View source for Specific Process Knowledge/Etch/Wet Silicon Oxide Etch (BHF)

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[[Category: Equipment|Etch Wet Silicon Oxide]]
[[Category: Etch (Wet) bath|Silicon Oxide]]

==Wet Silicon Oxide Etch (BHF, HF and SIO Etch (wetting agent))==

Silicon oxide can be etched using HF. At Danchip it is mainly used in a buffered version BHF (premixed). You can find the KBA [http://kemibrug.dk/KBA/CAS/106534/?show_KBA=1&portaldesign=1 here] The BHF has a more stable etch rate and is more gentle to photoresist due to an almost pH neutral solution which makes photoresist a good masking material for the oxide etch. 

SIO etch (BHF with wetting agent) can also be used for etching silicon oxide. This is mainly for etching small holes. If you have wetting problems in BHF try the SIO etch. It is also a good idea to wet the sample in water for a few minutes before etching.

Wafers with metals or other materials, not allowed in the dedicated oxide etch baths, can be etched in the PP-bath positioned in the fume hood in cleanroom 2 or in a '''plastic''' beaker. 

'''The user manual for Oxide etch 1: BHF, APV's and contact information can be found in LabManager''' [http://labmanager.dtu.dk/function.php?module=Machine&view=view&mach=389 by clicking here]

'''The user manual for Oxide etch 2: BHF (clean), APV's and contact information can be found in LabManager''' [http://labmanager.dtu.dk/function.php?module=Machine&view=view&mach=378 by clicking here]

'''The user manual for various HF baths in RCA and Fume hoods, APV's and contact information can be found in LabManager''' [http://labmanager.danchip.dtu.dk/function.php?module=Machine&view=view&mach=64 by clicking here]

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'''Process information:''' <br>
See more [[/BHF etch rates|etch rates]] in HF solutions.


{| border="2" cellspacing="0" cellpadding="2" 

