STS Pegasus 4/Processes/LNF Recipe 4

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About this Process
Process Details
Equipment	STS Pegasus 4
Technology	DRIE
Material	Si
Mask Materials	PR, SiO2
Gases Used	SF6, C4F8, O2
Date Created	Jan 1, 2011
Authored By	Kevin Owen

This highly specialized recipe is designed for high aspect ratio etching of small features (1-5 μm) with very low open area (<10%). The etch produces the most vertical sidewall with the least undercut, particularly at the top of the trench. It is primarily used with trench refill processes.

Procedure

Run LNF Recipe 4 for up to 20 minutes with the 1 minute automated clean recipe, longer etches should be run with the 3 minute automated clean recipe.

Recipe Parameters

Parameter	Dep	Etch
		Boost	Main
ICP Power	2000 W	2500 W
Bias Power	0 W	80-100 W*	30 W
Bias Pulsing	N/A	40 Hz 80%
Pressure	25 mTorr	30 mTorr
C4F8 Flow	90-140 sccm*	0 sccm
SF6 Flow	0 sccm	110 sccm
O2 Flow	0 sccm	10 sccm
Time	2.5 s	3 s	4 s
Chuck Temperature	10°C

* Ramped through process. Must be adjusted according to process time.

Characterization

Etch Rate

The etch rate will vary with the size of the trench being etched. Larger trenches tend to etch faster, this trend can be seen below.

• 

  Recipe 4 Etch Rate vs. Feature Size

Mask Selectivity

• Photoresist Etch Rate
  • SPR 220: 600 A/min
  • Thermal oxide/HTO: unknown

Side Profile

Trench

Running recipe 4 for 20 minutes with 3 µm of SPR 220 on a silicon wafer with our standard DRIE characterization mask can produce a profile like this. The minimum trench size is 0.24 µm.

• 

  Recipe 4 for 20 min, 2 µm Trench

• 

  Recipe 4 for 20 min, 10 µm Trench

• 

  Recipe 4 for 20 min, 100 µm Trench

Scallop

• 80 nm wide X 300 nm tall

Undercut

• 225 nm

Grassing

An example of grassing can be seen below. This can happen if there is too much exposed area (>25%) on the mask.

• 

  Grass (brown area) on perimeter of wafer

• 

  XXX find some SEM of grass XXX

Limitations

Etch Length

Unknown

Feature Size

Feature sizes of 1-10 μm (exposed) are known to work well. Larger features may cause grass.

Aspect ratio

Unknown

Open area

An exposed area of <10% across the wafer is recommended. Larger exposed area may cause grass.

Multi-step etching

Multi-step processing (i.e. running two or more etches with overlapping features) with the Bosch process is known to cause undesirable results. Please contact the tool engineers if you wish to run such a process so we can help reduce or eliminate issues.

Qualification

Currently Recipe 4 is not routinely qualified.