Specific Process Knowledge/Thin film deposition/Deposition of NiFe

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Contents by DTU Nanolab staff except where otherwise noted.

Deposition of NiFe alloy

NiFe has been deposited in the Sputter System (Lesker) here at Nanolab. You will find information on the pressure, max power and expected deposition rate here in LabAdviser. To see all the deposition parameters used in that machine by others, search the Process Log in LabManager.

Below you will find some results on optimizing the film crystalline quality for NiFe by Bjarke Thomas Dalslet. Bjarke also investigated the surface roughness of NiFe as a function of change in the substrate bias, but found little variation.

Film quality optimization

By Bjarke Thomas Dalslet @Nanotech.dtu.dk

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

Strain estimations was done on 30 nm Ni$_{81}$Fe$_{19}$ thin films using low angle x-ray diffraction, for various substrates. It was found that the strain of the film influenced the resistance (R) and anisotropic magneto resistance (AMR) of the films (this relationship is also documented in literature); A Ta interface layer reduced R and increased AMR on both Si and SiO$_{2}$ substrates while reducing strain.

This study was then done on 30 nm Ni$_{81}$Fe$_{19}$ thin films deposited on 3 nm Ta on top of a SiO$_{2}$ substrate, using R and AMR as an indication of strain. As seen in the tables, applying a substrate bias increases AMR and conductance (1/R). An equivalent effect is seen when heating the substrate during deposition. This heating can also be done after deposition without loosing the effect.

Name	Substrate bias (W)	AMR	1/R (S)	Crystal strain
0029 NiFe3_stack_RF20	20	0.02724278	1.308044474
0018_NiFe1_stack_RF	10	0.025850358	0.898311175
0030 NiFe3_stack	0	0.020103598	0.71772052	0.8

Name	Temperature (C)	AMR	1/R (S)	Crystal strain
0030 NiFe3_stack	25	0.020103598	0.71772052	0.8
BDT-NiFe1-blank30	200	0.019319002	1.095770327
BTD-NiFe-Blank22	250	0.021768497	1.047668937
BTD-NiFe-Blank14	300	0.02983617	1.724137931
BTD-NiFe-Blank13	350	0.033944331	1.887504719
BTD-NiFe-Blank15	400	0.031176801	1.655903295	0.2
BTD-NiFe-Blank16	450	0.030843457

Stress in films deposited at high temperature

In 2017, Radu Malureanu measured a tensile stress of about 100-200 MPa on thin films of Invar (a type of NiFe alloy) deposited at 600 °C with varying thicknesses between 120 and 330 nm, DC power of 80 or 120 W and Ar pressure of 5 or 10 mTorr. Note that this high a temperature is no longer allowed in the Sputter-System (Lesker), but may be used in the cluster sputter system.

Read more about stress in thin films deposited with the Lesker sputter system here, where you will also find further reading about stress in sputtered films in general.