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> trenches following the edges of my mask pattern. However this was very |
> sparse throughout the wafer, while the marks I've shown cover the whole |
> surface and I could not find anything correlating to this large scale |
> effect (I used our optical profilometer for this). But interesting that |
> liquid being trapped under the overhang of a lift-off mask can cause this, |
> which means we need to be more careful with the rinse steps. |
> |
> Dave Hollingshead suggested the MLA150 laser causing surface |
> modifications. Unfortunately I had the same issues when working with a |
> contact aligner, so I guess that this is not the case. |
> |
> Malcom Hathaway suggested a change in the substrate reflectivity, which is |
> my current hypothesis. However this seems to affect both Si and oxide, |
> since I see this effect on both cases, so this may be in fact a case of |
> chemicals sticking to the surface and not coming out even during long |
> piranha baths. I have AFM and other surface characterization options |
> planned, it is a matter of finding a good time to have it done now. |
> |
> Thank you all again for the suggestions and references. I'll make sure to |
> post an update here if I have anything useful. |
> |
> Best, |
> -- |
> Gustavo de Oliveira Luiz, PhD |
> Applications/Research Specialist |
> nanoFAB, University of Alberta |
> |
> On Fri, Mar 24, 2023 at 3:21?PM Hathaway, Malcolm R < |
> hathaway at cns.fas.harvard.edu> wrote: |
> |
>> Hi Gustavo, |
>> |
>> Another thought (from a non-photo-expert, for sure!): |
>> |
>> It may be the prior photo steps are changing the reflectivity of the |
>> silicon (or aluminum, on Travis's samples), especially as it shows up as |
>> having an effect on dose. Surface roughening? A very thin chemical |
>> residue? |
>> |
>> Perhaps an AFM scan would be revealing... |
>> |
>> |
>> Mac Hathaway |
>> Harvard CNS |
>> |
>> ------------------------------ |
>> *From:* labnetwork <labnetwork-bounces at mtl.mit.edu> on behalf of Massey, |
>> Travis <massey21 at llnl.gov> |
>> *Sent:* Friday, March 24, 2023 2:30 PM |
>> *To:* Gustavo de Oliveira Luiz <deolivei at ualberta.ca>; |
>> labnetwork at mtl.mit.edu <labnetwork at mtl.mit.edu> |
>> *Subject:* Re: [labnetwork] Strange "sample memory" with LOR 5B |
>> |
>> |
>> Hi Gustavo, |
>> |
>> |
>> |
>> I don?t have a definitive answer for you, and I?m certainly no chemist, |
>> but also consider the role of AZ Developer (another base) and reactions of |
>> NMP with residual water or alkaline solutions. |
>> |
>> |
>> |
>> First, the pair of alkaline developers *may* actually be enough to break |
>> through the relatively thin oxide created by the piranha, at which point |
>> the bases will start attacking the silicon. Second, if this is only |
>> happening with LOR, it?s also possible that residual liquid (likely |
>> alkaline) is being trapped under the AZ 1512 then reacting with the NMP. |
>> Spinning may not do a great job of removing this liquid trapped beneath the |
>> resist overhang. I suspect a bulk attack, though, since the residual |
>> patterns in the wafer reflect the resist pattern itself rather than the |
>> perimeters of the resist patterns. I haven?t noticed this before on SiO2, |
>> but NMP alone ? and especially water-contaminated NMP ? can attack some |
>> metals (Al, Cu, etc.). This paper suggests that acidic or alkaline |
>> contaminants in NMP may exacerbate the problem. I see these ghosts of |
>> previous patterns all the time in aluminum-coated wafers I pattern and |
>> reuse repeatedly for process development/characterization, and I?ve |
>> recently started seeing it on Ti as well ? no LOR, just an assortment of |
>> positive resists. |
>> |
>> https://ieeexplore.ieee.org/stamp/stamp.jsp?tp=&arnumber=9211805 |
>> <https://urldefense.proofpoint.com/v2/url?u=https-3A__ieeexplore.ieee.org_stamp_stamp.jsp-3Ftp-3D-26arnumber-3D9211805&d=DwMGaQ&c=WO-RGvefibhHBZq3fL85hQ&r=TEMLD8-VsxCGtcVzmvpT5GFNSczskEKHzW6aYlttmIY&m=1-k7qvkCMYMPtYpozWsK_KGAJGieHTpEbECqW_3lIM8S9M8eXG8-e5DadL6e-7pS&s=Z-bdFigBPa6X1HeTz5-YGnfzpYQPP0zbhVFxbzVW_0A&e=> |
>> |
>> |
>> |
>> Best, |
>> |
>> Travis Massey |
>> |
>> Center for Micro and Nanotechnology |
>> |
>> Lawrence Livermore National Laboratory |
>> |
>> |
>> |
>> *From:* labnetwork <labnetwork-bounces at mtl.mit.edu> * On Behalf Of *Gustavo |
>> de Oliveira Luiz |
>> *Sent:* Friday, March 24, 2023 10:37 AM |
>> *To:* labnetwork at mtl.mit.edu |
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