Specific Process Knowledge/Thin film deposition/Deposition of Gold

4th Level - Comparison

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Gold can be deposited by e-beam evaporation or sputtering. In the chart below you can compare the different deposition equipment.

Adhesion of Au on Si

The adhesion of Au on Si is not very good, and an adhesionlayer is often deposited on the wafer, before the Au layer evaporated. A good metal to use as adhesionlayer is Ti, but Cr is also often used. The most commonly used thickness of the Ti adhesionlayer is 10 nm. Also thinner layers, for example 5 nm, can be used.

	E-beam evaporation (Alcatel)	E-beam evaporation (Wordentec)	Sputter (Lesker)	E-beam evaporation (Physimeca)	Sputter coater Hummer	Sputter coater Balzer
General description	E-beam deposition of Au	E-beam deposition of Au	Sputter deposition of Au	E-beam deposition of Au	Sputter deposition of Au	Sputter deposition of Au
Pre-clean	RF Ar clean	RF Ar clean	RF Ar clean
Layer thickness	10 Å to 5000Å*	10 Å to 5000Å*	10 Å to	10Å to about 3000Å*
Deposition rate	2 Å/s to 10 Å/s	1 Å/s to 10 Å/s		From 5 Å/s up to 10Å/s	Not measured	Not measured
Batch size	Up to 1x4" wafers smaller pieces	24x2" wafers or 6x4" wafers or 6x6" wafers	Pieces or 1x4" wafer or 1x6" wafer	1x 2" wafer or 1x 4" wafers or Several smaller pieces	1x4" wafer Several smaller samples	1 large sample (< 4" wafer) Several smaller samples
Allowed materials	Silicon oxide Silicon (oxy)nitride Photoresist PMMA Mylar SU-8 Metals	Silicon oxide Silicon (oxy)nitride Photoresist PMMA Mylar SU-8 Metals	Silicon Silicon oxide Silicon nitride Silicon (oxy)nitride Photoresist PMMA Mylar SU-8 Metals Carbon	III-V materials Silicon wafers Quartz wafers Pyrex wafers	.	.
Comment	For thicknesses above 200 nm permission is required An adhesion layer (of Cr or Ti) is recommended under Au.	For thicknesses above 200 nm permission is required An adhesion layer (of Cr or Ti) is recommended under Au.			Used to gold sputter coating of samples mainly before SEM characterization	Used to gold sputter coating of samples mainly before SEM characterization

* For thicknesses above 200 nm permission from ThinFilm group (thinfilm@danchip.dtu.dk) is required.

Studies of Au deposition processes in the Wordentec

Roughness of Au layers - Roughness of Au layers deposited with different equipment and settings

Wafer temperature

The wafer temperature during e-beam deposition of 200 nm Au on six wafers has been measured using thermal labels on the backside of the wafers. The following results were obtained:

Wafer	Temperature [C]
1	48
2	60
3	65
4	71
5	71
6	77

The temperatures are accurate within approximately +/- 3C and probably underestimating the actual wafer temperature slightly. It is observed that the wafer temperature increases with each wafer, thus if wafer temperature is of concern it is advised to reduce the number of wafers per run.