Specific Process Knowledge/Thin film deposition/Deposition of Titanium Oxide/IBSD of TiO2

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Acceptance test for TiO2 deposition (done in 2011 by bghe@nanolab):

. Acceptance Criteria

Acceptance Results recipe 1

Acceptance Results recipe 2 Acceptance Results recipe 2
Substrate information
  • 50 mm SSP Si wafer
  • 525 µm thick
  • Supplied by Nanolab
  • 100 mm SSP Si wafer
  • 525+-25 µm thick
  • 100 mm SSP Si wafer
  • 525+-25 µm thick
  • 100 mm SSP Si wafer
  • 525+-25 µm thick
Material to be deposited
  • TiO2

The purpose of the TiO2 is to be part of a mirror: <br\> 5 quarterwavelength pairs of <br\> SiO2 <br\> TiO2 <br\> Extra quarterwavelength layer of <br\> TiO2 <br\> 5 quarterwavelength pairs of <br\> SiO2 <br\> TiO2 <br\> Design wavelength (for refractive indices and layer thicknesses):1300nm <br\> The acceptance criteria is set up for the single SiO2 and TiO2 layers. <br\> Five runs in a row for each material.

  • TiO2
  • TiO2

TiO2

Deposition thickness
  • 147nm
  • ~184 nm
  • 121 nm
  • 43.3nm in 10min 2013-10-07
Deposition rate
  • 2.8 nm/min
  • 3.54nm/min +- 0.03nm/min

One stdev - wafer to wafer

  • 3.03nm/min

Only done once

  • 4.33 nm/min 2013-10-07
Thickness uniformity
  • <+-1%
  • <+-1.00%
  • <+-0.90%
  • Not tested
Reproducibility
  • <+-1.5%
  • +-0.9% on 5 wafers in a row
  • not tested
  • not tested
Stress
  • <500 MPa
  • ~300 MPa
  • Not measured expect ~300 MPa
  • Not tested
Refractive index .
  • 2.451+-0.004 (stddev wafer to wafer)
  • 2.437+-0.005 (stddev on wafer)
  • 2.108 test done shortly after pump down


Recipe 1 Recipe 2
Platen angle 50 degrees 30 degrees
Platen rotation speed 20 rpm 20 rpm
Ar(N) flow 4 sccm 4 sccm
Ar(dep. source) flow 9 sccm 9 sccm
O2(dep. source) flow 2 sccm 2 sccm
O2(etch source) flow 8 sccm 8 sccm
I(N) 459 mA 450 mA
Power 875W 875W
I(B) 390 mA 390 mA
V(B) 1300V 1300V
Vacc(B) 400V 400V
Deposition time 52min 40min


Repetitions of the acceptance test

Made on 100mm wafers. Test1-3 were done without a bakeout. 1 Hour after a user had run several hours of runs with the same recipe.
Test4-6 were done after a bakeout. Several hours after the system had been used and with out heat-up recipe and conditioning run.
Test7-13 were done after a change to deposition mode (the chamber has been open), a bakeout for 8 hours, a heat-up of the deposition source and then the 7 wafers in a row.The run to run reproducibility improves after the two first wafers. This is consistent with the advice from Oxford Plasma Systems to run a 40 min conditioning run before your real wafers (or wafer with multiple layers).

Acceptance recipe TiO2 2 Deposition thickness (0,0) Deposition thickness average Deposition time Deposition rate (0,0) Refractive index@632.8nm
2014-06-16 test1 60.7 nm 58.4 nm 20 min 3.04nm/min 2.42679
2014-06-16 test2 59.4 nm 59.6 nm 20 min 2.97nm/min 2.42651
2014-06-16 test3 59.3 nm 59.2 nm 20min 2.97nm/min 2.4249
2014-06-19 test4 60.62/60.51 59.49/59.38 20 min 2.97nm/min 2.42776/2.43090
2014-06-19 test5 59.92/59.84 59.80/59.73 20 min 2.99nm/min 2.42776/2.42983
2014-06-19 test6 60.31 59.53 20 min 2.98nm/min 2.42776


Acceptance recipe TiO2 2 Deposition thickness min (edge) Deposition thickness max (center) Deposition time Deposition rate (0,0)
2014-07-22 test7 56.6 nm 57.6 nm 20 min 2.88 nm/min
2014-07-22 test8 55.4 nm 56.4 nm 20 min 2.82 nm/min
2014-07-22 test9 53.5 nm 55.6 nm 20 min 2.78 nm/min
2014-07-22 test10 54.3 nm 55.4 nm 20min 2.77nm/min
2014-07-22 test11 54.1 nm 55.2 nm 20 min 2.76nm/min
2014-07-22 test12 54.0 nm 55.2 nm 20 min 2.76nm/min
2014-07-22 test13 53.8 nm 54.9 nm 20 min 2.75nm/min

Other results

Roughness of the surface

Measured with the Optical profiler - PSI mode (on one sample from the acceptance test): Sa= ~1 nm


How to pattern TiO2

TiO2 can be difficult to pattern since TiO2 is a very hard material that is also difficult to etch wet. Hot sulfuric acid can remove it (not allowed at DTU Nanolab without special permission). HF will etch it at a very low etch rate. It can be sputtered by IBE but also at a very low etch rate and there is no masking material with a reasonable selectivity to TiO2. If you want to pattern a TiO2 that you deposit in the IBSD Ionfab then we advice you to do it with a lift-off process. Make your resist pattern, deposit TiO2 on top and do the lift-off in an appropriate solvent depending on the resist chosen..