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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 High Flow Plenum Upgrade.

The modification was also done on Pegasus 2 before we started using it.

Comparison of continuous processes on Pegasus 1

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
Continuous black silicon recipe on blank wafer		S003900	Wafer edge		S004679	Wafer edge

Comparison of switched processes on Pegasus 1

Process A

Recipe	Name	Temp.	Deposition step						Etch step							Comments
Recipe	Name	Temp.	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	20	4	25	200	0	0	2000	7.0	25(1.5s) 150	0	350(1.5s) 550	5	2800	140(1.5s) 45	Old	1
	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	20	4	25	200	0	0	2000	7.0	25(1.5s) 150	0	350(1.5s) 550	5	2800	140(1.5s) 45	New	1	Profile improved

SOI

Recipe	Name	Temp.	Deposition step						Etch step							Comments
Recipe	Name	Temp.	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
Recipe	Name	Temp.	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!