Silicon doping

[Asad]

HI,

How can I perform doping of silicon manually?

Asad

 

[fungus]

HI,

How can I perform doping of silicon manually?

I'm very skeptical about whether or not
it can be done.


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In science it often happens that scientists say, 'You know
that's a really good argument; my position is mistaken,'
and then they actually change their minds and you never
hear that old view from them again. They really do it.
It doesn't happen as often as it should, because scientists
are human and change is sometimes painful. But it happens
every day. I cannot recall the last time something like
that happened in politics or religion.

- Carl Sagan, 1987 CSICOP keynote address

 

[[email protected]]

you do realize that device grade silicon needs to be 99.99999% pure.
Then you normally dope it in a vacuum chamber. It's not something you
can really do by hand.

 

[Rene Tschaggelar]

HI,

How can I perform doping of silicon manually?

Well, you need a cleanroom of the class appropriate to the size of
your structures. If you stick with 2N3055 size, that should
be doable. Then a ultra high vacuum chamber with handlers.
It is less a the problem of a thight box than of the gear inside.
Since it shouldn't gaz out, the materials have to be carefully
selected. Then you'd need a source of ultrapure silicon and a way
to handle, saw, etch, [whatever] it.
I guess the dopants could be added in the etching chamber that runs
with Ar-Ions.
Our local University, the biggest around here, aspiring to belong
to the top league decided against Silicon, but for GaAs to keep
the cost limited. I once heard a number, but forgot it.

Rene

 

[Mac]

HI,

How can I perform doping of silicon manually?

Asad

I don't think you can. I'm struggling to remember how it all works. I
think the initial doping is done by the people who make the ingot. Making
an ingot is pretty involved. You would have a very high utility bill if
you decided to make an ingot yourself. But maybe you could buy ingots.

So, let's say it is a P-type ingot. Now you have to create N-type
pockets in order for it to be useful. I think there are two main ways
to do this. (I'm trying to remember. It's all a bit hazy.) I believe
the normal way is that they mask off areas which are to remain P, and
leave the N areas unmasked. Then they heat the wafer and allow N-type
dopant to diffuse in. Like I say, it is all kind of hazy.

There would then be additional rounds of masking and diffusing where you
convert part of your new N-type well back into P-type material (that's
your base). And then there are also metalization steps. Then you would
have to somehow attach leads to the metalized areas. It just seems too
painful, and it's not like would be able to make anything fancier than the
stuff you can buy.

Also, I do remember that nasty chemicals are involved, and the process
control details are critical. Time, temperature, concentration/pressure.
Clean rooms.

--Mac

 

[Bob Monsen]

HI,

How can I perform doping of silicon manually?

Asad

sci.skeptic?

 

[Jim Thompson]

HI,

How can I perform doping of silicon manually?

Asad

Rub Arsenic on the surface with your hand ?

...Jim Thompson

 

[[email protected]]

"How can I perform doping of silicon manually? "

What dopant do you want to apply? What is the nature of the silicon
substrate? In general, you need a way to apply a closely controlled
concentration of the dopant onto the surface. Arsnic and phosphorus
can be applied as a liquid. Boron is typically applied in a vacuum
either through ion implantation or LPCVD. There are many texts that
explain the theory.

 

[fungus]

Rub Arsenic on the surface with your hand ?

Wear gloves...arsenic is poison!!!



--
<\___/>
/ O O \
\_____/ FTB. For email, remove my socks.

In science it often happens that scientists say, 'You know
that's a really good argument; my position is mistaken,'
and then they actually change their minds and you never
hear that old view from them again. They really do it.
It doesn't happen as often as it should, because scientists
are human and change is sometimes painful. But it happens
every day. I cannot recall the last time something like
that happened in politics or religion.

- Carl Sagan, 1987 CSICOP keynote address

 

[Jim Thompson]

Wear gloves...arsenic is poison!!!

You missed the smiley ??

...Jim Thompson

 

[Dwayne]

HI,

How can I perform doping of silicon manually?

Asad

You need either a particle accelerator or an extremely deadly gas (Arsine,
Phosphine or Di-borine depending on you dopant type). Once the dopant is on
the surface of the wafer you will need to activate the dopant with a high
temp furnace (typically a drive-in is done at 950C-1100C). If you used the
particle accelerator you will need to aneal the wafer to restore the smooth
surface. If you only want to dope certain sections of the wafer then you
will need a lithography system. You should be able to pick up used equipment
for about $1million US. Or you can hire a fab to do the work for you.

Also, you will get a better response from sci.engr.semiconductors.

Dwayne

 

[Matt Giwer]

HI,

How can I perform doping of silicon manually?

You can't.

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[James Meyer]

You can't.

I remember that back in the late 50's that Bell Labs was distributing
science project kits to schools to promote education. Remember that this was
back when the US was playing catch-up to the Russians.

