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SU-8 photoresist

January 01, 1970

"Su-8" redirects here. For the aircraft, see Sukhoi Su-8.

SU-8 is a commonly used epoxy-based negative photoresist. Negative refers to a photoresist whereby the parts exposed to UV become cross-linked, while the remainder of the film remains soluble and can be washed away during development.

SU-8 molecule

As shown in the structural diagram, SU-8 derives its name from the presence of 8 epoxy groups. This is a statistical average per moiety. It is these epoxies that cross-link to give the final structure.

It can be made into a viscous polymer that can be spun or spread over a thickness ranging from below 1 micrometer up to above 300 micrometers, or Thick Film Dry Sheets (TFDS) for lamination up to above 1 millimetre thick. Up to 500 µm, the resist can be processed with standard contact lithography.[1] Above 500 µm, absorption leads to increasing sidewall undercuts and poor curing at the substrate interface. It can be used to pattern high aspect ratio structures. An aspect ratio of (> 20) has been achieved with the solution formulation[2] and (> 40) has been demonstrated from the dry resist.[3] Its maximum absorption is for ultraviolet light with a wavelength of the i-line: 365 nm (it is not practical to expose SU-8 with g-line ultraviolet light). When exposed, SU-8's long molecular chains cross-link, causing the polymerisation of the material. SU-8 series photoresists use gamma-butyrolactone or cyclopentanone as the primary solvent.

SU-8 was originally developed as a photoresist for the microelectronics industry, to provide a high-resolution mask for fabrication of semiconductor devices.

It is now mainly used in the fabrication of microfluidics (mainly via soft lithography, but also with other imprinting techniques such as nanoimprint lithography[4]) and microelectromechanical systems parts. It is also one of the most biocompatible materials known[5] and is often used in bio-MEMS for life science applications.[6]

Composition and processing edit

SU-8 is composed of Bisphenol A Novolac epoxy that is dissolved in an organic solvent (gamma-butyrolactone GBL or cyclopentanone, depending on the formulation) and up to 10 wt% of mixed Triarylsulfonium/hexafluoroantimonate salt as the photoacid generator.[7]

SU-8 absorbs light in the UV region, allowing fabrication of relatively thick (hundreds of micrometers) structures with nearly vertical side walls. The fact that a single photon can trigger multiple polymerizations makes the SU-8 a chemically amplified resist which is polymerized by photoacid generation.[8] The light irradiated on the resist interacts with the salt in the solution, creating hexafluoroantimonic acid that then protonates the epoxides groups in the resin monomers. The monomer are thus activated but the polymerization will not proceed significantly until the temperature is raised as part of the post-expose bake. It is at this stage that the epoxy groups in the resin cross-link to form the cured structure. When fully cured, the high crosslinking degree gives to the resist its excellent mechanical properties.[9]

The processing of SU-8 is similar to other negative resists with particular attention on the control of the temperature in the baking steps. The baking times depend on the SU-8 layer thickness; the thicker the layer, the longer the baking time. The temperature is controlled during the baking in order to reduce stress formation in the thick layer (leading to cracks) as the solvent evaporates.

The soft bake is the most important of the bake steps for stress formation. It is performed after spin coating. Its function is to remove the solvent from the resist and make the layer solid. Typically at least 5% of the solvent remains in the layer after the soft bake, however the thicker the coating, the harder it becomes to remove the solvent, as evaporating solvent through thick layers becomes increasingly difficult with coating thickness. The bake is performed on a programmable hot plate to reduce the skinning effect of solvent depletion at the surface creating a dense layer which makes the remainder of the solvent more difficult to remove. In order to reduce stress, the bake procedure is generally a two-step process made up of holding at 65 °C before ramping to 95 °C and holding again for a time dependent on the layer thickness. The temperature is then lowered slowly to room temperature.

When dry films are used, the photoresist is laminated rather than spin-coated. As this formulation is essentially solventless (less than 1% solvent remaining), it does not require a soft bake step and does not suffer stress or skinning. For enhanced adhesion, a post lamination bake can be added. This step is carried out in a similar way to the solution based resist - i.e. holding at 65 °C then 95 °C, the time dependent on film thickness.

