VPI Technical Analysis: Why Do Sputtering Targets Need Backing Plates?

In the process of using VPI's high-vacuum magnetron series sputtering coating instruments, sputtering targets are essential components for achieving high-quality thin films. However, to ensure the stability and efficiency of the sputtering process, targets usually need to be equipped with backing plates. So, why do targets need backing plates? What role do backing plates play during sputtering? Engineer Li from VPI will provide a brief technical explanation.

Main Functions of Backing Plates

1. Enhancing Heat Transfer to Prevent Target Overheating

During the sputtering process, high-energy ions continuously bombard the target surface, generating a large amount of heat. If this heat is not dissipated promptly, the target will overheat, which may lead to cracking or even breaking. One of the primary functions of the backing plate is to improve the thermal conductivity between the target and the cathode, quickly transferring heat away and maintaining the target's temperature stability.

2. Securing the Target to Extend Its Service Life

The backing plate provides mechanical support; even if the target develops cracks due to thermal stress, the backing plate can still hold the target in place, ensuring the continuity of the sputtering process. This not only extends the target's service life but also improves production efficiency.

Selection of Backing Plate Materials

Choosing the appropriate backing plate material requires considering multiple factors, including thermal conductivity, mechanical strength, and matching the thermal expansion coefficient with the target material. Common backing plate materials include:

• Oxygen-Free Copper: Excellent thermal conductivity, can be reused multiple times, suitable for most metal targets.

• Stainless Steel: High mechanical strength and corrosion resistance, suitable for applications requiring strong support.

• Molybdenum: Suitable for high-temperature conditions or targets that have mismatched thermal expansion coefficients with ceramics.

• Tungsten and Graphite: Less commonly used but viable choices under specific conditions.

Methods of Bonding Targets to Backing Plates

1. Diffusion Bonding

By pressing the target and backing plate together under high temperature and high pressure, the atoms of both materials diffuse into each other, forming a strong bond. This method achieves a bonding area close to 100%, suitable for applications requiring high thermal conductivity and reliability.

2. Solder Bonding

Uses solder (such as indium) to connect the target and backing plate. Indium has good thermal conductivity and flexibility, accommodating the thermal expansion of the target. However, indium has a low melting point (156.6°C) and is not suitable for high-temperature applications.

3. Elastomer Bonding

Suitable for brittle and high-melting-point targets like alumina and silicon. Elastomers can withstand operating temperatures up to 250°C and have ultra-high vacuum compatibility, making them suitable for temperature-sensitive and low-density targets.

4. Other Bonding Methods

   • Electron Beam Welding: Uses a high-energy electron beam in a vacuum environment to achieve local welding.

   • Plasma Arc Welding: Utilizes high temperatures generated by an arc to fuse materials.

   • Friction Stir Welding: Achieves material bonding in the solid state by generating heat through mechanical friction.

The Critical Role of Backing Plates in Sputtering Targets

Backing plates play a crucial role in sputtering targets. Correctly selecting backing plate materials and appropriate bonding methods can not only improve the stability and efficiency of the sputtering process but also extend the target's service life and reduce production costs. As engineers at VPI, we are committed to providing our customers with the highest quality sputtering solutions. If you have any questions or needs regarding the application of backing plates in targets, please feel free to contact us at any time.