Specific Process Knowledge/Thin film deposition/Deposition of Silicon Oxide

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Deposition of Silicon Oxide can be done with either LPCVD, PECVD, by sputter technique or ALD. You can also make a silicon oxide layer by growing a thermal oxide in a hot furnace but that requires a silicon surface as a starting point.

Deposition of Silicon Oxide using LPCVD

The LPCVD oxide you can deposit at DTU Nanolab is called TEOS oxide. It can be made in the LPCVD TEOS furnace. It is a batch process meaning you can run a batch of 13 wafers at a time. The deposition takes place at temperatures of 725 degrees Celsius. The TEOS oxide has good step coverage and hole filing/covering properties and the film thickness is very uniform over the wafer. We have two standard TEOS processes: One for depositing standard layers ~(0-1.5 µm) and one for deposition thick layers ~(1.5µm-4µm). The TEOS oxide has a dielectric constant very close to the one for thermal oxide (3.65 for TEOS).

• Deposition of Silicon Oxide using LPCVD TEOS

Deposition of Silicon Oxide using PECVD

PECVD oxide can be deposited in one of the PECVD systems. You can run 1-3 wafers at a time depending on which one of the PECVD's you use. The deposition takes place at 300 degrees Celcius. This can be of importance for some applications but it gives a less dense film and the oxide is expected to have some hydrogen incorporated. The step coverage and thickness uniformity of the film is not as good as for the LPCVD TEOS oxide. PECVD oxide has excellent floating properties when doped with boron and/or phosphorus. Then it can be used eg. as top cladding for waveguides or encapsulation of various structures/components. In one of our PECVD systems (PECVD3) we allow small amounts of metal on the wafers entering the system, this is not allowed in the LPCVD and in PECVD4.

• Deposition of Silicon Oxide using PECVD

Deposition of Silicon Oxide using sputter deposition technique

At DTU Nanolab you can also deposit silicon oxide using Lesker, PVD co-sputter/evaporation or IBE Ionfab300 sputter systems. One of the advantages here is that you can deposit on many kind of material.

• Deposition of Silicon Oxide using Lesker sputter tool
• Deposition of Silicon Oxide using IBE/IBSD Ionfab300

Deposition of Silicon Oxide using ALD

Thin films of silicon oxide up to 50 nm can also be deposited in the ALD2. The ALD2 uses the plasma source and can therefore only deposit on one wafer at a time. The deposition takes place at 300 ^oC, where the growth rate is 0.1222nm on flat samples. It is also possible to deposit uniform layers on high aspect ratio structures with a growth rate of 0.1629 nm/cycle.

• Deposition of Silicon Oxide using ALD2

Comparison of the methods for deposition of Silicon Oxide

	LPCVD(TEOS)	PECVD	IBE/IBSD Ionfab300	Sputter System Lesker	ALD2
General description	Low Presure Chemical Vapor Deposition TEOS gives a good quality SiO2 and is a batch process.	Plasma Enhanced Chemical Vapor Deposition has the advantage that a silicon oxide and be deposited with a quit high deposition rate at a rather low temperature.	Sputter deposition: can be done on top of a large range of materials. This system can only run in deposition mode in certain periods.	Sputter deposition: can be done on top of a large range of materials	Atomic Layer deposition provides an uniform layer with a good covering even on high aspect ratio structures.
Stochiometry	SiO2	SixOyHz Can be doped with boron, phosphorus or germanium	Not measured (a sputter target with stoichiometry SiO2 is used		SiO2
Film thickness range	~300nm - 4µm	~40nm - 30µm	~10nm - ~1µm(>2h)	Thin layers (up to 200-300 nm)	Thin layers (up to 50 nm)
Process Temperature	725 oC	300 oC	Expected to be below 100oC		300 oC
Step Coverage	Excellent. Very high surface mobility. Deposition on both sides of the substrate.	Less good When doped with phosphorus and/or Boron the oxide can float at about 1000 oC in a wet oxidation. Deposition on one side of the substrate	Not Known Deposition on one side of the substrate	Not Known Deposition on one side of the substrate	Excellent.
Film Quality	Less than thermal oxide. Annealing makes it more dense. Few defects	Less dense film Incorporation of hydrogen in the film
Substrate size / Batch size	1-13 100 mm wafers	Several small samples 1-7 50 mm wafers 1-3 100 mm wafers 1 150 mm wafer	Several small samples mounted with capton tape 1 50 mm wafer 1 100 mm wafer 1 150 mm wafer 1 200 mm wafer	Pieces or 1x4" wafer or 1x6" wafer	Several small samples 1 50 mm wafers 1 100 mm wafers 1 150 mm wafer
Allowed materials	Silicon wafers with layers of silicon oxide or silicon (oxy)nitride Quartz wafers	Silicon with layers of silicon oxide or silicon (oxy)nitride Quartz IIIV materials (in PECVD2) Small amount of metal (in PECVD3)	Almost any material not Pb and very poisonous materials	Silicon Silicon oxide Silicon nitride Silicon (oxy)nitride Photoresist PMMA Mylar SU-8 Metals Carbon	Silicon Silicon oxide, silicon nitride Quartz/fused silica Al, Al2O3 Ti, TiO2 Other metals (use dedicated carrier wafer) III-V materials (use dedicated carrier wafer) Polymers (depending on the melting point/deposition temperature, use carrier wafer)