[labnetwork] a-Si PECVD ↑ uniformity

[Demis D. John]

Additional info:
I also checked the "tool health": Our process control data shows ~3%
uniformity for the standard SiO2 & Si3N4 films.
I also had interns run 4 wafers (100mm each) at a time of these std.
SiO2/Si3N4, which also showed good uniformity (<10%).

So SiO2 and Si3N4 look great on both PECVD tools.
(PlasmaTherm 790 @250°C &
Plasma-Therm Vision 310 Advanced Vacuum @ 300°C,
2% SiH4 on both).

Only a-Si has extremely high non-uniformity from center to edge on the
platen, on two different PECVD tools, where a single 100mm wafer in the
platen center shows
*2-3x thicker on the edge of the wafer*, than the center.

Lastly, this user is running 100mm Glass wafers.
Both systems are open-load and it takes ~5-6min before the dep starts (so I
think wafer is at temperature), and dep is 20-40min long @ ~12nm/min on the
P.T. 790, targeting ~300nm.

SiO2 std recipe: 3.7% uniformity:
[image: image.png]

User's a-Si on Glass (100mm borosilicate wf. for example):
*3x thicker at edge than center*
[image: image.png]

-- Demis (contact info <https://wiki.nanotech.ucsb.edu/wiki/Demis_D._John>)
*Reminder*: The NanoFab has a publications policy
<https://wiki.nanotech.ucsb.edu/wiki/Frequently_Asked_Questions#Publications_acknowledging_the_Nanofab>


On Thu, Sep 25, 2025 at 12:59 PM Demis D. John <demis at ucsb.edu> wrote:

> Does anyone have processes for higher uniformity for amorphous Silicon
> PEVCD dep?
> On both our PECVD tools, the a-Si recipes are extremely non-uniform (~50%
> reduced rate from center to edge of the platen!).
>
> The user has tried ↑ SiH4 flow, and ↑ ↓ Bias Power.  They may have tried
> pressure as well, but no dice yet.
>
> Does any one have experience with how to improve this?
>
> Thanks!
> -- Demis
>
> ----------------------------------------
> *     Process Group Manager*
>  *UCSB Nanofabrication Facility* <https://www.nanotech.ucsb.edu/>
>          Demis' Contact Info
> <https://wiki.nanotech.ucsb.edu/wiki/Demis_D._John>
> ----------------------------------------
> *Reminder*: The NanoFab has a publications policy
> <https://wiki.nanotech.ucsb.edu/wiki/Frequently_Asked_Questions#Publications_acknowledging_the_Nanofab>
>
>
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