Currently, integrated circuits–the microelectronic devices or components–are moving toward high speed, small size, and narrow pitch.
An integrated circuit usually uses a certain process to interconnect components and wirings such as transistors, diodes, resistors, capacitors, and inductors required in a circuit; and these components are fabricated on one or several tiny semiconductor wafers or dielectric substrates; and then they are packaged in a single package to becomes a tiny structure with the required circuit function.
In order to make the chip better connected to the metal electrode, a metal film is usually deposited on the chip. Among many coating materials, gold films made of high-purity gold evaporation pellets or gold sputtering targets have excellent chemical stability, good electrical and thermal conductivity, and are easy to bond and easy to form. Therefore, gold film coating materials have been widely used as coating materials for semiconductor chips in various industries.
The quality of the gold film applied on the semiconductors directly affects the operation of the devices or even the entire circuit, so defects in the gold coating process need to be strictly detected. This case study is about black particles appeared in the gold evaporation processes.
The gold evaporation materials used in production are mostly granular or linear. The production process is smelting – cleaning – drawing – granulation / winding (according to customer requirements) – culling – washing – drying. After supplying the material to the customer, the customer needs to clean and melt the material before it evaporates. However, in the actual painting process, customers found that no matter which batch of products are used, the following problems will inevitably occur:
1 After melting, the surface of the liquid has black particles.
2 After cooling, the substance on the black surface appears.
3 After plating, the surface of the chip has black particles.
In the past, the industry has always believed that these floating black particles are carbon particles, which are caused by graphite crucibles. However, in reality, the essence of this black substance is gold.
But why are the substances we see black rather than gold? That’s because the gold surface is coated with carbon oxide, so it looks black. The cause of these substances may be related to residual lubricants or human contamination.
In order to avoid this kind of pollution, you can start from the following aspects: reduce the concentration of lubricating fluid, reduce the drawing speed, increase the pickling time, increase the drying temperature, prolong the drying time, and avoid direct contact with the evaporation gold surface.
You can visit Stanford Advanced Materials for high purity gold coating materials. Or you can contact the author Julissa Green via email julissa@samaterials.com for more information.
Vacuum Evaporation Coating 