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Vacuum Trapping for Atomic Layer Deposition Process
(ALD)
ALD is a vacuum deposition process that has become widely used in many different industries including the semiconductor, optoelectronic, LEDS, and the medical to name a few. It offers certain advantages over the traditional CVD type processes. Since this process deposits material on a atomic level it offers the advantages for more precise uniformity on the given substrate and can be achieved at a much lower reactor temperature.
As with any given vacuum deposition process byproducts are generated. These byproducts pose a serious threat to the vacuum pump. Process byproducts such as particulate and unreacted precursors coming off the ALD reactor if allowed to enter the vacuum pump can cause premature pump failure as well as unscheduled system down time.
Vacuum pump inlet traps are used to trap out this material there by protecting the vacuum pump from the contamination. There are a wide variety of traps used in the industry as well as certain approaches to be taken depending upon your specific process parameters and ultimate goals.
The following lists the approaches currently taken and their success level.
I. Small Laboratory Systems
Homemade research systems running very low gas flows and using small vacuum pumps usually do not generate a large amount of byproduct but still pose a threat to the vacuum pump over an extended period of time. The byproducts are normally a combination of particulate and unreacted organic precursor vapors. An approach that has been used very successfully is to install two small traps in series, one with a stainless steel gauze mesh filter to trap out the particulate and the second with an activated charcoal filter installed on the vacuum pump inlet, to adsorb any unreacted precursor vapors.
Our POSI-TRAP 4 with NW-25 ports is compact and can be installed in series very easily. We currently have many traps installed in this configuration in Universities and Research Facilities through out the world.
Small System Manufacturers- Homemade, Anric, Arradiance, Beneq, Denton, Ultratech to name a few.
2. Medium Size Laboratory Systems
Manufacturers or homemade research systems running higher gas flows or using larger vacuum pumps do generate a larger amount of byproducts. In this case, using a multi-stage high capacity vacuum inlet trap will effectively trap out the byproducts. In addition the high capacity design enables the end user to go extended periods of time before the trap has to be serviced.
Our MV MULTI-TRAP 10 with NW-40/50 ports offers three stage of filtration. This includes a cylindrical baffle section and two stages of filtration, each stage holding 5 filters. We recommend stainless steel gauze in the first filtration stage to trap out the particulate and activated charcoal in the second to adsorb unreated precursor vapors. Typically in a medium size research ALD systems the filters only have to be changed once or twice a year.
Medium Size Systems- Lesker, ALD Nanosolutions, Beneq, Picosun, FHR, ATV to name a few.
3. Medium Size Production Systems
Medium size production systems run even higher gas flows and in most cases use dry running vacuum pumps, screw or claw style. Here it is critical to install the correct inlet trap to protect the pump as they are very costly to rebuild. The common dry pumps used on these systems include Edwards, Ebara, Leybold, and Pfieffer/Alcatel to name a few.
Our MV MULTI-TRAP 10″/12″, with (NW-40 to ISO-100 ) ports with the stainless steel gauze and activated charcoal filters installed have proven to be very effective in trapping out the byproducts and protecting these expensive dry running vacuum pumps.
Medium Size Production Systems- Oxford Instruments, SVT. SPTS, Picosun, Beneq to name a few.
4. Large Size Production Systems
Production systems used in the semiconductor industry have very high gas flows and use large very expensive dry running vacuum pumps. These systems tend to generate large amounts of byproducts that have to be handled in various locations of the system. Typically the vacuum line coming of the ALD system can run from the cleaning room where the system is located down to a subfab where the dry pump is located. The throttle valve is usually located in the clean room not far away from the system exit port. Material can build up in the throttle valve resulting in frequent cleaning requirements and unscheduled system down time.
Our POSI-TRAP 8 modified to have ISO-80/100 ports and stainless steel gauze filters installed have been effective in trapping out the byproducts and protecting the throttle valve from material build up. In this case customer will install a heater jacket on the POSI-TRAP and heat up to 180C. The trap’s function here, is to serve as a secondary ALD reaction chamber and the material deposits in the trap and filters.
It is important to note, although this approach will effectively protect the throttle valve, due to the high gas flow/ process inefficiencies, large amounts of material will also accumulate in the subfab dry pump over a period of time. If not trapped, this material can cause premature dry pump failure.
Our MULTI-TRAP 16 with ISO-160 ports set up to hold one large high surface area filter has been very effective in trapping out this material before the subfab dry pump.
Another approach that has been used effectively is a reactive style trap. In this situation the end user uses our MULTI-TRAP set up for 9.5″ long stainless steel gauze filters and a NW-16/25 port is installed in the inlet tube of the trap. The end user installs a needle valve on this port and bleeds in ambient air into the trap while running the ALD system. This results in a reaction between the two as the precursor enters the trap and the byproducts are trapped on the baffle and 9.5″ long stainless steel gauze filters.
This is a reactive approach that is normally only used in production semiconductor fabs. It is important to note that this approach should only be used by experts that are familiar with the stability of the ALD precursor in question.
Large Size Production Systems- ASM, AMAT, LAM Jusung to name a few.