Sputtering Targets for Thin Film Deposition - MetalsTek

A sputtering target is a material that is used to create thin films in a technique called sputter deposition or thin film deposition.

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During the sputtering process, the sputtering target material, which starts as a solid, is bombarded by gaseous ions and broken up into tiny particles that form a spray. This spray then coats another material, called the substrate, depositing a thin film on its surface.

Sputtering targets are commonly made of metallic elements or alloys, though some ceramic targets are also used to create hardened thin coatings. The size and shape of sputtering targets can vary greatly depending on the specific application, ranging from less than 1 inch in diameter to over 1 yard in length. Some sputtering systems use rotating cylindrical targets to provide more even thin film deposition.

The effectiveness of a sputtering target depends on factors like its composition and the type of ions used to break it down. The choice of inert gas, usually argon, to ionize and initiate the sputtering process is also important for producing a high-quality thin film. The atomic weight of the gas ions should be like that of the target material molecules.

Sputtering targets are used in a wide range of applications, including the production of semiconductors, computer chips, solar cells, low-E glass, optical coatings, and various electronic components.

It takes place in a vacuum chamber filled with a low-pressure inert gas, typically argon. A negatively charged target material, known as the sputtering target, is placed in the chamber. A high voltage is applied between the target and the substrate, which causes the inert gas to become ionized, creating a plasma.

The positively charged gas ions in the plasma are accelerated towards the negatively charged target. When these high-energy ions collide with the target, they knock off atoms from the target material. The sputtered atoms from the target travel through the vacuum and deposit onto the substrate, forming a thin film coating.

The sputtering process continues until the desired thickness of the thin film is achieved. The rate of deposition can be controlled by adjusting factors like the power applied, gas pressure, and target material.

Sputtering is used to deposit a wide variety of thin film materials, including metals, alloys, and ceramics, onto substrates for applications in semiconductors, optics, electronics, and more.

The sputtering process can be influenced by various parameters, such as the energy of the ions, the angle of incidence, the target material, and the background gas pressure. Adjusting these parameters can help control the deposition rate, film properties, and overall efficiency of the process.

Sputtering targets come in a variety of materials and forms, each suited for specific applications. Some common types of sputtering targets include:

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By Materials

The type of material used for a sputtering target significantly influences the properties and quality of the final thin film. Choosing the right material for a sputtering target depends on the intended application of the thin film, the required properties (e.g., electrical conductivity, hardness, optical properties), and compatibility with the sputtering equipment and process parameters. Each material brings distinct characteristics to the thin films, which can dramatically affect performance in their final application.

Here’s an overview of the common types of materials used for sputtering targets, categorized by their nature and applications:

1. Metallic Sputtering Targets

• Pure Metals: Includes metals like Aluminum (Al), Copper (Cu), Gold (Au), Silver (Ag), Tungsten (W), and Titanium (Ti). These targets are widely used for conductive and reflective coatings.
• Alloys: Common alloy targets include Brass, Bronze, and Stainless Steel. These are used when a combination of properties from different metals is desired in the thin film.

2. Oxide Sputtering Targets

• Simple Oxides: Such as Aluminum Oxide (Al2O3), Zinc Oxide (ZnO), and Titanium Dioxide (TiO2). These oxides are typically used for optical coatings, insulating layers, and barrier films.
• Complex Oxides: Examples include Indium Tin Oxide (ITO) and Yttrium Barium Copper Oxide (YBCO). ITO is extremely important in the production of transparent conductive coatings for displays, while YBCO is used in superconducting films.

3. Sulfide Sputtering Targets

• Common Sulfides: Include Zinc Sulfide (ZnS) and Cadmium Sulfide (CdS). These materials are often used in photovoltaic solar cells and as phosphor materials in TV screens.

4. Nitride Sputtering Targets

• Popular Nitrides: Such as Silicon Nitride (Si3N4), Titanium Nitride (TiN), and Boron Nitride (BN). These compounds are used for hard protective coatings in tools and bearings, as well as in semiconductor processes.

5. Carbide Sputtering Targets

• Typical Carbides: Include Silicon Carbide (SiC), Tungsten Carbide (WC), and Boron Carbide (B4C). These are used for wear-resistant coatings and in semiconductor electronics.

6. Fluoride Sputtering Targets

• Fluorides like: Magnesium Fluoride (MgF2) and Calcium Fluoride (CaF2) are primarily used in optical coatings due to their high transparency from ultraviolet to infrared wavelengths.

7. Selenide and Telluride Sputtering Targets

• Important Compounds: Include Cadmium Telluride (CdTe) and Zinc Selenide (ZnSe). CdTe is crucial in thin-film solar cells, whereas ZnSe is used in infrared optics.

8. Rare Earth and Other Exotic Sputtering Targets

• Rare Earths and Other Elements: Such as Gadolinium (Gd) and Europium (Eu) are used for specific applications in high-tech industries like nuclear reactors and fluorescent lamps.

By Shapes

Sputtering targets not only vary significantly in material composition but also in shape. The shape of a sputtering target can influence the efficiency of the sputtering process, the uniformity of the film deposition, and the overall utilization of the material. Below are the common shapes of sputtering targets used in thin film deposition processes:

1. Planar Sputtering Targets

Rectangular Targets

• Often used in large-area coating processes.
• Common in flat panel display (FPD) technology and large-scale photovoltaic cell manufacturing.
• Provides consistent deposition over wide areas.

Circular Targets

• Typically used in smaller scale research and development settings.
• Compatible with many standard sputtering systems.
• Efficient for uniformly coating round substrates.

2. Rotary (Cylindrical) Sputtering Targets

Rotary Targets

• These targets are tubular and rotate during the sputtering process.
• Offers higher material utilization compared to planar targets.
• Reduces the need for frequent target changes, making them cost-effective for large production volumes.
• Common in the manufacturing of coatings for architectural glass and web-coating applications.

3. Custom Shapes

Tube Targets

• Specific to certain types of coating systems that require internal coating, such as tubes or cylinders.
• These are used in specialized applications such as coating the inside of narrow tubes.

Ring Targets

• These are used for specific applications where the target geometry helps achieve uniform thickness across complex-shaped substrates.

Segmented Targets

• Consist of multiple pieces that can be individually replaced.
• Useful for complex deposition patterns and for conserving expensive materials.

4. Target Tiles

• Small, square, or rectangular pieces of target material that can be assembled to form a larger sputtering target.
• Allows for flexibility in size and design while maintaining high material utilization and easy replacement.

Considerations for Choosing Target Shapes

The choice of target shape is influenced by several factors:

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• System Compatibility: Must fit the physical constraints of the sputtering system and the type of sputtering being conducted (e.g., magnetron sputtering, ion beam sputtering).
• Material Utilization: Rotary and other dynamic target shapes generally offer better material utilization rates compared to static planar targets.
• Deposition Uniformity: Certain shapes may provide more uniform deposition over the substrate depending on the application.
• Production Volume and Cost: Rotary targets might be more economically viable for high-volume production due to their longer life and better material usage.