Specific Process Knowledge/Thin film deposition/Deposition of Tungsten

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Tungsten deposition

Tungsten (W) can be deposited by e-beam evaporation and sputtering. However, in case of evaporation the precess generates a lot of heat (despite water cooling), and this means the pressure rises as the chamber is baking out. It is therefore not easy to deposit films much thicker than 50-60 nm. In the Temescal we stopped the deposition every 20 nm to let the pressure drop. Also, the rate needs to be low, to avoid overheating. Talk to staff when you want to deposit W (write to thinfilm@danchip.dtu.dk). Sputtering can be used without any sufficient issues. In the chart below you can compare the deposition equipment.

	E-beam evaporation (Temescal)	E-beam evaporation (Lesker)
General description	E-beam evaporation of W	Sputtering of W
Pre-clean	Ar ion beam	None
Layer thickness	10Å to 50nm	10Å to 600nm*
Deposition rate	0.5 Å/s to 1 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 Up to 1x6" wafer 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.