spin_coating_photoresist (1063542), страница 2
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If such defects cannot be First resist filmavoided, double coating is a good work-around, since twoparticles or bubbles on top of each other are very improb- Substrateable.Double coating can only be realized with high-viscosity resists, since a high solvent concentration will cause a dissolution of the existing resist film.
The lower the resist viscosity is, themore important is i) a softbake between the two coating steps, and ii) spin-coating immediately after the second resist dispension in combination with a high acceleration in order tosuppress the dissolution of the first resist film.Measuring the Film ThicknessThe resist film thickness can be determined via optical methods such as transmission or reflection spectroscopy. The required optical properties of many resist families are listed in thedocument Optical Properties of Photoresists.Another simple way to determine the film thickness is to scratch the softbaked resist on adummy wafer with e. g. a scalpel or tweezers, and measure the depth of the scratch with asurface profilometer.Photoresists, wafers, plating solutions, etchants and solvents ...Phone: +49 731 977343 0www.microchemicals.eusales@microchemicals.eu3-MicroChemicals GmbH - Spin Coating of PhotoresistsThick Resist Films: Suited Spin ProfilesGenerally, there are two ways to attain resist film thicknesses of several 10 µm via spin coating: Either by reducing the spin speed, or by reducing the spin time.Low spin speeds, however, cause a pronounced edge bead and sometimes even prevent theresist from tearing off the substrate with a non reproducible resist film thickness as a consequence.Therefore, a much better suited spin profile for thick resist films is a high spin speed ofapprox.
2000 rpm in combination with a high acceleration of approx. 1000 rpm/s for a shorttime, such as few seconds.Multiple Coating for Thick Resist FilmsIn case of thick resist films, the rather high remaining solvent concentration after spin coating promotes softening (causing an pronounced edge bead, and reduced edge coverage)during softbake. For a homogeneous drying of the resist without significant loss in thicknesshomogeneity, we recommend a double- or multiple coating as follows:Spin CoatingRamp: 900 rpm/s*1500 rpm for 3 sSolvent Evap.20-30 min atroom temperatureSoftbake 15 min 60°CSoftbake 25 min100°CEdge BeadRemovalwith AZ ® EBRSolventSoftbake100°C for 1min/µm filmthicknessapprox.
35 µm per cycle160 µmExample: 160 µm with AZ® 9260Parameters (attained cross-section right-hand):Coating:5-fold spin coatingExposure:4.9 J/cm2 (i-line dose)Development: AZ® 400K, 10 : 38, 75 minMultiple coating requires thick resists such as AZ®9260 or AZ® 4562 with a high viscosity (= low solvent concentration).Otherwise, a second coating step will partially orcompletely dissolve the resist film coated before, thus leading to strong inhomogeneities inthe resist film thickness.Thick (Highly Viscous) Photo Resists for Thick Film Single-CoatingFor resist film thicknesses of 5-30 µm, we recommend the positive AZ® 4562 (g-, h-, and iline sensitive), or the AZ® 9260 with enhanced resolution and aspect ratio (h-, and i-linesensitive).
If a negative resist is required, the AZ® nLOF 2000 series (only i-line sensitive) isa good choice for resist film thicknesses up to approx. 20 µm.For very high resist film thicknesses up to 150 µm, the positive AZ® 40 XT i-line resist, or thenegative AZ® 15 nXT and AZ® 125 nXT i-line resists are recommended.Please contact us for further technical information!Photoresists, wafers, plating solutions, etchants and solvents ...Phone: +49 731 977343 0www.microchemicals.eusales@microchemicals.eu4-.
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