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CMI etchers

Dry etching in MEMS fabrication by Cyrille Hibert in charge of etching activities in CMI clean room. CMI etchers. Alcatel 601E. STS Multiplex ICP. Other etcher manufacturers for MEMS processing: Oxford, Unaxis, AKT (Applied Material). ICP reactors. Basic of ICP reactors.

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CMI etchers

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  1. Dry etching in MEMS fabricationby Cyrille Hibertin charge of etching activities in CMI clean room CMI-Comlab revue, june 4th, 2002

  2. CMI etchers Alcatel 601E STS Multiplex ICP Other etcher manufacturers for MEMS processing: Oxford, Unaxis, AKT (Applied Material). CMI-Comlab revue, june 4th, 2002

  3. ICP reactors Basic of ICP reactors Plasma density and ions energy are decoupled CMI-Comlab revue, june 4th, 2002

  4. Complementarity of the two ICP etchers in CMI CMI-Comlab revue, june 4th, 2002

  5. Si etching • 1) Deep anisotropic etching: • Bosch process, • Room T continuous process, • Cryogenic process. • 2) Thin film etching. • 3) Isotropic etching. Interdigit structure etching on SOI wafer using A601E. CMI-Comlab revue, june 4th, 2002

  6. SiF4 F+ions SF6 plasma masque Si thin fluoro-carbon polymer film (passivation) ions C4F8 plasma Si SF6 plasma Si Basic on Bosch process Si etching using Bosch process - scalloping effect (on A601E) CMI-Comlab revue, june 4th, 2002

  7. Bosch process on A601E • State of the art at CMI: • Anisotropy at 90° (vertical sidewall), • Etching uniformity (2 % to 5 %), • Selectivity Si:SiO2 (1:200 to 400) et Si:RP (1:100 to 200), • Etching rate: 6 to 12 um/min (loading effect + ARDE), • Sidewall roughness (actual process developpment), • Notching (hardware modification + process developpment). Under control In developpment CMI-Comlab revue, june 4th, 2002

  8. Bosch process: sidewall roughness (a) (b) Sidewall roughness at the top of a deep anisotropic etching of Si (Bosch process on A601E) as a function of pulse duration: (a) SF6/C4F8 = 7s/2s (b) SF6/C4F8 = 3s/1s. CMI-Comlab revue, june 4th, 2002

  9. Si Si SiO2 Bosch process: notching effect 380 um x min etching notching notching Si Si SiO2 Si SiO2 Etching through a Si wafer and stop on SiO2 (A601E) x min + overetch time CMI-Comlab revue, june 4th, 2002

  10. SF6 + C4F8 plasma SiF4 CxFy+F+ions mask 20 °C Si thin fluoro-carbon polymer film Room T continuous process • very good anisotropy, • low roughness, • low etch rate, • well suited for low depth (<5 um). RIB waveguide on SOI wafer etch in A601E (optosimox project) CMI-Comlab revue, june 4th, 2002

  11. SiF4 O+F+ions masque SF6 + O2 plasma m m m m m m m m m m m m 96 87 70 100 105 102 Si - 110 °C m 5 m m 10 m m 15 m m 20 m m 25 m m 30 m 4 inches in diameter, Si load 25 % , 40 min, 2/3 um/min Ultra thin layer of SiO2 Limitation of spontaneous chemical reaction and improvement of O sticking Cryogenic process • No polymer contamination (reactor, substrate), • Low sidewall roughness (20 nm P to P), • BUT sensible process and not so flexible than Bosch process! Etching of different trenches width in bulk Si (A601E). CMI-Comlab revue, june 4th, 2002

  12. Anisotropic etching of thin Si film 20 nm SiO2 PR polySi Stop on 20 nm gate oxide SiO2 100 nm Poly-Si Si Chlorine chemistry is highly selective on SiO2 (STS Multiplex ICP) Cryogenic process is highly selective on SiO2 (A601E) CMI-Comlab revue, june 4th, 2002

  13. Al membrane aSi SiO2 Si isotropic etching Largely used process for metal membranes releasing, More efficient dry release compare to polymer sacrficial layer, Carateristics: • Undercut etch rate can reach 7 um/min (for 1 um aSi), • Selectivity Si:SiO2 > 1000, • lateral aspect ratio > 200. Isotropic Si etching (A601E). CMI-Comlab revue, june 4th, 2002

  14. SiF4,SiF2 COx, COF2 CxFy plasma C-F + F+ ions Fluorcarbon polymer deposition on sidewall mask Fluorocarbon interface on SiO2 surface. SiO2 20 °C Deep SiO2 etching (1) Key parameters: mask material, ions flux and energy (pressure, rf source power, DC bias), C/F ratio (chemistry). Bulk fused silica etching (40 um depth) on STS Multiplex ICP CMI-Comlab revue, june 4th, 2002

  15. Deep SiO2 etching (2) • Discussion: • Anisotropy (vertical sidewall), • Masque material (PR, aSi, Al, Cr, Ni…), • Selectivity SiO2:mask (C/F, pressure, DCbias), • Reactor contamination (hardware problem), • Etch rate (till 1 um/min), • Roughness and slope sidewall, • Increase the aspect ratio. Under control challenges CMI-Comlab revue, june 4th, 2002

  16. O2 plasma COx O + ions Passivation layer formed by the redeposition of sputtered material mask 20 °C thick polymer layer hold substrate Deep polymer etching • Mask (PR, SiO2, Al, Pt), • ER: 1 um/min. 6 um polyimide etching on STS Multiplex ICP CMI-Comlab revue, june 4th, 2002

  17. Metal etching • Pt etching using Cl2/Ar chemistry (on STS Multiplex ICP) • selectivity Pt:RP  1:8, • ER: 30 nm/min. • AlSi etching using Cl2/BCl3 chemistry (on STS Multiplex ICP) • selectivity Al:RP  2:1, • ER: 0.2 to 0.5 um/min. CMI-Comlab revue, june 4th, 2002

  18. Conclusion • CMI etching process evolution: • Maintaining existing processes (Si, SiO2, Si3N4, Polymer, Al, Pt, Ti, AlN, Saphir), • Deep Si etching : sidewall roughness. • Equipements evolution: • A601E Upgrade for notching control (Si etching), • Etcher dedicated to silice: • At the present time done on the 2 ICP not dedicated for this, • Increased ask for deep silica etching (microchannel, waveguide, holes), • Exclusive equipement (new internal/external pojects). CMI-Comlab revue, june 4th, 2002

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