The invention pertains to physical vapor deposition (PVD) target/backing plate constructions, and to methods of forming such constructions.
Physical vapor deposition is commonly utilized for forming thin layers of material across semiconductor substrates.
Construction 10 comprises a PVD target 14 and a backing plate 16. The assembly is shown comprising an ENDURA™ configuration, such as is available from Honeywell International Inc. Backing plate 16 has a configuration suitable for retaining construction 10 within the sputtering apparatus. Target 14 can comprise any suitable composition, and in the shown application comprises a conductive material.
Target 14 is shown directly bonded to backing plate 16 (i.e., physically against the backing plate). Accordingly, target 14 has a bonding surface 19 directly against a bonding surface 17 of the backing plate 16. The bond between the target and backing plate can be formed by, for example, a diffusion bonding process.
An exposed surface 18 of target 14 can be referred to as a sputtering surface. High energy particles are impacted against surface 18 to cause material to be released from surface 18. The released material is diagrammatically illustrated by arrows 20. The released material forms a film 22 across an upper surface of substrate 12.
The surfaces 18 and 19 of the target can be referred to as opposing primary surfaces. The surfaces are referred to as “primary” surfaces to indicate that the surfaces have more area than other surfaces of the target (such as the sidewall surfaces), and are thus major surfaces of the target.
Although target 14 is shown comprising a conductive material, it is to be understood that the target can comprise any suitable construction for forming a desired film, and accordingly can also comprise non-conductive materials, such as, for example, ceramic materials.
The removal of material from target 14 reduces a thickness of the target. Eventually, the target is eroded to an extent that the target is no longer suitable for utilization in a PVD operation. The duration of time that a target can be utilized in PVD operations before the target is eroded to the point that it is no longer useful can be referred to as a lifetime of the target.
A tradeoff occurs in utilizing target/backing plate constructions during sputtering operations in attempting to obtain a maximal lifetime from a target, while also avoiding having the sputtering tracks 30 or 32 extending through the target and into the backing plate (i.e., punching through the interface of the target surface 19 and the backing plate surface 17). If the sputtering tracks penetrate entirely through the target during a PVD operation, material from the backing plate can be sputtered which can adversely impact a film deposited from construction 10.
Target 14 has sidewalls 40 extending between bonding surface 19 and sputtering surface 18. The thickness of target 14 along the edges can be measured as a length of sidewalls 40 if the entirety of the sidewalls is exposed. However, target 14 is inset within backing plate 16 so that only a portion of the sidewall surfaces 40 is exposed for measurement. Further, even if the sidewalls are exposed, the thickness of the target at the edges only accurately reflects the thickness of the target at interior regions if the target thickness is uniform across the interior regions and the edges. Rather than assuming the target thickness to be uniform across the interior regions and edges, it is frequently desired to confirm the uniformity of the target thickness during the determination of the target thickness.
The desire to accurately measure target thickness and to confirm the uniformity of target thickness across edge and interior regions has lead to development of ultrasound methods for determining the thickness of target 14. An ultrasound transducer 42 is shown in
Each interface within the target can reflect a fraction of the ultrasound radiation impacting it while transmitting the remaining fraction of ultrasound radiation. The relative amount of radiation reflected, versus the amount transmitted for a given interface can, for the reasons discussed above, depend on the difference in compositions of the materials joining at the interface. If the materials have different compositions that in turn lead to significant differences in acoustic impedance, a large reflection will occur; and if the materials are about the same in acoustic impedance, very little, if any, reflection will occur.
For the shown construction 10, ultrasound reflections are expected from surface 18; from the interface between surface 19 of target 14 and surface 17 of backing plate 16; and from a back surface 50 of backing plate 16.
Ultrasound techniques work well when the target is very different in composition from the backing plate 16 of
The signals shown in
The time between peaks 51 and 52 is directly related to the thickness of target 14, and the relationship between the time and the thickness can be readily determined by persons of ordinary skill in the art. A problem which can occur, as discussed above, is that if materials 14 and 16 are very similar in acoustic amplitude relative to one another, peak 52 can be essentially undetectable. Thus, the ultrasound methodology for determining target thickness can fail in applications in which the target and backing plate of construction 10 have similar acoustic impedance relative to one another. Unfortunately, many common applications comprise targets and backing plates having similar acoustic impedances relative to one another. For instance, it is common for the target and backing plate to both predominately comprise the same material. In particular applications, the target and backing plate can both comprise relatively high purity compositions of the same element. For example, the target and backing plate can both comprise high purity aluminum or high purity copper. The term “high purity” refers to any composition having a purity of greater than 99 atomic %. In many applications, if the target and backing plate both predominately comprise the same element (with the term “predominately comprise” indicating that a material comprises more than 50 atomic % of the element) the acoustic impedance of the target and backing plate can be too similar to one another to allow the process of
Ultrasound technology has many advantages for determining target thickness. Among them, ultrasound technology can be relatively quick and convenient. Accordingly, it would be desirable to develop methods by which ultrasound technology can be utilized for determining target thicknesses in constructions in which a target and a backing plate have similar acoustic impedances to one another.
In one aspect, the invention pertains to a method of forming a PVD target/backing plate construction. A PVD target is provided. The target has a pair of opposing primary surfaces, with one of the primary surfaces being a sputtering surface and the other of the primary surfaces being a bonding surface. A backing plate is provided, and the backing plate has a bonding surface. A hole is extended into the target through the target bonding surface. The target is bonded to the backing plate. After the target is bonded to the backing plate, the hole is utilized to estimate a thickness of the target.
