[labnetwork] Phosphorous doping methods

[Tony L Olsen]

Iulian

As already mentioned, there are a few options.  In the old days, we actually used 100% phosphine.  Newer days, POCl3.  For high volume, POCl3 was a decent choice, but has definite safety issues.

I prefer the idea of spin-on dopants, and I will always keep them as a standby.  They come in multiple concentrations.  However, they can get pricey and don't have the best shelf life.  With low usage rates (as in my case), you may discard a fair amount of material.  There are some minor safety concerns due to the solvents and particulates in the mixtures.

Solid source is a reasonable option.  They basically have no safety issues.  There are two primary suppliers:  St. Gobain (formerly Carborundum) and Techneglas.

When we opened this facility, we had decided not to support phosphorous or boron doping internally.  We didn't have the furnaces to support the single-digit number of runs per year processed in the old facility.  We wanted to outsource it.  I had 2 atmospheric oxidation furnaces - one for undoped substrates and another for doped (PSG, doped poly, outsourced material, etc.).  Well, almost immediately we were pushed into solid source phosphorous doping and had to add that to our doped furnace.  Then, a few months later - against my strong objections - I was required to add boron solid source doping TO THE SAME FURNACE!!

Now, solid source wafers should really remain in the furnace when not being used.  They like to absorb moisture and the idle conditions of the furnace will keep them dehydrated.  Well, since I don't have a dedicated furnace, the sources are often stored in ambient.  It's a lousy way to treat the sources.  I do, however, require a dehydration bake in the furnace each time the sources are returned to use.  It's not great, but it is the best I can do under the circumstances and meets our basic needs.  35 years ago, the Carborundum boron sources couldn't be treated that way at all.  The techneglas sources seem to survive reasonably well - they use a different base material and seem to be more robust.  I don't have any experience with today's St. Gobain products - they may be ok.

tonyO

Tony Olsen
Nanofab Cleanroom Supervisor/Process Engineer
University of Utah
36 S Wasatch Dr, Suite 2500
Salt Lake City,  UT  84112
801-587-0651 office
801-587-3077 fax
www.nanofab.utah.edu




-----Original Message-----
From: Iulian Codreanu <codreanu at udel.edu> 
Sent: Friday, September 14, 2018 09:25
To: Fab Network <labnetwork at mtl.mit.edu>
Subject: [labnetwork] Phosphorous doping methods

Dear All,

I am working on providing phosphorous doping capability at a tube furnace that will be used for fabrication classes (the first class will make a solar cell).

My research to date uncovered POCl3 and solid sources as possible methods for P diffusion. As expected, each seems to come with benefits and drawbacks.

I am hoping that you are willing to share your experience/advcie with me and/or the group so I can make a quick and smart decision.

Thank you very much,

Iulian

--
iulian Codreanu, Ph.D.
Director of Operations, UD NanoFab
163 ISE Lab
221 Academy Street
Newark, DE 19716
302-831-2784
http://udnf.udel.edu


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