Thickness Uniformity In Dry High Temperature Oxidation Process??
Thickness Uniformity In Dry High Temperature Oxidation Process??
(OP)
I'm trying to increase my thickness uniformity in SiO2 deposition for a dry, high temperature oxidation process. My wafer profile is thin in the middle and thicker towards the outsides. The film is thin (~100-50 Angstroms) and the proces temperature is relatively low (~780). It appears to be a heat transfer problem as the outside of the wafer heats faster than the center (higher temperature, faster reaction). Anyone have any suggestions? Any help would be greatly appreciated!!





RE: Thickness Uniformity In Dry High Temperature Oxidation Process??
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RE: Thickness Uniformity In Dry High Temperature Oxidation Process??
RE: Thickness Uniformity In Dry High Temperature Oxidation Process??
>> temperature: have you actually measured the temperature profile of the wafer
>> reactants: does your process provide sufficient reactants to prevent depletion of same in the middle of the wafer?
>> access: does your process provide equal access to different parts of the wafer?
>> initial conditions: do your wafer start out uniform with their native oxide and are the same porosity across the wafer?
>> surface prep: is your surface preparation resulting in uniform surface condition?
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RE: Thickness Uniformity In Dry High Temperature Oxidation Process??
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RE: Thickness Uniformity In Dry High Temperature Oxidation Process??
RE: Thickness Uniformity In Dry High Temperature Oxidation Process??
How fast is the deposition? The slower the deposition, the more uniform; supposedly, anyway, since that's one way to mitigate depletion.
If this is a CVD, then pressure also affects the uniformity; not sure why, myself, I wasn't involved in that part of the process. LP works better than atmospheric. We were able to switch from a planar APCVD to diffusion furnace LPCVD with boats, etc., and got better uniformity to boot.
Nitrides can be a funny, in a bad way, material. We had a nitride film deposition that refused to be uniformly annealed unless it was cut into thin strips, despite the face that the strips were something like 20 microns across, and the film was only 400&angstrom; thick. You may need to do sone nonstandard analysis of the nitride layer to determine whether there's a difference in dangling bonds, or whatever.
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RE: Thickness Uniformity In Dry High Temperature Oxidation Process??
I realize I may be a little late on this (just joined/first post) but I'll assume you can't answer process questions so I'll just think out loud.
if we are talking about a tube operation (diffusion tube)then the item to be oxidized should be loaded in to your hot zone in an N2 environment, and because you are looking for a precise layer, give it 20 to 30 minutes to warm up before turning on O2.
If (in a diffusion tube)you already are loading in N2 then 1 of 3 thing are a problem, 1:tube has a leak (causing ambient O2 to start the process), 2: N2 flow to high (Not likely, but should be looked at), 3: N2 flow to low (not keeping out ambient O2 and more likely).
If this process is being done in something like a kiln then, you get what you get (opening the door/access port/etc allows O2 to come in with the samples).
Hope it helps
Brent
RE: Thickness Uniformity In Dry High Temperature Oxidation Process??
I had a situation where I had to control a very precise Boron/shallow diffusion, I used an O2 descum tool to give me about 200A on oxide to slow things down.
If you have access to an O2 plasma cleaner, oxide thicknesses can be very well controlled using this method.
Just a thought
Brent