After this stage the SU-8 layer can now be exposed. Typically this is through a photomask with an inverse pattern, as the resist is negative. The exposure time is a function of exposure dose and film thickness. After exposure the SU-8 needs to be baked again to complete the polymerization. This baking step is not as critical as the prebake but the rising of the temperature (again to 95 °C) needs to be slow and controlled. At this point the resist is ready to be developed.

The main developer for SU-8 is 1-methoxy-2-propanol acetate.[10] Development time is primarily a function of SU-8 thickness.

After exposing and developing, its highly cross-linked structure gives it high stability to chemicals and radiation damage - hence the name "resist". Cured cross-linked SU-8 shows very low levels of outgassing in a vacuum.[11] [12] However it is very difficult to remove, and tends to outgas in an unexposed state.[13]

Newer formulations edit

SU-8 2000 series resists use cyclopentanone for the primary solvent and can be used to create films between 0.5 and 100 µm in thickness. This formulation may offer improved adhesion on some substrates versus the original formulation.[14]

SU-8 3000 series resists also use cyclopentanone for the primary solvent and are designed to be spun into thicker films ranging from 2 to 75 µm in a single coat.[14]

SU-8 GLM2060 series of low-stress photoresist consist of epoxy GBL and silica formulation CTE 14.[15]

SU-8 GCM3060 Series of GERSTELTEC conductive SU8 with nanoparticles of silver.[15]

SU-8 GMC10xx Series of GERSTELTEC colored SU8 Red, Bleau, Green, black and others.[15]

SU-8 GMJB10XX Series of GERSTELTEC low viscosities epoxy for inkjet applications.[15]

SU8 GM10XX Series of Classic GERSTELTEC epoxy.[16]

Its polymerization process proceeds upon photoactivation of a photoacid generator (triarylsulfonium salts, for example) and subsequent post exposure baking. The polymerization process it a cationic chain growth, which takes place by ring opening polymerization of the epoxide groups.

SUEX is a Thick Dry Film Sheet (TDFS) which is a solventless formulation applied by lamination. As this formulation is a dry sheet, there is high uniformity, no edge-bead[17] formation and very little waste. These sheets come in a range of thicknesses from 100 µm to over 1mm.[18] DJMicrolaminates also sell a thinner range, ADEX TFDS, which are available in thicknesses from 5 µm through to 75 µm.[18]

External links edit

  • SU-8: Thick Photo-Resist for MEMS A webpage with a lot of material data and process tricks.
  • http://www.gersteltec.ch/
  • Microchem data sheet
  • SU 8 Information Provides information on how to use SU 8 to create desired thicknesses.
  • SU-8 Spin Speed Calculator Selects a SU-8 type and calculates RPM for a given thickness.
  • Suppliers: The solution based SU-8 can be obtained from Microchem or Gersteltec ; the SUEX dry sheets are obtained from DJ Microlaminates , formerly known as DJ Devcorp

