Large Area Multi-wafer MOCVD of Transparent and Conducting ZnO Films
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Large Area Multi-Wafer MOCVD of Transparent and Conducting ZnO Films Gary S. Tompa1, S. Sun1, L. G. Provost1, Dan Mentel1, D. Sugrim1, Philip Chan2, Keny Tong2, Raymond Wong2, and A. Lee2 1 Structured Materials Industries, Inc., 201 Circle Drive North, Unit 102/103, Piscataway, NJ, 08854 2 Podium Photonics, Ltd., Kowloon, Hong Kong
ABSTRACT ZnO thin films are of interest for an array of applications, including: light emitters, photovoltaics, sensors and transparent contacts, among others. Production routes for ZnO include sputtering, MBE and MOCVD. This paper focuses on our efforts to produce a large scale MOCVD thin film production tool and the results obtained from the reactor. Specifically, we have constructed a tool with a 16" wafer carrier that uniformly deposits ZnO films on 38x2" wafers simultaneously. The reactor operates at low pressure (2000 hrs in air @ ~100C, and are easily etched as shown in the ~3”x 5” patterned display glass (d).
Other films were fabricated into transparent heaters and exhibited high stability, failing well after 2000 hours when the contact pads failed – not the film. Another very important feature of MOCVD growth of ZnO films is that the film structure can be greatly tuned on almost any surface by changing the process parameters, as shown in Figure 2. Specifically, we have grown fully dense epitaxial or amorphous films, close packed columnar structures, porous films (not shown), and nanowires. Each of these films has different properties with respect to light emission and metal contacting. The objective of this work has been to develop a viable production method for superior transparent conductive contacts to GaN-based p-type terminated surface-emitting LEDs. In this case viable production means uniform and repeated production of films that offer efficiency enhancements deposited at sufficient rates to meet continuous GaN LED production, without adding cost to the product. SMI has worked with both static and high-speed rotating disc reactors. Based upon past efforts and a desire to mitigate chemical prereactions, we elected to scale the high speed rotating disc reactor for depositing ZnO over large areas. The high speed rotating disc reactor offers unique advantages in growth rate, uniformity and freedom from particulates.
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500nm
Figure 2. Example of the range of film structures that can be produced by MOCVD a) Highly crystalline continuous film, b) close packed oriented crystalline columns, and c) arrayed nanowires. In high speed (several hundred rpm) rotating disc reactors the substrate holder is a disc in the horizontal plane in a vertically oriented reactor. The substrate holder is typically heated radiatively from below. Precursors in vapor form, along with carrier gases, are injected downwardly from the top of the reactor. Without high speed rotation, natural thermally-driven buoyancy pushes gases heated at the deposition plane upward and thus disruptively against the downward flow, which would lead to increased prereactions of the precursors and
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