Difference between revisions of "Soft Lithography"

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==Process Flow==
 
==Process Flow==
 
[[File: SoftLitho Protocol Oct2025.PNG|thumb|right|upright=1.75|'''Standard QNF Soft Lithography Protocol, Updated May 2025.''' <br>Images from [https://www.fabublox.com/process-editor/70e6195b-900a-48e8-8b05-70dd807d973f "Microfluidics at QNF" Process on Fabublox] ]]
 
[[File: SoftLitho Protocol Oct2025.PNG|thumb|right|upright=1.75|'''Standard QNF Soft Lithography Protocol, Updated May 2025.''' <br>Images from [https://www.fabublox.com/process-editor/70e6195b-900a-48e8-8b05-70dd807d973f "Microfluidics at QNF" Process on Fabublox] ]]
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*The master used can be fabricated out of photoresist or etched silicon. The most commonly used materials are epoxy-based negative photoresist (SU8 or HARE SQ). For a negative photoresist, the parts exposed to UV become cross-linked, while the remainder of the film remains soluble and can be washed away during development. The height of this structure is determined by the thickness of the resist, which we control through our application method. The length and width of features are patterned through the UV exposure, either by mask or direct write tools.<br>
+
*The master used can be fabricated out of photoresist or etched silicon. The most commonly used materials are epoxy-based negative photoresist (SU8 / HARE SQ). For a negative photoresist, the parts exposed to UV become cross-linked, while the remainder of the film remains soluble and can be washed away during development. The height of this structure is determined by the thickness of the resist, which we control through our application method. The length and width of features are patterned through the UV exposure, either by mask or direct write tools.<br>
 
*For molding success, there are two important components to think about -- master durability and PDMS removal. Etched silicon molds will be more durable than patterned photoresist. However, an O2 plasma treatment under vacuum before applying resist has shown more than sufficient adhesion for patterned HARE SQ in our own tests. To enable easy release of the PDMS from the mold, it can be beneficial to do a silanization treatment before applying the PDMS.<br>
 
*For molding success, there are two important components to think about -- master durability and PDMS removal. Etched silicon molds will be more durable than patterned photoresist. However, an O2 plasma treatment under vacuum before applying resist has shown more than sufficient adhesion for patterned HARE SQ in our own tests. To enable easy release of the PDMS from the mold, it can be beneficial to do a silanization treatment before applying the PDMS.<br>
 
*An O2 plasma step is included if applying the PDMS to glass or another piece of PDMS to make a device.
 
*An O2 plasma step is included if applying the PDMS to glass or another piece of PDMS to make a device.
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* [https://wiki.nano.upenn.edu/wiki/images/c/cf/Microfluidics_Process_Flow.pdf Making a Master - detailed instructions]
 
* [https://wiki.nano.upenn.edu/wiki/images/c/cf/Microfluidics_Process_Flow.pdf Making a Master - detailed instructions]
 
* [https://wiki.nano.upenn.edu/wiki/images/0/0c/SOP_Microfluidics.pdf Making a Device: PDMS to PDMS bonding]
 
* [https://wiki.nano.upenn.edu/wiki/images/0/0c/SOP_Microfluidics.pdf Making a Device: PDMS to PDMS bonding]
 +
 +
=====Tips & Tricks=====
 +
* Be sure to mix the PDMS base and curing agent together VERY well for ~5 minutes! If not mixed well, the cured PDMS may adhere to the master and ruin it.
 +
* An aluminum tray that can accommodate a wafer is a very helpful container for applying the PDMS -- available in the [https://nemo.nano.upenn.edu/stockroom/ QNF Stockroom]
 +
* A 1mm biopsy punch is a great way to add inlet/outlet ports. We have these available for use in our PDMS room.
 +
* A main cause of failure of the master is cracking of the wafer. Be careful not to score the wafer when cutting out your devices!
 +
* A drop of IPA can be a helpful lubricant when cutting and removing the PDMS mold can be very helpful.
 +
* Trying to remove the wafer from the PDMS mold can easily crack the wafer. It is easier to cut out only the devices needed.
 +
* Applying trichloro(1H, 1H, 2H, 2H-perfluoro-octyl) silane in a vacuum desiccator before applying PDMS can make it easier to remove the mold from the master. This is really only necessary if there are small features with high aspect ratios.
  
