Presentation 8 photolithography

Presentation 8 photolithography - Photolithography...

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Photolithography Process ) bstrate covered with silicon (a) Substrate covered with silicon dioxide barrier layer (b) Positive photoresist applied to afer surface wafer surface (c) Mask in close proximity to surface (d) Substrate following resist exposure and development (e) Substrate after etching of oxide layer (f) Oxide barrier on surface after resist removal (g) View of substrate with silicon i id tt th f dioxide pattern on the surface
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Photoresist
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Photoresist
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High Aspect Ratio Microstructures
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Photoresist
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Photolithography Process Surface cleaning and/or dehydration baking Prepares surface for hotoresist application yg photoresist application HMDS Application Adhesion promoter typically spun on the wafer Resist Application Resist spun on wafer, typically 3000-6000 rpm, forming an - 0.5 μm resist layer Pre-bake resist Typically 10 - 30 min @ 90 - 100 ÞC lign wafer Typically aligned at each Align wafer, expose resist exposure site, exposed at 150 mJ cm -2 Post exposure bake Sometimes used to minimize standing waves in resist ypically 10 min @ 100ÞC Typically 10 min @ 100ÞC Resist develop Typically 30 - 60 sec @ room T using spray or immersion Post-bake resist Typically 10 - 30 min @ 100 - 140 ÞC
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Surface Pretreatment fter treatment, surface After treatment, surface becomes more hydrophobic and adherent to photoresist
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Spin Coating r SU Photoresist For SU 8 Photoresist
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Spin Coating
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Spin Coating lm Profile and Film Profile and Spinning Artifact • Striations – ~ 30 nm variations in resist thickness due to nonuniform drying of solvent uring spin coating during spin coating – ~ 80-100 mm periodicity, radically out from center of wafer • Edge Beads – residual ridge in resist at edge of wafer – can be up to 20-30 times the nominal thickness of the resist – radius on wafer edge greatly reduces the edge bead height on- ircular wafers greatly increase the edge bead height non circular wafers greatly increase the edge bead height – edge bead removers are solvents that are spun on after resist coating and which partially dissolve away the edge bead Streaks • Streaks – radial patterns caused by hard particles whose diameter are greater than the resist thickness
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Soft Bake (pre bake) Typical thermal cycles: – 90-100°C for 20 min. in a convection oven – 75-85°C for 45 sec. on a hot For SU 8 Photoresist plate Hot plating the resist is usually faster, more controllable, and does not trap solvent like convection oven baking.
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UV Exposure
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Development
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Hard Bake The resist may be ramp/step hard baked between 150-200°C on a hot plate or in a convection oven to further cross link the material.
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This note was uploaded on 10/27/2009 for the course ENGR MSE 401 50 taught by Professor Drwang during the Fall '09 term at LA Tech.

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Presentation 8 photolithography - Photolithography...

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