Specific Process Knowledge/Thin film deposition/Deposition of Titanium

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Titanium deposition

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

	E-beam evaporation (Alcatel)	E-beam evaporation (Wordentec)	E-beam evaporation (PVD co-sputter/evaporation)	E-beam evaporation (Physimeca)	Sputter deposition (Wordentec)	Sputter deposition (Lesker)	E-beam evaporation (III-V Dielectric evaporator)
General description	E-beam deposition of Titanium	E-beam deposition of Titanium	E-beam deposition of Titanium	E-beam deposition of Titanium	Sputter deposition of Titanium	Sputter deposition of Titanium	E-beam deposition of Titanium
Pre-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 2000Å	10Å to 1000Å	.	.	10Å to 1000Å
Deposition rate	2Å/s to 15Å/s	10Å/s to 15Å/s	About 1Å/s	About 10Å/s	Depending on process parameters, see here.	Depending on process parameters, about 1 Å/s.	About 1Å/s
Batch size	Up to 1x4" wafers smaller pieces	24x2" wafers or 6x4" wafers or 6x6" wafers	12x2" wafers or 12x4" wafers or 4x6" wafers	1x 2" wafer or 1x 4" wafers or Several smaller pieces	24x2" wafers or 6x4" wafers or 6x6" wafers	Smaller pieces Up to 1x6" wafers	2" wafer or Smaller pieces
Allowed substrates	Silicon wafers Quartz wafers Pyrex wafers	Silicon wafers Quartz wafers Pyrex wafers	Silicon wafers Quartz wafers Pyrex wafers	III-V materials 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	Silicon oxide Silicon (oxy)nitride Photoresist PMMA Mylar SU-8 Metals	Silicon oxide Silicon (oxy)nitride Photoresist Metals	Silicon oxide Silicon (oxy)nitride Photoresist
Comment			Only very thin layers (up to 100nm).

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

Comments: Choise of equipment

Thick layers

Practical experience has shown that at some occation it is better to use the Wordentec than the Alcatel for thicker Ti layers. Deposition of 5000 Å Ti on Si is working fine in both machines. However, with the same thickness of Ti deposited on pyrex+resist, the metal layer deposited in Alcatel may have metal flakes in the center of the wafer. The process workes without problems in Wordentec.

Comments: Adhesion layer

Ti as adhesion layer

Titanium is most often used as a adhesion layer for other metals, like for example gold. Gold does not stick very well to Si, and to prevent it to come off in future process steps or in the final application, a layer of Ti (or Cr) is often deposited onto the wafer.

The most common thickness of the Ti adhesion layer is 10 nm. Also layers with a thickness of 5 nm is used.

Very thin adhesion layers

If it is important to have a very thin Ti layer, it is possible to use even thinner adhesion layers. There are some experiences of using a 3 nm Ti as adhesion layer for a 200 nm thick gold layer. In this case a Si wafer was dipped in buffer and rinsed in water immediately before being placed in the PVD equipment (Wordentec). After a RF clean process of the wafer, 3nm of Ti and 200 nm of Au was deposited, and this worked fine during futher processing.