 
====Videos====
 
====Videos====
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==Equipment at QNF==
 
==Equipment at QNF==
 +
<u><small>'''NOTE</u>:'''</small> To minimize contamination, we have a separate room within the Soft Materials area dedicated to PDMS mixing and molding. Uncured PDMS may not be removed from this room. Cutting PDMS or punching out inlets/outlets must be kept to inside this room or completely outside of the cleanroom. Many researchers use PDMS in their own (non-cleanroom) labs with very satisfactory results.
 +
 
==== Soft Materials ====
 
==== Soft Materials ====
 
* '''DE-07:''' [[Anatech SCE-106 Barrel Asher | Anatech SCE-106 Barrel Asher]]
 
* '''DE-07:''' [[Anatech SCE-106 Barrel Asher | Anatech SCE-106 Barrel Asher]]
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* '''SPN-09:''' [[ CEE Apogee Spinner | CEE Apogee Spinner - PDMS]]
 
* '''SPN-09:''' [[ CEE Apogee Spinner | CEE Apogee Spinner - PDMS]]
 
* '''LW-02:''' [[Nanoscribe Photonic Professional GT | Nanoscribe Photonic Professional GT]]
 
* '''LW-02:''' [[Nanoscribe Photonic Professional GT | Nanoscribe Photonic Professional GT]]
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===== Main Cleanroom =====
+
==== Main Cleanroom ====
 
* '''LW-01:''' [[Heidelberg DWL 66+ Laser Writer | Heidelberg DWL 66+ Laser Writer]]
 
* '''LW-01:''' [[Heidelberg DWL 66+ Laser Writer | Heidelberg DWL 66+ Laser Writer]]
 
* '''LW-03:''' [[DMO MicroWriter ML3 Pro | DMO MicroWriter ML3 Pro ]]
 
* '''LW-03:''' [[DMO MicroWriter ML3 Pro | DMO MicroWriter ML3 Pro ]]

Latest revision as of 11:14, 11 November 2025


About

Soft lithography is the transfer of patterned microstructures with molded elastomer. The most common elastomer used in this technique is PDMS (polydimethylsiloxane), which is soft, low cost and easy to mold. It is also bio-compatible with high thermal stability and high chemical stability, is chemically inert, insulating, transparent to UV and visible light, mechanically flexible and durable, allowing many applications. The most common devices fabricated with this technique are microfluidics.
NOTE: You might hear soft lithography equated to "microfluidics fabrication." However, it is important to remember that not all microfluidic devices are fabricated by soft lithography and not all soft lithography is for microfluidic applications!

Process Flow

Standard QNF Soft Lithography Protocol, Updated May 2025.
Images from "Microfluidics at QNF" Process on Fabublox
  • The master used can be fabricated out of photoresist or etched silicon. The most commonly used materials are epoxy-based negative photoresist (SU8 / HARE SQ). For a negative photoresist, the parts exposed to UV become cross-linked, while the remainder of the film remains soluble and can be washed away during development. The height of this structure is determined by the thickness of the resist, which we control through our application method. The length and width of features are patterned through the UV exposure, either by mask or direct write tools.
  • For molding success, there are two important components to think about -- master durability and PDMS removal. Etched silicon molds will be more durable than patterned photoresist. However, an O2 plasma treatment under vacuum before applying resist has shown more than sufficient adhesion for patterned HARE SQ in our own tests. To enable easy release of the PDMS from the mold, it can be beneficial to do a silanization treatment before applying the PDMS.
  • An O2 plasma step is included if applying the PDMS to glass or another piece of PDMS to make a device.

QNF Standard Protocols

Tips & Tricks
  • Be sure to mix the PDMS base and curing agent together VERY well for ~5 minutes! If not mixed well, the cured PDMS may adhere to the master and ruin it.
  • An aluminum tray that can accommodate a wafer is a very helpful container for applying the PDMS -- available in the QNF Stockroom
  • A 1mm biopsy punch is a great way to add inlet/outlet ports. We have these available for use in our PDMS room.
  • A main cause of failure of the master is cracking of the wafer. Be careful not to score the wafer when cutting out your devices!
  • A drop of IPA can be a helpful lubricant when cutting and removing the PDMS mold can be very helpful.
  • Trying to remove the wafer from the PDMS mold can easily crack the wafer. It is easier to cut out only the devices needed.
  • Applying trichloro(1H, 1H, 2H, 2H-perfluoro-octyl) silane in a vacuum desiccator before applying PDMS can make it easier to remove the mold from the master. This is really only necessary if there are small features with high aspect ratios.

Videos

Equipment at QNF

NOTE: To minimize contamination, we have a separate room within the Soft Materials area dedicated to PDMS mixing and molding. Uncured PDMS may not be removed from this room. Cutting PDMS or punching out inlets/outlets must be kept to inside this room or completely outside of the cleanroom. Many researchers use PDMS in their own (non-cleanroom) labs with very satisfactory results.

Soft Materials

Main Cleanroom

Want to Know More?

Related Wiki Pages

Internal Reports & Presentations

External Resources

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