Specific Process Knowledge/Thin film deposition/Deposition of Nickel/Stress Wordentec Ni films

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Stress in Wordentec deposited Nickel films

Thin films of Ni have tensile stress. It was examined if different deposition rates will give different amounts of stress in Wordentec deposited Ni films and the result is presented here.

Depositions and measurments were made in March and April 2014, KNIL.

Rate dependence

The deposition rate was changed between the depositions. In most cases 200 nm of Ni was deposited (on a blank Si wafer).

The graph below shows the tensile stress (MPa) in the Ni films for different deposition rates (Å/s). All depositions were made in the Wordentec. Stress was measured with the Dektak 8 stylus profilometer (this instrument is no longer in the cleanroom as of 2020, but one may instead use the P17 Stylus profiler).

As seen in the graph the tensile stress in the films is decreased for films with lower deposition rate. To obtain a film with lower stress a deposition rate of 1 Å/s or 3 Å/s is recommended. However, for films with thicknesses above 100 nm it is not recommended to use as low deposition rate as 1 Å/s, since the wafers will be heated up during the very long process time.

Tensile stress in Wordentec deposited Ni thin films as a function of deposition rate. Click on the image to see it with higher resolution.

Deposition rate (Å/s)	Stress, average (MPa)		Film thicknesses (nm)	Comment	Soak 2 setting to achive desired rate**
	Tesile	Compressive
15 Å/s*	1046 MPa	0 MPa	200 nm, 200 nm, 200 nm	Average calculated for three films	43%
10 Å/s	941 MPa	0 MPa	200 nm, 200 nm	Average calculated for two films	40.5%
7 Å/s	903 MPa	0 MPa	200 nm, 200 nm	Average calculated for two films	37%
3 Å/s	725 MPa	0 MPa	110 nm, 200 nm, 200 nm	Average calculated for three films	32%
1 Å/s*	395 MPa	5 MPa	50 nm, 190 nm	Average calculated for two films	25 %

The stress measurements presented in the table were performed the same day as the deposition.

* Before changing the deposition rates to 15 Å/s or 1 Å/s first contact responsible Nanolab staff. These deposition rates are not recommended for all thicknesses and applications.

** With the correct setting of "soak 2" (power) you will obtain the right deposition rate already from the beginning of the process. Contact responsible Nanolab staff before changing this setting.

Time dependence

It was observed that the stress in the films decreases with time.

The stress in the Ni films deposited with 15 Å/s was measured on the same wafer at different occasions, both directly after the depositions were done and some days later. The data is presented in the graph below, where it is seen that the film stress decreased over time.

Tensile stress in Wordentec deposited Ni thin films measured on the same wafer with some days in between the measurements. The tensile stress was seen to decrease for the wafers deposited with 15 Å/s. Click on the image to see it with higher resolution.

Data

The measurement data is saved in this file: File:Ni stress Wordentec.xlsx