Oerlikon PVD production solution for in-situ large scale deposition of PZT 2nd International Workshop on Piezoelectric MEMS Materials - Processes - Tools - Devices Lausanne, 06./07.09.2011 M. Kratzer, L. Castaldi and B. Heinz Oerlikon Systems R&D, Liechtenstein D. Kaden, H.J. Quenzer Fraunhofer ISIT, Germany A. Mazzalai, S. Harada, P. Muralt EPFL, Switzerland
Agenda piezovolume project Sputter equipment Key hardware factors Results of in-situ PZT deposition process Summary and outlook
EU project piezovolume Sputter cooperation and goals F. Tyholdt -14:00 FP7 piezovolume Development of automated high volume sputter system M. Kratzer, L. Castaldi and B. Heinz Process development D. Kaden and H.J. Quenzer Process development A. Mazzalai, S. Harada and P. Muralt Overview Project goals Goal of this cooperation is to develop in-situ PZT processes on a Oerlikon sputter system which meet commercial production requirements High quality PZT films on 8 substrates Dielectric constant ~ 1200 and dielectric loss tanδ < 0.03 Piezoelectric coefficients d 33,f > 100pm/V and - e 31,f > 14 C/m2 Thickness uniformity < ± 5% at max. thickness 4-5 µm Throughput > 3.6 wafer/hr µm (= 1nm/s)
Equipment for PZT in-situ sputtering RF magnetron sputtering from single ceramic target CLN200 sputter tool RF sputter module equipped with 8 Very Hot Chuck Robot handling D C A Support stations Aligner (A) Degasser (D) Cooler (C) Loadlocks
Key hardware factors Overview Anode & Shieldings RF cathode PZT sputter equipment Heated chuck RF Bias & master oscillator Magnet array & Target
Key hardware factors Very Hot Chuck Heated substrate holder for 6 and 8 wafer enable deposition process in the temperature range needed for in-situ sputtered PZT films 6 Very Hot Chuck Temperature sense wafer vs. Heater set point (6" and 8" Very Hot Chuck) 650 600 6" wafer 8" wafer Temperature_sense wafer [ C] 550 500 450 400 Operational range 8 Very Hot Chuck 350 450 500 550 600 650 700 750 800 850 Heater set point [ C]
Key hardware factors Temperature uniformity 8 Very Hot Chuck Optimization of process settings to achieve highest wafer temperatures and excellent temperature uniformity by Back gas flow ID / OD heating (Alpha factor) Uniformity (Temperatur) Temperature uniformity 100 80 60 40 20 0-20 -40-60 y [mm] 458.0-460.0 456.0-458.0 454.0-456.0 452.0-454.0 450.0-452.0 448.0-450.0 446.0-448.0 444.0-446.0 442.0-444.0 440.0-442.0 438.0-440.0 436.0-438.0 434.0-436.0 432.0-434.0 Measurement Statistics Uniformity 2.44% Mean Range Max Min 430.76 [ C] 10.50 [ C] 434.70 [ C] 424.20 [ C] 8 Very Hot Chuck -80 430.0-432.0 428.0-430.0 Chuck temperature: 600 C Backside gas: 4 sccm Wafer temperature: 430 C -100-80 -60-40 -20 0 20 x [mm] 40 60 80 100-100 426.0-428.0 424.0-426.0 422.0-424.0 420.0-422.0
Key hardware factors RF target self bias voltage Target self bias voltage influenced by Process pressure RF power Anode area RF C C S USB A d A U A Plasma d B U B B 1. RF power Target self bias voltage [V] 0 1 kw 2 kw -50 3 kw -100-150 -200-250 -300 0 10 20 30 40 50 60 70 80 90 100 110 2. Anode area Ar flow [sccm] 0 U Plasma U A U B U SB Cathode area ~ Anode area Cathode area < Anode area U SB = U A -U B Target self bias voltage [V] -50-100 -150-200 -250 Higher anode area Lower anode area U B = U Plasma U A / U B = (Area B / Area A ) n -300 0 10 20 30 40 50 60 70 80 90 100 110 Ar flow [sccm]
