Is it generally safe for kids to handle silicon wafers?

[austinuni]

I volunteer in an 8th grade classroom and I wanted to bring in some silicon wafers for the students to examine for a "show and tell" session, in order to get them interested in technology. Are there any dangers to the students if they are allowed to handle a wafer? I don't really care if the wafers are damaged, but I don't want to see any student hurt.

I am told that if the wafer breaks, then the edges can be as sharp as a razor blade. Kids being who they are, I might expect there's a non-zero chance of that happening. I wonder if I should just hold the wafer up and allow them to look at it, but not touch it, or maybe I can watch them closely while they handle it to make sure there's no horseplay involved. I could also use something to protect the wafers, around the edges and on the backsides.

 

[berkeman]

I volunteer in an 8th grade classroom and I wanted to bring in some silicon wafers for the students to examine for a "show and tell" session, in order to get them interested in technology. Are there any dangers to the students if they are allowed to handle a wafer? I don't really care if the wafers are damaged, but I don't want to see any student hurt.

I am told that if the wafer breaks, then the edges can be as sharp as a razor blade. Kids being who they are, I might expect there's a non-zero chance of that happening. I wonder if I should just hold the wafer up and allow them to look at it, but not touch it, or maybe I can watch them closely while they handle it to make sure there's no horseplay involved.

Here is an old PF thread that should help: https://www.physicsforums.com/threads/how-should-doped-silicon-wafers-be-handled.788096/

 

[Andy Resnick]

I volunteer in an 8th grade classroom and I wanted to bring in some silicon wafers for the students to examine for a "show and tell" session, in order to get them interested in technology. Are there any dangers to the students if they are allowed to handle a wafer? I don't really care if the wafers are damaged, but I don't want to see any student hurt.

I am told that if the wafer breaks, then the edges can be as sharp as a razor blade. Kids being who they are, I might expect there's a non-zero chance of that happening. I wonder if I should just hold the wafer up and allow them to look at it, but not touch it, or maybe I can watch them closely while they handle it to make sure there's no horseplay involved.

I can't speak to chemical (dopant) hazards, but it is true that if one breaks, the edges are razor sharp: the original boule was a single crystal, and the wafers will fracture along crystal planes, producing extremely sharp edges and points.

By the time I get wafers, they have been exposed to air and so the silicon is passivated (coated with a thin layer of silicon dioxide), I'm not touching anything biologically hazardous.

I handle them as through they were made of glass, that seems ok.

 

[CrysPhys]

I volunteer in an 8th grade classroom and I wanted to bring in some silicon wafers for the students to examine for a "show and tell" session, in order to get them interested in technology. Are there any dangers to the students if they are allowed to handle a wafer? I don't really care if the wafers are damaged, but I don't want to see any student hurt.

I am told that if the wafer breaks, then the edges can be as sharp as a razor blade. Kids being who they are, I might expect there's a non-zero chance of that happening. I wonder if I should just hold the wafer up and allow them to look at it, but not touch it, or maybe I can watch them closely while they handle it to make sure there's no horseplay involved. I could also use something to protect the wafers, around the edges and on the backsides.

I would mount the wafer centered onto a rigid metal square plate, with edge length ~2 inches greater than the wafer diameter; make sure the edges and corners of the metal plate are rounded and smooth. You can use special thermal mounting resin if you have it around; but bee's wax will do.

By the way, what's the diameter and thickness of the wafer?

 

[austinuni]

By the way, what's the diameter and thickness of the wafer?

They are 6" diameter; not sure of the thickness since I don't have them in my possession yet.
How about using cardboard to mount the wafers instead of steel? Give it a little impact cushioning in case it was dropped.

 

[CrysPhys]

They are 6" diameter; not sure of the thickness since I don't have them in my possession yet.
How about using cardboard to mount the wafers instead of steel? Give it a little impact cushioning in case it was dropped.

