Hot wire CVD systems attract attention for amorphous silicon
11/01/1996
Hot wire CVD systems attract attention for amorphous silicon
In the last few years, hot wire CVD deposition technology, originally used in the diamond-like coating arena, has attracted attention in the amorphous silicon field. "People want higher deposition rates and lower hydrogen concentration because of instability in the amorphous silicon area," noted Arun Madan, president of MVSystems Inc., Golden, CO. "It`s possible that hot wire can provide both, and can make polycrystalline silicon at low temperatures. It can be a very useful technique down the road."
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Figure 1. Hot wire CVC assembly allows for adjustable grids.
MVSystems supplies hot wire CVD tools. Customers at the University of Michigan and the University of the Western Cape, South Africa, will use their systems for amorphous silicon technology development in the areas of flat panel displays and amorphous silicon solar cells, respectively.
A hot wire CVD system consists of a process chamber capable of holding substrate sizes ranging from 10 cm ? 10 cm to 30 cm ? 40 cm and with a substrate temperature >550?C. The hot wire assembly includes a grid design (Fig. 1) with substrate/grid distance variable, and automated movement of substrate during deposition (Fig. 2).
Four electronic mass flow controllers pump process gases with electropneumatic actuation. A corrosion resistant turbomolecular and a rotary vane pump with chemical filter are installed. For controls, the system displays mass flow control, current power supply, turbo pump power supply, and pressure control, and features a Pirani type gauge, ion gauge, and capacitance manometer. Systems sell for between $100,000 and $400,000 depending on the number of chambers, the type of diagnostic tools included, and other options.
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Figure 2. The substrate level oscillates during deposition.
Hot wire now competes with plasma-enhanced CVD, but demand for hot wire is growing. "I am amazed," said Madan. "MVS has entered the field less than a year ago, and we`ve sold four systems, two to overseas entities. This many sales in a year for a new technology is amazing. I believe that demand for hot wire will catch up with plasma if hot wire materials can be developed to be better than plasma CVD."- L.S.