[labnetwork] Phosphorous doping methods

Sun Sep 16 00:49:50 EDT 2018

Hello,
First answering your specific question, I suggest to use Solid Phosphor 
Source vs POCl3.
The process is very mature, reliable, very accurate controllable and safe.
It requires at least 2 furnaces: one for source storage and activation 
and one for prediffusion
and drive-in after glass removal. Please note they are dedicated 
furnaces for this application only.
This in-house doping fits very well with the timing constrains of a 
teaching class.

Second, as part of a discussion about doping in an university clean room 
operation, I think that
in general the best option is to outsource the wafers for Ion Implantation.
It is the most accurate and precision doping method, with a very large 
range of doping level values,
can use photoresist as a mask, and might require one single furnace for 
annealing and drive-in for
all Boron, Phosphor, Arsenic and Stibium if implanted through a thin 
oxide cap which blocks the
exdiffusion. One dedicated tube. It is the most cost effective and 
versatile method too, in this setup.
The Ion Implantation is the best doping method that fits with the 
available process TCAD simulation software.
More: exposing the students to this Ion Implantation process package 
will increase their chances to get
a job in nowadays semiconductor industry.

Solid Source Doping of Boron and Phosphor requires separate dedicated 
furnaces for source storage and
activation, for drive in and one for Boron glass deglazing a total of 5 
tubes.

POCl3 tube gets very dirty and that spreads around the loading area, 
requires a lot of maintenance
and are safety issues too. Also if it used for drive-in steps too to 
save a tube, then it limits the
low doping values capability.

The Spin On Doping depends on the manufacturer brand, its large 
variability in handling by different
users during coat, solvent removal and drive-in. It is wafer by wafer 
operation; the solution shelf life
is limited and becomes expensive. The drive-in furnace is metal free but 
could get contaminated
with Carbon on long term; so a dedicated furnace.

Doping from doped LPCVD/PECVD  Polysilicon or PSG oxides are other 
option for a limited doping level too.

Sputtering or Ebeam source deposition require a dedicated expensive 
system for Silicon operation.

All the above mentioned techniques but Ion Implantation require an extra 
cleaning for the source removal
before/after the drive-in step, and involve a large number of dedicated 
furnaces.

Thanks, Bernard

On 9/14/18 5:42 PM, Tony L Olsen wrote:
> 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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