Secondary Plasma Surface Treatment for Sensitive Electronics

What Is Secondary Plasma?

Secondary plasma provides two additional modes: Downstream Secondary Plasma and Ion-Free Plasma (IFP). Secondary plasma is typically used when a less intense plasma exposure is desired, or the sample is sensitive to specific components of a primary plasma. Downstream secondary plasma is a more benign but similar alternative to primary plasma.

Downstream Secondary Plasma for Sensitive Electronics

Downstream secondary plasma contains the same types of active species as a primary discharge, but with lower kinetic energy. The configuration relies on the transfer of the active species (ions, electrons, radicals, and byproducts) from an upstream primary discharge to a secondary process chamber or sample placement area. The secondary downstream plasma is initiated by the diffused ions and electrons and sustained with additional process gas in the secondary chamber. This configuration relies on both the physical and chemical plasma mechanisms. It has the advantage of relatively benign plasma processing, but applications can lack uniformity of treatment.

Ion-Free Plasma (IFP) for Extremely Sensitive Devices

Ion-Free Plasma (IFP) is a purely chemical plasma, free of both ions responsible for the physical component and photons. The IFP process consists of generating active species upstream of the sample processing area, then diffusing them through a gas baffle assembly. The gas baffle removes ions, electrons, and photons, allowing only the plasma-generated free radicals and byproducts to reach the sample area for chemically reactive plasma processing. The removal of ions and light eliminates the concerns of processing extremely sensitive devices, as there is no ion bombardment or UV light exposure at the sample.

Specific applications of the IFP technology include cases where exposure to active species in a traditional primary plasma may cause damage due to ion bombardment sensitivity or UV light susceptibility. Specifically, devices such as pre-programmed ASIC or memory devices, and CMOS image detectors may require an unfamiliar strategy for plasma processing – the isolation and use of specific components within the plasma. The newly defined secondary mode of IFP plasma has enabled successful applications where more traditional plasma configurations have failed. The IFP plasma approach, while it is not necessary for most traditional packaging applications, has proven to be an enabling technology for advanced memory components and hybrid packages. Additional plasma applications with similar damage concerns that benefit from an IFP plasma include: pre-programmed ASICs susceptible to erasure, CMOS image detectors, thin-film substrates with bond pad thicknesses sensitive to sputtering, and flip-chip and wafer-level devices.

Applications for Advanced Electronics Manufacturing

Qualification and implementation of a plasma process, in most cases, will rely on configurations familiar to most of us, utilizing a directional direct plasma mode that relies on ions, electrons, and free radicals of a specific gas chemistry for process enhancement. There is a growing realization that traditional methods and configurations that do not work for new advanced memory components can now benefit from a newly defined plasma mode. This plasma mode, which is free of electrons, ions, and light but full of chemically reactive species and capabilities beyond what was previously available, may be the answer to the challenges we face now and in years to come.

Choosing the Right Plasma Treatment System

For additional support on which plasma mode is right for your process, please contact us at [email protected].