If you want to protect the wafer from cracking if dropped, cardboard won't do. Cardboard will flex. Also, Murphy's Law predicts that the assembly will hit the ground with the wafer face down and crack. If you want to keep it cheap and simple, you can use double-sided sticky tape to mount the wafer onto a plastic or masonite board (you can cut up a clipboard). You probably can't remove the wafer without cracking it though. With a metal plate and wax, you can remove the wafer if you wish by reheating. Anyway, mount the wafer onto a rigid plate of some sort. Then mount the plate into a foam-lined shadow box with sufficiently high sidewalls, and line all the exterior surfaces of the shadow box with foam as well (use self-adhesive foam sheet and strips).

 

[mfb]

If the wafer falls down and breaks, you can tell the students to go away from it and clean up. I would be more worried about a student bending and breaking it in their hands. Gluing or taping it to some plastic board would be sufficient to prevent that, and it gives some impact protection when falling down as well. You don't get a direct feeling for the thickness that way, however.

 

[Scrumhalf]

I handle silicon wafers for a living. They are not that flimsy. Have the students handle the wafers a few inches over a table and they'll be fine. If they break by any chance, just have the students step back and vacuum the debris.

 

[CrysPhys]

To OP:

Looks like you have the following considerations.

(1) How many wafers will you have? If you will have only one or two, you will need to be cautious and take steps to protect them from damage. If you will have a stash of ten or more, you can afford to be cavalier, at least in the beginning, and see how quickly the kids break them; then, when you have only a couple left, you can take steps to protect the remaining ones (assuming you don't want to keep ordering more).

(2) Are you content with sweeping up, or vacuuming up, the fragments should a wafer break? If so, nothing special needed. If not, the entire back of the wafer should be affixed (via glue, double-sided sticky tape, wax, or thermal resin) to a backing plate. That way, if the wafer fractures, the pieces will stay adhered to the backing plate. No fuss, no muss.

(3) How freely will the wafers be handled? Will the students raise them a max of only several inches over a tabletop? Or will the students pass them around, perhaps carrying them from one row of benches to another? If so, do you want the inconvenience of reloading the wafers into carriers each time someone walks around with them, or do you want the wafers mounted and protected such that they can sustain a fall of several feet onto the floor? (And this is assuming you don't have at least one clown who will be tempted to toss a wafer like a Frisbee.)

 

[CWatters]

Perhaps put them in CD cases?

Edit: removed the bit that holds the cd first.

 

[CrysPhys]

Perhaps put them in CD cases?

Edit: removed the bit that holds the cd first.

A 6" diam wafer won't fit in a CD case.

 

[TeethWhitener]

I doubt there will be any chemical hazard. Unless you're doing something specialized, it's likely that the dopant is boron for p-doped silicon or phosphorus for n-doped silicon. Neither of them are harmful. I will second that the edges can be sharp, but also that the wafers aren't particularly flimsy. The really annoying thing (especially for Si cut along the <111> plane) is that the wafers have a tendency to shatter rather than snap cleanly, and the little slivers formed when they shatter can be wicked. So if one breaks, make sure to use a heavy duty paper towel or rag to wipe up the area so you don't get a little silicon splinter.

 

[austinuni]

Many thanks for all the replies. I re-used the packaging that came with the shipping container. It was enclosed in a cardboard box
and had a thin piece of wood backing the wafer. I put some sticky tape on the backside of the wafer and attached it to the wood.
I left the top of the box open. No damage done!

The students had never seen a wafer before, but I am not sure they were that impressed with it. They asked a few questions like
how much did it cost and how many die were on the wafer. Maybe next time I will bring in a disassembled smartphone and show
them the components inside. It may be harder than I thought to get 8th graders interested in technology.

 

[Scrumhalf]

Stick the wafer under a microscope and let the kids observe the circuits. Then maybe show them an actual circuit board taken from a gadget - an old vcr or radio or whatever and talk to them about miniaturization. That may connect with them better than a wafer.

 

[sophiewilson0191]

Better not let them hold it, you can show them but not let them hold it.
Children are children anyway they can be curious and playful.
Put them in a protective case or transparent box.