Physical vapor deposition target/backing plate assemblies

Details Physical vapor deposition target/backing plate assemblies Physical vapor deposition target/backing plate assemblies

2000-10-27

2002-04-23

Nelms, David (Department: 2818)

Semiconductor device manufacturing: process

Packaging or treatment of packaged semiconductor

Including adhesive bonding step

C438S643000

Reexamination Certificate

active

06376281

ABSTRACT:

TECHNICAL FIELD
The invention pertains to physical vapor deposition target/backing plate assemblies, and to methods of forming physical vapor deposition target/backing plate assemblies. In particular applications, the invention pertains to methods of incorporating a bonding layer between a target and a backing plate in a physical vapor deposition target/backing assembly, with an exemplary bonding layer being a layer capable of forming a strong diffusion bond to the target at a temperature of less than or equal to about 500° C. in a time of less than or equal to about 24 hours. A “strong” diffusion bond is defined as a bond capable of passing a peel test described herein. In further applications, the invention pertains to methods of incorporating one or more of titanium, zirconium, and copper in a bonding layer between a target and a backing plate in a physical vapor deposition target/backing assembly.
BACKGROUND OF THE INVENTION
Physical Vapor Deposition (PVD) targets have wide application in fabrication processes where thin films are desired, and include, for example, sputtering targets. An exemplary PVD process is a sputtering process, and an exemplary application of a PVD process is to form thin films across semiconductor substrates in semiconductor processing applications.
A prior art PVD process is diagrammatically illustrated in FIG.
1
. More specifically,
FIG. 1
illustrates an apparatus
10
comprising a PVD target/backing plate assembly
12
above a substrate
14
. Assembly
12
comprises a sputtering target
16
joined to a backing plate
18
. Target
16
can comprise any of numerous metallic elements and alloys, and backing plate
18
can comprise numerous electrically and thermally conductive materials, such as, for example, copper or aluminum.
Target
16
has a surface
20
from which material is ejected, and which can be referred to as a sputtering surface. In operation, surface
20
is exposed to ions or atoms which impact the surface and are utilized to eject material from the surface toward substrate
14
. The ejected material is illustrated by arrows
22
in FIG.
1
. Such ejected material lands on substrate
14
to form a thin film (not shown) over the substrate.
Backing plate
18
provides several functions during the sputtering application illustrated in FIG.
1
. For instance, backing plate
18
is typically provided with a shape configured to enable assembly
12
to be removably retained within a sputtering apparatus chamber (not shown). Also, backing plate
18
is typically formed of an electrically/thermally conductive material and is utilized for passing an electric field to sputtering target
16
. An interface between target
16
and backing plate
18
should preferably comprise a bond strong enough to retain target
16
to backing plate
18
during a sputtering operation, and yet also comprise a continuous, uniform and electrically conductive construction so that an electric field can be passed uniformly across the interface from backing plate
18
to target
16
. Among the methodologies presently utilized for forming a target-to-backing plate interface is a methodology of providing solder (shown as
15
in
FIG. 1
) between a target and backing plate to bond the target to the backing plate. The solder can comprise, for example, one or both of tin and indium.
A difficulty in utilizing solders is that the solders frequently do not adhere well to a target material, and accordingly a target can separate from a backing plate if only solder is utilized in the backing plate/target bond. Such problem can be particularly pronounced with targets comprising one or more of tantalum, cobalt, zirconium, platinum, iron, niobium, molybdenum, chromium, aluminum, copper and manganese. In order to overcome such difficulty, a transition layer
19
is frequently provided over a target surface prior to bonding the target surface to a backing plate. In the shown target/backing plate construction, target
16
has a surface
17
which is ultimately to be utilized in forming a bond with backing plate
18
. Transition layer
19
is formed over surface
17
prior to bonding the target with the backing plate.
Transition layer
19
typically comprises nickel. The nickel is considered to adhere better to various target materials than does an indium or tin-based solder, and in turn an indium or tin-based solder is considered to adhere better to the nickel than to the target material. Accordingly, the nickel layer
19
can be ultimately bonded with solder
15
to retain the target
16
to backing plate
18
Nickel-containing transition layers improve adhesion of various target materials to backing plates. However, it is found that even when such layers are provided, problems can still be encountered with separation or delamination of a PVD target from a target/backing plate assembly during a sputtering process. Nickel-containing transition layers can be particularly unsatisfactory when utilized with target compositions comprising one or more of Ta, Co, Zr, Pt, Fe, Nb, Mn, Cr, Al, Cu. The separation of a target and backing plate can occur, for example, at an interface between the nickel transition layer and the target. If delamination exceeds more than about 5% of the area of a target surface, the target/backing plate assembly can be rendered inoperable in that it will not perform within desired parameters. In some instances, a delamination of greater than or equal to about 1% can render a target/backing plate assembly inoperable. It would, accordingly, be desirable to develop new methodologies for adhering targets to backing plates to avoid the delamination problems associated with nickel transition layers.
SUMMARY OF THE INVENTION
In one aspect, the invention comprises a PVD target/backing plate assembly. The assembly includes a PVD target having a surface, and a bonding layer on the surface. The bonding layer has a different composition than the target surface, and a backing plate is provided to be separated from the PVD target surface by at least the bonding layer. The bonding layer can comprise a material capable of forming a strong diffusion bond to the target in less than or equal to about 24 hours at a temperature of less than or equal to about 500° C., and can comprise, for example, one or more of copper, titanium and zirconium. In particular embodiments, the bonding layer can consist of, or consist essentially of, one or more of copper, titanium and zirconium. A “strong” diffusion bond is defined as a bond capable of passing a peel test described herein.
In another aspect, the invention includes a method of forming a PVD target/backing plate assembly. A bonding layer is formed on a surface of a PVD target, and a backing plate is joined to the bonding layer. Accordingly, the backing plate is separated from the PVD target surface by at least the bonding layer. The bonding layer can comprise, for example, one or more of copper, titanium and zirconium.


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