Patent Application
20050236270
The present invention relates generally to the field of sputter targets and, more particularly, relates to controlled cooling of sputter targets through surface area alteration.
The process of sputtering is widely used in a variety of fields to provide thin film material deposition of a precisely controlled thickness with an atomically smooth surface, for example to coat semiconductors and/or to form films on surfaces of magnetic recording media. In the sputtering process, a sputter target is positioned in a chamber filled with an inert gas atmosphere, and is exposed to an electric field to generate a plasma. Ions within this plasma collide with a surface of the sputter target causing the sputter target to emit atoms from the sputter target surface. The voltage difference between the sputter target and the substrate that is to be coated causes the emitted atoms to form the desired film on the surface of the substrate.
During sputtering, heat often builds up on the sputter target, negatively affecting control of the sputter process and shortening the lifetime of the sputter target.
Conventional sputter target 101 is placed in a vacuum chamber, and clamped onto ring-shaped support 110. An air-tight and water-tight seal is created between gasket 111 and backside surface 106. A cooling fluid such as water is pumped into the cavity created by ring-shaped support 110, and the cooling fluid dissipates heat generated on sputter surface 102. After prolonged sputtering, sputter area 104 erodes or wears down as atoms of sputter target 101 are emitted from sputter surface 102. This erosion causes grooves to be formed on sputter surface 102, illustrated with dashed lines.
Success in the sputter coating of thin-film materials, especially sputter coating of thin films in the magnetic data storage industry, is highly dependent on effective heat dissipation. Specifically, high temperatures on a sputter target increase the rate at which sputtering occurs, and affect the uniformity of thin-film deposition. If sputtering occurs too quickly, the useful life of a particular sputter target will decrease, resulting in higher replacement costs and more frequent system downtimes. Moreover, if the sputter target gets too hot, the bond between the different materials comprising the sputter target can melt, degrading the efficiency of the sputtering process and causing unnecessary interruptions to the sputtering process.
Conventional sputter targets do not have enhanced or selective control over the cooling of the sputter target, other than by modifying sputtering equipment or by selecting backing materials with desirable heat retention properties. Accordingly, it is desirable to provide a method for controlling the cooling of sputter targets during sputtering. In particular, it is desirable to provide a method for selectively controlling the cooling of specific locations on the major surface of a sputtering target by surface area alteration of the backside surface, in order to improve sputtering safety and efficacy.
The buildup of heat is an inherent side-effect of the sputtering process. Too much heat can negatively affect the life-cycle of a sputter target, and degrade uniformity of thin-film deposition. In this regard, it is an object of the invention to address disadvantages found in conventional sputter targets, particularly with regard to those disadvantages which relate to the buildup of heat on a sputter target during sputtering.
In one aspect of the invention, a sputter target in which cooling rates are selectively controlled through surface area alteration is manufactured by generating a sputter surface and a backside surface obverse to the sputter surface. The backside surface includes at least a first textured region, where the first textured region aids in cooling a region of the sputter target adjacent to the first textured region, by effectuating heat dissipation.
By manipulating the surface area of a textured region, the cooling rate at specific areas of a sputter target can be controlled, and the wear pattern of the sputter area can be controlled. For example, by increasing the cooling rate at selected locations on a sputter target, the sputtering process can be slowed down, resulting in an extended service life for a particular sputter target, and reduced operating costs. By including more than one textured region, the sputtering rate can be adjusted or tuned to different rates at selected locations on the surface of the sputter target, further enhancing control over the sputtering process.
The backside surface also includes at least a first non-textured region. By placing a non-textured region on the backside surface of the sputter target, cooling rates can be decreased or left alone at other locations. Non-textured regions may be located on an obverse surface to non-sputter areas on the sputter surface, which are often cooler than sputter areas and consequently wear at a slower pace. Furthermore, a non-textured region could be placed adjacent to a vacuum seal gasket in order to effectuate a vacuum seal and prevent a gas-liquid exchange from occurring between the cooling fluid and the vacuum chamber.
The first textured region is generated using grit blasting, random machining, laser ablation, or using a lathe. Each of these texturing methods provides for a textured backside region with an increased surface area over a polished backside region. The increase in surface area allows greater contact to the cooling fluid applied to the first textured region, increasing the cooling rate of the sputter target at a location obverse to the first textured region.
In a second aspect the present invention is a sputter target in which cooling rates are selectively controlled. The sputtering target includes a sputter surface and a backside surface obverse to the sputter surface, where the backside surface further includes at least a first textured region. The backside surface further includes at least a first non-textured region.
The textured region aids in cooling a region of the sputter target adjacent to the textured region, by effectuating heat dissipation. Texturing the backside surface of the sputter target allows for greater contact with cooling fluids, increasing heat dissipation. The sputter target may be circular, rectangular, or hexagonal.