One of the lits was put together to allow school kids to make silicon
solar cells right in the classroom with ordinary stuff found there. The kit
included silicon wafer slices, some chemicals, a 115 volt heating element
similar to the ones used in small radiant room heaters, some asbestos sheets for
insulation, some fine carbide sandpaper, and a list of instructions.

You built an oven from the heater and the asbestos sheets. The heater
was a ceramic cylinder with nichrome wire coiled around the outside and an
Edison screw base. The inside of the cylinder was open and you broke the
silicon wafer into pieces small enough to fit inside.

The wafer pieces were dipped into a water slurry of the chemical, I
forget exactly which chemical (probably something with phosphorous in it), and
placed in the heater/oven to get red hot. The original wafer pieces were
probably grown with an N or P dopant and the subsequent difusion created a
complemental doping.

The wafers were allowed to cool and then the carbide was used to remove
the surface on one side of the wafer to get back down the original silicon. I
forget exactly how the wires were added to each side, probably a loose flat
spiral of bare copper held in contact mechanically. When finished the kids had
a working solar cell.

My brother was given the kit by his science teacher to put together on
his own for "extra credit". I suspect the teacher just wasn't up to the task of
using the kit the way it was intended. I got the kit and played around with it.

So, in short, you CAN manually dope silicon without Billions of dollars
of equipment. I know because I've done it.

Jim

 

[Jonathan Kirwan]

I remember that back in the late 50's that Bell Labs was distributing
science project kits to schools to promote education. Remember that this was
back when the US was playing catch-up to the Russians.

One of the lits was put together to allow school kids to make silicon
solar cells right in the classroom with ordinary stuff found there. The kit
included silicon wafer slices, some chemicals, a 115 volt heating element
similar to the ones used in small radiant room heaters, some asbestos sheets for
insulation, some fine carbide sandpaper, and a list of instructions.

You built an oven from the heater and the asbestos sheets. The heater
was a ceramic cylinder with nichrome wire coiled around the outside and an
Edison screw base. The inside of the cylinder was open and you broke the
silicon wafer into pieces small enough to fit inside.

The wafer pieces were dipped into a water slurry of the chemical, I
forget exactly which chemical (probably something with phosphorous in it), and
placed in the heater/oven to get red hot. The original wafer pieces were
probably grown with an N or P dopant and the subsequent difusion created a
complemental doping.

The wafers were allowed to cool and then the carbide was used to remove
the surface on one side of the wafer to get back down the original silicon. I
forget exactly how the wires were added to each side, probably a loose flat
spiral of bare copper held in contact mechanically. When finished the kids had
a working solar cell.

My brother was given the kit by his science teacher to put together on
his own for "extra credit". I suspect the teacher just wasn't up to the task of
using the kit the way it was intended. I got the kit and played around with it.

So, in short, you CAN manually dope silicon without Billions of dollars
of equipment. I know because I've done it.

Jim

Thanks, Jim, for that post. I had started to respond similarly here,
with my own twists and then read what you wrote -- with more detail
than I remembered, actually.

I think the kit that Bell Labs put out was back in the early-to-mid
1960's. I recently spoke with the people who currently own the rights
to this kit (recently being a few years ago) and they are/were still
selling it. Unfortunately, it would be very difficult for me to find
the phone number, today -- it was in 2001 when I last had this
information at hand. But they were on the east coast.

to the OP:

Modern, pure silicon wafers are rather cheap, thanks to the number of
them being processed. I haven't directly purchased any, but someone
at HP's Deer Creek facility told me they were only a "few dollars
each" (my memory says the figure was near $4) when I pointed to the
boxes and boxes of them they had laying around. This is sliced,
polished, and cleaned so that no particles larger than a micron
remained, if memory serves. Perhaps you could contact a fab or
someone who might know someone at one who might help you get fragments
of broken ones. I use such broken pieces (which I treat rather
poorly) as convenient and well studied reflectors/filters, sometimes.

However you proceed, if it is based on choices you are making and not
on someone else's well-thought-out design, you should research it
well. If you are considering doing this "manually," then you should
study how these things were done when there were no fabs and they were
just experiments in laboratories. And run anything you come up with
by a knowledgeable chemist before you try it. You will want an
informed opinion about the risks and mitigations and advise about what
to consider trying. Hot materials can easily produce noxious gases.

