Specific Process Knowledge/Thin film deposition/Lesker

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LESKER Sputter Tool

The purpose of the "Sputter-system (Lesker)" is to deposit magnetic metals and dielectrica on a single 4" or 6" wafer at a time.

It can be a problem to take wafers from the sputter and into the other machines in the cleanroom, since it is not very clean. In principle the sputter should be the last step before you take your wafers out of the cleanroom. If you need to take process your wafers further please contact the Thin Film group so they can help you.

Lift-off of magnetic materials should never be done in the normal lift-off bath in RR4. It should always be done in the dedicated lift-off bath in the fumehood next to the sputter.

The user manual, user APV and contact information can be found in LabManager:

Sputter-System(Lesker) in LabManager

Materials for sputtering

• Gold (Au)
• Nickel (Ni)
• Silver (Ag)
• Silicon (Si)
• NiV alloy
• Iron (Fe)
• + many more (see list below or ask)

Contact the Thin Film group if you have special needs (thinfilm@danchip.dtu.dk).

Sputter rate

The sputter rate depends on

• target material
• gun power (increasing power gives in general higher rate). Be aware of limitations on the power for different materials.
• chamber pressure (increasing pressure gives in general lower rate). Too low a pressure can make the plasma unstable.
• gas in chamber (Ar, N2, O2 or mixture).

In the table below (Relative Sputter rates) there is a list of relative sputter rates for different materials (Al is set to 1). This means that you can estimate the sputter rate for a new material if you have the rate for another material under the same conditions (may only work for non-reactive sputtering, i.e., with Ar as the gas).

Thickness uniformity

We have measured the thickness of a TiO_x film deposited on a 6" Si wafer. The thickness measurement was done in the VASE ellipsometer.

Deposition parameters were:

Recipe	source 3 with oxygen
time	600 s
Gas	O2/Ar Ratio 10/100
Pressure	3 mtorr
Gun	3
Target	Ti
Power	200 W
Voltage	370V
Date	November 3rd 2015

Overview of the performance of Sputter-System(Lesker) and some process related parameters

Purpose	Deposition of magnetic metals and dielectrica	Sputtering of magnetic metals and Silicon
Performance	Film thickness
	Deposition rates
Process parameter range	Process Temperature	usually room temp Sample can be heated to more than 400°C *
	Process pressure	3-10 mTorr
	Process Gases	Ar N$_{2}$ O$_{2}$ 2%O$_{2}$ in Ar mixtures of the above
Substrates	Batch size	chips 4" 6"
	Substrate material allowed	Silicon wafers and almost any other
	Material allowed on the substrate	almost any

* For temperatures above 400°C, please contact thinfilm@danchip.dtu.dk, as higher temperatures may damage the machine.

Film quality optimization

By Bjarke Thomas Dalslet @Nanotech.dtu.dk

The Lesker CMS 18 sputter system can produce films in a wide range of crystalline qualities. The crystalline quality of a film depends strongly on the substrate (lattice matching), but also on the energy the sputtered material can utilize for annealing.

You will find detailed information on film quality optimization for NiFe films here.

Surface roughness optimization

By Bjarke Thomas Dalslet @Nanotech.dtu.dk

The Lesker CMS 18 sputter system provides thin films of varying surface roughness. This roughness was verified to be dependent on the sputtered material, sputter mode (DC or RF) and the substrate bias strength. Other probable factors include sputter power and pressure. Below is a table for three cases.

The "From SiO$_{2}$ target (RF sputter)" study was done on clean Si substrates. The sputter power was 157W and the pressure 3.5 mTorr using RF sputtering of a SiO$_{2}$ target. The film thicknesses were around 42 nm.

The "From Si target (DC sputter)" study was done on clean Si substrates. The sputter pressure 3 mTorr using DC reactive sputtering of a Si target. Oxygen was added to the argon sputter gas. Above 10% O$_{2}$ the gun seems to oxidize (at this sputter power). Figure 1 shows the difference in AFM images between no RF bias (wafer 12) and RF bias (Wafer 21).

The "Ta" study was done on clean Si substrates. The sputter pressure was 3 mTorr using DC sputtering of a Ta target. Some O$_{2}$ was added to wafer 25 and 26 to make Ta$_{2}$O$_{5}$. In order to get fully oxidized films, up to 30-45% O$_{2}$ should be added. Consult the thesis of Carsten Christensen for details on Ta$_{2}$O$_{5}$.

Other studies on metals (NiFe/MnIr) show only limited effect of the substrate bias on the roughness.

From Si target (DC sputter)

Wafer nr	RF bias (W)	Reactive O2 (%)	Power(W)	Rq (RMS) (nm)	Thickness
12	0	5	135	1.44	123 nm (ellipsometry)
13	0	9	130	1.32	98 nm (ellipsometry)
14	0	13	100	1.37	71.5 nm (ellipsometry)
15	10	9	90	0.984	56.25 nm (ellipsometry)
21	20	9	90	0.112
22	15	9	90	0.509

Ta

Wafer nr	RF bias (W)	Reactive O2 (%)	Power(W)	Rq (RMS) (nm)	Thickness
blank1	0	0	180	0.209
16	10	0	180	0.36	56
24	20	0	180	0.357
25	20	9	180	0.202	110
26	20	5	180	0.194	95
27	15	0	180	0.413
28	25	0	180	0.164
31	30	0	180	0.3

Figure 1:Left: no RF bias (wafer 12) gives high roughness. Right: RF bias (Wafer 21) gives low roughness

Stress in deposited films

Sputter deposition causes stress in the deposited material. Depending on the sputter parameters, the stress can be either tensile or compressive. In 2017 Radu Malureanu investigated the stress in Si, Cr and Cu films deposited with the Lesker sputter system under a range of circumstances.