While sputtering, the intense heat develops in the sputter target, due to the collisions betweens ions and atoms of target material in the sputter area. As a consequence of the rising temperature, the rate in which sputtering occurs increases, further increasing the amount of target material ejected from the sputter area. This, in turn, causes increased wear on the sputter area, shortening the usable life of the sputter target.
By placing the textured region obverse to the sputter area, heat is dissipated from the textured region at an increased rate, selectively cooling the sputter area. Controlling the cooling rate of the sputter area through alteration of the surface area of the backside surface allows the sputter area to be cooled faster, slower, or at the same rate as the non-sputter areas of the sputter target.
In an alternative arrangement, the sputter surface further includes a sputter area for sputtering and at least a first non-sputter area, and the textured region is obverse to the non-sputter area. The sputter rate can be controlled at any selected area across the entire sputter surface, not just at the sputter area.
The sputter target is comprised of a either a metal alloy or a ceramic material, although the present invention will impact materials with high thermal conductivity, such as metals, more than those with a lower thermal conductivity, such as ceramics.
The textured region either protrudes from the backside surface or cuts into the backside surface. Moreover, the textured region is textured with a random texture, such as grit blasting or random machining.
In the case where a sputter target is directly cooled by contact with a chilled fluid on the backside surface, the cooling rate of the sputter target depends on the thermal conductivity of the sputter target. Since the cooling fluid is rapidly flowing over the backside surface, the cooling fluid is itself not being heated to any marked extent. As such, by increasing the surface area of the backside surface, contact between the cooling fluid and the sputter target increases, increasing the amount of heat dissipated into the cooling fluid in a given time interval.
The textured region may alternatively be textured with cross-hatches, concentric circles, rectangular shapes, parallel lines or curved lines, where the curved lines facilitate rapid flow or turbulent flow of a cooling fluid which is in contact with the backside surface. Curved lines can create channels, facilitating rapid flow of the cooling fluid from a fluid inlet to a fluid outlet, or the curved lines can create rough spots perpendicular to the direction of flow of the cooling fluid, facilitating turbulent flow.
In a third aspect, the present invention is a sputter target assembly in which cooling rates are selectively controlled through surface area alteration. The sputter target assembly includes a sputter target, where the sputter target further includes a sputter surface, and a backing plate, where the backing plate further includes a backside surface. The backside surface further includes at least a first textured region. The sputter target and the backing plate are bonded together, so that the sputter surface is obverse to the backside surface. The textured region aids in cooling a region of the sputter target assembly adjacent to the textured region, by effectuating heat dissipation.
Typically, sputter targets are bonded to backing plates in order to enhance the effect of the cooling fluid. The sputter surface is generated on a sputter target and the backside surface can be generated on a backing plate in order to increase the surface area of the backing plate and, consequently, the overall sputter target assembly. The sputter target and the backing plate are bonded together prior to or after the generation of the sputter surface or the backside surface.
In a fourth aspect, the present invention is a method for manufacturing a sputter target assembly in which cooling rates are selectively controlled through surface area alteration. The method includes the steps of generating a sputter surface on a sputter target, and generating a backside surface on a backing plate, where the backside surface includes at least a first textured region. The method also includes the step of bonding the sputter target and the backing plate together, so that the sputter surface is obverse to the backside surface. The first textured region aids in cooling a region of the sputter target assembly adjacent to the first textured region, by effectuating heat dissipation.
In the following description of the preferred embodiment, reference is made to the accompanying drawings that form a part thereof, and in which is shown by way of illustration a specific embodiment in which the invention may be practiced. It is to be understood that other embodiments may be utilized and changes may be made without departing from the scope of the present invention.
Referring now to the drawings in which like reference numbers represent corresponding parts throughout:
The present invention allows for improved control over the cooling of a sputter target and for extending the useful life of a sputter target, by controlling the cooling of the sputter target at selected areas through surface area alteration.
In more detail, sputter target 201 includes sputter surface 202, where sputter surface 202 further includes sputter area 204 for sputtering, and non-sputter areas 205. Sputter target 201 also includes backside surface 206 obverse to sputter surface 202.
Backside surface 206 includes textured regions 210. Textured regions 210 aids in cooling a region of sputter target 201 adjacent to textured regions 210 through heat dissipation. Backside surface 206 also includes at least non-textured region 212. In an alternate arrangement, non-textured region 212 is omitted, and textured regions 210 covers the entire surface of backside surface 206.
Sputter target 201 is comprised of a metal alloy and/or a ceramic material, and can be of any shape, including but not limited to circular, rectangular, or hexagonal shape. The present invention will impact materials with high thermal conductivity, such as metals, more than those with a lower thermal conductivity, such as ceramics.
