may admit to other equally effective embodiments.
To facilitate understanding, identical reference numerals have been used, where possible, to designate identical elements that are common to the figures. It is contemplated that elements disclosed in one embodiment may be beneficially utilized on other embodiments without specific recitation.
The present invention generally comprises a PVD apparatus and a PVD method. Extending an anode across the processing space between the target and the substrate may increase deposition uniformity on a substrate. The anode provides a path to ground for electrons that are excited in the plasma and may uniformly distribute the electrons within the plasma across the processing space rather than collect at the chamber walls. The uniform distribution of the electrons within the plasma may create a uniform deposition of material on the substrate. The anodes may be cooled with a cooling fluid to control the temperature of the anodes and reduce flaking. The anodes may be disposed across the process space perpendicular to the long side of a magnetron that may scan in two dimensions across the back of the sputtering target. The scanning magnetron may reduce localized heating of the anode.
The invention is illustratively described and may be used in a PVD system for processing large area substrates, such as a PVD system, available from AKT®, a subsidiary of Applied Materials, Inc., Santa Clara, Calif. However, it should be understood that the sputtering target may have utility in other system configurations, including those systems configured to process large area round substrates and those produced by other manufacturers.
As the demand for larger flat panel displays increases, so must the substrate size. With increasing substrate size comes various challenges. Among those challenges is uniform deposition. Electrons within the sputtering plasma are attracted to elements within the apparatus 100 that are grounded. Traditionally, the chamber walls 132 and the susceptor 112 or substrate support are grounded and thus, function as an anode in opposition to the sputtering target 102, which functions as the cathode.
The grounded chamber walls 132 functioning as an anode attract electrons from the plasma and hence, may tend to create a higher density of plasma near the chamber walls 132. A higher density of plasma near the chamber walls 132 may increase the deposition on the substrate near the chamber walls 132 and decrease the deposition away from the chamber walls 132. The grounded susceptor 112, on the other hand, also functions as an anode. The susceptor 112 may span a significant length of the processing space 158. In many cases, the susceptor 112 encompasses an area as large as the substrate. Thus, the susceptor 112 may provide a path to ground for electrons not only at the edge of the susceptor 112, but also at the middle of the susceptor 112. The path to ground at the middle of the susceptor 112 may balance out the path to ground at the edge of the susceptor 112 and the chamber walls 132 because each anode, be it the chamber walls 132 or the susceptor 112, may equally function as an anode and uniformly spread the plasma across the processing space 158. By uniformly distributing the plasma across the processing space 158, uniform deposition across the substrate may occur.
When the substrate is an insulating substrate (such as glass or polymer), the substrate is non-conductive and thus electrons do not follow through the substrate. As a consequence, when the insulating substrate substantially covers the substrate support, the substrate support does not provide sufficient anode surfaces near the center of the processing region 158. For large area substrates, such as solar panels or substrates for flat panel displays, the size of the substrate blocking the path to ground through the susceptor 112 may be significant. Substrates having an area as large as 1 square meter are not uncommon in the flat panel display industry. For a 1 square meter insulating substrate, a path to ground through the susceptor 112 is blocked for an area of 1 square meter. Therefore, the chamber walls 132 and the edges of the susceptor 112 that are not covered by the substrate are the only paths to ground for the electrons in the plasma. No path to ground exists near the center of the substrate. With a large area substrate, a high density plasma may form near the chamber walls 132 and the edge of the susceptor 112 that is not covered by the substrate. The high density plasma near the chamber walls 132 and the susceptor 112 edge may thin the plasma near the center of the processing region 158 where no path to ground exists. Without a path to ground near the center of the processing area 158, the plasma may not be uniform and hence, the deposition on the large area substrate may not be uniform.
To help provide uniform sputtering deposition across a substrate, an anode 134 may be disposed between the target 102 and the substrate (not shown). In one embodiment, the anode 134 may be bead blasted stainless steel coated with arc sprayed aluminum. In another embodiment, the anode 134 may be bead blasted. By bead blasting or arc spraying the anode 134, the anode 134 surface may be textured to capture material sputtered thereon and reduce any flaking or falling of material onto the substrate.
The anode 134 may be disposed a distance “A” from the target 102. The distance “A” may be small enough so as to reduce any shadowing of the substrate during deposition. The anode 134 may also be shaped to reduce any shadowing of the substrate and maximize deposition uniformity. The anode 134 may be sized to ensure that the anode 134 can support its own weight and the weight of the cooling fluid across the chamber. In one embodiment, the anode 134 may have a circular cross section. In another embodiment, the anode 134 may have an oblong cross section.
