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New member
New to the forum been been a perpetual lurker before sighing up so had limited access previously. Just after some advice on Oxidation on a silicon wafer and the process it goes through. I'm a technician working on furnace tubes and have been having trouble with one particular tube and it's driving us insane. We don't have a dedicated engineer or many people that know exactly how it works and I'm a bit embarrassed asking them since I've been working there for over 6 months. I don't have a chemistry degree or qualifications which hinders my knowledge so if any answers could be made easy to understand that would be great.

We have an 8 inch horizontal oxidation tube and the deposition time has increased nearly 50% 3 years ago and remained at 9hrs46mins instead of 6hrs40mins for a 2um run. We have 2 other oxidation tubes that are 6 inch and they work perfect. All deposition times are as expected and variation is less than 3% across the tube from load to source.

6 inch tube has 6slpm o2 and 11slpm H2, 8 inch has 8slpm o2 and 15slpm H2. All tubes have a direct nitrogen feed through to the manifold that carries the H2 into the tube. Is the N2 used as carrier gas to bring the H2 into the tube and is it used to maintain safety? We aren't sure if the level of N2 is "diluting" the H2 on the way in and causing the increase in deposition time or if there is any further problem elsewhere.

I just want to understand the process better so I can better understand how to fix the issue. If that's with some guidance here or if I can be pointed in the right direction of text books etc, anything at all would be perfect. I've tried searching and can understand the chemical symbols and haven't seen N2 mentioned at all in them so it's left me confused as to it's role.

Apologies for the long winded thread and thanks in advance


New member
Hi alanmcm,

>>and I'm a bit embarrassed asking them since I've been working there for over 6 months
Still, ask around if someone has an answer. And even if this is not the case, maybe someone has a clever idea. There is nothing embarrassing in asking for advice.

About the technical part: do you have logged process data, for instance from a flow controller or pressure gauge? This could indicate if a change was made to the system or the process.
I am not sure if I understand the setup, but I have the following assumptions:

- the nitrogen is used for flushing
- the nitrogen with the hydrogen serves as forming gas. It might work in a reducing manner and so slow down the oxidation process or serve in homogenizing the oxidation
- nitrogen is used for dilution to get a better control of the oxidation
- nitrogen serves as carrier gas and for safety reasons
- a combination of these things

Eventually the composition of the gas mixture and/or the temperature being used for the process is not right.
I am not an expert on this topic, these are just some ideas I had!