Prior to sputtering, sputter target 201 is placed in a vacuum chamber, and clamped onto a ring-shaped support (not depicted). An air-tight and water-tight seal is created between a gasket (not depicted) on top of the ring-shaped or rectangular-shaped support, and backside surface 206. A cooling fluid such as water is pumped into the cavity created by the support, and the cooling fluid absorbs the dissipated heat which is generated on sputter surface 202.
Textured regions 210 can be textured with many different texture shapes, including but not limited to concentric circles, cross hatches, rectangular shapes, parallel lines, curved lines and/or random textures, such as grit blasting or random machining. Curved lines on textured regions 210 can facilitate rapid flow or turbulent flow of a cooling fluid which is in contact with the backside surface. Textured regions 210 can protrude from and/or cut into backside surface.
Each of these texturing methods provides for a textured backside region with an increased surface area over a polished backside region. The increase in surface area allows greater contact to the cooling fluid applied to textured regions 210, increasing the cooling rate of the sputter target at a location obverse to textured regions 210.
By placing a non-textured region on the backside surface of the sputter target, cooling rates can be decreased or left alone at selected locations. Non-textured regions may be located on an obverse surface to non-sputter areas on the sputter surface, which are often cooler than sputter areas, and consequently wear at a slower pace. Moreover, a non-textured region could be placed adjacent to a vacuum seal gasket in order to effectuate a vacuum seal and prevent a gas-liquid exchange from occurring between the cooling fluid and the vacuum chamber.
By manipulating the surface area of a textured region, the cooling rate at specific areas of a sputter target can be selectively controlled. By increasing the cooling rate at selected locations on a sputter target, heat dissipates faster, and the sputtering process slows. As a result, the useful life of a particular sputter target is extended, and operating costs are reduced.
Textured regions 210 is obverse to sputter area 204. In an alternate arrangement, textured regions 210 is obverse to non-sputter areas 205. It is advantageous to locate non-textured regions obverse to non-sputter areas on the sputter surface, which are often cooler than sputter areas, and which typically wear at a slower pace.
The sputter area is the hottest portion of sputter surface 202 because of the collisions betweens ions in the plasma and atoms on the sputter target. The sputtering rate increase as temperatures increase, causing increased wear on the sputter area. By placing the textured region obverse to the sputter area, heat can be quickly dissipated from the textured region, selectively cooling the sputter area, and decreasing wear. By locating the textured region obverse to the sputter area, the cooling rate of the sputter area can be fine-tuned, allowing the sputter area to be cooled faster, slower, or at the same rate as the non-sputter areas of the sputter target.
In the case where a sputter target is directly cooled by contact with a chilled fluid on the backside surface, the cooling rate of the sputter target depends on the thermal conductivity of the sputter target. Since the cooling fluid is rapidly flowing over the backside surface, the cooling fluid is itself not being heated to any marked extent. As such, by increasing the surface area of the backside surface, contact between the cooling fluid and the sputter target increases, therefore increasing the amount of heat dissipated into the cooling fluid per unit time.
Textured regions 210 can be used to facilitate rapid flow or turbulent flow of the cooling fluid. In
In
Textured regions 210 is obverse to sputter area 204. As such, textured regions 210 aids in cooling a region of sputter target 201 adjacent to textured regions 210 through heat dissipation. By placing textured regions 210 obverse to the sputter area, heat which has built up at sputter area 204 can be quickly dissipated, selectively cooling sputter area 204, and decreasing overall wear on sputter target 201. By locating textured regions 210 obverse to sputter area 204, the cooling rate of sputter area 204 can be fine-tuned, allowing sputter area 204 to be cooled faster, slower, or at the same rate as the non-sputter areas of sputter target 201.
Combined, first textured regions 210, second textured region 801, and third textured region 802 are obverse to sputter area 204. As was the case with the
In more detail, the process begins (step S901), and a sputter surface is generated (step S902). The sputter target is generated on two different target materials, where a sputter target assembly is clamped or bonded to a backing plate, in order to enhance the cooling effect of a cooling fluid. As such, the sputter surface is generated on a first material, where the sputter surface includes a sputter area for sputtering, and at least a first non-sputter area. The process of generating a sputter surface on a sputter target is well known in the material science art.
A backside surface is generated (step S904). The backside surface is generated on a second material, such as a backing plate, in order to increase the surface area of the backing plate and the overall target assembly. The backside surface includes at least a first textured region, where the first textured region aids in cooling a region of the sputter target adjacent to the first textured region, by effectuating heat dissipation. The backside surface also includes at least a first non-textured region.
By manipulating the surface area of a textured region, the cooling rate at specific areas of a sputter target can be controlled, and the wear pattern of the sputter area can controlled. By increasing the cooling rate at selected locations on a sputter target, the sputtering process can be slowed down, resulting in an extended service life for a particular sputter target, and reduced operating costs. By including more than one textured region, the sputtering rate can be adjusted or tuned to different rates at selected locations on the surface of the sputter target, further enhancing control over the sputtering process.
