Specific Process Knowledge/Etch/ICP Metal Etcher
The ICP Metal Etcher in short
Despite its name the metal etcher doesn't etch metals in general. Currently, the list of metals that you can etch is quite short:
- aluminium
- titanium
- chromium
Over time it is our intention to add other materials to the list such as molybdenum, tungsten, titaniumtungsten, titaniumoxides or piezo-materials such as ZnO. However, currently you are not even allowed to expose other metals to the plasma. To etch other metals use the IBE/IBSD Ionfab 300.
Recipes on the Metal Etcher
Aluminium etch
The aluminium etch has two steps:
- Breakthrough
- The breakthrough step is designed to break through the native aluminium oxide layer that is present on all aluminium surfaces. The duration of this step should remain fixed.
- Main
- The main step etches bulk aluminium.
| Parameter | Process step | |
|---|---|---|
| Breakthrough | Main | |
| Time (secs) | 20 | 40 (variable) |
| HBr (sccm) | - | 15 |
| Cl2 (sccm) | 20 | 25 |
| Pressure (mTorr) | 4, Strike 3 secs @ 15 mTorr??? | 1 |
| Coil power (W) | 600 | 500 |
| Platen power (W) | 125 | 100 |
| Temperature (oC) | 20 | 20 |
| Spacers (mm) | 30 | 30 |
Titanium etch
| Parameter | Process 1 | Process 2 |
|---|---|---|
| Cl2 (sccm) | 30 | 30 |
| HBr (sccm) | - | - |
| Pressure (mTorr) | 3, Strike 3 secs @ 15 mTorr??? | 3 |
| Coil power (W) | 800 | 900 |
| Platen power (W) | 100 | 50 |
| Temperature (oC) | 20 | 20 |
| Spacers (mm) | 30 | 30 |
| Etch rate (nm/min) | 152 | 64 |
| AZ resist selectivity | 0.67 | 0.83 |
Chromium etch
The Chromium etch has ONLY been carried out on the following substrate stack: The Chromium is sputter deposited onto a 2" quartz wafer and pattered by e-beam with Zep520A resist. This 2" QZ wafer is bonded with crystal bond to a 65mmx65mm quartz plate with the thickness: 6.35mm. This QZ plate is bonded to a Si wafer.
| Parameter | Cr etch |
|---|---|
| Cl2 (sccm) | 65 |
| O2 (sccm) | 15 |
| Pressure (mTorr) | 15 |
| Coil power (W) | 500 |
| Platen power (W) | 15 |
| Temperature (oC) | 50 (no back side cooling) |
| Spacers (mm) | 100 |
| Etch rate (nm/min) | ~40 |
| Zep520A resist selectivity | ~0.9 |
Etching of nanostructures in silicon using the ICP Metal Etcher
A series of experiments with etching nanostructures in silicon has been carried out. The common process parameters are:
- Substrates
- A pattern containing 30 nm, 60 nm, 90 nm, 120 nm and 150 nm wide lines has been transferred using E-beam lithography onto three separate batches of 2" wafers (with three different thicknesses of zep resist). In order to make sure that the narrowest features are fully opened they are intentionally over-exposed in the E-beam writer (400 muC/cm2) causing the lines to widen. The resist profiles are:
- The 180 nm zep resist profiles (Wafer WF_2B1_feb06_2011)
- The 340 nm zep resist profiles (Wafer WF_2C1_feb2011)
- The 211 nm zep resist profiles (Wafer WF_2E02_mar23_2011)
The exposed area is very small. The 211 nm batch has the same lines distributed in a different way that allows you monitor the progress of the etch in three different durations by cleaving off a piece of the wafer 3 times. After E-beam exposure the wafers have been developed: N50 for 2 minutes followed by 30 seconds of IPA.
- Substrate mounting
- The 2" wafers are mounted with crystalbond in the center of 4" Si carriers that have an oxide layer facing the plasma.
- Conditioning the process chamber
| Recipe Sinano | 3.0 | 3.1 | 3.2 | 3.3 | 3.4 | 4.0 | 3.5 | 3.6 | 3.3 | 3.7 | 3.31 | 3.31 | 3.32 |
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Cl2 (sccm) | 0 | 0 | 0 | 0 | 0 | 20 | 15 | 15 | 0 | 0 | 0 | 0 | 0 |
| BCl3 (sccm) | 5 | 3 | 5 | 5 | 5 | 0 | 5 | 5 | 5 | 5 | 5 | 5 | 5 |
| HBr (sccm) | 15 | 17 | 15 | 15 | 15 | 0 | 0 | 0 | 15 | 15 | 15 | 15 | 15 |
| Coil power (W) | 900 L | 900 F | 900 F | 900 F | 900 F | 900 L | 900 L | 900 F | 900 F | 900 L | 900 F | 900 F | 900 F |
| Platen power (W) | 50 | 50 | 60 | 75 | 90 | 60 | 60 | 60 | 75 | 60 | 75 | 75 | 30 |
| Pressure (mtorr) | 2 | 2 | 2 | 2 | 2 | 2 | 5 | 10 | 2 | 10 | 2 | 2 | 2 |
| Temperature (oC) | 20 | 20 | 20 | 20 | 20 | 20 | 20 | 20 | 20 | 50 | 50 | 50 | 50 |
| Spacers (mm) | 100 | 100 | 100 | 100 | 100 | 100 | 100 | 100 | 100 | 100 | 100 | 30 | 100 |
| Process time (s) | 150 | 180 | 120 | 180 | 120 | 90 | 120 | 180 | 300 | 180 | 180 | 180 | 180 |
| Etch rates (nm/min) | |||||||||||||
| Averages | 311 | 104 | 92 | 105 | 116 | 169 | 108 | 79 | 101 | 66 | 91 | 98 | 59 |
| Std. Dev | 44 | 15 | 15 | 21 | 22 | 9 | 11 | 31 | 29 | 4 | 28 | 18 | 12 |
| Zep etch rate (nm/min) | |||||||||||||
| 30 | 40 | 51 | 67 | 45 | 59 | 53 | 36 | 19 | |||||
| Sidewall angle (degrees) | |||||||||||||
| Averages | 82 | 82 | 82 | 82 | 82 | 84 | 81 | 83 | 83 | 85 | 80 | 83 | 79 |
| Std. Dev | 2 | 2 | 1 | 1 | 1 | 1 | 1 | 2 | 2 | 1 | 3 | 2 | 2 |
| CD loss (nm pr edge) | |||||||||||||
| Averages | 65 | -11 | -15 | -2 | -11 | 67 | 63 | -29 | -5 | -29 | 10 | -14 | -17 |
| Std. Dev | 30 | 5 | 2 | 4 | 3 | 29 | 27 | 6 | 5 | 8 | 7 | 8 | 10 |
| Bowing (nm) | |||||||||||||
| Averages | 31 | 31 | 15 | 6 | 5 | 22 | 12 | 15 | 28 | 13 | 25 | 1 | -2 |
| Std. Dev | 6 | 7 | 3 | 6 | 4 | 5 | 2 | 6 | 9 | 7 | 5 | 2 | 2 |
| Bottom curvature | |||||||||||||
| Averages | -9 | -6 | -9 | -11 | -9 | 9 | -4 | -8 | -24 | -2 | -9 | -13 | -10 |
| Std. Dev | 22 | 19 | 19 | 11 | 7 | 17 | 15 | 15 | 12 | 15 | 13 | 17 | 18 |