CMI etchers
description
Transcript of CMI etchers
C. Hibert, EPFL-CMI CMI-Comlab revue, june 4th, 2002
Dry etching in MEMS Dry etching in MEMS fabricationfabrication
by Cyrille Hibertby Cyrille Hibert
in charge of etching activities in charge of etching activities in CMI clean roomin CMI clean room
É C O L E P O L Y T E C H N I Q U EF É D É R A L E D E L A U S A N N E
C. Hibert, EPFL-CMI CMI-Comlab revue, june 4th, 2002
CMI etchersCMI etchers
Alcatel 601E STS Multiplex ICP
Other etcher manufacturers for MEMS processing: Oxford, Unaxis, AKT (Applied Material).
C. Hibert, EPFL-CMI CMI-Comlab revue, june 4th, 2002
ICP reactorsICP reactors
Basic of ICP reactors Plasma density and ions energy are decoupled
C. Hibert, EPFL-CMI CMI-Comlab revue, june 4th, 2002
Complementarity of the two ICP etchers Complementarity of the two ICP etchers in CMIin CMI
Alcatel 601E STS Multiplex
chuck Mechanical clamping Electrostatic 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-CMI CMI-Comlab revue, june 4th, 2002
Si etchingSi 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-CMI CMI-Comlab revue, june 4th, 2002
Basic on Bosch processBasic on Bosch process
SF6 plasma
C4F8 plasma
SF6 plasma
SiF4F+ions
thin fluoro-carbon polymer film (passivation)
Si
Si
Simasque
ions
Si etching using Bosch process - scalloping effect (on
A601E)
C. Hibert, EPFL-CMI CMI-Comlab revue, june 4th, 2002
Bosch process on A601EBosch 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-CMI CMI-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 Bosch process: sidewall roughnessroughness
C. Hibert, EPFL-CMI CMI-Comlab revue, june 4th, 2002
Bosch process: notching effectBosch process: notching effect
Si
Si
SiO2
Si
Si
SiO2
notchingx min etching
x min + overetch timeEtching through a Si wafer and
stop on SiO2 (A601E)
SiO2
Si
380 um
notching
C. Hibert, EPFL-CMI CMI-Comlab revue, june 4th, 2002
Room T continuous processRoom T continuous process SF6 + C4F8
plasmaSiF4
CxFy+F+ions
thin fluoro-carbon polymer film
20 °CSi
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-CMI CMI-Comlab revue, june 4th, 2002
Cryogenic processCryogenic process
SF6 + O2 plasma
SiF4
O+F+ions
Ultra thin layer of SiO2
- 110 °C
Limitation of spontaneous chemical reaction and improvement of O sticking
Si
masque
15 m 10 m20 m25 m30 m5 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-CMI CMI-Comlab revue, june 4th, 2002
Anisotropic etching of thin Si filmAnisotropic etching of thin Si film
20 nm SiO2
100 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
polySiSiO2
Si
C. Hibert, EPFL-CMI CMI-Comlab revue, june 4th, 2002
Si isotropic etchingSi 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-CMI CMI-Comlab revue, june 4th, 2002
Deep SiO2 etching (1)Deep SiO2 etching (1)
CxFy plasma
SiF4, SiF2
COx, COF2
C-F + F+ ions
Fluorcarbon polymer deposition on sidewall
20 °CSiO2
maskFluorocarbon interfaceon SiO2 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-CMI CMI-Comlab revue, june 4th, 2002
Deep SiO2 etching (2)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-CMI CMI-Comlab revue, june 4th, 2002
Deep polymer etchingDeep polymer etchingO2
plasma COx
O + ions
Passivation layerformed 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-CMI CMI-Comlab revue, june 4th, 2002
Metal etchingMetal 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-CMI CMI-Comlab revue, june 4th, 2002
ConclusionConclusionCMI 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).