References edit

  1. ^ . MicroChem. Archived from the original on 17 May 2009. Retrieved 21 Jul 2011.
  2. ^ Liu J, Cai B, Zhu J, et al. (2004). "Process research of high aspect ratio microstructure using SU-8 resist". Microsyst. Technol. 10 (4): 265–8. doi:10.1007/s00542-002-0242-2. S2CID 111062837.
  3. ^ Johnsona DW, Goettertb J, Singhb V, et al. (2012). "SUEX Dry Film Resist – A new Material for High Aspect Ratio Lithography" (PDF). Louisiana State University Proceedings.
  4. ^ Greener J, Li W, Ren J, et al. (February 2010). "Rapid, cost-efficient fabrication of microfluidic reactors in thermoplastic polymers by combining photolithography and hot embossing". Lab on a Chip. 10 (4): 522–4. doi:10.1039/B918834G. PMID 20126695.
  5. ^ Nemani KV, Moodie KL, Brennick JB, et al. (2013). "In vitro and in vivo evaluation of SU-8 biocompatibility". Materials Science and Engineering: C. 33 (7): 4453–9. doi:10.1016/j.msec.2013.07.001. PMC 3843949. PMID 23910365.
  6. ^ Arscott S (2014). "SU-8 as a material for lab-on-a-chip-based mass spectrometry". Lab on a Chip. 14 (19): 3668–89. doi:10.1039/C4LC00617H. PMID 25029537.
  7. ^ (PDF). Microchem.com. 2011. Archived from the original (PDF) on 2012-04-25. Retrieved 12 Jun 2019.
  8. ^ del Campo A, Greiner C (2007). "SU-8: a photoresist for high-aspect-ratio and 3D submicron lithography". J. Micromech. Microeng. 17 (6): R81–R95. doi:10.1088/0960-1317/17/6/R01. S2CID 18148474.
  9. ^ Martinez-Duarte R, Madou M (2011). "SU-8 Pholithography and its impact on microfluidics". In Mitra SK, Chakraborty S (eds.). Microfluidics and Nanofluidics Handbook: Fabrication, Implementation and Applications (1st ed.). New York: CRC Press. pp. 231–268. ISBN 9781138072381.
  10. ^ . Lambers Wiki (Material Safety Data Sheet). 2005. Archived from the original on 11 December 2017. Retrieved 12 Jun 2019.
  11. ^ "SU-8 photosensitive epoxy". 2003. Archived from the original on 30 May 2012. Retrieved 12 Jun 2019.
  12. ^ Melai J, Salm C, Wolters R, et al. (2009). "Qualitative and quantitative characterization of outgassing from SU-8" (PDF). Microelectronic Engineering. 86 (4–6): 761–764. doi:10.1016/j.mee.2008.11.008. S2CID 137789516.
  13. ^ (PDF). engineering.tufts.edu. 2007. Archived from the original (PDF) on 9 November 2009. Retrieved 12 Jun 2019.
  14. ^ a b (PDF). Microchem. Archived from the original (PDF) on 15 April 2017.
  15. ^ a b c d "SU-8 Functional Polymer". Gersteltec Engineering Solutions. Retrieved 12 Jun 2019.
  16. ^ "SU8". Gersteltec Engineering Solutions. Retrieved 12 Jun 2019.
  17. ^ S. Arscott, ‘The limits of edge bead planarization and surface levelling in spin-coated liquid films', J. Micromech. Microeng. 30, 025003, (2020).
  18. ^ a b "SUEX". djmicrolaminates.com. Retrieved 15 Feb 2017.

