Operation-Spec-Oxford-System-100-Rev-C.pdf - 第6页

Oxford Instruments Plasmalab 100 ICP-RIE Page 6 of 8 Appendix B : Co mmon Substrate Chemistry Recipe s Table 1. Etchan t-etch gas com binations Material Bein g Etched Etch Gas Si SF 6 SiO 2 CHF 3 , SF 6 Si 3 N 4 , SiN x …

100%1 / 8
Oxford Instruments Plasmalab 100 ICP-RIE
Page 5 of 8
Appendix A: Recipe Parameter Information
• Step time [hh:mm:ss]: Amount of time the step should run.
• Ignore tolerance: Certain parameters have certain tolerances. For example, if the table
temperature setpoint is 20 °C and the actual value is 30 °C, then it is out of tolerance. By
checking this box, the recipe will continue to run if the tolerances are not satisfied.
• Hold: When “Hold” is on, the plasma is continuous between steps. If NOT selected, the plasma
will turn off between steps while the APC stabilizes.
• Automatic Pressure Controller (APC): The APC controls the chamber pressure automatically
based on the gas flow rates and pressure setpoint.
o Chamber Pressure [mTorr]: Pressure in the process chamber.
o Strike Pressure [mTorr]: Value at which the RF should turn on and strike the plasma. If a
zero is entered, the feature is disabled, and the RF will turn on once the pressure has
stabilized at the requested process pressure
o DC Bias Minimum [V]: Enter a positive number for the minimum DC bias value
expected once the plasma has struck. Enter zero if DC bias cannot be read because the
substrate (and any wafer clamp) completely covers the electrode, or if the electrode has
an insulating coating. A non-zero value is used by the software to detect if the plasma has
been properly established. If a zero is entered, then the software assumes the plasma has
struck once the RF reflected power goes low.
o Ramp Rate [s]: Sets the rate at which the pressure is reduced from the strike value to the
set point. The higher the number entered, the faster the transition to process conditions
will be. Too high a value can cause the plasma to go out.
• RF Generator:
o Forward Power [W]: Value of the RF power applied to the plasma.
▪ MAXIMUM = 200 W
▪ Increasing RF power increases etch rate, increases anisotropy/directionality, and
decreases selectivity
▪ DC Bias [V] and Reflected Power [W] are functions of the forward power and
other parameters. If DC Bias is larger than 500 V, an error will occur, and the
tool will abort the process.
• ICP (Inductively Coupled Plasma):
o Forward Power [W]: Value of ICP power applied to the plasma.
▪ MAXIMUM = 2000 W
▪ Increasing RF power increases etch rate, decreases anisotropy/directionality, and
increases selectivity.
• Helium Backing: Used to cool wafers.
o Pressure controller [Torr]: Pressure of helium on the wafer’s backside.
o Sccm [SCCM]: Helium flow rate.
• Cryo [°C]: Temperature of the process chamber.
o MAXIMUM RANGE = -100 °C to 30 °C
• Gases [SCCM]: Flow rates of the provided gases (SF6, O2, Ar, CHF3). Larger etch gas flow rates
(SF6, CHF3) increase etch rate.
o MAXIMUM = 100 SCCM
Oxford Instruments Plasmalab 100 ICP-RIE
Page 6 of 8
Appendix B: Common Substrate Chemistry Recipes
Table 1. Etchant-etch gas combinations
Material Being Etched
Si
SiO
2
Si
3
N
4
, SiN
x
SiC
Poly-Si
Graphene (C)
W
TiW
GaN
Photoresist
Oxford Instruments Plasmalab 100 ICP-RIE
Page 7 of 8
Appendix C: Cryogenic Deep Reactive-Ion Etching
Managing Heat
If the sample is smaller than a 4” wafer, some type of thermal grease must be used between the sample
and carrier wafer to promote thermal conduction. If the sample gets too hot, anisotropy will decrease
significantly. So, there are three ways to promote sample cooling:
• Thermal conductor: COOL-GREASE ZXM is a thermal grease used for heatsinks. It is ZnO-
filled and has a thermal conductivity of approximately 20 W/m-°C. This goes between the sample
and the carrier wafer.
• Backside helium cooling: Helium is used for cooling the wafer. Set the pressure to 10 mTorr and
flow rate to 38 SCCM.
• Chamber temperature: -100 °C is the lowest temperature the tool can safely handle.
To apply the grease, gently push some out of the syringe and dab it on the sample’s backside. Once there
is a large-enough dab, place the sample onto the carrier wafer. Press across the sample to spread the
grease, then move the sample a bit in all four directions (up, down, left, right) to further spread the grease.
Do not go so far that grease escapes from underneath the sample. Applying a vacuum will also spread the
grease. When complete apply Kapton tape as normal and run the DRIE recipe.
To remove the sample, remove the Kapton tape and slide the sample to the edge of the wafer or push
around in circles to remove the grease’s adhesion. To clean up the residual grease, a cotton swap covered
with a cleanroom wipe works well. Ensure all the grease is removed from the carrier wafer’s surface.
Recipe Guidelines
It has been determined that cryogenic recipes work best when two things occur:
• The process chamber is cleaned beforehand with an O2-based plasma.
• The etching gas (SF6, CHF3) is gradually introduced into the plasma.
Begin the process with a 15:00+ min O2 clean, then decrease the chamber temperature to your desired
value.
To gradually introduce the etching gas, first strike a plasma using the supplementary gas (O2, Ar) if you
are using one at a pressure of X mTorr, Y W ICP power, and Z W RF power. Hold this plasma for 10-20
s, then add 1 SCCM of the etching gas and decrease both the supplementary gas flow and RF power
slightly. Hold for 5 s, then repeat: increase etching gas flow and decrease supplementary gas flow and RF
power slightly. See the example recipe below (Table 2), where ICP power, temperature, and helium
backside cooling remain constant throughout (holding ICP power constant is optional, but cooling
parameters should remain constant). The O2 environment is stabilized in step 1, an O2 plasma is formed
in step 2, then SF6 is slowly introduced in steps 3-8, with RF power, pressure, and O2 flow rate also
decreasing. The “Ignore tolerance” (second bullet point of Appendix A) and “Hold” options (last bullet
point of Appendix A) must be selected for this to work properly.