Specific Process Knowledge/Etch/Etching of Silicon Oxide

Silicon oxide can be etched using either wet chemistry or dry etch equipment. Wet chemistry is mainly used to remove all the oxide on the surface (backside and front side) of a wafer or for isotrotropic etching. Dry etching etches anisotropic. It etches one side of the wafer at a time and can be used to etch structures with several masking materials.

Etch of silicon oxide can be done by either wet etch or dry etch. The standard setups for this here at DANCHIP are:

Wet etches:

• Wet Silicon Oxide Etch

Dry etches:

• Dry etch using RIE1 or RIE2
• Dry etch using AOE
• IBE/IBSD Ionfab 300

Comparison of wet Silicon Oxide etch and dry etches (RIE and AOE) etch for etching of Silicon Oxide

	Wet Silicon Oxide etch (BHF, SIO Etch (wetting agent), 5%HF)	RIE	AOE
General description	Isotropic etch	Anisotropic etch: vertical sidewalls	Anisotropic etch: vertical sidewalls, especially good for deep etch and high aspect ratio etch
Possible masking materials	Photoresist Silicon nitride	Photoresist (Poly)Silicon Aluminium Other metals that covers less the 5% of the wafer area (ONLY RIE2!)	Photoresist (Poly)Silicon Aluminium Chromium (ONLY if the other masking materials can not be used!)
Etch rate	~75 nm/min (Thermal oxide) in BHF ~90 nm/min (Thermal oxide) in SIO Etch ~25 nm/min (Thermal oxide) in 5%HF	Typically 40-120 nm/min can be increased or decreased by using other recipe parameters.	Typically 200-600 nm/min can be increased or decreased by using other recipe parameters.
Batch size	1-25 wafers at a time	1 wafer at a time	1 wafer at a time
Size of substrate	4" wafers	4" wafers or smaller pieces	6" or 4" depending on the setup (smaller pieces if you have a carrier wafer)
Allowed materials	Silicon Silicon Oxide Silicon Nitride Silicon Oxynitride Photoresist Blue film Gold (Au) and Nickel (Ni) (but only in BHF2 (KOH)!)	Silicon Silicon Oxide Silicon Nitride Silicon Oxynitride Photoresist E-beam resist Aluminium Other metals that covers less the 5% of the wafer area (ONLY RIE2!)	Silicon Silicon Oxide Silicon Nitride Silicon Oxynitride Photoresist E-beam resist Aluminium Chromium (ONLY as masking material if the other masking materials can not be used!)

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Comparing silicon oxide etch methods at Danchip

There are a broad varity of silicon oxide etch methods at Danchip. The methodes are compared here to make it easier for you to compare and choose the one that suits your needs.

• Wet Silicon Nitride Etch
• Etch of Silicon Nitride using RIE
• Etch of Silicon Nitride using AOE
• IBE/Ion Beam Etching using IBSD Ionfab 300

Compare the methods for Silicon Oxide etching

	Wet Silicon Nitride Etch	BHF	RIE (Reactive Ion Etch)	AOE (Advanced Oxide Etch)	IBE/IBSD Ionfab 300
Generel description	Isotropic etch Well suited for removing all nitride on a wafer surface (nitride strip) without a mask. High selectivity Si3N4/Si (>100) and Si3N4/SiO2 (>20) @ 180 C.	Isotropic etch Well suited for removing all PECVD nitride on a wafer surface (nitride strip) without a mask. Etches LPCVD nitride very slowly	Anisotropic etch: vertical sidewalls	AOE	Primarily for pure physical etch by sputtering with Ar-ions
Possible masking materials	Silicon Oxide PolySilicon	Photoresist PolySilicon Blue film	Photoresist E-beam resist Silicon Oxide Silicon Nitride Aluminium Metals if they cover less than 5% of the wafer area (ONLY RIE2!)	AOE Photoresist and zep resist Silicon Oxide Silicon Nitride Aluminium oxide	Any material that is accepted in the machine
Etch rate range	Si3N4 @ 180 oC: ~84 Å/min Si3N4 @ 160 oC: ~60 Å/min	PECVD nitride: ~400-1000 Å/min	Typically 40-50 nm/min can be increased or decreased by using other recipe parameters.	AOE	Process dependant. Has not been tested yet.
Substrate size	#1-25 100 mm wafers	#1-25 100mm wafers in our 100mm bath	As many small samples as can be fitted on the 100mm carrier. #1 100mm wafer (or smaller with carrier) #1 150mm wafer (only when the system is set up for 150mm)	As many small samples as can be fitted on a 100mm wafer #1 50 mm wafer fitted on a 100mm wafer #1 100 mm wafer #1 150 mm wafers (only when the system is set up to 150mm)	As many samples as can be securely fitted on a up to 200mm wafer #1 50 mm wafer with special carrier #1 100 mm wafer with special carrier #1 150 mm wafers with special carrier #1 200 mm wafer
Allowed materials	Silicon Silicon Oxide Silicon Nitride Silicon Oxynitride	Silicon Silicon Oxide Silicon Nitride Silicon Oxynitride Photoresist Blue film	Silicon Silicon Oxide Silicon Nitride Silicon Oxynitride Photoresist E-beam resist Other metals if they cover less than 5% of the wafer area (ONLY RIE2!) Quartz/fused silica	Silicon Silicon Oxide Silicon Nitride Silicon Oxynitride Photoresist zep resist Aluminium Chromium (try to avoid it) Quartz/fused silica	Silicon Silicon oxides Silicon (oxy)nitrides Metals from the +list Metals from the -list Alloys from the above list Stainless steel Glass III-V materials Resists Polymers Capton tape