5 angstrom per second is 0.5 nanometers per second. That is 10 times to low a rate of deposition.
I thought the deposition rate was supposed to be 5 to 20 nanometers per second to ensure sufficient impact force on the surface. I don't think your tungsten is hot enough. James Lerch did the math once and told me that the impact speed of 1200 deg F aluminum steam is like 1 mile per second. If you don't get your coil hot enough you don't get hot enough aluminum steam ( what is technically coming off our tungsten emitters) .
My old XMS-1 thickness controller displays evaporation rate in angstroms and I run between 40 and 50 angstroms per second. I pass the ( blue painters ) masking tape test most of the time.
Spectrum Coatings claims to deposit at 500 angstroms per second ( 50 nm / sec ) . Paul is very good at this so I would think that what he does is pretty close to as good as you could get.
From their website :
Coating Process Overview:
A brief description of our front surface mirror coating process will be discussed below.
- Old coating is stripped by soaking in Ferric Chloride (very mild - does not react with glass).
- Glass blank is now cleaned with acetone and lastly methanol.
- Blank is loaded into coating fixture (which rotates during coating process for a very uniform deposition) the coating fixture is then loaded into the vacuum system facing down.
-System is rough pumped, then the high vacuum valve is opened and the chamber is in a "high vacuum" state (better than 2x10-6 torr).
- Quartz lamps are switched on to bake water off of the chamber walls.
- System is left to pump until deposition pressure is reached.
- The Substrate (Mirror) is prepared for deposition (proprietary process - NO ADHESION LAYERS ARE USED). This is very important. Most coating companies use some form of adhesion layer. This is unnecessary if the correct process has been developed. Adhesion layers are, more times than not, very difficult to remove, and, they must be removed before re coating the mirror
- Aluminum is flash evaporated at very high deposition rates (~500-700?/sec.). Flash evaporation is the best method for making highly reflective, no scattering aluminum and silver films.
- Oxygen ion source is switched on just as SiO (silicon monoxide) deposition starts. As the SiO film grows it is fully oxidized by the reactive oxygen ion beam which transforms the SiO into a hard durable layer of Quartz (SiO2). No optical interference of the quartz thin film through the visible to the UV. This method is the only method proven to produce pure quartz. Methods without an efficient ion source, even using very high substrate temperature (higher than 270¡ãC) produce what is know as SiOx, which has varying index a of refraction and hardness problems. TiO2 films are produced in the same manner for the EAL and MaxR coatings.
From: VacuumX@... [mailto:VacuumX@...] On Behalf Of Attila
Sent: Friday, September 02, 2011 10:50 AM
To: VacuumX@...
Subject: [VacuumX] Aluminium adhesion problem
Hi All,
I ran into a trouble during my evaporation session.
My aluminium coating doesn't pass the tape test for adhesion.
My cleaning methode is:
-First I clean the mirror with isopropanol
- Next I use Balzers substrate cleaner no.1.
-Then the Balzers substrate cleaner no.2 so as the manual said.
After this I immediately put the mirror into the chamber and evacuate to 0.02-0.03 Torr.
Then I let run Argon into the chamber and glow discharge for 15 min.
After this I go down to 6x10-5 Torr, and again let the Argon into the chamber to 0.1 Torr and low discharge at 10Kv and 20mA for another 15 min.
Then evacuate as deep as possible, last time 4x10-5 Torr.
I evaporate aluminum using e-beam at 5 Angstrom per sec. Meantime the optics are turned by the planetary holder.
After this I can let the optic so or make an overcoat of Sio2 or Sio2 and Tio2, doesn't matter the adhesion does not pass the test(bare alu, protected or enhanced does not matter)
What could be wrong?
Or should I apply 10nm of chromium as an adhesive layer?
Just I don't know later how can I strip off the chromium?
Also does not matter the glass type of the substrate.
Thank's for the suggestions.
Attila
The Hun
