Hi This patent contains some hints on how to build our polysilicon gates with low resistance: -> https://patents.google.com/patent/US6387788
It's as Tim said, there is usually a film of conducting metal added onto the polysilicon and then heated to reacht with the polisilicon and form a conducting ceramic: -> https://en.wikipedia.org/wiki/Tungsten_disilicide -> https://en.wikipedia.org/wiki/Titanium_disilicide
Just that we have to turn the thin metal layer, which we deposit into a conducting ceramic in order to make it resist the temperatures during further processing and the unreacted metal needs to be removed: -> https://patents.google.com/patent/DE69931068T2
The sputterer at HKUST can do Titanium -> http://www.nff.ust.hk/en/equipment-and-process/equipment-list/dry-etching-an...
And we can grow polysilicon: -> http://www.nff.ust.hk/en/equipment-and-process/equipment-list/thermal-diffus...
But I think we can first just use polysilicon. At least it conducts, even when the resistance is very high, and then in the next step we can start tinkering around with reducing the resistance of the gate electrode.
What do you think?
Cheers David
On Wednesday, 7 March 2018 7:25:42 PM HKT David Lanzendörfer wrote:
Figured it out... Doesn't depend on the machine, but on what elementary metal we deposit on top of the silicon... Ok. I think I change the process to gate-first with silicides and go through the pain of dimensioning the temperature and time for the silicide formation... Aaand updating the equations for the threshold calculation for accounting for the changed gate potential....
Cheers David
On Wednesday, 7 March 2018 7:22:08 PM HKT David Lanzendörfer wrote:
Hi These rapid thermal process machines AW610 RTP (DIF-R2) and AW610 RTP (DIF-R3) can both deposite silicides: http://www.nff.ust.hk/en/equipment-and-process/equipment-list/thermal-diff u sion-and-ion-implantation-module.html
I will check which materials are available. -> "Is it WSi2 or AlSi2?" plays into the threshold equation!
I'll keep you updated!
Cheers
David
On Wednesday, 7 March 2018 6:45:15 PM HKT David Lanzendörfer wrote:
Hi What I'm taling about in indeed a mix between our metal and polysilicon as described here in these lecture slides: https://web.stanford.edu/class/ee311/NOTES/Silicides%20&%20Metal%20gate %20Slides.pdf
This polycrystal resulting from this process step would be resistant against the temperatures during annealing after implantation.
However. Getting the reaction of Aluminum and Polysilicon right will be very very tricky.
Anyone experience with this step, or knows someone who does, who could assist me with setting the parameters for time and temperature and atmosphere?
Otherwise I would have to experiment around a few times until I get it right with orientation numbers I find with Googling ^^'
Cheers
David
On Wednesday, 7 March 2018 5:04:05 PM HKT Staf Verhaegen wrote:
(Now send to the list.)
R. Timothy Edwards schreef op di 06-03-2018 om 16:48 [-0500]:
Hello Staf,
Could you summarize again what the problem is with poly gate? In the industry polysilicon has been the gate for all technologies I know from 1um up to at least 65nm.
What is commonly drawn as a poly gate is actually a "salicide", or poly coated with a thin layer of metal. This is what David is referring to. The difference between a poly salicide and plain polysilicon is a few ohms per square vs. a hundred ohms per square.
AFAIK, David is talking about aluminum gates. Silicidation or salidication is indeed a step done after poly formation to decrease sheet resistance of the poly. AFAIR also the diffusion regions are silicided but I think you need spacers then.
greets, Staf.