Specific Process Knowledge/Thin film deposition/Deposition of Gold

The content on this page, including all images and pictures, was created by DTU Nanolab staff, unless otherwise stated.

Feedback to this page: click here

Gold can be deposited by e-beam evaporation or sputtering. In the chart below you can compare the different deposition equipment. We also describe the temperature rise on the wafer during gold deposition, the adhesion layers that can be used for gold deposition, the roughness of gold deposited in the Wordentec, and issues with particulates on the gold films in the Temescal and the Wordentec.

Au deposition

Below you can compare the different equipment that allows Au deposition.

	E-beam evaporation (E-beam evaporator (Temescal) and E-beam evaporator (10-pockets))	Resistive thermal evaporation (Thermal Evaporator)	Sputter (Lesker)	Sputter (Sputter-system Metal-Oxide (PC1) and Sputter-system Metal-Nitride (PC3))	Sputter coater (Sputter coater 03)	Sputter coater (Sputter coater 04)
General description	E-beam deposition of Au	Resistive thermal deposition of Au	Sputter deposition of Au	Sputter deposition of Au	Sputter deposition of Au	Sputter deposition of Au
Pre-clean	Ar ion etch (only in E-beam evaporator Temescal)			RF Ar clean
Layer thickness	10 Å to 600 nm *	10 Å to 200 nm	10 Å to 500 nm *	10 Å to 500 nm *	very thin, few nm range	very thin, few nm range
Deposition rate	1-5 Å/s	1 Å/s (can be adjusted to around 5 Å/s)	Depends on process parameters, 1-10 Å/s	Depends on process parameters	Not measured	Not measured
Batch size	Up to 4x6" wafers or Up to 3x8" wafers (ask for special holder) many smaller pieces	4x2" wafers or 3x4" wafers or 1x6" wafer 1x8" wafer many smaller pieces	Pieces or 1x4" wafer or 1x6" wafer	Up to 10x6" or 4" wafers Many small pieces	Several smaller samples 1x4" wafer	Several smaller samples 1x4" wafer
Heating	to 250 C (in 10-pocket evaporator)	no	no	to 600 C	no	no
Allowed materials	See the cross-contamination sheet	Almost any as long as it does not outgas - see cross-contamination sheets in Labmanager	Silicon Silicon oxide Silicon nitride Silicon (oxy)nitride Photoresist PMMA Mylar SU-8 Metals Carbon	Almost any as long as it does not outgas - see cross-contamination sheets in Labmanager	All samples allowed in the SEM Supra 1	All samples allowed in the SEM Supra 2 or 3
Comment	Pumpdown approx 20 min.	Make sure that all pellets are melted beforehand Pumpdown approx. 20 min	Takes approx. 10 minutes to load and transfer sample	Takes approx. 12 minutes to load and transfer samples	Used for gold sputter coating of samples before SEM inspection Very fast.	Used for gold sputter coating of samples before SEM inspection Very fast.

* For thicknesses above 200 nm write to metal@nanolab.dtu.dk as extra deposition costs a higher fee.

Resistive thermal evaporation of Au

• Resistive thermal evaporation of Au in Thermal Evaporator

Adhesion of Au on Si

The adhesion of gold on Silicon or Silicon with native oxide is not very good. The Si substrate is often deposited an adhesion layer before the gold deposition. A few nm of Chromium or Titanium works well and they react with the Oxygen of Silicon oxide and present a metallic bond with gold. You can also use polymer or organosilane adhesion layers as exemplified by the work in the next section.

For Cr and Ti adhesion layers, a 5 nm to 10 nm thick layer is commonly used and it is important to deposit Cr or Ti and then immediately Au. If the vacuum chamber is opened in between, the surface of Cr or Ti will get oxidized and that will give a poor adhesion. If a gold layer needs to be deposited directly on Silicon, then native oxide has to be removed by a dip in diluted HF and wafer must be immediately loaded into the evaporation chamber. And after the deposition, the wafer has to be heated up to get some Au-Si diffusion which improves the adhesion.

• Read more about Ti and Cr adhesion layers.

Thin Au layer using APTMS adhesion layer and sputter system Lesker

For depositing very thin, down to 6nm continuous Au layers on Si/SiO₂ substrates. Works also with ALD deposited Al₂O₃ and TiO₂ as substrate.

Adhesion promoter: aminopropyltrimethoxysilane (APTMS). MSDS here.
Adhesion promoter deposition: 3h immersion in 95%IPA, 2.5% H₂O, 2.5% APTMS.

NOTE: the APTMS layer is degrading quickly in atmosphere, so deposit it as close to the Au deposition as possible.

Lesker deposition parameters:

Gun #	Power [W]	Ramp rate [W/s]	Pressure [mtorr]	Atmosphere	Deposition rate [nm/s]
2	300	5	3	Ar	1

NOTE: As a general rule, the lower the pressure and higher the power (i.e. higher the deposition rate), the better.

Film characteristics (5-10 wafers for each thickness):

Thickness [nm]	Roughness min [nm]	Roughness max [nm]
6	0.25	0.4
10	0.3	0.5
24	0.3	0.5

NOTE: After depositing 10 layers of 10nm each, one on top of each other, the roughness increased to 0.8nm RMS

Work done by Johneph Sukham (@ DTU Fotonik) and Radu Malureanu (@ DTU Fotonik and DTU Nanolab) in 2016-2017.

Particulates in e-beam evaporated films

Au droplets on an Au film (image by Evgeniy Shkondin, Au identified by EDX).

We have found that the amount of particulates on the e-beam evaporated films depends on the deposition parameters. Specifically for gold it is hard to avoid tiny gold droplets on the films, but they can be minimized with careful attention to the sweep parameters, cleanliness of the target, etc.

The droplets appear to be inconsequential for many users, for instance if the Au layer is simply used as an electrical contact. However, for some users it is very important, for instance when the exact resistivity of the Au layer is critical.

You can read more about this issue here.

Quality control of e-beam evaporated TiAu films

Quality control (QC) for the E-beam Evaporator (Temescal) and the E-beam Evaporator (10-pockets)

TiAu or CrAu is tested approximately once a month on both of Nanolab's e-beam evaporators. You can find the QC procedures and data in LabManager here (requires login): QC procedure, E-beam Evaporator (Temescal) Newest QC data, E-beam Evaporator (Temescal) QC procedure, E-beam Evaporator (10-pockets) Newest QC data, E-beam Evaporator (10-pockets) QC Recipe: Standard recipes/TiAu or Cr/Au Deposition rate 2 Å/s Thickness 10 nm / 90 nm Pressure Below 1*10-6 mbar QC limits Both e-beam evaporators Deposition rate deviation ± 20 % Measured average thickness ± 10 % Thickness deviation across a 4" wafer ± 5 % Thickness is measured in 5 points with a stylus profiler. Additionally we examine the newly deposited films for particles using the particle scanner (if available, otherwise we use the Jenatech microscope in darkfield mode) and we monitor the sheet resistance of the Ti/Au or Cr/Au films.