Plasma Etch: Oxide Etch Overview

Oxide Plasma Etching

The following information is provided to SNF users to aid in the determination of appropriate equipment for their etching needs. Standard or typical programs and results are given. The user may want to tailor the programs to fit their specific process. Etch rates and selectivities are given as a starting point only and should not be considered to be current. It is highly recommended that users establish the etch rates for their work by the use of test wafers as close in material and masking pattern as possible to the device wafers to be etched.

Amtetcher (Contact Etch, Via Etch and Etch Back Processes)

Difference Between Contact and Via Etch Processes
The Contact etch process is optimized for stopping on silicon, and as such, has a high selectivity (8 to 10) of oxide to silicon. To achieve a high selectivity, the process has a high polymer deposition rate, which comes from runnin a high CHF3/O2 flow ratio (typically 85/6). The downside of having a high polymer dep rate is that one needs special post etch steps to remove this polymer and this deposition leads to sloped etch profiles. In Via etching, high silicon selectivity is not needed, so one can run at a lower CHF2/O2 flow ratio (typically 50/40 - check logs). This leads to less sidewall polymer deposition and more vertical etch profiles.

Amtetcher Contact Etch Process
Pre-treatments:

To prevent 3612 resist burning, wafers should get 15 mins UV exposure and 60 min 110C bake before etching.

SPR220-7 (thick) resist may burn or reticulate. Consult staff before etching.

Contact Etch Process Conditions, Program 3 (typical program):

Pressure	50 mTorr
O2	6 sccm
CH3	85 sccm
RF Power	1400 W
Electrode Bias	-530 VDC

Post-treatments:

Wafers need a plasma polymer cleanup step, even if they are going into a H2SO4/H2O2 strip/clean. This is especially important after a contact etch, where the CHF3 flow is high and the O2 flow is low. A common cleanup process is one done in drytek2, using C2ClF5 for 30 seconds. This process has the advantage that it removes the polymer/oxide layers at the contact bottoms along with a few hundred angstroms of damaged silicon. However, it does not remove the thick sidewall polymer. A hot H2SO4/H2O2 clean after the short plasma cleanup will remove the sidewall polymer. If you are not worried about leaving a little silicon damage, a short O2 plasma in either drytek2 or the matrix can be used instead of the C2ClF5 plasma. A long matrix O2 resist strip will most likely remove the sidewall polymer, but such a process has not been qualified. For via etching which stops on metals, the via etch processs with its high O2 flow shold be used since the sidewall polymer is much thinner.

Etch Rates and selectivities:

Material	Etch Rate
Thermal Oxide	371A/min
LTO- undensified	429A/min
LTO- undensified, 4%	390A/min
LTO- undensified, 8%	530A/min
LTO- densified	360A/min
LTO- densified, 4%	350A/min
LTO- densified, 8%	375A/min
Nitride, Std	170A/min
Nitride, low-stress	233A/min
Poly, undoped	60A/min
Photoresist	123A/min
Si	0A/min
2%950 PMMA	197 A/min
Polymer	35 A/min

Amtetcher Via Etch Process

Via Etch Process Conditions (check log book)

Pressure	50m Torr
O2	30 sccm
CH3	50 sccm
RF Power	1400 Watts
Electrode Bias	(-530) VDC

Post-treatments:

See Contact Etch process for amtetcher.

Etch Rates and selectivities:

Material	Etch Rate
Thermal Oxide	371 A/min
LTO- undensified	416 A/min
LTO- undensified, 4%	420 A/min
LTO- undensified, 8%	515 A/min
LTO- densified	395 A/min
LTO- densified, 4%	380 A/min
LTO- densified, 8%	500 A/min
Nitride, Std	680 A/min
Nitride, low-stress	445 A/min
Poly, undoped	305A/min
Photoresist	295 A/min
Si	380 A/min

Amtetcher Etch Back Process

Etch back Process Conditions (Check log book)

Pressure	50 mTorr
O2	20 sccm
CH3	75 sccm
RF Power	1400 Watts
Electrode Bias	(-530) VDC

Post Etch Treatment:

See Contact etch process

Measured Rates for Etch Back Process

Material	Etch Rate
Thermal Oxide	377 A/min
LTO- undensified	400 A/min
LTO- undensified, 4%	460 A/min
LTO- undensified, 8%	545 A/min
LTO- densified	440 A/min
LTO- densified, 4%	415 A/min
LTO- densified, 8%	490 A/min
Nitride, Std	500 A/min
Nitride, low-stress	789 A/min
Poly, undoped	277 A/min
Photoresist	384 A/min
Si	230 A/min

P5000etch

Comment:

The current process uses a high CF4/CHF3 ratio and gives near vertical profiles. We are currently working on a process with a lower CF4/CHF3 ratio to give higher resist and poly-Si selectivities.

Pre-treatments:

Photoresist should be removed from outer 5mm of wafer by using the Edge Bead Removal for Dry Etchers process.

Etch Process, CH.B OXIDE (typical program):

Operation	Set Up	Main Etch
Pressure	250 mT	250 mT
CHF3	25 sccm	25 sccm
CF4	50 sccm	50 sccm
Ar	100 sccm	100 sccm
RF	0 W	500 W
Mag Field	0 Gauss	60 Gauss

Endpoint program: su_ox_lg.alg or su_ox_sm.alg

Etch Rates and Selectivities:

Operation	Etch Rate	Selectivity
Main Etch	Ox 3000A/min	Ox:PR >3:1 Ox:Si >7.5:1

Post-treatments:

Resist ashing in Matrix must be done in order to remove polymer build-up.

MRC

Pre-treatments:

To prevent 3612 resist burning, wafers should get 15 min UV exposure and 60 min 110C bake.

Gold contaminated equipment.

Etch Process (typical program):

Pressure	50 mT
SF6	3 sccm
F115	15 sccm
Electrode Bias	-500 to -600 VDC

Note: Etch rate for this program is about 200A/min.

Post-treatments:

Wafers need polymer cleanup program in Drytek1 after etch to remove polymer build-up before resist can be stripped.

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Stanford Nanofabrication Facility
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Last Modified 08/29/2003