High everyone,
I'm trying to etch ~3 micrometer of SiO2 without barely etching the Silicon nitride underneath, basically having the etch stop on the nitride.
The nitride needs to come out clean and even in thickness.
The Silicon nitride layer is a PECVD layer and has a refractive index (RI) of ~1.897 at a wavelength of 632nm.
The Silicon oxide is a HDP layer (high density plasma, ~ pinhole free).
Now the problem is if I use BOE (7:1) I can clearly see that flat parts do not come out even as there's an obvious color difference from place to place (indicating slight differences in thickness because of interferometry).
I'm hoping to achieve an uniform thickness of the nitride at all flat places of around ~1-5nm.
Any suggestions are welcome.
A two step or three step etch process is totally fine with me if it will produce good and fairly consistent results.
Hello Bob,
First you can try different enchants like KOH, HF (the buffer in BOE reacts with SiN) or as describes in this link:
http://www.montana.edu/tjkaiser/ee505/homework/Williams_etch_rates.pdf
Assuming that the difference of etch rate between SiN is not infinite, it's possible to use a combination of 2 processes:
1. Etch with RIE down to the bottom of the Oxide, leave a thin unetched layer of Oxide, as thin as possilbe.
2. clean resist, and etching residues.
3. Chemical wet etch with one of the above suggestions.
Hope this will help you...
Hi Amir,
Thank you very much for the reply.
The problem I have with the table is that it's missing most of the SiN PECVD (Low RI) values. Nonetheless diluted HF (10:1), etches the other silicon nitrides which means that it should etch SiN PECVD (Low RI) faster.
The reason I'm trying to avoid RIE (ICP) is because:
I might try some diluted HF and see how that comes out.
The chemical used to selectively burn SiO2 on PECVD SiN is
SiCl4. 2H2O
Hi Abdelkader Hafdallah,
First of all thank you for the reply.
Could you please explain a bit more how.
Do I use it for wet etching or RIE/ICP?
Also as far as I know I can use SiCl4 to form SiO2 suspended in water, I haven't heard about it SiCl4 being able to etch SiO2.
Could you please explain a tiny bit how it works? or give a source that explains it?
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