Specific Process Knowledge/Etch/ICP Metal Etcher

From LabAdviser

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.
Al etch
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

Ti 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.

Cr etch
Parameter Cr etch
Cl2 (sccm) 65
O2 (sccm) 15
Pressure (mTorr) 15
Coil power (W) 300
Platen power (W) 15
Temperature (oC) 50 (no back side cooling)
Spacers (mm) 100
Etch rate (nm/min) ~14
Zep520A resist selectivity ~0.9
Comment }

Etching of nanostructures in silicon

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 of the three batches are:

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


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