IES Tech Blog

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 technical sales, distribution, and value added solutions provider serving the high technology vacuum, temperature, flow and metrology markets in the northeast U.S. and eastern Canada.  

How Do I Get This Crazy Thermal PID Loop to Tune?!

Most temperature controllers today have sure fire tuning algorithms that are simple to use; just press the “auto-tune” button, go get a cup of coffee, and when you get back your system is running like a champ. Of course this makes you look like a genius … when it works.    But sometimes you run across a system with an older temperature control that either doesn’t have “auto-tune” or the algorithm just isn’t working for your specific system.  Trying to manually “tune” your system by tweaking the three PID values (Proportional , Integral, and Derivative) can be a very humbling experience.   People who have mastered this art are held in very high regard – on a par with Yoda of Star Wars fame.

One such “PID Jedi” is Owen Hensinger, now retired after 45+ years in the control business. Owen has experienced first hand every technology invented to control temperature in the industrial equipment world.   I have seen him time after time walk into impossible “tuning” situations with nothing more than a screwdriver and emerge later with happy customers who think he walks on water.

You too can be a “PID Jedi” – if you know the master secret:

The ‘OWEN-Tune’ Procedure

Assume that the process is at setpoint and has the default PID values of P 45, I 60, D 15, F (input filter) 2

For thermal loops, set the input filter to a value equivalent to 3 second response time.  This will be determined by the sample rate of the controller.  As an example, if the controller has a sample rate of 1 sample per second, set the input filter to 3.

To set the P term

Step	Description
1	Set I to 1000
2	Set Control Mode to Manual
3	Set P to ½ of current setting
4	Set Control Mode to Auto
5	Check to see that the output is stable (look at output % not PV)
6	If output is stable proceed to the I term
7	If output is NOT stable, set Control Mode back to Manual
8	Increase P by 10
9	Set Control Mode to Auto
10	Check to see that the output is stable (look at output % not PV)
11	If output is stable proceed to Setting the I term
12	If output is still NOT stable, set Control mode back to manual, go back to step 8

 To set the I term

Step	Description
1	Set I to 60
2	Set Control Mode to Auto
3	Check to see that the output is stable (look at output % not PV)
4	If output is stable
5	Set I to ½ of current setting
6	Check to see that the output is stable (look at output % not PV)
7	If output is stable go to step 5
8	If output is NOT stable
9	Increase I by  ½ of current setting
10	If output is still unstable increase I by ½ the delta from the old setting until stable
11	When output is stable leave Control Mode in Auto and proceed to the D term.

To set the D term:

Step	Description
1	Set D to 1/6th of the I term above
2	Set the Digital Filter (Output) to 2 or 3

It turns out it’s not that hard to be a PID Jedi.  You just need to be trained by a master.

IES Technical Sales is a technical sales, distribution, and value added solutions provider serving the high technology vacuum, temperature, flow and metrology markets in the northeast U.S. and eastern Canada.  

Where Do Desktop SEMs Fit In?

Most SEM usage requires 20,000x or lower magnification.  A new category of SEMs are called "Desktop SEMs" or "Tabletop SEMs" or "Mini SEMs."  One such instrument is the Phenom made by Phenom-World (www.phenom-world.com).  It is about the size of a large PC workstation, and offers features such as an intuitive touch screen, automatic motorized stage, automatic focus, and "NeverLost" navigation which allows the user to always know exactly what part of the sample is being imaged. 

Are you a current SEM user but find it hard to get access to make a quick measurement because you have to wait for your turn at the instrument?

Or do you often wish you could make a quick measurement for QC or product development purposes but find that your optical microscope lacks enough magnification?

Or are you a teacher wishing to open your students' eyes to the wonders of biology or materials science but lack the ability to show them enough to get them excited?

Take a look at Desktop SEMs.  They fill the huge gap between optical microscopes and true "big" SEMs that only large companies and institutions can usually afford. 

 

IES Technical Sales is a technical sales, distribution, and value added solutions provider serving the high technology vacuum, temperature, flow and metrology markets in the northeast U.S. and eastern Canada.