Specific Process Knowledge/Etch/Etching of Silicon Nitride

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

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

Comparison of wet Silicon Nitride etch and RIE etch for etching of Silicon Nitride

	Wet Silicon Nitride etch	Buffered HF (BHF)	RIE
General 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
Possible masking materials	Silicon Oxide PolySilicon	Photoresist PolySilicon Blue film	Photoresist Silicon Oxide Aluminium Chromium (ONLY RIE2!) Other metals if they cover less than 5% of the wafer area (ONLY RIE2!)
Etch rate	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.
Batch size	1-25 wafers at a time	1-25 wafers at a time	1 wafer at a time
Size of substrate	4" wafers	4" wafers	4" wafers or smaller pieces
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 Aluminium Chromium (ONLY RIE2!) Other metals if they cover less than 5% of the wafer area (ONLY RIE2!)

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Comparing silicon etch methodes at Danchip

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

Wet etches:

• KOH Etch
• Wet PolySilicon etch

Dry etches:

• Si etch using RIE1 or RIE2
• Si etch using ASE (Advanced Silicon Etch)
• Si etch using DRIE-Pegasus (Silicon Etch)
• Si etch using IBE/IBSD Ionfab 300

Compare the methodes for Si etching

	KOH Etch	Wet PolySilicon etch	RIE (Reactive Ion Etch)	DRIE-Pegasus (Silicon Etch)	ASE (Advanced Silicon Etch)	ICP Metal Etch	IBE/IBSD Ionfab 300
Generel description	Anisotropic etch in the (100)-plan High selectivity to the other plans Anisotropic etch: vertical sidewalls independent of the crystal plans	Isotropic etch in Silicon and Polysilicon	Can etch isotropic and anisotropic depending on the process parameters	State-of-the-art dry silicon etcher with atmospheric cassette loader Extremely high etch rate and advanced processing options	As RIE but better for high aspect ratio etching and deep etches (higher etch rate) Good selectivity to photoresist The ASE is dedicated to polymer etch, which can affect the Si etch stability.	This is dedicated to metal etch. So fare only Si etch of nanostructures has been explored on the system.	Primarily for pure physical etch by sputtering with Ar-ions
Possible masking materials	Silicon Nitride Silicon Oxide	Photoresist	Photoresist E-beam resist Silicon Oxide Silicon Nitride Aluminium Chromium (ONLY RIE2!) Other metals if they cover less than 5% of the wafer area (ONLY RIE2!)	Photoresist and zep resist Silicon Oxide Silicon Nitride Aluminium oxide	Photoresist Silicon Oxide Silicon Nitride Aluminium	Photo-, DUV- and e-beamresist Silicon Oxide Silicon Nitride Aluminium Cr Ti	Any material that is accepted in the machine
Etch rate range	Si(100) @80oC: 1.29+0.05 µm/min Si(100) @70oC: ~0.7 µm/min Si(100) @60oC: ~0.4 µm/min	~100-200 nm/min, highly dependent on doping level	<40nm/min to >600nm/min depending on recipe parameters and mask design	Up to 18-20 µm/min depending on recipe, mask design and aspect ratio.	<130nm/min to >5.6 µm/min depending on recipe, mask design and aspect ratio.	Process dependant. The nano etch is in the range 59-311 nm/min	Process dependant. Has been tested in the range 17-31 nm/min
Substrate size	#25 wafers of 100mm in our 100mm bath #1-5 wafers of 100mm or 50mm in "Fumehood KOH" #25 wafers of 100mm or 150mm in our 6" bath	#25 100 mm 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 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 small samples as can be fitted on a 150mm wafer #5 50 mm wafer fitted on a 150mm wafer #1 100 mm wafer on a 150mm wafer #1 150 mm wafers (The system is normally 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 Other materials (only in "Fumehood KOH")	Silicon Silicon Oxide Silicon Nitride Silicon Oxynitride Photoresist	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 oxide Quartz/fused silica	Silicon Silicon Oxide Silicon Nitride Silicon Oxynitride Photoresist E-beam resist Aluminium Quartz/fused silica	Silicon Photoresist/e-beam resist PolySilicon Silicon oxide Silicon (oxy)nitride Aluminium Titanium Chromium 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