C. Hibert, EPFL-CMICMI-Comlab revue, june 4th, 2002 Dry etching in MEMS fabrication by Cyrille Hibert in charge of etching activities in CMI clean room

C. Hibert, EPFL-CMICMI-Comlab revue, june 4th, 2002 CMI etchers Alcatel 601ESTS Multiplex ICP Other etcher manufacturers for MEMS processing: Oxford, Unaxis, AKT (Applied Material).

C. Hibert, EPFL-CMICMI-Comlab revue, june 4th, 2002 ICP reactors Basic of ICP reactorsPlasma density and ions energy are decoupled

C. Hibert, EPFL-CMICMI-Comlab revue, june 4th, 2002 Complementarity of the two ICP etchers in CMI Alcatel 601ESTS Multiplex chuckMechanical clampingElectrostatic clamping Chemistry and material to be etched Fluorine: Si (anisotropic, isotropic), Si3N4, CxFy: SiO2(thin film). Cl: metal (Al, Ti, Pt) and others Si, Saphir, AlN, O2: Polymer, CxFy: SiO2 (deep).

C. Hibert, EPFL-CMICMI-Comlab revue, june 4th, 2002 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.

C. Hibert, EPFL-CMICMI-Comlab revue, june 4th, 2002 Basic on Bosch process SF 6 plasma C 4 F 8 plasma SF 6 plasma SiF 4 F+ions thin fluoro-carbon polymer film (passivation) Si masque ions Si etching using Bosch process - scalloping effect (on A601E)

C. Hibert, EPFL-CMICMI-Comlab revue, june 4th, 2002 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

C. Hibert, EPFL-CMICMI-Comlab revue, june 4th, 2002 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. (a)(b) Bosch process: sidewall roughness

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

C. Hibert, EPFL-CMICMI-Comlab revue, june 4th, 2002 Room T continuous process SF 6 + C 4 F 8 plasma SiF 4 C x F y +F+ions thin fluoro-carbon polymer film 20 °C Si mask RIB waveguide on SOI wafer etch in A601E (optosimox project) very good anisotropy, low roughness, low etch rate, well suited for low depth (<5 um).

C. Hibert, EPFL-CMICMI-Comlab revue, june 4th, 2002 Cryogenic process SF 6 + O 2 plasma SiF 4 O+F+ions Ultra thin layer of SiO °C Limitation of spontaneous chemical reaction and improvement of O sticking Si masque 15  m 10  m 20  m 25  m 30  m 5  m 70  m 87  m 100  m 102  m 105  m 96  m 4 inches in diameter, Si load 25 %, 40 min, 2/3 um/min Etching of different trenches width in bulk Si (A601E). No polymer contamination (reactor, substrate), Low sidewall roughness (20 nm P to P), BUT sensible process and not so flexible than Bosch process!

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

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

C. Hibert, EPFL-CMICMI-Comlab revue, june 4th, 2002 Deep SiO2 etching (1) C x F y plasma SiF 4, SiF 2 CO x, COF 2 C-F + F+ ions Fluorcarbon polymer deposition on sidewall 20 °C SiO 2 mask Fluorocarbon interface on SiO 2 surface. Bulk fused silica etching (40 um depth) on STS Multiplex ICP Key parameters: mask material, ions flux and energy (pressure, rf source power, DC bias), C/F ratio (chemistry).

C. Hibert, EPFL-CMICMI-Comlab revue, june 4th, 2002 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

C. Hibert, EPFL-CMICMI-Comlab revue, june 4th, 2002 Deep polymer etching O 2 plasma CO x O + ions Passivation layer formed by the redeposition of sputtered material 20 °C thick polymer layer mask hold substrate 6 um polyimide etching on STS Multiplex ICP - Mask (PR, SiO2, Al, Pt), - ER: 1 um/min.

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

C. Hibert, EPFL-CMICMI-Comlab revue, june 4th, 2002 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).