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 Danchip	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	<500MPa	~300MPa	Not measured expect ~300MPa	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	20rpm	20rpm
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)	459mA	450mA
Power	875W	875W
I(B)	390mA	390mA
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 reproduciblity improves after the two first wafers. This is consistent with the advise from Oxford Plasma Systems to run a 40min 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)	Refrative index@632.8nm
2014-06-16 test1	60.7 nm	58.4 nm	20min	3.04nm/min	2.42679
2014-06-16 test2	59.4 nm	59.6 nm	20min	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	20min	2.97nm/min	2.42776/2.43090
2014-06-19 test5	59.92/59.84	59.80/59.73	20min	2.99nm/min	2.42776/2.42983
2014-06-19 test6	60.31	59.53	20min	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	20min	2.88nm/min
2014-07-22 test8	55.4 nm	56.4 nm	20min	2.82nm/min
2014-07-22 test9	53.5 nm	55.6 nm	20min	2.78nm/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	20min	2.76nm/min
2014-07-22 test12	54.0 nm	55.2 nm	20min	2.76nm/min
2014-07-22 test13	53.8 nm	54.9 nm	20min	2.75nm/min

Other results

Roughness of the surface

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

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.