Specific Process Knowledge/Thin film deposition/Deposition of Tungsten

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Tungsten deposition

Tungsten (W) can be deposited by e-beam evaporation. It requires very high temperature to evaporate, so it is at the performance limit of the 6 kW power supplies of our systems. This means the deposition rate is limited. Additionally, the chamber (and substrate) will get hot during deposition despite water cooling, and this means the pressure rises during the deposition as the chamber is baked out. It is therefore not easy to deposit films much thicker than 50-60 nm. Talk to staff when you want to deposit W (write to thinfilm@danchip.dtu.dk). In the chart below you can compare the deposition equipment.

	E-beam evaporation (Temescal)	E-beam evaporation (Physimeca)
General description	E-beam evaporation of W	E-beam evaporation of W
Pre-clean	Ar ion beam	None
Layer thickness	10Å to 600Å*	10Å to 500Å*
Deposition rate	0.5 Å/s to 2 Å/s	about 1 Å/s
Batch size	Up to 4x6" wafers Up to 3x8" wafers (ask for holder) small pieces	Up to 1x4" wafers small pieces
Allowed materials	Silicon Silicon oxide Silicon (oxy)nitride Photoresist PMMA Mylar SU-8 Metals	Silicon Silicon oxide Silicon (oxy)nitride Photoresist PMMA Mylar
Comments	Substrate gets hot during deposition (for a 60 nm film it rose above 123 C)

* For thicknesses above 20 nm talk to staff (write to thinfilm@danchip.dtu.dk), as the heat and subsequent pressure rise means the deposition needs to be carried out in steps.