January 01, 1970
photoresist, redirects, here, aircraft, sukhoi, commonly, used, epoxy, based, negative, photoresist, negative, refers, photoresist, whereby, parts, exposed, become, cross, linked, while, remainder, film, remains, soluble, washed, away, during, development, mol. Su 8 redirects here For the aircraft see Sukhoi Su 8 SU 8 is a commonly used epoxy based negative photoresist Negative refers to a photoresist whereby the parts exposed to UV become cross linked while the remainder of the film remains soluble and can be washed away during development SU 8 molecule As shown in the structural diagram SU 8 derives its name from the presence of 8 epoxy groups This is a statistical average per moiety It is these epoxies that cross link to give the final structure It can be made into a viscous polymer that can be spun or spread over a thickness ranging from below 1 micrometer up to above 300 micrometers or Thick Film Dry Sheets TFDS for lamination up to above 1 millimetre thick Up to 500 µm the resist can be processed with standard contact lithography 1 Above 500 µm absorption leads to increasing sidewall undercuts and poor curing at the substrate interface It can be used to pattern high aspect ratio structures An aspect ratio of gt 20 has been achieved with the solution formulation 2 and gt 40 has been demonstrated from the dry resist 3 Its maximum absorption is for ultraviolet light with a wavelength of the i line 365 nm it is not practical to expose SU 8 with g line ultraviolet light When exposed SU 8 s long molecular chains cross link causing the polymerisation of the material SU 8 series photoresists use gamma butyrolactone or cyclopentanone as the primary solvent SU 8 was originally developed as a photoresist for the microelectronics industry to provide a high resolution mask for fabrication of semiconductor devices It is now mainly used in the fabrication of microfluidics mainly via soft lithography but also with other imprinting techniques such as nanoimprint lithography 4 and microelectromechanical systems parts It is also one of the most biocompatible materials known 5 and is often used in bio MEMS for life science applications 6 Contents 1 Composition and processing 2 Newer formulations 3 External links 4 ReferencesComposition and processing editSU 8 is composed of Bisphenol A Novolac epoxy that is dissolved in an organic solvent gamma butyrolactone GBL or cyclopentanone depending on the formulation and up to 10 wt of mixed Triarylsulfonium hexafluoroantimonate salt as the photoacid generator 7 SU 8 absorbs light in the UV region allowing fabrication of relatively thick hundreds of micrometers structures with nearly vertical side walls The fact that a single photon can trigger multiple polymerizations makes the SU 8 a chemically amplified resist which is polymerized by photoacid generation 8 The light irradiated on the resist interacts with the salt in the solution creating hexafluoroantimonic acid that then protonates the epoxides groups in the resin monomers The monomer are thus activated but the polymerization will not proceed significantly until the temperature is raised as part of the post expose bake It is at this stage that the epoxy groups in the resin cross link to form the cured structure When fully cured the high crosslinking degree gives to the resist its excellent mechanical properties 9 The processing of SU 8 is similar to other negative resists with particular attention on the control of the temperature in the baking steps The baking times depend on the SU 8 layer thickness the thicker the layer the longer the baking time The temperature is controlled during the baking in order to reduce stress formation in the thick layer leading to cracks as the solvent evaporates The soft bake is the most important of the bake steps for stress formation It is performed after spin coating Its function is to remove the solvent from the resist and make the layer solid Typically at least 5 of the solvent remains in the layer after the soft bake however the thicker the coating the harder it becomes to remove the solvent as evaporating solvent through thick layers becomes increasingly difficult with coating thickness The bake is performed on a programmable hot plate to reduce the skinning effect of solvent depletion at the surface creating a dense layer which makes the remainder of the solvent more difficult to remove In order to reduce stress the bake procedure is generally a two step process made up of holding at 65 C before ramping to 95 C and holding again for a time dependent on the layer thickness The temperature is then lowered slowly to room temperature When dry films are used the photoresist is laminated rather than spin coated As this formulation is essentially solventless less than 1 solvent remaining it does not require a soft bake step and does not suffer stress or skinning For enhanced adhesion a post lamination bake can be added This step is carried out in a similar way to the solution based resist i e holding at 65 C then 95 C the time dependent on film thickness After this stage the SU 8 layer can now be exposed Typically this is through a photomask with an inverse pattern as the resist is negative The exposure time is a function of exposure dose and film thickness After exposure the SU 8 needs to be baked again to complete the polymerization This baking