P5000 RIE/Processes/POLY PAT BKM

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About this Process
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Process Details
Equipment	P5000 RIE
Technology	RIE
Material	Polysilicon
Mask Materials	PR, SiO2
Gases Used	HBr, Cl2
Date Modified	4/10/2014
Authored By	AMAT, Kevin Owen

The POLY PAT BKM recipe is a general recipe for etching polysilicon and amorphous silicon films on the P5000 RIE/Processes. It has a fast etch rate (3800 Å/min) and reasonable selectivity to photoresist and silicon dioxide. It can also be used for shallow etches (< 4 μm) in silicon substrates. This recipe can be run in chamber Chamber C on CMOS Clean samples.

Procedure

1. Review the material restrictions for each chamber and choose the appropriate one for the application.
2. Follow the procedure outlined in the SOP.
3. Open the POLY PAT BKM Process Program.
4. Edit the time in the MAIN ETCH.
5. Select POLYPATBKM from Wafer Lot Names.

Characterization

The POLY PAT BKM etch has three main steps: breakthrough, main etch, and over etch.

1. The breakthrough step is designed to etch through any native oxide or photoresist residue on the surface of the polysilicon. It is rarely modified.
2. The main etch is a fast etch with reasonable selectivity and is used to etch through a polysilicon film.
3. The over etch is a slower, very high selectivity etch that can be used for the final portion of a polysilicon film when stopping on a thin or sensitive film underneath. This is rarely used for normal processing circumstances.

All of the characterization data below is for the main etch.

Etch rate

Bulk etch rates for various oxides, nitrides, and masking materials are shown below. High aspect ratio (narrow) trenches will etch slower.

Material	Etch rate
Polysilicon	3800 Å/min
Si (22% open area, SPR mask)	2480 Å/min
Thermal oxide	350 Å/min
HTO	unknown
LTO	unknown
PECVD oxide	unknown
Stoichiometric nitride	unknown
Low stress nitride	unknown
SPR 220	1300 Å/min

Uniformity

• Within-wafer uniformity: <4% (3 mm edge exclusion)
  • Etch rate is faster at the edge
• Wafer-to-wafer uniformity: <2%

Mask selectivity

Mask selectivity of polysilicon to a selection of materials is shown below. Selectivity for your material can be calculated using the etch rates listed above.

Mask selectivity is based on bulk material etch rates (above). Selectivity will vary slightly with feature size.

Material	Etch rate
SPR 220	3:1
Thermal oxide	10.9:1
Stoichiometric nitride	unknown
Low stress nitride	unknown

Sidewall profile

Warning:

not verified

• 88 degrees

Parameters

Parameters are shown below for the recipe. The first STAB, STRIKE, and BT are for the breakthrough step (BT being the etching portion). The second STAB and MAIN ETCH are for the main etch step. The OVER ETCH step has not been tested, please contact a tool engineer if you wish to test this step.

Parameter	STAB	STRIKE	BT	STAB	MAIN ETCH	OVER ETCH
Chamber Selection	C Only
Step end control	By Time
Maximum step time	20 s	1 s	10 s	20 s		0 s
Endpoint selection	No Endpoint
Pressure	Servo 20 mTorr		Servo 10 mTorr	Servo 125 mTorr		Servo 100 mTorr
Pressure ramp rate	0 mTorr/Second
RF Power	0 W	300 W		0 W	400 W	150 W
RF match, mode	Auto, B-to-B				Auto, RF Off
RF tune setpoint	0.0 V
DC Bias Limit	-1000 to 0 V
Magnetic field	0 G			30 G
Argon Flow	120 sccm		50 sccm
HBr Flow				40 sccm		60 sccm
Cl2 Flow				40 sccm		20 sccm
O2He Flow						12 sccm

Limitations

Etch time

Etch rate is very linear, tested down to 5 seconds. Maximum etch time is mask dependent, have demonstrated up to 4 µm etch depth.

Loading

This etch is not significantly load dependent.

Passivation removal

This etch deposits a bromine-based passivation layer to achieve anisotropy. Removal has been shown using a series of alternating BHF and Nanostrip processes.

Qualification

The bulk etch rate of polysilicon is verified occasionally by running the recipe for 1 minute.