Key hardware factors Magnetron design PZT thickness and composition uniformity influenced by Erosion profile Emission characteristic of sputtered atoms Scattering (~ pressure distance) Substrate temperature Normalized Uniformity thickness Thickness uniformity Thickness uniformity of PZT films on Pt substrates 1.15 1.10 1.05 1.00 0.95 Standard setup 0.90 Improved setup 0.85 0 10 20 30 40 50 60 70 80 90 100 Radius [mm] Actual sputter performance Deposition rate > 40 nm/min Composition uniformity 1.03 Estimated target life time ~ 1600 µm film thickness for 4mm target Composition (normalized) 1.02 1.01 1.00 0.99 ID OD 0.98 0.97 620 C, ID 620 C, OD Pb/(Zr+Ti) 1.000 1.004 Zr/(Zr+Ti) 1.000 0.989
In-situ PZT deposition process General trends Relative Pb content can be influenced Pb decrease with temperature increase Pb decrease with Ar flow increase Pb increase with RF power increase Composition (normalized) Variation of substrate temperature 1.40 1.20 1.00 0.80 0.60 Pb/(Zr+Ti) 0.40 Zr/(Zr+Ti) 0.20 0.00 500 C 550 C 600 C 650 C 700 C 750 C Variation of RF power 2.00 Variation of Ar flow 1.40 1.80 1.60 1.20 Composition (normalized) 1.40 1.20 1.00 0.80 0.60 0.40 0.20 Pb/(Zr+Ti) Zr/(Zr+Ti) Composition (normalized) 1.00 0.80 0.60 0.40 0.20 Pb/(Zr+Ti) Zr/(Zr+Ti) 0.00 1.5 kw 2.0 kw 2.5 kw 0.00 50 sccm 100 sccm 250 sccm 350 sccm
In-situ PZT deposition process 6 PZT with PTO seed layer Best PZT films achieved with a PTO seed layer to promote the nucleation of the PZT perovskite structure For films sputtered at 1 kw ε ~ 1500 tanδ = 3.2% d 33,f = 100pm/V -e 31,f = 7.5 C/m 2 Performance of films deposited at 2 kw
In-situ PZT deposition process 8 PZT with TiO 2 seed layer Best piezoelectric data ε ~ 1200 tanδ = 3% d 33,f = 120 pm/v -e 31,f = 12.6 C/m 2 Similar performance for films without TiO 2 seed layer Polarisation [µc/cm 2 ] 50 40 T h = 600 C 30 20 10 0-10 -20 E c (avg) = 49.6 kv/cm -30 P rem (avg) = 23.5 µc/cm 2-40 P max (avg) = 42.5 µc/cm 2-50 -300-250 -200-150 -100-50 0 50 100 150 200 250 300 Field [kv/cm] Intensity [a.u] 38.25, PZT (111) 40.02, Pt (111) 44.88, PZT (200) 55.47, PZT (211) 69.132, Si (400) 85.71, Pt (222) 25 30 35 40 45 50 55 60 65 70 75 80 85 90 2 Theta Displacement vs. voltage Polarisation vs. displacement 4.0 3.5 T h = 600 C 0.05 0.04 T h = 600 C Displacement [nm] 3.0 2.5 2.0 1.5 1.0 0.5 0.0 Polarisation [µc/cm2] 0.03 0.02 0.01 0.00-0.01-0.02 => d 33,f pm/v -0.03 => d => e 31,f = 2 33,f = 120 pm/v => -e 31,f = 12.6 C/m 2-0.04-0.5-30 -25-20 -15-10 -5 0 5 10 15 20 25 30 Voltage [V] -0.05-2000 -1500-1000 -500 0 500 1000 1500 2000 Displacement [nm]
In-situ PZT deposition process Summary The existing sputter equipment is capable to deposit PZT films in-situ with the required perovskite structure Therefore no additional annealing step is needed in the process sequence Electrodes and PZT films can be deposited consecutively in a cluster tool without breaking the vacuum Piezoelectric performance of best films comparable to state-of-the-art films deposited by chemical solution deposition (CSD) Further improvements achievable by Magnetron design Target properties Process optimization => Thickness and composition uniformity, deposition rate => Deposition rate => Piezoelectric properties
The research leading to these results has received funding from the European Community's Seventh Framework Programme (FP7/2010-2013) under grant agreement n 229196 Thank you for your attention