!colspan="2" border="none" style="background:silver; color:black;" align="center"|Etchant 
|style="background:WhiteSmoke; color:black"|<b>[[Specific_Process_Knowledge/Etch/Wet_Silicon_Oxide_Etch_(BHF)#Comparing_different_BHF_baths|BHF]]</b>
|style="background:WhiteSmoke; color:black"|<b>[[Specific_Process_Knowledge/Etch/Wet_Silicon_Oxide_Etch_(BHF)#Comparing_different_5.25_HF_baths|5% HF]]</b>
|style="background:WhiteSmoke; color:black"|<b>[[Specific_Process_Knowledge/Etch/Wet_Silicon_Oxide_Etch_(BHF)#Comparing_different_40.25_HF_baths|40% HF]]</b>
|style="background:WhiteSmoke; color:black"|<b>[[Specific_Process_Knowledge/Etch/Wet_Silicon_Oxide_Etch_(BHF)#SiO_etch_bath|SiO etch]]</b>
|-
!style="background:silver; color:black;" align="center" width="60" rowspan="2"|Purpose 
|style="background:LightGrey; color:black"|Etching of silicon oxide  
|style="background:WhiteSmoke; color:black"|
*Etching of silicon oxide with a stable etch rate
|style="background:WhiteSmoke; color:black"|
*Mainly for removing native oxide
|style="background:WhiteSmoke; color:black"|
*Mainly for etching deep into borofloat or quartz wafers
|style="background:WhiteSmoke; color:black"|
*Etching of silicon oxide - especially for etching small holes
|-
|style="background:LightGrey; color:black"|Link to safety APV and KBA
|style="background:WhiteSmoke; color:black"|
*:[http://labmanager.danchip.dtu.dk/d4Show.php?id=1897&mach=64 see APV here]
*:[http://kemibrug.dk/KBA/CAS/106534/?show_KBA=1&portaldesign=1 see KBA here]
|style="background:WhiteSmoke; color:black"|
*:[http://labmanager.danchip.dtu.dk/d4Show.php?id=1897&mach=64 see APV here]
*:[http://kemibrug.dk/KBA/CAS/106231/?show_KBA=1&portaldesign=1 see KBA here]
|style="background:WhiteSmoke; color:black"|
*:[http://labmanager.danchip.dtu.dk/d4Show.php?id=2479&mach=146 see APV here]
*:[http://kemibrug.dk/KBA/CAS/100648/?lang=da&show_KBA=1&portaldesign=1 see KBA here]
|style="background:WhiteSmoke; color:black"|
*:[http://labmanager.danchip.dtu.dk/d4Show.php?id=1897&mach=64 see APV here]
*:[http://kemibrug.dk/KBA/CAS/106534/?show_KBA=1&portaldesign=1 see KBA here]
|-
!style="background:silver; color:black" align="center" valign="center" rowspan="3"|Performance
|style="background:LightGrey; color:black"|Isotropic
|style="background:WhiteSmoke; color:black"|
*Isotropic
|style="background:WhiteSmoke; color:black"|
*Isotropic
|style="background:WhiteSmoke; color:black"|
*Isotropic
|style="background:WhiteSmoke; color:black"|
*Isotropic
|-
|style="background:LightGrey; color:black"|Etch rates 
[[/BHF etch rates|See more]] 
|style="background:WhiteSmoke; color:black"|
*Wet thermal oxide:75-80nm/min 
|style="background:WhiteSmoke; color:black"|
*Wet thermal oxide:~25nm/min 
|style="background:WhiteSmoke; color:black"|
*Boronfloat and quartz: ~3-4 μm/min
|style="background:WhiteSmoke; color:black"|
*A little higher etch rates than BHF
|-
|style="background:LightGrey; color:black"|Lifetime of photoresist
|style="background:WhiteSmoke; color:black"|
*~½ hour
|style="background:WhiteSmoke; color:black"|
*~½ hour
|style="background:WhiteSmoke; color:black"|
*~½ hour
|style="background:WhiteSmoke; color:black"|
*~½ hour
|-
!style="background:silver; color:black" align="center" valign="center" rowspan="2"|Process parameter range
|style="background:LightGrey; color:black"|Chemical solution
|style="background:WhiteSmoke; color:black"|
*BHF (12%HF with Ammoniumflouride)			
|style="background:WhiteSmoke; color:black"|
*5% HF
|style="background:WhiteSmoke; color:black"|
*40% HF
|style="background:WhiteSmoke; color:black"|
*SiO etch (BHF with a wetting agent)
|-
|style="background:LightGrey; color:black"|Temperature
|style="background:WhiteSmoke; color:black"|
*Room temperature
|style="background:WhiteSmoke; color:black"|
*Room temperature
|style="background:WhiteSmoke; color:black"|
*Room temperature
|style="background:WhiteSmoke; color:black"|
*Room temperature
|-
!style="background:silver; color:black" align="center" valign="center" rowspan="1"|Substrates
|style="background:LightGrey; color:black"|Masking material
|style="background:WhiteSmoke; color:black"|
*Silicon nitride
*Poly silicon
*Photoresist
*Blue film
|style="background:WhiteSmoke; color:black"|
*Silicon nitride
*Poly silicon
*Photoresist
*Blue film
|style="background:WhiteSmoke; color:black"|
*Photoresist 
*Silicon nitride (Only on quartz wafers) 
*Poly silicon (Only on quartz wafers) 
*Blue film 
*Chromium and gold 
|style="background:WhiteSmoke; color:black"|
*Silicon nitride
*Poly silicon
*Photoresist
*Blue film
|-
|}

==Life time of the photoresist and blue film in BHF==
Photoresist delaminates from the substrate in BHF. For standard photoresist this process starts after about or less than ½ hour but the time can vary with resist pattern. It starts by under etching the photoresist at the edges. The life time can be prolonged a little to ½ hour - 40 minutes if the photoresist is baked at 120<sup>o</sup>C.

Blue film also has a limited life time in BHF. Blue film is mainly used for back side protecting the wafer while etching on the front side. The life time of Blue film is also about ½ hour.

