Edwards hot trap pumping solution enables extended maintenance cycles in depositing TCO films

Edwards has introduced a patented hot trap designed to thermally decompose the liquid diethyl zinc (DEZ) used in depositing some transparent conductive oxide (TCO) films in thin film solar manufacturing. Edwards’ iXH harsh process dry pumps have been optimized for photovoltaic device manufacturing processes. They are designed to handle the high powder loads, high flows of corrosive cleaning gases, and large hydrogen flows associated with thin film silicon deposition processes. Two-pronged solution extends pump maintenance intervals from a week to up to six months, lowering cost of ownership and increasing productivity 

 

Problem

 

TCO films are used in manufacturing large-scale thin film solar cells, where they provide a transparent electrical contact that does not block sunlight from reaching the active area of the photovoltaic device. While such films have traditionally been made of indium tin oxide and deposited with a plasma vapor deposition (PVD) process, PV manufacturers have recently been transitioning to a zinc oxide film deposited by a CVD process, which uses DEZ as a precursor. Zinc oxide-based TCO films deliver a surface topology that improves the light capturing process. However, should unreacted DEZ enter the vacuum pumps during the deposition process, it decomposes, coating pump surfaces and significantly degrading pump operating lifetimes. 

 

Solution

 

Gases leaving the process chamber pass through the Edwards hot trap before entering the vacuum pump. The gases flow through the trap’s replaceable cartridges, which are heated to a temperature that optimizes DEZ decomposition. The trap incorporates a carefully designed gas path that provides sufficient time for decomposition without restricting flow. Cartridges only require replacement on a monthly basis, and can be easily cleaned and reused, helping to lower the cost of this solution. The hot trap can extend pump maintenance intervals up to six months, a significant improvement over the weekly intervals required when it is not used. 

 

Applications

 

Zinc oxide-based TCO films deposition.

 

Platform

 

The iXH also offers a range of operating temperatures that can be tuned to specific process requirements. This makes it ideal for CVD processes depositing TCO films using a DEZ precursor, since the pump can be operated at a low temperature to minimize DEZ decomposition within the pump. In addition, the iXH is up to 40% more energy efficient than pervious generation pumps and is capable of running at greatly reduced power during idle modes, further lowering the cost of ownership of this solution. 

 

Availability

 

May 2011 onwards.