Updated: July 2002

1. Equipment overview

Perfluorocompounds (PFCs) are used throughout the semiconductor and liquid crystal display (LCD) industries for a variety of process applications. Since PFCs were specified as global warming gases at the 3rd Conference of the Parties (COP3) held in Kyoto in 1997, it has become increasingly important to abate or neutralize them. The semiconductor industry has faced an ongoing problem since PFCs possess from thousands to tens of thousands times as high global warming potential as carbon dioxide, and are very stable and difficult to break down. Hitachi has solved this problem by successfully developing proprietary catalytic decomposition technology and PFCs such as CHF3, C2F6, C3F8, C4F8, C5F8, SF6, NF3, and even CF4, the most difficult PFC to decompose in general, can be broken down by more than 99% at around 750 degrees Celsius, including carbon monoxide (CO), while maintaining the lowest CoO (Cost of Ownership) available today.

2. Characteristics

(1) Using the proprietary catalyst
The catalyst is popular for environmental protection
(EX. automobile, power-plant, chemical-plant)
(2) Low running costs
Although PFCs are chemically very stable and require temperatures of more than 1200 degrees Celsius to decompose, they can be decomposed by more than 99% at only 750 degrees Celsius by using the proprietary catalyst. Small water consumption and small exhaust gas also helps to reduce running costs.
(3) Simple, easy and safe to operate
Heated by electricity, No fuel required, SEMI-S2, CE compliant.
(4) Environmentally friendly
Used catalyst can be recycled as material in the steel manufacturing industry. No thermal NOx, Low energy consumption.

3. Performance

Fig.1 shows the PFC treatment system flow. Exhaust gases from an etch process, which include PFCs, are washed in a pre-packed tower and pre-sprayed to remove solids such as SiO2. The gases are heated with DI water and Air to 750 degrees Celsius in the heater and PFCs are then decomposed into HF and CO2 by the catalyst. The hot decomposed gases are then cooled in a cooling room. Since HF gas is formed by the catalytic reaction, a post-packed tower is included to remove the acidic gas from the decomposed gases. The final exhaust by-products are CO2 and fluoridated water. The unit is shown in Fig.2.

Fig.1 PFC treatment system flow

Fig.2 PFC Catalytic Decomposition System

The temperature dependence of PFC conversion is shown in Fig.3. PFCs are decomposed at 750 degrees Celsius with more than 99% conversion rate.
As toxic CO is often utilized in the etching process, it is also necessary to remove CO when considering actual usage. The catalyst is also useful for oxidation of CO. A temperature of 300 degrees Celsius is sufficient to remove CO.
The catalyst can maintain its decomposition performance for more than 1 year.

Fig.3 Conversion rate for PFC and CO

4. Application

1) Semiconductor manufacturing factory
2) LCD manufacturing factory

5. Others

3 types that each have a gas treatment capacity of 60L/min, 120L/min, 200L/min are released.