The manufacturing of semiconductors requires very controlled materials and processes, particularly when very thin films are being deposited on wafers and other substrates. One way to form these layers is by sputtering, and the type of material in the target is a crucial factor in determining the properties of the film. Selection of an appropriate target demands consideration of the purity, composition, deposition characteristics, equipment compatibility, and application needs. These factors can assist manufacturers, and engineers in making an informed choice of materials for semiconductor-related processes.
Start With the Required Film Properties
The first step is to determine the objectives of the deposited film. Layers with particular electrical, thermal, mechanical or barrier properties may be needed to meet the requirements of semiconductor applications.
The material for the film must then be chosen for the purpose of the film. Conductive layers can be made from different materials, as can insulating, protective or diffusion barrier layers.
The thickness of the deposit may also affect the deposition method. The same sputtering system can be used to make a thin film with different materials that have different properties.
Purity Is Especially Important
Unwanted contamination can be very critical to semiconductor processes. The presence of small quantities of impurities can influence the electrical properties, film performance or process consistency.
For this reason, Sputtering targets for semiconductors are often evaluated according to strict purity and composition requirements. The material specifications available to the buyer should be checked to see if the desired material is suitable for the process.
When consistent and controlled deposition is important, chemical analysis, and material certification can give helpful information.
Consider Metal and Ceramic Options
Although ceramic materials have a significant role in semiconductor processing, metal targets are widely used for conductive and functional thin films.
The choice of ceramic sputtering targets may be made when properties of the deposited layer that cannot be easily obtained by using conventional metals are needed. Ceramics can offer beneficial electrical, optical, thermal or chemical properties depending on their composition.
The selection of metal or ceramic material should not only depend on the type of material, but should be determined by the function of the film.
Match the Target with the Sputtering System
The target should also be suitable for the equipment to be used. Magnetron configuration, power requirements, target size, cooling system, and deposition conditions may influence material selection.
The thickness and shape of the target should be consistent with the specifications of the equipment. Even if the material is suitable, practical problems may occur due to the physical configuration and the deposition system.
Engineers are therefore advised to carefully consider equipment requirements before ordering, particularly for non-standard target dimensions.
Think About Film Uniformity
Uniform film deposition is crucial if the semiconductor wafers have many small features or multiple processing areas. Inconsistent deposition can impact the operation, and performance of the completed devices.
Uniformity can be affected by the target density, the structure of the material, the deposition parameters, the movement of the substrate, or the system design.
While a suitable target may address all deposition problems, consistent material quality can offer a more solid foundation for process control.
Consider Target Manufacturing Quality
The quality of the manufactured product may affect the behavior of the target in multiple sputtering processes. Some of the following parameters can be considered: density, grain structure, bonding, size, surface condition.
Repeatability is especially critical for production environments. Replacement targets should have similar material properties such that existing process conditions will be as stable as possible.
Technical documentation can be useful to the engineers to compare the products before they decide upon a specific source.
Plan for Application and Production Needs
The research laboratories might need small amounts, and semiconductor manufacturing can involve recurring target needs. Purchase strategy should be based on usage and production plan.
When materials are required regularly, lead times, target availability, quality consistency, packaging and technical support can become important.
It is also helpful to provide information about the application to the supplier. Specifications can help narrow down the choices of materials and configurations.
Conclusion
For semiconductor applications, purity, composition, film properties, equipment compatibility, target design and manufacturing consistency are all important factors to consider when choosing sputtering targets. Depending on the application, both metals and ceramics can play an important role. Engineers should not select a target based on the material type but on the entire deposition process. For those companies looking at specialized sputtering materials, they can go to regmetals.com and discuss their project needs and the options available. The careful selection process can aid in process control and consistent thin-film results.