Development and Characterization of an Integrated Thick Resist Film Processing ToolD. Goustouridis1, I. Raptis1, E. Valamontes2, I. Karanikas3,

N. Tsikrikas1 , M. Chatzichrisitidi1,4

1Institute of Microelectronics, NCSR ‘Demokritos’, Athens, 15310 Greece2 Department of Electronics, TEI of Athens, 12210 Aegaleo, Greece

3 Datec Electronics S.A. Dorieon 28, Athens 11852, Greece 4 Chemistry Department, University of Athens, Zografou 15771, Greece

E-mail: mchatzi@chem.uoa.gr

Spreader set-up

IntroductionIntroduction: In micromachining – microsystems applications the patterning of resist films with thickness of several tens of microns is common. The processing conditions of such thick resist films are quite different from the ones used in mainstream microelectronics. For example in the case of SU-8 the Post Apply Bake (PAB) should be done in two different temperatures. In this direction several processing tools have been developed, e.g. [1]. In addition, for the preparation of thick films, more than one spin coating steps are required.In the present work a thick resist film processing tool capable to resist application, PAB and PEB is presented and applied in case of the UV-patterning of thick epoxy based resist films.

Photo of the spreader set-up

Computer communication port

Leveling mechanism

Computer software

Spreader

Temperature controller

Experimental procedureTwo epoxy based CARs capable to form high viscosity solutions were investigated.A)TADEP resist [2,3] with Propylene Glycol Methyl Ether Acetate (PGMEA) as casting solvent andB)SU-8 2015 with Gamma Butyrolactone (GBL).

TADEP was used for 25μm thick films and SU-8 for 100 μm thick films (this SU-8 formulation is used for max. 40μm thick films with spin coating).

ResultsWafer Uniformity

24.3μm

24.6μm

24.5μm

24.9μm

24.6 μm

97.9μm

100.6μm

99.3μm

100.1μm

100.6 μm

99.7μm

102.3μm

101.8μm

102.8μm

101.9 μm

Casting Solvent EvaporationBlade

Wafer holder and hot plate

Leveling mechanism

Interferometer module

TADEP SU-8PAB 60°C/30min +

100°C/60min65°C/5min + 95°C/20min

Micrometers Adjustment

100 μm 200 μm

Exposure (365nm) 1100 mJ/cm2 250 mJ/cm2

PEB 95°C/8min 65°C/2min + 95°C/10min

Development TMAH/10min PGMEA/12minFinal Thickness 25.6 μm 99.4 μm

Inside the spreader

Lithographic Results

TADEP resist. Top-down optical micrograph. Line-width is 5 μm and the resist thickness is 25 μm.

SU-8 resist. Top-down optical micrograph. 10 μm squares and circle diameter. The resist thickness is 100 μm.

Wafer uniformity for a) TADEP resist b, c) SU-8 resist. The wafer uniformity maximum deviation is 1.4% and the spreader repeatability is 1.9%

Conclusions: In the present work, a thick resist film processing tool capable of resist application and PAB was presented and applied in case of the UV-patterning of thick resist films. This particular tool could be equipped with UV-exposure capability in the future allowing the complete processing of the thick resist films except the development-drying steps that allowing the penetration of micromachining technology in research labs without easy access in conventional lithography equipment.References1. G. Bleidiessel, G. Gruetzner, F. Reuther, S. Fehlberg, B. Loechel, A. Maciossek Microelectron. Eng. 41-42

433(1998)2. M. Chatzichristidi, I. Raptis, P. Argitis J. Everett, J. Vac. Sci. Technol. B 20, 2968 (2002)3. M. Chatzichristidi, E. Valamontes, P. Argitis, I. Raptis, J.A. van Kan, F. Zhang, F. Watt Microelectron. Eng. 85 945

(2008)

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TADEPTADEP SU-8 2015SU-8 2015

TADEP resist has PGMEA (b.p. 146°C) as casting solvent whereas SU-8 has GBL (b.p. 205°C). TADEP shows a high evaporation in the first 5min (~100nm/sec), then the evaporation rate decreases and when the temperature reaches 100°C the rate initially increases and then is very low. SU-8 has a slower evaporation rate in the beginning (~30nm/sec) at 65°C that decreases with time (~12nm/sec) and then it increases again with temperature elevation (~35nm/sec) and after 3min at 95°C it is very low.Processing Conditions

Acknowledgments: This work was partially financially supported by Greek Secretariat for Research & Technology through the 05-NONEU-467 (Greece-Singapore project).