Specific Process Knowledge/Thin film deposition/Deposition of Aluminium

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

	LPCVD	PECVD
Generel description	Low Pressure Chemical Vapour Deposition (LPCVD furnace process)	Plasma Enhanced Chemical Vapour Deposition (PECVD process)
Stoichiometry	Si3N4 SRN (only 4" nitride furnace) Si3N4: Stoichiometric nitride SRN: Silicon rich (low stress) nitride	SixNyHz SixOyNzHv Silicon nitride can be doped with boron, phosphorus or germanium
Film thickness	Si3N4: ~50 Å - ~1400 Å SRN: ~50 Å - ~2800 Å Thicker nitride layers can be deposited over more runs	~40 nm - 10 µm
Process temperature	780 oC - 845 oC	300 oC
Step coverage	Good	Less good
Film quality	Deposition on both sides og the substrate Dense film Few defects	Deposition on one side of the substrate Less dense film Incorporation of hydrogen in the film
KOH etch rate (80 oC)	Expected <1 Å/min	Dependent on recipe: ~1-10 Å/min
BHF etch rate	Very low	Very high compared the LPCVD nitride
Batch size	1-25 100 mm wafers 1-25 150 mm wafers (only 6" furnace) Depending on what furnace you use	Several smaller samples 1-several 50 mm wafers 1-3 100 mm wafers 1 150 mm wafer Depending on what PECVD you use
Allowed materials	Silicon Silicon oxide Silicon nitride Pure quartz (fused silica) Processed wafers have to be RCA cleaned	Silicon Silicon oxide (with boron, phosphorous and germanium) Silicon nitrides (with boron, phosphorous and germanium) Pure quartz (fused silica)

	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

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.