Specific Process Knowledge/Etch/DRIE-Pegasus/showerheadchange
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Modification of showerhead in december 2014
The showerhead that distributes the process gasses inside the plasma source was changed. In the old design, the showerhead had a number of 300 µm diameter holes intended to distribute the gas uniformly inside the plasma source. The passage through the holes had a flow resistance that would cause the gasses coming from the MFC in a Bosch process to get mixed up - in this way working against the separation of the etch and dep cycles.
In the new design, the gas flow resistance has been reduced by using 1 mm diameter holes in the showerhead instead. This has very little or no impact on processes that have a continuous gas flow - i.e. processes that are not switched. However, for processes with several gas flows that switch on and off, the switching from one gas flow to another will be much more well defined. This has enabled us to run Bosch processes with shorter cycles times. Shorter cycles times means smaller scallops and hence lower roughness and better control.
Comparison of continuous processes
Black silicon recipe
| Process | Before (Old showerhead) | After (New showerhead) | |||||
|---|---|---|---|---|---|---|---|
| Name/Type | Description/parameters | Wafer ID | Comment | SEM images | Wafer ID | Comment | SEM images |
| Continuous black silicon recipe on blank wafer | 15 mins, -10 degrees, 32 mtorr, 60 sccm SF6, 55 sccm O2, 70 W platen | S004592 | Wafer centre | 
|
S004679 | Wafer centre | 
|
| S003900 | Wafer edge | 
|
S004679 | Wafer edge | 
| ||
Comparison of switched processes
Process A
| Recipe | Name | Temp. | Deposition step | Etch step | Comments | |||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Time | Pres. | C4F8 | SF6 | O2 | Coil | Time | Pres. | C4F8 | SF6 | O2 | Coil | Platen | Showerhead | Runs | Key words | |||
| Process A | Step1 11 cyc | 20 | 4 | 25 | 200 | 0 | 0 | 2000 | 7.0 | 25(1.5s) 90>>150 | 0 | 350(1.5s) 550 | 5 | 2800 | 120>>140(1.5s) 45 | Old | 1 | |
| Step2 44 cyc | 4 | 25 | 200 | 0 | 0 | 2000 | 7.0 | 25(1.5s) 150 | 0 | 350(1.5s) 550 | 5 | 2800 | 140(1.5s) 45 | |||||
| Step1 11 cyc | 20 | 4 | 25 | 200 | 0 | 0 | 2000 | 7.0 | 25(1.5s) 90>>150 | 0 | 350(1.5s) 550 | 5 | 2800 | 120>>140(1.5s) 45 | New | 1 | Profile improved | |
| Step2 44 cyc | 4 | 25 | 200 | 0 | 0 | 2000 | 7.0 | 25(1.5s) 150 | 0 | 350(1.5s) 550 | 5 | 2800 | 140(1.5s) 45 | |||||
SOI
| Recipe | Name | Temp. | Deposition step | Etch step | Comments | |||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Time | Pres. | C4F8 | SF6 | O2 | Coil | Time | Pres. | C4F8 | SF6 | O2 | Coil | Platen | Showerhead | Runs | Key words | |||
| SOI etch | SOI | 20 | 2 | 25 | 250 | 0 | 0 | 2000 | 3 | 30 | 0 | 400 | 40 | 2800 | 75 (0.025s, 75%) | Old | 1 | |
| SOI | 20 | 2 | 25 | 250 | 0 | 0 | 2000 | 3 | 30 | 0 | 400 | 40 | 2800 | 75 (0.025s, 75%) | New | 1 | OK | |
Process D
| Recipe | Name | Temp. | Deposition step | Etch step | Comments | |||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Time | Pres. | C4F8 | SF6 | O2 | Coil | Time | Pres. | C4F8 | SF6 | O2 | Coil | Platen | Showerhead | Runs | Key words | |||
| Process D | Original | 0 | 2 | 20 | 150 | 0 | 0 | 2000 | 2.4 | 26 | 0 | 275 | 5 | 2500 | 35 | Old | 1 | |
| Original | 0 | 2 | 20 | 150 | 0 | 0 | 2000 | 2.4 | 26 | 0 | 275 | 5 | 2500 | 35 | New | 1 | ||
| New Process D | 0 | 1 | 20 | 150 | 0 | 0 | 2000 | 3 | 26 | 0 | 275 | 5 | 2500 | 35 | New | 4 | Large undercut | |
| PrD01 | 0 | 1 | 20 | 150 | 0 | 0 | 2000 | 2.4 | 26 | 0 | 275 | 5 | 2500 | 35 | New | 2 | ||
| PrD02 | 0 | 1.1 | 20 | 150 | 0 | 0 | 2000 | 2.4 | 26 | 0 | 275 | 5 | 2500 | 35 | New | 1 | ||
| PrD-3 | 0 | 1 | 20 | 150 | 0 | 0 | 2000 | 2.5 | 26 | 0 | 275 | 5 | 2500 | 35 | New | 1 | ||
| PrD-4 | 0 | 1 | 20 | 150 | 0 | 0 | 2000 | 2.2 | 26 | 0 | 275 | 5 | 2500 | 35 | New | 1 | Best one so far! | |