step is not as critical as the prebake but the rising of the temperature again to 95 C needs to be slow and controlled At this point the resist is ready to be developed The main developer for SU 8 is 1 methoxy 2 propanol acetate 10 Development time is primarily a function of SU 8 thickness After exposing and developing its highly cross linked structure gives it high stability to chemicals and radiation damage hence the name resist Cured cross linked SU 8 shows very low levels of outgassing in a vacuum 11 12 However it is very difficult to remove and tends to outgas in an unexposed state 13 Newer formulations editSU 8 2000 series resists use cyclopentanone for the primary solvent and can be used to create films between 0 5 and 100 µm in thickness This formulation may offer improved adhesion on some substrates versus the original formulation 14 SU 8 3000 series resists also use cyclopentanone for the primary solvent and are designed to be spun into thicker films ranging from 2 to 75 µm in a single coat 14 SU 8 GLM2060 series of low stress photoresist consist of epoxy GBL and silica formulation CTE 14 15 SU 8 GCM3060 Series of GERSTELTEC conductive SU8 with nanoparticles of silver 15 SU 8 GMC10xx Series of GERSTELTEC colored SU8 Red Bleau Green black and others 15 SU 8 GMJB10XX Series of GERSTELTEC low viscosities epoxy for inkjet applications 15 SU8 GM10XX Series of Classic GERSTELTEC epoxy 16 Its polymerization process proceeds upon photoactivation of a photoacid generator triarylsulfonium salts for example and subsequent post exposure baking The polymerization process it a cationic chain growth which takes place by ring opening polymerization of the epoxide groups SUEX is a Thick Dry Film Sheet TDFS which is a solventless formulation applied by lamination As this formulation is a dry sheet there is high uniformity no edge bead 17 formation and very little waste These sheets come in a range of thicknesses from 100 µm to over 1mm 18 DJMicrolaminates also sell a thinner range ADEX TFDS which are available in thicknesses from 5 µm through to 75 µm 18 External links editSU 8 Thick Photo Resist for MEMS A webpage with a lot of material data and process tricks http www gersteltec ch Microchem data sheet SU 8 Information Provides information on how to use SU 8 to create desired thicknesses SU 8 Spin Speed Calculator Selects a SU 8 type and calculates RPM for a given thickness Suppliers The solution based SU 8 can be obtained from Microchem or Gersteltec the SUEX dry sheets are obtained from DJ Microlaminates formerly known as DJ DevcorpReferences edit SU 8 Resists FAQs MicroChem Archived from the original on 17 May 2009 Retrieved 21 Jul 2011 Liu J Cai B Zhu J et al 2004 Process research of high aspect ratio microstructure using SU 8 resist Microsyst Technol 10 4 265 8 doi 10 1007 s00542 002 0242 2 S2CID 111062837 Johnsona DW Goettertb J Singhb V et al 2012 SUEX Dry Film Resist A new Material for High Aspect Ratio Lithography PDF Louisiana State University Proceedings Greener J Li W Ren J et al February 2010 Rapid cost efficient fabrication of microfluidic reactors in thermoplastic polymers by combining photolithography and hot embossing Lab on a Chip 10 4 522 4 doi 10 1039 B918834G PMID 20126695 Nemani KV Moodie KL Brennick JB et al 2013 In vitro and in vivo evaluation of SU 8 biocompatibility Materials Science and Engineering C 33 7 4453 9 doi 10 1016 j msec 2013 07 001 PMC 3843949 PMID 23910365 Arscott S 2014 SU 8 as a material for lab on a chip based mass spectrometry Lab on a Chip 14 19 3668 89 doi 10 1039 C4LC00617H PMID 25029537 NANO SU 8 Negative Tone Photoresist formulations 50 100 PDF Microchem com 2011 Archived from the original PDF on 2012 04 25 Retrieved 12 Jun 2019 del Campo A Greiner C 2007 SU 8 a photoresist for high aspect ratio and 3D submicron lithography J Micromech Microeng 17 6 R81 R95 doi 10 1088 0960 1317 17 6 R01 S2CID 18148474 Martinez Duarte R Madou M 2011 SU 8 Pholithography and its impact on microfluidics In Mitra SK Chakraborty S eds Microfluidics and Nanofluidics Handbook Fabrication Implementation and Applications 1st ed New York CRC Press pp 231 268 ISBN 9781138072381 SU 8 Developer Lambers Wiki Material Safety Data Sheet 2005 Archived from the original on 11 December 2017 Retrieved 12 Jun 2019 SU 8 photosensitive epoxy 2003 Archived from the original on 30 May 2012 Retrieved 12 Jun 2019 Melai J Salm C Wolters R et al 2009 Qualitative and quantitative characterization of outgassing from SU 8 PDF Microelectronic Engineering 86 4 6 761 764 doi 10 1016 j mee 2008 11 008 S2CID 137789516 SU 8 Photoresist Processing PDF engineering tufts edu 2007 Archived from the original PDF on 9 November 2009 Retrieved 12 Jun 2019 a b SU 8 2000 Permanent Epoxy Negative Photoresist Processing Guidelines PDF Microchem Archived from the original PDF on 15 April 2017 a b c d SU 8 Functional Polymer Gersteltec Engineering Solutions Retrieved 12 Jun 2019 SU8 Gersteltec Engineering Solutions Retrieved 12 Jun 2019 S Arscott The limits of edge bead planarization and surface levelling in spin coated liquid films J Micromech Microeng 30 025003 2020 a b SUEX djmicrolaminates com Retrieved 15 Feb 2017 Retrieved from https en wikipedia org w index php title SU 8 photoresist amp oldid 1177800073, wikipedia, wiki, book, books, library,

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