Transcript Dry etching in MEMS fabrication par Cyrille Hibert en

ÉC OLE POLY TEC HNIQU E
FÉDÉRALE D E LAUSANNE
Dry etching in MEMS
fabrication
by Cyrille Hibert
in charge of etching activities
in CMI clean room
C. Hibert, EPFL-CMI
CMI-Comlab revue, june 4th, 2002
CMI 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 reactors
Basic of ICP reactors
C. Hibert, EPFL-CMI
Plasma density and ions energy
are decoupled
CMI-Comlab revue, june 4th, 2002
Complementarity of the two ICP etchers
in CMI
chuck
Alcatel 601E
STS Multiplex
Mechanical clamping
Electrostatic clamping
Chemistry and
Fluorine: Si (anisotropic,
material to be etched isotropic), Si3N4,
CxFy: SiO2(thin film).
C. Hibert, EPFL-CMI
CMI-Comlab revue, june 4th, 2002
Cl: metal (Al, Ti, Pt) and
others Si, Saphir, AlN,
O2: Polymer,
CxFy: SiO2 (deep).
Si etching
1) Deep anisotropic etching:
• Bosch process,
• Room T continuous process,
• Cryogenic process.
2) Thin film etching.
3) Isotropic etching.
C. Hibert, EPFL-CMI
Interdigit structure etching on
SOI wafer using A601E.
CMI-Comlab revue, june 4th, 2002
Basic on Bosch process
F+ions
SF6 plasma
SiF4
masque
Si
thin fluoro-carbon
polymer film (passivation)
C4F8 plasma
ions
Si
SF6 plasma
Si
C. Hibert, EPFL-CMI
CMI-Comlab revue, june 4th, 2002
Si etching using Bosch process
- scalloping effect (on A601E)
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).
C. Hibert, EPFL-CMI
CMI-Comlab revue, june 4th, 2002
Under control
In developpment
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.
C. Hibert, EPFL-CMI
CMI-Comlab revue, june 4th, 2002
Bosch process: notching effect
Si
380 um
Si
SiO2
x min etching
notching
notching
Si
Si
SiO2
SiO2
Si
x min + overetch time
C. Hibert, EPFL-CMI
Etching through a Si wafer and
stop on SiO2 (A601E)
CMI-Comlab revue, june 4th, 2002
Room T continuous process
SF6 + C4F8
plasma
SiF4
• very good anisotropy,
• low roughness,
• low etch rate,
• well suited for low depth (<5 um).
CxFy+F+ions
Si
mask
20 °C
RIB waveguide on SOI wafer etch
in A601E (optosimox project)
thin fluoro-carbon polymer film
C. Hibert, EPFL-CMI
CMI-Comlab revue, june 4th, 2002
Cryogenic process
SiF4
O+F+ions
SF6 + O2
plasma
• No polymer contamination (reactor,
substrate),
• Low sidewall roughness (20 nm P to P),
• BUT sensible process and not so flexible
than Bosch process!
masque
Si
- 110 °C
30mm
25mm
20mm
15mm 10mm 5mm
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
Etching of different trenches width in
bulk Si (A601E).
C. Hibert, EPFL-CMI
CMI-Comlab revue, june 4th, 2002
Anisotropic etching of thin Si film
PR
polySi
SiO2
20 nm SiO2
Stop on 20 nm
gate oxide
100 nm Poly-Si
Si
Chlorine chemistry is
highly selective on SiO2
(STS Multiplex ICP)
C. Hibert, EPFL-CMI
Cryogenic process is highly
selective on SiO2
(A601E)
CMI-Comlab revue, june 4th, 2002
Si isotropic etching
Al membrane
aSi
SiO2
Isotropic Si etching
(A601E).
C. Hibert, EPFL-CMI
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.
CMI-Comlab revue, june 4th, 2002
Deep SiO2 etching (1)
CxFy
plasma
SiF4, SiF2
COx, COF2
C-F + F+ ions
Fluorcarbon polymer
deposition on sidewall
Fluorocarbon interface
on SiO2 surface.
mask
SiO2
20 °C
Key parameters: mask material, ions
flux and energy (pressure, rf source
power, DC bias), C/F ratio (chemistry).
C. Hibert, EPFL-CMI
Bulk fused silica etching (40 um
depth) on STS Multiplex ICP
CMI-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.
C. Hibert, EPFL-CMI
CMI-Comlab revue, june 4th, 2002
Under control
challenges
Deep polymer etching
O2
plasma
COx
O + ions
Passivation layer
formed by the
redeposition of sputtered
material
20 °C
mask
thick polymer layer
hold substrate
- Mask (PR, SiO2, Al, Pt),
- ER: 1 um/min.
C. Hibert, EPFL-CMI
6 um polyimide etching on
STS Multiplex ICP
CMI-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.
C. Hibert, EPFL-CMI
Pt etching using Cl2/Ar chemistry
(on STS Multiplex ICP)
• selectivity Pt:RP  1:8,
• ER: 30 nm/min.
CMI-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).
C. Hibert, EPFL-CMI
CMI-Comlab revue, june 4th, 2002