Design of a radio-frequency facing-target sputtering system for low-damage thin film deposition
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Thin film devices are becoming increasingly important in the electronic semi- conductor industry. For example, organic light-emitting diodes provide many advantages for the development of flat panel displays used in mobile phones, while thin film transistors have provided solutions in the fabrication of OLED backplanes. Organic photovoltaics have the potential to provide our planet with a vast supply of clean, cheap energy. Thin film deposition processes today have a number of drawbacks, including complicated and time-consuming operation procedures, high cost of construction, and laborious maintenance procedures. While these methods are currently being used effectively in premier research laboratories, addressing these problems would open up the field to researchers with less time and fewer resources. For this purpose, we have designed and constructed a state-of-the-art thermal evaporator which is inexpensive, simple and quick to operate, and easy to maintain. While common thermal evaporators are situated inside the glove box, the evaporator developed in this project is mounted instead beneath the glove box floor with top-loading substrate access from inside the glove box. A retractable base plate elevator system enables access to the chamber from outside the glove box through the chamber floor. These improvements maximize space inside the glove box and accessibility of the evaporator chamber, and the chamber’s compact size significantly reduces construction costs and pump-down times. We have also designed a radio-frequency facing-target magnetron sputtering system, which shares these features. However, current sputter deposition processes face additional problems. The fabrication of many semiconductor devices involves deposition onto a substrate previously coated with an organic thin film. Energetic particles in the sputtering plasma have been shown to cause critical damage to underlying organic layers on substrates during sputter deposition. Consequently, our sputtering system takes advantage of the facing target configuration, which has been shown to effectively confine the sputtering plasma below the substrates, thereby protecting previously deposited organic layers. The design also features high strength magnets positioned above the sputter guns to create a high magnitude magnetic field near the substrates for further protection from high energy electrons and ions. Radio frequency excitation of the sputtering plasma allows for the deposition of insulating materials. CAD designs for both the evaporator and the sputtering system were created in SolidWorks, and Finite Element Analysis (FEA) was performed using Maxwell 3D. The evaporator has been built and is operating smoothly with no user errors. The total cost was under $40K. The chamber takes less than 3 minutes to pump down, while deposition takes less than 10 minutes. Cleaning is as easy as switching out the metal sleeve, which takes 15 minutes at most.