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

Deposition of Silicon Oxide can be done with either LPCVD, PECVD or by sputter technique. 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 DANCHIP 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 ex. 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 the other PECVD (PECVD1). It is also a possibility to dope the silicon oxide with Germanium for altering the refractive index of the oxide.

• Deposition of Silicon Oxide using PECVD

Deposition of Silicon Oxide using sputter deposition technique

At DANCHIP 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 any material you like.

• Deposition of Silicon Oxide using PVD co-sputter/evaporation tool

• Deposition of Silicon Oxide using Lesker sputter tool

Comparison of the methods for deposition of Silicon Oxide

	LPCVD (TEOS)	PECVD	Sputter technique (PVD co-sputter/evaporation tool)
Stoichiometry	SiO2 Can be doped with boron	SixOyHz Can be doped with boron, phosphorus or germanium	Not measured (a sputter target with stoichiometry SiO2 is used)
Film thickness	~300nm-4µm	~40nm - 30µm	Thin layers (up to 300-400 nm)
Process Temperature	725 oC	300 oC	Can be between room temp. and 400 oC
Step coverage	Excelent. Very high surface mobility.	Less good When doped with phosphorus and/or Boron the oxide can float at about 1000 oC in a wet oxidation.
Film quality	Less than thermal oxide. Annealing makes it more dense. Few defects	Less dense film Incorporation of hydrogen in the film
Batch size	1-13 4" wafer per run deposition on both sides of the substrate	1-3 4" wafers or 1 6" wafer or many smaller chips per run deposition on one side of the substrate	1-12 4" wafers or 1-4 6" wafer or many smaller chips per run Deposition time for 1 and 3 wafers are the same
Substrate material allowed	Silicon wafers with layers of silicon oxide or silicon (oxy)nitride Quartz wafers	Silicon with layers of silicon oxide or silicon (oxy)nitride Quartz Small amount of metal (in PECVD3)	Silicon with layers of silicon oxide or silicon (oxy)nitride Quartz Metals