C-317 The Practice of Reactive Sputtering
This tutorial is intended for engineers, technicians, materials scientists, and coating developers, who have a desire and need to understand how the reactive sputter deposition process really works. The goal of the tutorial is to give the student a thorough understanding of all of the factors that affect the reactive sputtering process in order that the student can apply this knowledge to improve their reactive deposition process and achieve both high deposition rates and excellent film properties.
This tutorial covers the basics of reactive sputtering followed by a comparison of the use of flow control versus partial pressure control of the reactive gas. The latter allows operation in the transition region between the metallic and poisoned states of the target, and films can be deposited at much higher rates with excellent properties using partial pressure control compared to flow control of the reactive gas. Along with using partial pressure control, it is important to use the right type of power to assure that there is no arcing during the deposition. Which type of power to use and along with which partial pressure sensor are reviewed. Large area coating presents special challenges for the control of the reactive gas, and the need for multiple gas inlets along the length of a long cathode and sensing in each gas inlet zone are discussed. The requirements for a partial pressure control system along with commercially available controllers are presented. Multiple gas reactive sputtering and reactive high power pulsed magnetron sputtering (HPPMS) are emerging areas that are advancing the state of the art for reactive sputtering. How they work and what factors are important for controlling these two processes are discussed.
- Basics of reactive sputtering
- Flow control versus partial pressure control of the reactive gas
- Power supplies for reactive sputtering
- Reactive gas sensors
- Large area reactive sputtering
- Control systems for reactive sputtering
- Multiple gas reactive sputtering
- Reactive high power pulsed magnetron sputtering
The tutorial begins with an introduction to the basics of reactive sputtering and the interaction of the reactive gas with not only the growing film but also with the target surface. Hysteresis effects are discussed and the advantages and disadvantages of using either flow control or partial pressure control of the reactive gas are discussed. Flow control of the reactive gas usually results in operation of the sputtering target in the poisoned mode, which results in a loss of deposition rate and the growth of films with less than optimum properties. However, use of partial pressure control of the reactive gas allows operation in the transition region between the metallic and poisoned states of the target, and compound films can be deposited at high deposition rates with excellent properties. Power supply technology greatly influences the reactive sputtering process, and the different types of power and how it affects the process are presented. Reactive gas sensors play a very important role in the reactive deposition process, and the four common sensors are reviewed to give the student a better understanding of which sensor to use for a particular reactive sputtering process. Large area reactive deposition, as is practiced in the architectural glass or web coating industries, presents special challenges for reactive sputtering such as the need for multiple gas inlet manifolds and control of the partial pressure of the reactive gas in each of the inlet zones. The requirements for the reactive gas control system are presented, and commercial reactive gas control systems are reviewed. Multiple gas reactive sputtering is a more complex process due to the interaction of both gases with the target surface. One gas may trap the target in a poisoned mode, but methods to prevent such trapping are presented. Finally high power pulsed magnetron sputtering (HPPMS), where a very high power pulse, which can be on the order of megawatts, is applied to the target for a short period of time on the order 100 ?s is an emerging technology that will be beneficial for reactive sputtering. With HPPMS, a large fraction of the sputtered atoms becomes ionized, and the ions can be used to produce dense films with enhanced properties. Since the ion to neutral ration is high for the species arriving at the substrate, low substrate biases on the order of 20 eV can be used to attract the ions. With such conditions, the film stress will be reduced, which means that thicker films than now can be deposited should be able to be produced with reactive HPPMS.Instructor: Bill Sproul, Reactive Sputtering, Inc. and Gencoa Ltd.
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