What is the Indium Bonding for Sputtering Target?

The term “indium bonding” in thin film coating industry, simply speaking, refers to bond two (or more) sputtering targets with indium (In), or one (or more) with indium plate together.

Indium

Indium can be uniquely used in lower temperature solders, is one of the softest materials. Indium is preferred for target bonding because of its excellent thermal conductivity of all available bonds. In addition, indium is the most efficient material at drawing heat away from the sputtering target. Most materials can be indium bonded and there are just a few exceptions.

Apart from indium bonding, indium is also popular for a variety of uses and purposes, such as creating alloys, photoconductors, and thermistors.

Indium bond

Sputtering target can be cracked, warped or damaged due to inadequate cooling, low hardness or other reasons. From this point of view, although target bonding does generate a fee, it can well protect your target from damage. It is especially true for those less-strong target materials and precious metal materials.

Elastomer is an alternative bonding method that touts a higher temperature capability over the indium bond. Elastomer bonds are recommended when you are consistently melting indium bonds. We also recommend elastomer bonding for low melting point target materials, as well as, temperature sensitive compounds and targets that have either low density or are especially fragile.

indium target bonding

Indium bonding is preferred in applications where:

Cryogenic stability is needed

Sealing requires high levels of hermeticity

Maximum thermal transfer is required

Bonding to not-metallic surfaces

Flux cannot be used

Backing plates

OFHC Copper Backing Plate is another well-known backing plate. It is frequently used to bond ceramic targets because of its non-magnetism and low coefficient of thermal expansion. This metal has good electrical and thermal characteristics while also being easy to machine, easy to soften, and readily available at a low cost. Copper backing plates can be re-used, with care, 20 or more times.

Molybdenum plate is usually used to substitute copper plate if copper is not appropriate in the application. For instance, the coefficient of expansion for copper is mismatched with some ceramics. And for high-temperature bonding, copper may also oxidize badly or warp. In these conditions, molybdenum is a more suitable material.

SAM Sputter Target

If you are looking for an indium bonding manufacturer, SAM is undoubtedly your best choice. Stanford Advanced Materials is devoted to machining standard backing plates and working together with the Taiwan Bonding Company for providing bonding services. For questions about target bonding materials, methods and services, please see our listing of frequently asked questions (FAQs).

Related blog: When do you need target bonding?

When do you need target bonding?

This post gives an answer when should require a target bonding service and how to choose different bonding services.

SAM®Sputtering targets are the material that is indispensable during a sputtering process. Sputtering targets are normally comprised of one to three distinct parts, including the backing tube, a bonding layer, and the target material. The figure shown below is an example of rotatory sputtering target. Among them, the former two parts are not unnecessary, depending on the type of materials required for the sputtering process and the manufacturing techniques that are available to produce the target. If the target material is brittle and can be easily broken during the sputtering process, it is necessary to require a target bonding service.

parts of rotatory target
parts of rotatory target

 

In terms of the target material, sputtering target varies from pure metal to ceramics. Many pure metal targets are stronger, thus some of them can be made into single piece or monolithic targets without the backing tube or a bonding layer. In contrast, ceramic targets usually require the three-layer construction technique because they are not strong enough to support their own weight and the pressure inside the tube.

Ceramic targets are usually bonded to a stainless steel backing tube because of its non-magnetism and low coefficient of thermal expansion. The thermal expansion coefficients of the backing tube material and the target can never be ignored, because a great difference between these two coefficients can lead to large stress concentrations in the target material during the sputtering process that can cause the ceramic materials to crack and break off.

In addition to stainless steel backing, indium bonding is used more frequently due to its low melting point, good thermal conductivity, low chemical reactivity, and good adhesion to most materials. Indium has the best thermal conductivity of all available bonds and is the most efficient at drawing heat away from the target. Most materials can be indium bonded but there are a few exceptions, mainly due to the low melting point of indium. Indium has a melting point of 156.6°C so temperatures in excess of 150°C will cause the bond to melt and fail.

Stanford Advanced Materials is devoted to machining standard backing plate. Please visit https://www.sputtertargets.net/ for more information.

What should we do when the target is broken?

For most of the time, people consider the purity, and maybe the shape, of the sputtering target when they are purchasing the target materials. But one thing should not be ignored is the target bonding. Well, you think it unnecessary and costly? Then just think about what to do when your target is broken.broken target

Target bonding is necessary

Maybe you can use a copper plate to stick the broken pieces of the target and then polish the target so that the broken areas have minimum exposure to plasma. The second step is very important because the power would suddenly breakdown to zero when plasma strike to broken area of target. And obviously, the film quality will be affected if breakdown is frequent. Although it may help solve the problem when the target is broken, it is still a remedial measure. To avoid target from breaking, you need to give a target bonding service to the target. It is necessary for those brittle targets, and is not expensive compared with the losses of the broken target.

Continue reading “What should we do when the target is broken?”