Specific Process Knowledge/Etch/DRIE-Pegasus/showerheadchange

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Modification of showerhead on Pegasus 1 in december 2014

This page describes why the showerhead has been changed and what process changes have been found. SPTS calls this modification the 'High Flow Plenum upgrade'.

Motivation

The showerhead that distributes the process gasses inside the Pegasus 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 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. We have not seen any changes to the uniformity of the plasma nor any other side effect.

This modification is described by SPTS File:SPTS High Flow Plenum Upgrade for Pegasus Nov 2012.pdf.

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!
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