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Critical Seals in HDPCVD Processes
Extending Lifetime of Critical Seals in HDPCVD Processes
The Challenge
As the semiconductor industry continues to invest in 300 mm wafer fabrication, the spotlight is on process improvement and the greater demands this technology makes on process equipment. In HDPCVD processes elastomer sealing materials can be a weak link because of the need for seal replacement during preventive maintenance (PM) procedures.
Exhaustive testing of sealing materials on CVD platforms reveals that potential risks of contamination can be reduced and mean time between replacement (MTBR) extended by careful selection of sealing materials. A recent breakthrough in perfluoroelastomer (FFKM) seal technology promises significant improvements in seal life and a potential reduction in in-chamber particulate contamination.
The Solution
One of the roles of the international research center IMEC (Leuven, Belgium) is to prove next-generation technologies, including prototypes of wafer fabrication equipment for its strategic partners (Fig. 1). This is done by replicating typical process conditions in the industry, and then pushing materials and equipment to anticipated production-level demands 3-5 years ahead of production. With several “one-of-a-kind” tools in the facility, learning cycles are of the utmost importance in supporting R&D needs.
The cost of O-ring seal replacement is significant. A complete seal kit for a CVD chamber can cost as much as €5000 (~US$7400). The organization has tested a variety of FFKM seals in top nozzle, gate valve, and turbo and roughing isolation valve positions in its Centura® Ultima 200 mm high-density plasma CVD platforms.
Two types of FFKM O-rings were extensively attacked in the top nozzle position in an environment of phosphine (PH3), oxygen (O2), silane (SiH4) and nitrogen trifluoride (NF3) plasma cleaning gas. These seals also exhibited signs of high stress in some locations — probably induced by high-temperature excursions typical of this type of application. Similar problems were observed in both shallow trench isolation (STI) and intermetal dielectric (IMD) deposition applications.
The O-rings composed of older FFKM compounds (typically nano-silica or metallic-oxide filled) positioned in the roughing isolation valve and exposed to all of the gases, in particular to NF3 plasma were cracking and deforming. These seals had to be replaced every 5000 wafer cycles. That meant dismounting the isolation valve from the pump lines, conducting a leak check, cleaning the process kit and closing the chamber an expensive operation in materials cost, installation time and labor. Similar results were observed with the gate valve seal, where the O-rings were subjected to mechanical stresses as well as heavy chemical attack.
Key Advantages
Kalrez® 9100 perfluoroelastomer parts were tested in some of the most critical seal positions. Initially, the equivalent service time of 5000 cycles was used in the identical process environment. The 9100 seals appeared undamaged in the isolation valve and top nozzle positions and exhibited no sign of cracking (Fig. 2).
The engineers determined that next-generation O-rings withstand 10,000 cycles, and it is possible this lifetime can be extended further. Because there is no need to remove the top nozzle or dismount the isolation valve, there is also no need to perform a leak check afterwards. Based on these results, users can expect to double or even triple the lifetime of seals in CVD platforms. IMEC has plans to change the FFKM seals on all positions to Kalrez® 9100 seals, starting with the 200 mm line. Similar results are expected in 300 mm tools.
Features
Standard Kalrez® O-Ring Compounds
Kalrez® Compounds – 4079
4079 perfluoroelastomer parts are a black, low compression set product for use in many dry and wet semiconductor process environments. It has excellent chemical resistance, good mechanical properties and outstanding thermal stability.
Kalrez® Compounds – 6375
6375 is designed to give outstanding performance in the widest possible range of chemicals and temperatures. This product is an excellent choice for use in acids, bases, amines, steam, ethylene oxide, and many other aggressive chemicals.
Kalrez® Compounds – 7075
7075 is designed for general-purpose use as O-rings or custom sealing components in the chemical and hydrocarbon processing industries. It is a carbon black-filled compound with mechanical properties designed for improved sealing performance in temperature cycling applications. 7075 has improved thermal resistance that extends maximum service temperature to 327 °C (620 F).
Kalrez® Compounds – 0090
0090 perfluoroelastomer parts deliver durable, reliable sealing solutions for applications requiring excellent rapid gas decompression (RGD) properties as well as high hardness and high modulus properties. Some application areas include downhole equipment such as drilling and completion tools as well as industrial equipment including pumps and valves.
Specialty Kalrez® O-Ring Compounds
Kalrez® Spectrum™ – 7375
Kalrez® Compounds -6380
6380 is a non-black product specifically developed for chemical processes involving hot, aggressive amines. It has also been successfully used in applications involving highly oxidizing chemicals. In addition, it has excellent overall chemical resistance. This cream colored product is easily identifiable when selecting an O-ring material for harsh chemical plant services.
Kalrez® Compounds -7090
7090 is a product for uses requiring higher hardness/higher modulus than more typical applications. Kalrez® 7090 perfluoroelastomer parts are well suited for both static and dynamic applications as well as specific sealing applications requiring extrusion resistance at high temperatures.
Kalrez® Compounds -0040
0040 -is a black product specifically designed for low temperature environments where significant chemical resistance is required. Kalrez® 0040 parts maintain elasticity and seal force at temperatures unattainable by other perfluoroelastomers.
Kalrez® Compound – W240
Kalrez® is a registered trademark of E.I. du Pont de Nemours and Company or its affiliates