In one embodiment, one end of the anode 134 is mounted to the chamber wall 132 by a bracket 144 which may be coupled with a mounting ledge 146. As shown in
The other end of the anode 134 passes through the dark space shield 136 and the chamber wall 132. As shown in
The anode 134 provides a charge in opposition to the target 102 so that charged ions will be attracted thereto rather than to the chamber walls 132 which are typically at ground potential. By providing the anode 134 between the target 102 and the substrate, the plasma may be more uniform, which may aid in the deposition.
When a substrate enters the apparatus 100, lift pins 114 rise up to receive the substrate. The lift pins 114 then lower and the susceptor 112 raises to receive the substrate. As the susceptor 112 raises to a processing position, the susceptor 112 encounters the shadow frame 118 and raises the shadow frame 118 up to a processing position with shadow frame lift pins 120. The shadow frame 118 reduces the amount of material that may deposit on exposed areas of the susceptor 112. When not raised, the shadow frame 120 rests on an under shield 122. The under shield 122 may be coupled with a cooling manifold 124.
Because the shadow frame 122 moves up and down, any material that deposits on the shadow frame 122 may flake off. To reduce flaking of material from the shadow frame 122, an additional shield 116, which is substantially stationary, may be positioned within the apparatus 100 to shield the shadow frame 122. Shield 116 is coupled with the cooling manifold 124. The cooling manifold 124 controls the temperature of the shield 116. Expansion and contraction of the shield 116 from temperature changes may cause flaking within the apparatus 100 and contaminate the substrate. By controlling the temperature of the shield 116, expansion and contraction of the shield 116 may be reduced. The cooling manifold 124 rests on a manifold shelf 126 and may be cooled by a cooling fluid that passes through cooling channels 128. The cooling fluid may be any conventional cooling fluid known to one of ordinary skill in the art.
By being within the processing space 158, material may deposit on the anode 134 during sputtering. Material deposited on the anode 134 may also be a source of contamination. During a sputtering process, the temperature may be significantly higher than during downtime. Changing the temperature of the anode 134 may lead to expansion and contraction of the anode 134 and hence, flaking of material deposited thereon. Additionally, the plasma temperature may be high enough to increase the temperature of the material deposited on the anode 134 to approach or reach its melting point. When the material deposited on the anode 134 reaches its melting point, the material may melt and hence, drip off of the anode 134 and onto the substrate. The flaking and dripping may be sources of contamination for the substrate.
To reduce flaking and material dripping, the anode 134 may be cooled. Cooling the anode 134 may control the temperature of the anode 134 and hence, reduce expansion and contraction of the anode 134 during processing and downtime. Additionally, cooling the anode 134 may reduce the material dripping. The cooled anode 134 cools any material that deposits on the anode 134 so that the temperature of the material does not approach its melting point. When the temperature of the material deposited on the anode 134 does not approach its melting point, dripping may be reduced.
A cooling assembly 150 may be coupled to the apparatus 100 by a bracket 152.
While the invention has been described above with reference to a target 102, it is to be understood that multiple targets may be present. For example, large area targets necessary to sputter deposit on large area substrates can be quite expensive. Therefore, multiple targets with small gaps therebetween may be spaced across a backing plate. The multiple targets are smaller than one large area target, but may essentially function as a single large area target. Examples of such targets are disclosed in United States Patent Publication No. 2007/0056850, U.S. patent application Ser. No. 11,424,467, filed Jun. 15, 2006, and U.S. patent application Ser. No. 11/424,478, filed Jun. 15, 2006, all of which are hereby incorporated by reference in their entirety.
The targets 102 that may be used are not limited to square shaped targets. Target strips and target tiles are examples of other suitable targets 102 that may be used to practice the invention. For non-square shaped targets 102, the anodes 134 may span the processing space 158 in the direction of the longest edge of the target 102. In another embodiment, the anodes 134 may span the processing space in a direction perpendicular to the longest edge of the target 102.
Similar to
To prevent localized heating of the anode and to ensure uniform target erosion, the magnetron assembly may be scanned across the backing plate.
For large area substrates, it is beneficial to provide a path to ground in the middle of the processing area so that uniform deposition may occur. An anode that spans the processing area between the target and the substrate may provide the path to ground for electrons within the plasma to increase uniform plasma distribution across the processing space and hence, uniform deposition on the substrate. Cooling the anode may reduce flaking and material dripping.
While the foregoing is directed to embodiments of the present invention, other and further embodiments of the invention may be devised without departing from the basic scope thereof, and the scope thereof is determined by the claims that follow.
This application claims benefit of U.S. provisional patent application Ser. No. 60/807,391 (APPM/11277L), filed Jul. 14, 2006, which is herein incorporated by reference.
| Number | Date | Country | |
|---|---|---|---|
| 60807391 | Jul 2006 | US |
