I am trying to use a small size crucible (smaller in volume) in ebeam evaporator for depositing expensive materials such as Au and AuGe. I also want the crucible to fit the pocket of the evaporator. Attached you can see the original size crucible that is being used and below that you can my design of smaller crucible. Smaller crucible is made by thickening the walls of the original size crucible (crucible material can be graphite copper or tungsten). However, the issue here is that the thick walls of the crucible may degrade the cooling process and result in crucible to break (crack).
What is the possible solution for having a smaller size crucible here?
I heard from a friend of using something like a "reducer" that I can fit inside the original size crucible and deposit my material. This reducer can be made of copper for example, which has good heat transfer.
I put the smaller size crucible inside the larger size and it worked ! just make sure to adjust the beam so that it does not hit the outer crucible.
Adjusting the beam scanning width and type of scan could be helpful in curtailing the heat. Does your evaporator come with resistive heating option? If so you may want to consider usign resistive heating. Their crucibles are usually more compact.
You can still use the original sized crucible, and instead of filling it entirely end to end, just melt a few pellets in the middle, creating a small coin/pancake/shot of Au or AuGe that can move around. We do this pretty regularly for expensive metals. Of course this requires you to be able to see exactly where your e-beam hits through a viewing port on your chamber. During melt-preparation as you ramp power up, you will need to control the beam sweep shape (infinity-shape is best) precisely, such that it hits only the unmelted pellets. For all subsequent evaporations, you can remember the beam settings and make sure it hits just the material and not the graphite.
I use a 7CC crucible when evaporating gold from either a 40CC pocket or a 20CC pocket... You do not need to have the crucible the same size... just make sure your beam is hitting directly in the middle of the pocket. Additionally, for Au... why not just add a thermal source? You dont need to put a shutter over it. In my experience I was using about 6 grams of gold to get 150nm onto the substrate with the ebeam... I can use 1.5 grams of gold with a thermal source to get the same. It is way more cost effective. Additionally, you don't need to buy a fancy thermal power supply to do this.. I spent 800 bucks on a variac and a transformer and maybe 1000 bucks on the thermal feed thrus and everything works just fine :)
- Badges
- Science topic
- Similar topics
- Engineering
- Electrical Engineering
- Electrodes