Specific Process Knowledge/Etch/Etching of Silicon/Si etch using RIE1 or RIE2

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This page is written by Berit Herstrøm @ DTU Nanolab (BGHE) if nothing else is stated

Both RIE's (RIE1 and RIE2) for silicon based etching has been decommissioned

RIE (Reactive Ion Etch) can be used for etching silicon - both crystalline and polycrystalline silicon. The etch can be isotropic or anisotropic with vertical sidewalls depending on the process recipe and the masking material and geometry. The Si is etched by flour radicals that are created from SF₆(g) in a RF generated plasma.

Most used recipe:

Quality Controle (QC) for RIE2

The QC procedure for RIE2 The newest QC data for RIE2 QC Recipe: OH_POLYA SF6 flow 32 sccm O2 flow 8 sccm Pressure 80 mTorr RF-power 30 W Etch Load 50% QC limits RIE2 Etch rate in Si 358 - 554 nm/min Non-uniformity <11.0 %

Hint: When using resist as masking material then do a 15 sec. buffer dip before the etch to remove any residual of resist which is normally left after the photo lithography step. A short O₂ plasma will also do.

Recipe:	OH_POLYA
SF6 flow	32 sccm
O2 flow	8 sccm
Pressure	80 mTorr
RF-power	30 W

	Expected results in RIE1 (has been decommissioned)	Expected results in RIE2	RIE2 results for almost 100% load by Yannick Seis@nbi.ku.dk May 2017 (4min etch)
Etch rate in Si	~0.40 µm/min	~0.45 µm/min	0.35µm/min (center) 0.30 (half way) 0.28 (edge)
Etch rate in Si3N4	.	~0.05 µm/min
Etch rate in SiO2	.	~0.02 µm/min	.
Etch rate in photoresist	~0.06 µm/min	~0.05 µm/min	.

The etch load affects the results

The etching results are dependent on the mask geometry, primarily the etch load (meaning the area fraction of the silicon substrate that is exposed to the plasma).

To illustrate this, you can see on the images below the effect of etch load on the results of the OH_PolyA recipe. The first one has a very low load of 1-10% and the second has a load of 50%. It can be seen that the sidewalls are closer to vertical with 50% load than with 1-10 % load. Also the etch rate is effected by the load.

Etch load <50%:

• The etch rate is approximately the same.
• The etch profile is more isotropic

Etch load >50%:

• The etch rate decreases almost linear with the exposed area. The etch rate of a 100% load has once been seen to be reduced to about 65% of the etch rate of a 60% load.
• The etch profile is not expected to change significantly.

RIE1: OH_Polya on etch load 10% Etch rate:~0.61 µm/min

RIE1: OH_Polya on etch load 50% Etch rate:~0.49 µm/min

RIE Travka results - Silicon etch rate and profile as function of etch load

More information about the etch rate and profile as function of the etch load for RIE1 and RIE2 can be found here:

RIE1 Travka results - RIE1 has been decommissioned

RIE2 Travka results

A description of the Travka mask set can be found here:

Travka mask set

Etch of small structures

RIE2:

A Design Of Experiment (DOE) has been performed. Here is a short summary:

Recipe:
SF6 flow	30 sccm
O2 flow	20-29 sccm
CHF3 flow	5-15 scmm
Pressure	36 mTorr
RF-power	20 W

Angle of sidewall on 1.5 µm trenches

More details on the DOE can be seen here: "DOE RIE2 silicon etch of small structures" (not available yet).

Here are a few images of some of the single experiments in the DOE. The width of the trenches are roughly 1.5µm:

O2:24.5sccm CHF3:10sccm	O2:29sccm CHF3:15sccm	O2:20sccm CHF3:5sccm

More details on the DOE can be seen here: "DOE RIE2 silicon etch of small structures": DOE of RIE2

RIE1: RIE1 HAS BEEN DECOMMISSIONED

A Design Of Experiment (DOE) has been performed. Here is a short summary:

Recipe:
SF6 flow	30 sccm
O2 flow	20-29 sccm
CHF3 flow	5-15 scmm
Pressure	31-41 mTorr
RF-power	20 W

Angle of sidewall on 1.5 µm trenches - independent on pressure within the given pressure range

More details on the DOE can be seen here: "DOE RIE1 silicon etch of small structures": Media:RIE1_of_Silicon_20070306.pdf

Here are a few images of some of the single experiments in the DOE. The width of the trenches are roughly 1.5µm:

O2:24.5sccm CHF3:10sccm Pressure:36mTorr	O2:29sccm CHF3:15sccm Pressure:31mTorr	O2:20sccm CHF3:5sccm Pressure:31mTorr