The first textured region is generated using a process such as grit blasting or random machining, laser ablation, or using a lathe. The first textured region can be textured with many different texture shapes, including but not limited to concentric circles or ovals, cross-hatches, rectangular shapes, parallel lines, curved lines, and/or random textures. Curved lines on the first textured region can facilitate rapid flow or turbulent flow of a cooling fluid which is in contact with the backside surface. The first textured region can protrude from and/or cut into the backside surface.
Each of these texturing methods provides for a textured backside region with an increased surface area over a polished backside region. The increase in surface area allows greater contact to the cooling fluid applied to the first textured region, increasing the cooling rate of the sputter target at a location obverse to the first textured region.
Typically, sputter targets are bonded to backing plates in order to enhance the effect of the cooling fluid. The sputter surface is generated on a sputter target and the backside surface can be generated on a backing plate in order to increase the surface area of the backing plate and, consequently, the overall sputter target assembly. The sputter target and the backing plate are bonded together prior to or after the generation of the sputter surface or the backside surface.
In more detail, sputter target assembly 1001 includes sputter target 1014, where sputter target 1014 includes sputter surface 1002. Sputter surface 1002 further includes sputter area 1004 for sputtering, and first non-sputter area 1005. Sputter target assembly 1001 also includes backing plate 1015, where backing plate 1015 further includes backside surface 1006. Sputter target 1014 and backing plate 1015 are bonded together, so that sputter surface 1002 is obverse to backside surface 1006.
Backside surface 1006 includes textured region 1010. Textured region 1010 aids in cooling a region of sputter target assembly 1001 adjacent to textured region 1010 through heat dissipation. Backside surface 1006 also includes at least first non-textured region 1012. In an alternate arrangement, first non-textured region 1012 is omitted, and textured region 1010 covers the entire surface of backside surface 1006.
Sputter target 1014 is comprised of a metal alloy and/or a ceramic material, and can be of any shape, including but not limited to circular, rectangular, or hexagonal shape. The present invention will impact materials with high thermal conductivity, such as metals, more than those with a lower thermal conductivity, such as ceramics.
Prior to sputtering, sputter target assembly 1001 is placed in a vacuum chamber, and clamped onto a ring-shaped support (not depicted). An air-tight and water-tight seal is created between a gasket (not depicted) on top of the ring-shaped or rectangular-shaped support, and backside surface 1006. A cooling fluid such as water is pumped into the cavity created by the support, and the cooling fluid absorbs the dissipated heat which is generated on sputter surface 1002.
Textured region 1010 can be textured with many different texture shapes, including but not limited to concentric circles, cross hatches, rectangular shapes, parallel lines, curved lines and/or random textures, such as grit blasting or random machining. Curved lines on textured region 1010 can facilitate rapid flow or turbulent flow of a cooling fluid which is in contact with the backside surface. Textured region 1010 can protrude from and/or cut into backside surface.
Textured region 1010 is obverse to sputter area 1004. In an alternate arrangement, textured region 1010 is obverse to first non-sputter area 1005. It is advantageous to locate non-textured regions obverse to non-sputter areas on the sputter surface, which are often cooler than sputter areas, and which typically wear at a slower pace.
In more detail, the process begins (step S1101), and a sputter surface is generated on a sputter target (step S1102). The sputter surface is generated on a sputter target, where the sputter surface includes a sputter area for sputtering, and at least a first non-sputter area. The process of generating a sputter surface on a sputter target is well known in the material science art.
A backside surface is generated on a backing plate (step S1104). The backside surface is generated on the backing plate in order to increase the surface area of the backing plate and the overall target assembly. The backside surface includes at least a first textured region, where the first textured region aids in cooling a region of the sputter target adjacent to the first textured region, by effectuating heat dissipation. The backside surface also includes at least a first non-textured region.
The first material and the second material are bonded (step S1105), and the process ends (step S1106). The first material and the second material can be bonded by physically joining the two materials together, or by clamping. In alternate arrangements, the first material and second material can be bonded prior to or after the generation of the sputter surface or the backside surface.
Sputter target assembly 1001 includes a sputter target and a backing plate, bonded together along an interface. The bonding of materials, such as metal alloys, is well known in the metallurgical art. Sputter targets are typically formed of two or more bonded or clamped materials in order to enhance the cooling effect of a cooling fluid applied to the backside surface.
The invention has been described with particular illustrative embodiments. It is to be understood that the invention is not limited to the above-described embodiments and that various changes and modifications may be made by those of ordinary skill in the art without departing from the spirit and scope of the invention.
