Specific Process Knowledge/Thin film deposition/Deposition of Aluminium

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Deposition of Aluminium

Aluminium can be deposited by e-beam evaporation, by sputtering and by thermal evaporation. In the chart below you can compare the different methods on the different deposition equipment.

	E-beam evaporation (Alcatel)	E-beam evaporation (Wordentec)	E-beam evaporation (PVD co-sputter/evaporation)	Sputter deposition (PVD co-sputter/evaporation)	Sputter deposition (Wordentec)	Thermal evaporation (Wordentec)
Batch size	Up to 1x4" wafers smaller pieces	24x2" wafers or 6x4" wafers or 6x6" wafers	12x2" wafers or 12x4" wafers or 4x6" wafers	12x4" wafers or 12x4" wafers or 4x6" wafers	24x2" wafers or 6x4" wafers or 6x6" wafers	24x2" wafers or 6x4" wafers or 6x6" wafers
Pre-clean	RF Ar clean	RF Ar clean	RF Ar clean	RF Ar clean	RF Ar clean	RF Ar clean
Layer thickness	10Å to 1µm*	10Å to 1 µm*	10Å to 1000 Å	10Å to about 2000 Å	10Å to ~0.5µm (very time consuming )	10Å to 0.5 µm (this uses all Al in the boat)
Deposition rate	2Å/s to 15Å/s	10Å/s to 15Å/s	About 1Å/s	Dependent on process parameters (about 1 Å/s).	Depending on process parameters, up to ~2.5 Å/s	~2Å/s to 15Å/s
Comment	Thickness above 200 nm: ask for permission	Thickness above 200 nm: ask for permission	Only very thin layers (up to 100 nm).	Al sputter target: 99.995% Al		Recommended for unexposed e-beam resist
Allowed substrates	Silicon wafers Quartz wafers Pyrex wafers	Silicon wafers Quartz wafers Pyrex wafers	Silicon wafers Quartz wafers Pyrex wafers	Silicon wafers Quartz wafers Pyrex wafers	Silicon wafers Quartz wafers Pyrex wafers	Silicon wafers Quartz wafers Pyrex wafers
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 oxide Silicon (oxy)nitride Photoresist PMMA Mylar SU-8 Metals	Silicon oxide Silicon (oxy)nitride Photoresist PMMA Mylar SU-8 Metals	Silicon oxide Silicon (oxy)nitride Photoresist PMMA Mylar SU-8 Metals	Silicon oxide Silicon (oxy)nitride Photoresist PMMA Mylar SU-8 Metals

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

Aluminium deposition on ZEP520A for lift-off

This is a small study of which aluminium deposition that is best for aluminium lift-off on ZEP520A resist and a very thin layer of aluminium (~20nm).

The conclusion was that e-beam evaporation of aluminium in the Alcatel at 15Å/s gave the best result.

See details of the study here.

Aluminium deposition on AZ5214 for lift-off

Negative photolithographi process is recomended.

Positive photolithographi process from 1,5µ is possible especially for thin layers of metal.

The more pattern the easyer lift.

It was tried(jan09) to lift 2,5µ Al on 4,2µ negative resist on top of 11µ Apox SiO2 in acetone sonic-bath. This process was done in steps evaporating 5000Å a time with 5min pause and pressure down to at least 2E-6.

Comparison of roughness and other surface characteristics for different methods of Aluminium deposition

Studies by AFM was performed to examine differences in characteristics of the Al films, deposited with the differnt methods (sputter, e-beam, thermal). See details of the study here.