As a side bar, I've built ovens from spare parts that could easily
raise a wafer to passivating temperatures, such as near 1500 C for
rapid oxide growth, that sat in my garage. Just for testing some
optical ideas, not for making wafers, though. Got plenty of free
wafers from fabs, no problem. Used 'plenty' of dry nitrogen gas to
fill the chamber (1500 C and open air with 20% oxy isn't so good an
idea) and keep it at slightly higher pressure than ambient so oxygen
doesn't get inside. Cripes, do things become a mess if you forget to
run the nitrogen! You can construct quite a nice little "oven" of
your own with a water cooled quartz jacket and some tungsten lamps
from your local hardware or home construction store, a power
controller, and a nickel plated chamber (much, much cheaper than gold
and works "pretty good".) Just a tap water flow is usually enough.
You don't want the quartz to get too hot, as it grows more opaque
where it counts when it does and absorbs even more energy and melts in
the resulting positive feedback. With a few kW of lamp energy and not
enough cooling, bad things happen.

In any case, don't plan on building much other than a solar cell to
start. And keep things really simple and as safe as you can, as you
learn.

Jon

 

[James Meyer]

In any case, don't plan on building much other than a solar cell to
start. And keep things really simple and as safe as you can, as you
learn.

Jon

Of course, there's always the possibility of building point contact
transistors out of silicon in the comfort of your garage or kitchen. With a
flouride etchant to thin down a silicon wafer in the right spots and some indium
solder you could probably make a passable junction transistor.

Jim

 

[fungus]

Of course, there's always the possibility of building point contact
transistors out of silicon in the comfort of your garage or kitchen. With a
flouride etchant to thin down a silicon wafer in the right spots and some indium
solder you could probably make a passable junction transistor.

Or you could buy one for $0.10



--
<\___/>
/ O O \
\_____/ FTB. For email, remove my socks.

In science it often happens that scientists say, 'You know
that's a really good argument; my position is mistaken,'
and then they actually change their minds and you never
hear that old view from them again. They really do it.
It doesn't happen as often as it should, because scientists
are human and change is sometimes painful. But it happens
every day. I cannot recall the last time something like
that happened in politics or religion.

- Carl Sagan, 1987 CSICOP keynote address

 

[Matt Giwer]

I remember that back in the late 50's that Bell Labs was distributing
science project kits to schools to promote education. Remember that this was
back when the US was playing catch-up to the Russians.

One of the lits was put together to allow school kids to make silicon
solar cells right in the classroom with ordinary stuff found there. The kit
included silicon wafer slices, some chemicals, a 115 volt heating element
similar to the ones used in small radiant room heaters, some asbestos sheets for
insulation, some fine carbide sandpaper, and a list of instructions.

You built an oven from the heater and the asbestos sheets. The heater
was a ceramic cylinder with nichrome wire coiled around the outside and an
Edison screw base. The inside of the cylinder was open and you broke the
silicon wafer into pieces small enough to fit inside.

The wafer pieces were dipped into a water slurry of the chemical, I
forget exactly which chemical (probably something with phosphorous in it), and
placed in the heater/oven to get red hot. The original wafer pieces were
probably grown with an N or P dopant and the subsequent difusion created a
complemental doping.

Then you have the hard part of the job in the delivered kit.

The wafers were allowed to cool and then the carbide was used to remove
the surface on one side of the wafer to get back down the original silicon. I
forget exactly how the wires were added to each side, probably a loose flat
spiral of bare copper held in contact mechanically. When finished the kids had
a working solar cell.

My brother was given the kit by his science teacher to put together on
his own for "extra credit". I suspect the teacher just wasn't up to the task of
using the kit the way it was intended. I got the kit and played around with it.

So, in short, you CAN manually dope silicon without Billions of dollars
of equipment. I know because I've done it.

The problem is with the word _manually_. Obviously anything that can be done by a machine can be
done by hand. Obviously with enough hardware for doing it and testing it and enough experimentation
one can learn to get the results desired. However anyone who has looked into the process would know
the right answer and not ask the question.

The question appears in line with the kit you mention. Is there a simple way to do it? is more like
the question sounds and the answer is no. And with the kit efficiency was likely so low that a high
impedance voltmeter was needed and no way to measure the current short of lab equipment the
efficiency would be so low compared to even the cheapest commercial production.

So the answer is also no if the intention is a "try and see" bright idea. The idea might be sound
but the success so low as to be unmeasurable. So again the answer is no. And again anyone who knew
the difficulties involved would not ask the question.

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[Matt Giwer]

Of course, there's always the possibility of building point contact
transistors out of silicon in the comfort of your garage or kitchen. With a
flouride etchant to thin down a silicon wafer in the right spots and some indium
solder you could probably make a passable junction transistor.

But it is far more difficult than finding a sweet spot on a gallium crystal for a radio. You can go
through a lot of wafers before making one with little enough leakage to measure the effect. It took
Schokley and company a while to get an effect that could not be attributed to measurement error
beyond getting the effect in the first place.

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ancestors converted from Judaism to Islam does not
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[Matt Giwer]

Or you could buy one for $0.10

plus $4 shipping and handling