Operation-Spec-Oxford-System-100-Rev-C.pdf - 第8页
Oxford Instruments Plasmalab 100 ICP-RIE Page 8 of 8 Table 2. Example Recipe Steps Step Pressure (mTorr) RF Power (W) SF 6 Flow (SCCM) O 2 Flow Rate (SCCM) 1 30 0 0 60 2 30 100 0 60 3 27 85 1 55 4 24 70 5 50 5 21 55 10 4…
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
Etch Gas
Si
SF
6
SiO
2
CHF
3
, SF
6
Si
3
N
4
, SiN
x
CHF
3
, SF
6
SiC
SF
6
Poly-Si
SF
6
Graphene (C)
O
2
W
SF
6
TiW
SF
6
GaN
CHF
3
Photoresist
O
2
(Ashing)
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.
Oxford Instruments Plasmalab 100 ICP-RIE
Page 8 of 8
Table 2. Example Recipe Steps
Step
Pressure (mTorr)
RF Power (W)
SF
6
Flow (SCCM)
O
2
Flow Rate (SCCM)
1
30
0
0
60
2
30
100
0
60
3
27
85
1
55
4
24
70
5
50
5
21
55
10
45
6
18
40
20
40
7
15
30
40
35
8
15
20
90
30
Table 3. Optimal DRIE recipe parameters and values
Parameter
Value
Pressure
15 mTorr
Temperature
-100 °C
Helium Backing (Pressure, Flow)
10 Torr, 38 SCCM
SF
6
Flow
90 SCCM
O
2
Flow
20 SCCM
ICP Power
1000 W
RF Power
10 W
Table 4. Optimal DRIE recipe resulting values
Parameter
Value
Average Vertical Etch Rate
3.06 µm/min
Average Horizontal Etch Rate
0.085 µm/min
Selectivity (Cr, SiO
2
, AZ 5214 E-IR)
1700, 100, 20