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..