Joe Brindley, Lara Maroto-Diaz, Víctor Bellido-Gonzalez, Benoit Daniel, Gencoa Ltd, Liverpool, United Kingdom
With the need for higher quality and productivity of vacuum deposition, treatments and processes, it has become more important to control the outgassing of the process environment. Advanced vacuum condition monitoring and control are needed in order to achieve reproducible performance and quality of the process. Outgassing before and during the deposition and treatment is often not being monitored and moreover, controlled. This can result in frequent reductions in yield due to quality performance failures. Uncontrolled outgassing of processes presents a significant problem for meeting coating specifications such as uniformity, stoichiometry, optical, electronic, mechanical and tribological properties.
The most common forms of outgassing in vacuum deposition processes are humidity, organic volatile contaminations and substrate degradation. Effective management of this outgassing has the potential in some cases of being a benefit for the process. For example, in the case of ITO deposition by magnetron sputtering where the level of H₂O plays a crucial role in ITO quality and target nodule reduction. However, in most cases the process outgassing is very detrimental, as for example in the case of hard DLC coating depositions. Additionally, uncontrolled humidity could lead not only to coating and process failures but also to a long pumping time that is translated into a high process cost. Substrate materials and manufacturing methods often create challenges for vacuum process when they present a high content of volatile organic contamination that interact with the coating material. This is common to many polymeric substrates and would usually give problems when trying to engineer a very specific coating performance. Therefore, robust and easily implementable methods are needed in order to monitor and control outgassing in vacuum environments.
In this paper, sensing methods for detection and quantification of outgassing in vacuum processes are presented, focusing on the gas sensing technique of remote plasma emission monitoring (RPEM). Additionally, different methods of overcoming, controlling and solving these problems are presented such as: feedback process control, barrier coatings and plasma treatments. Results based on the deposition of antimicrobial copper based alloys, reactive sputtering for thin film electronics and PVD deposited ITO will be presented.