Patent Application
20080067058
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 monolithic sputtering target assembly for depositing material onto large area substrates. The sputtering target assembly may comprise both the sputtering target and the backing plate in one monolithic structure. By having the backing plate and sputtering target as a monolithic structure, bonding is not necessary. Additionally, cooling channels may be drilled into the monolithic structure so that cooling fluid may flow within the sputtering target assembly without the need for a separate cooling assembly resting on back of the sputtering target assembly.
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. An exemplary system in which the present invention can be practiced is described in U.S. patent application Ser. No. 11/225,922, filed Sep. 13, 2005, which is hereby incorporated by reference in its entirety.
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 assembly 104, 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. 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 balances 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, will 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 substrate substantially covers the substrate support, the substrate support does not provide sufficient anode surfaces. 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 as large as 1 meter by 1 meter are not uncommon in the flat panel display industry. For a 1 meter by 1 meter 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. With a large area substrate, a high density plasma may form near the chamber walls 132 and the edge of the susceptor 112 that are 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.
An anode 134 may be placed between the target assembly 104 and a substrate (not shown) to help provide uniform sputtering deposition across the substrate. In one embodiment, the anode is bead blasted stainless steel coated with arc sprayed aluminum. In one embodiment, one end of the anode 134 may be 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. At the end of the anode 134 is a connection assembly 142. The connection assembly 142 may be any conventionally known device for connecting fluid containing tubes together. An additional bracket 140 may couple the anode 134 to the chamber wall 132 and stabilize the connection assembly 142. In another embodiment, the anode 134 may be mounted with an anchor mount, which may be shielded from deposition by an anode shield. The anchor mount may be positioned on the shield 116.
The anode 134 provides a charge in opposition to the target assembly 104 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 assembly 104 and the substrate, the plasma may be more uniform, which may aid in the deposition. In one embodiment, six anodes are positioned between the target assembly 104 and the substrate. Exemplary anodes that may be used to practice the invention are disclosed in U.S. patent application Ser. No. 11/182,034, filed Jul. 13, 2005, U.S. patent application Ser. No. 11/247,705, filed Oct. 11, 2005, and U.S. patent application Ser. No. 11/247,438, filed Oct. 11, 2005, each of which is hereby incorporated by reference in their entirety.
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 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. Similar reasoning applies to the anode 134. In one embodiment, the anode 134 may be cooled.
The magnetron 110 may be scanned across the back of the target assembly 104 by a scanning mechanism 200.
A magnet chamber roof 212 may be supported on and sealed to the frame 240 with the gantry structure disposed therebetween. The magnet chamber roof 212 may include a rectangular aperture 220, an actuator recess 222, and a bracket recess 218. A bracket chamber 208 may fit within the bracket recess and be sealed to the chamber roof 212 around the rectangular aperture 220. The bracket chamber 208 may comprise sidewalls 216 and a top plate 202. Within the bracket chamber 208, the gantry bracket 206 may be housed. An actuator assembly 210 may be held in the actuator recess 222 by an angle iron 214 and a support bracket 204. In one embodiment, the magnetron may be scanned in a serpentine pattern across the back of the sputtering target assembly. In another embodiment, the magnetron may rest on roller balls and springs as described in U.S. patent application Ser. No. 11/347,667, filed Feb. 3, 2006 which is hereby incorporated by reference in its entirety.
The magnetron may have various shapes.
There are many benefits to using a monolithic target assembly. When using a monolithic sputtering target assembly, no delamination of the sputtering target from the backing plate may occur because a separate backing plate and target are not present. Without a separate backing plate and target, no bonding is present. When a separate sputtering target and backing plate are used, the backing plate may sometimes warp. Additionally, any cooling channels within the backing plate may occasionally need to be repolished to ensure that the cooling fluid continues to flow through the cooling channels at the desired flow rate. When warping occurs or repolishing is necessary, the backing plate may need to be refurbished.
A monolithic sputtering target may increase sputtering efficiency over a sputtering target and backing plate bonded together. In a monolithic sputtering target, the backing plate and the sputtering target are the same material without a bonding layer therebetween. Therefore, the heat transfer coefficient for the backing plate and the sputtering target is identical. Additionally, the backing plate and the sputtering target in a monolithic sputtering target would have the same conductivity. Thus, an applied current would follow through the sputtering target assembly in an efficient manner as compared to a current that travels through a backing plate, bonding material, and the sputtering target. Therefore, due to the same heat transfer coefficient and conductivity, the monolithic sputtering target may have a higher sputtering efficiency than a sputtering target bonded to a backing plate.
When refurbishing a backing plate or a sputtering target, the target and the backing plate may be debonded so that any warping of the backing plate may be corrected. For large area sputtering target assemblies (i.e., an area greater than about 1 or 2 square meters), the backing plate and the target may need to be transported to another location for the refurbishing and/or debonding. Because the target and backing plate have a large area, it may not simply be a matter of loading the target and backing plate onto a truck and transporting it. The target and backing plate may need to be transported as an “oversized load” and thus necessitate a road escort. At the very least, there are transportation costs, refurbishing costs, debonding costs, and re-bonding costs associated with a large area target assembly comprising a separate backing plate and target.
A monolithic target assembly, on the other hand, is beneficial because there is no backing plate to warp. Should any warping occur or should the target erode to the point where it is no longer useable, the assembly may simply be scrapped and replaced instead of refurbishing it. This is particularly true with aluminum monolithic sputtering target assemblies because aluminum is well known to be recyclable. The aluminum monolithic sputtering target assembly may be simply cut down to an appropriate size for transportation while on site at the production facility and then transported to an aluminum recycle center where it may be sold. While transportation costs are incurred, the need for an “oversized load” escort may be eliminated.
The costs associated with a monolithic sputtering target assembly represent a savings over a sputtering target with backing plate assembly. For example, to bond the sputtering target to the backing plate, a bonding material is necessary. Thus, bonding costs are present for the material and labor costs are necessary to bond the target to the backing plate. With a monolithic sputtering target assembly, the target and backing plate are integrated in a monolithic structure, so that the target and backing plate need not be bonded to each other because they are a single, monolithic piece. Therefore, the monolithic sputtering target assembly does not have bonding, or as necessary, debonding costs. The overall cost per substrate, when factoring in transportation, refurbishing, bonding, debonding, recycling, etc., may be lowered by using a monolithic sputtering target assembly as opposed to a traditional target bonded to backing plate assembly.
Monolithic sputtering target assemblies may produce films with consistent characteristics throughout the deposited layer. Because the target is monolithic, the composition and grain structure of the material sputtered may be uniform throughout the sputtering target and hence, the deposited layer. Due to the uniform composition and grain structure, erosion from the sputtering target during sputtering may be more uniform. Monolithic sputtering target assemblies are cost effective for depositing films having uniform composition and grain structure onto large area substrates.
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. 60/825,775 (APPM/011515L), filed Sep. 15, 2006, which is herein incorporated by reference.
| Number | Date | Country | |
|---|---|---|---|
| 60825775 | Sep 2006 | US |