<br clear="all" />

<gallery caption="Different places to do wet silicon oxide etch" widths="220px" heights="225px" perrow="5"> image:BHF clean.JPG|BHF clean wetbench 04 in D-3. Wet silicon oxide etch bath positioned to the right in the wetbench. This bath can also be used for BHF with wetting agent. 
image:KOH_BHF.JPG|BHF in wetbench 01 Si etch in D-3 (Oxide etch 1: BHF.) The BHF bath is positioned in the middle of the bench. This is primarily used to remove oxide before and after a Si etch.
image:BHF-PolySi-Al Etch.jpg|BHF etch in RCA bench in B-1. 
image:Stinkskab RR2.jpg|PP-bath: positioned in the upper right corner of the fumehood in cleanroom B-1. </gallery>


<br clear="all" />

==Comparing different BHF baths==
{|border="1" cellspacing="1" cellpadding="3" style="text-align:left;" 
|-

|-style="background:silver; color:black"
! 
! BHF (KOH) in D-3(Oxide etch 1: BHF)
! BHF clean in D-3 (Oxide etch 2: BHF)
! BHF in RCA Bench
! BHF in PP-bath
! BHF Plastic beaker

|- 
|-style="background:WhiteSmoke; color:black"
!Batch size!
|1-25 wafers at a time
|1-25 wafer at a time
|1-25 wafers at a time
|1-25 wafers at a time
|1-7 wafers at a time
|-

|-style="background:LightGrey; color:black"
!Size of substrate
|2"-6" wafers
|2"-6" wafers
|2"-6" wafers
|2"- 4" wafers or any that fits in a dedicated holder
|2"- 4" wafers or any that fits in a dedicated holder
|-

|-style="background:WhiteSmoke; color:black"
!Allowed materials
|
*Silicon
*Poly Silicon
*Silicon Oxide
*Silicon Nitride
*Silicon Oxynitride
*Photoresist
*Blue film
|
*Silicon
*Poly Silicon
*Silicon Oxide
*Silicon Nitride
*Silicon Oxynitride
*Photoresist
*Blue film
|
*Silicon
*Poly Silicon
*Silicon Oxide
*Silicon Nitride
*Silicon Oxynitride
|
*All materials
|
*All materials
|-
|-style="background:LightGrey; color:black"
!Restrictions
|Wafers have to be cleaned in 7UP or RCA before further processing.
|No wafers with metal are allowed in this bath
|Only for wafers with phosphor glass or boron glass that comes directly from one of the furnaces in stack A. All other substrates and material are strictly forbidden to go into the tank.
|None
|None
|-
|}

<br clear="all" />

==Comparing different 5% HF baths==
{|border="1" cellspacing="1" cellpadding="3" style="text-align:left;" 
|-

|-style="background:silver; color:black"
! 
! 5% HF in RCA Bench
! 5% HF PP-bath
! 5% HF Plastic beaker

|- 
|-style="background:WhiteSmoke; color:black"
!Batch size!
|1-25 wafers at a time
|1-25 wafer at a time
|1-7 wafers at a time
|-

|-style="background:LightGrey; color:black"
!Size of substrate
|2"-6" wafers
|2"- 4" wafers or any that fits in a dedicated holder
|2"- 4" wafers or any that fits in a dedicated holder
|-
|-style="background:WhiteSmoke; color:black"
!Allowed materials
|Only for wafers that are being RCA cleaned
|All materials 
|All materials 
|-
|}

<br clear="all" />

==Comparing different 40% HF baths==
{|border="1" cellspacing="1" cellpadding="3" style="text-align:left;" 
|-

|-style="background:silver; color:black"
! 
! 40% HF PP-bath
! 40% HF Plastic beaker

|- 
|-style="background:WhiteSmoke; color:black"
!Batch size!
|1-25 wafers at a time
|1 wafer at a time
|-

|-style="background:LightGrey; color:black"
!Size of substrate
|Any that fits to a dedicated holder
|Any that fits to a dedicated holder
|-
|-style="background:WhiteSmoke; color:black"
!Allowed materials
|All materials 
|All materials 
|-
|}

<br clear="all" />

==SiO etch bath==
{|border="1" cellspacing="1" cellpadding="3" style="text-align:left;" 
|-

|-style="background:silver; color:black"
! 
! SiO etch bath
|- 
|-style="background:WhiteSmoke; color:black"
!Batch size!
|1-25 wafers at a time
|-

|-style="background:LightGrey; color:black"
!Size of substrate
|4" wafers
|-
|-style="background:WhiteSmoke; color:black"
!Allowed materials
|
*Silicon
*Poly silicon
*Silicon nitrides 
*Silicon oxynitrides
*Silicon oxides 
*Photoresist

|-
|}