In one aspect, the invention encompasses a method of forming a PVD target/backing plate construction in which at least one hole is formed to extend into a backing plate through a backing plate bonding surface. The backing plate is then bonded to a PVD target, and the hole is utilized to estimate a thickness of the target.
In one aspect, the invention encompasses PVD target/backing plate constructions having one or more holes extending into a backing plate through a backing plate bonding surface and/or having holes extending into a target through a bonding surface of the target. The holes can have any suitable size. In a particular aspect, the holes can have a depth of from about 0.005 inch to about 0.1 inch, and can have a maximum width of from about 0.005 inch to about 0.1 inch.
The patent or application file contains at least one drawing executed in color. Copies of this patent or patent application publication with color drawing(s) will be provided by the Office upon request and payment of the necessary fee.
Preferred embodiments of the invention are described below with reference to the following accompanying drawings.
One aspect of the invention is to develop methodology for overcoming the problem described above with reference to prior art
An exemplary method of forming altered acoustic impedance regions within a target is described with reference to
Openings 100 can have any suitable shape and depth. It can be preferred, however, that the openings be relatively small so that the openings do not interfere with subsequent bonding of the target in a target/backing plate construction. Exemplary openings will have an approximately circular lateral periphery and a diameter “D” extending across the periphery. The diameter corresponds to a maximum width of the openings, and can be, for example, from about 5 thousandths of an inch to about 100 thousandths of an inch. The openings have a depth “X”, and such can be, for example, from about 5 thousandths of an inch to about 100 thousandths of an inch. In a particular aspect, the openings are formed to have a diameter of 0.050 inch, and a depth of 0.030 inch. All of the openings can be formed with identical widths and depths relative to one another, or can be formed with different widths and depths.
The openings have a bottom periphery 102, and such is preferably substantially planar, and also substantially parallel to sputtering surface 18. Accordingly, ultrasound waves which are orthogonal to sputtering surface 18 will also be orthogonal to surface 102 so that strong reflections of ultrasound waves can be obtained from both surface 18 and surface 102 using the same ultrasound transducer.
Referring next to
Backing plate 16 comprises the back surface 50 described previously with reference to
Referring to
A thickness of target 14 can be determined from the time delay between reflection 51 and reflection 110. Specifically, the time between reflection 51 and 110 can be related to a distance between sputtering surface 18 and peripheral surface 102 of opening 100. If the depth of opening 100 is known, then such can be added to the distance between sputtering surface 18 and surface 102 to determine a total thickness of target 14 at the location of an opening.
Openings 100 are left unfilled in construction 104 of the embodiment of
It can be preferred that material 120 have a substantially different acoustic impedance than the material of target 14 so that a strong acoustic reflection can be obtained from the interface of material 120 and a material of target 14 at surface 102 of the openings. It can also be preferred that material 120 have a coefficient of thermal expansion approximately equal to that of the material of target 14 so that the target material is not cracked during heating of the target material that can occur during bonding of the target to a backing plate and/or during utilization of the target in a physical vapor deposition apparatus. However, if material 120 comprises a different coefficient of thermal expansion than target 14, problems associated with the different rates of expansion of material 120 and target 14 can be alleviated by only partially filling the openings 100 with material 120.
Referring to
The various openings described in the constructions of
Although the embodiments described above comprise holes formed in a target of a target/backing plate construction, it is to be understood that the holes can alternatively, or additionally, be formed in a backing plate of the construction. Such aspect of the invention is described with reference to
A thickness of target 14 of construction 135 can be estimated by providing an ultrasound transducer over sputtering surface 18 (similar to the process described above with reference to
Although the embodiments described above with reference to
Openings 130 can be left empty of solid material (as shown), or alternatively can be at least partially filled with solid materials similar to the embodiment described above with reference to
The invention has been tested utilizing a target/backing plate construction in which the target is copper of about 99.9999 atomic % purity and the backing plate is copper with about 1.2 atomic % chromium. Typically, it would be difficult, and frequently impossible, to locate an interface between such target and backing plate utilizing prior art methods. However, methodology of the present invention readily detected holes formed in the backing plate. Such is illustrated in
Methodology of the present invention can be utilized in any application in which a bond between a target and backing plate will be difficult to detect by prior art methods, including applications in which the target and backing plate predominately comprise the same material as one another, or otherwise have substantially the same acoustic impedance as one another (with the term substantially the same acoustic impedance referring to an acoustic impedance which differs by less than 5%). Also, although the invention is described with reference to targets bonded directly to backing plates, it is to be understood that the invention can also be utilized in applications in which the target is bonded to the backing plate through an intervening material, such as, for example, a solder. The invention can be particularly advantageous relative to prior art processes if the intervening material has an acoustic impedance substantially the same as the target and backing plate.
In applications in which the target is directly bonded to the backing plate, the bonding methods can be conventional methods including, for example, hot isostatic pressing at high temperature and pressure to achieve diffusion bonding.
The holes utilized in methodology of the present invention preferably are small enough to have little to no effect on bonding between a target and backing plate, and also preferably would have little or no effect on electrical or thermal conduction between the target and backing plate.
This patent resulted from a continuation-in-part application of PCT/US2004/008343 which was filed Mar. 17, 2004, and is incorporated by reference herein; and which claims priority to U.S. Provisional Patent Application Ser. No. 60/460,151, which was filed Apr. 2, 2003, and is incorporated by reference herein.
Number | Date | Country | |
---|---|---|---|
60460151 | Apr 2003 | US |
Number | Date | Country | |
---|---|---|---|
Parent | PCT/US04/08343 | Mar 2004 | US |
Child | 11186213 | Jul 2005 | US |