Results of the study may be found here:

• Stress dependence on sputter parameters.

List of available targets for the Sputter-System(Lesker) (03 June 2013)

Deposition material	target thickness	Purity	Max. Power (W)	Max Ramp up and down (W/s)
Ag	0,250"	99,9%	314	20
Al	0,250"	99,99%	314	20
Au	0,125"	99,999%	314	20
Co	0,0625"	99,95%	126	10
Cr	0,125"	99,95%	251	20
Cu	0,250"	99,99%	314	20
Fe	0,0625"	99,9%	126	10
Ge	0,250"	99,999%	126	0.5
Mg	0.250"	99,95%	215	20
Mo	0,250"	99,95%	314	20
Nb	0,250"	99,95%	314	20
Ni	0,125"	99,9%	188	10
Pd	0,125"	99,95%	251	20
Pt	0,125"	99,95%	251	20
Ru	0,125"	99,95%	314	20
Si, Undoped	0,250"	99,999%	126	0.5
Ta	0,250"	99,95%	314	20
Te	0,250"	99,999%	16	0.5
Ti	0,250"	99,7%	251	20
Al2O3	0,125" + Cu backing plate	99,99%	63	0.5
Al2O3	0,250"	99,99%	63	0.5
Al/Cu99,5/0,5%	0,250"	99,99%	314	20
Co/Fe 50/50%	0,0625"	99,95%	126	10
Co/Fe 80/20%	0,0625"	99,95%	126	10
Co/Fe 90/10%	0,0625"	99,95%	126	10
Cr2O3	0,125" + Cu backing plate	99,8%	63	0.5
Cu/Ti/25%	0,125"	99,99%	251	20
Fe/Mn 50/50%	0,250"	99,95%	126	10
ITO (In2O3/SnO2) 90/10%	0,125"	99,99%	63	0.5
Mn/Ir80/20%	0,125"	99,9%	251	20
MgO	0,125"	99,95%	63	0.5
Ni/Co50/50%	0,0625"	99,95%	126	20
Ni/Co 50/50%	0,125"	99,95%	126	20
Ni/Fe 80/20%	0.125"	99,95%	126	20
NiV 93/7%	0,250"	99,95%	157	20
SiC	0,125" + Cu backing plate	99,5%	63	0.5
Si3N4/MgO 2%	0,125"	99,9%	63	0.5
SiO2	0,125"	99,995%	126	0.5
SiO2	0,250"	99,995%	126	0.5
Ta2O5	0,125"	99,900%	63	0.5
AZO (ZnO/Al2O3) 98%/2%	0,125"	99,99%	126	0.5
ZnO	0.250"	99,999%	63	0.5
ZrO(2)/Y(2)O(3)		99,900%	63	0.5
V	0.125"	99,500%	188	20
W	0.250"	99,500%	314	20
Hf	0.125"	-	188	20
Sn	0.250"	-	31	0.5

Relative Sputter rates

To use these charts, locate the material for which known conditions are available. Then multiply the rate by the relative factors to arrive at the estimated rate for the new material. For example, with previous data showing 3.5Å/s Aluminum at 100W, then Titanium at similar conditions will generate approximately

(0.53/1.00)·3.5 Å/s ≅ 2 Å/s

The rates in this table are calculated based on a 500V cathode potential. As the power is increased greater than two times the original rate, then the relative rate will drop slightly (up to 10%). For example, Aluminum at 250W

Al250W = 0.9·Al100W·(P1/P0)

0.9·3.5 Å/s·(250/100) ≅ 7.4 Å/s

The rates in the ceramics table assume the use of an RF power supply and account for the partial duty cycle of the RF generator as compared to a DC supply.

Metals and semiconductors

Deposition material	name	Relative depostion rate
Ag	Silver	2.88
Al	Aluminum**	1.00
Au	Gold	1.74
Be	Beryllium	0.21
C	Carbon	0.23
Cu	Copper	1.42
GaAs	Gallium Arsenide {100}	1.03
GaAs	Gallium Arsenide {110}	1.03
Ge	Germanium	1.50
Mo	Molybdenum	0.66
Nb	Niobium	0.76
Pd	Palladium	1.77
Pt	Platinum	1.00
Re	Rhenium	0.84
Rh	Rhodium	1.16
Ru	Ruthenium	0.98
Si	Silicon	0.60
Sm	Samarium	1.74
Ta	Tantalum	0.67
Th	Thorium	1.31
Ti	Titanium	0.53
V	Vanadium	0.50
W	Tungsten	0.57
Y	Yttrium	1.53
Zr	Zirconium	0.88

Oxides and Ceramics

Deposition material	name	Relative depostion rate
Al2O3	Alumina	0.05
SiC	Silicon Carbide	0.22
SiO2	Silicon Dioxide	0.21
TaC	Tantalum Carbide	0.09
Ta2O5	Tantalum Pentoxide	0.39

Magnetic Materials

Deposition material	name	magn.	Relative depostion rate
Co	Cobalt	Low	0.73
Cr	Chromium	Med	0.87
Fe	Iron	High	0.57
Mn	Manganese	Med	0.14
Ni	Nickel	Low	0.86
Ni80Fe20	Permalloy	High	0.80