Why Heat Vacuum Pump Forlines and Exhaust Lines?
Many thin film processes produce a high amount of effluent material that clogs up vacuum forelines and exhaust lines, causing lots of tool downtime to clean or replace the lines, as well as high particulate back-streaming. Common process examples are aluminum plasma etch, PECVD, and LPCVD.
A popular alternative is to use traps, which are a reasonable solution for some processes if you have enough installation room near your chamber exhaust port and are willing to break the trap open frequently for cleaning. Trapping is less expensive up front; but can lead to higher long term maintenance costs, and also does not do as much to reduce the threat of particulate back-streaming back into your process chamber.
Maintaining your lines above a certain temperature, depending on the process, causes the effluent to remain in a gaseous state until it reaches a cooler point such as a point of use scrubber. We have observed the time between foreline maintenance increase from as little as 2 months to well over 2 years after a closed loop temperature control system was installed.
The heaters are connected together electrically, in parallel, to form a closed loop zone. Each zone is controlled via a PID (Proportional, Integral, Derivative) loop. Once the desired temperature is set the loop will drive to the setpoint and then stay there with a trickle of power (~30%) which extends heater life.
Heaters for pump and exhaust lines are usually 1.5 to 6" in diameter, and are offered in standard straight lengths for any linear run, plus in configurations to fit TEEs, elbows, bellows, and a variety of valve types. Heaters for gas lines are offered in straight sections as well as "Stretch To Length" versions which are ideal for curving and/or tight sections.
The temperatures required vary based on exhaust pressure. Examples for some common applications are:
PECVD nitride: >120C at 1 Torr
LPCVD nitride: >150C at 1 Torr
Aluminum Etch: >75C at 0.1 Torr
IES Technical Sales is a value added technical sales, distribution, and solutions provider serving the high technology vacuum, plasma/thin film, temperature, fluid handling and metrology markets.