Fabrication Process Details

See below for alignment marks and mask layouts.

Wafer Cross-Section Step Notes/Details

after Step (2)

(1) RCA clean standard <100> 6" Si wafer
machine: rca-ICL (ICL)

oxidation recipe "4W1000" details:
-- wet oxide
-- 45 min. @ 1000° C
-- total recipe time: approx. 3hrs, 35 min.

take wafers straight to coater track after diffusion tube


(2) deposit 300-400nm thermal SiO2
machine: (ICL tube) 5D-ThickOx

after Step (3)
(3) photolithography:
Mask 1 – "KOH TIPS"
machines: coater6 (ICL), EV1 (TRL)

coater6: 1.2um recipe using SPR700 resist (2000RPM spin for 30 sec. gives 1.2um)

EV1: 2.0 sec. exposure
90 sec. LDD-26W developer; 30 min. postbake @ 120° C

after Step (4)

(4) etch windows in oxide - ~5 min. BOE
then strip resist – 10 min piranha
machine: acid-hood (TRL)

(last run did 4.5 min. BOE, then 10 min. piranha resist strip)

after Step (5)
(5) etch Si pits in KOH (depth ~15-20um), ~30min.
machine: ***KOH bath (Manalis Lab)***

after Step (6)
(6) post-KOH clean & oxide strip:
1. double piranha clean
-- 10 min. in yellow-dot fabware
-- then 10 min. in green-dot fabware

2. ~6 min. BOE in green-dot fabware (cleans + strips oxide)
machine: acid-hood (TRL)

after Step (8)
(7) RCA clean to prepare for SiNx deposition
machine: rca-ICL (ICL)
(8) deposit 800nm low-stress SiNx
machine: VTR (ICL)
measure nitride film thickness using UV1280 on five wafers spread throughout lot -- need ave. and range

after Step (9)

(9) photolithography:
1. front side: Mask 2 - "SINBOND FRONT"
2. back side: paint ~5mm wide ring of photoresist around outer edge of wafer
machines: HMDS-TRL, coater, EV1 (TRL)

HMDS: thumbwheel at 4
coater: spin at 2000 RPM for 1.1um resist

exposure: 3 sec. & use hard contact to make sure fingers come out

develop: 1 min. 15 sec.

after Step (10)
(10) etch silicon nitride, front and back
then strip resist
machine: AME5000, Chamber A (ICL), asher (ICL)

recipe: NITRIDE CF4
(50mTorr, 8 sccm CF4 and 6sccm 02, 100 Gauss magnetic field; selectivity to resist is ~2:1)

etch rates:
front side: ~31A/sec
back side: ~25A/sec

time to clear (from prev. run):
- back side 330 sec. for 8200 A, 360 sec. for 8500A
- front side 260 sec. for 8200A, 290 sec. for 8500A


after Step (11)

(11) photolithography:
Mask 3 – "GLASS ETCH"
machine: coater, EV1 (TRL)

after Step (12)

(12) etch Pyrex (2-3um deep) 20-30min. BOE
then strip resist - 10 min. piranha
machine: acid-hood (TRL)

(BOE may be too slow and resist may lift off too much in the 20-30 min. necessary)

good alternative may be Water/HF/Nitric Acid mixture, in ratio of 65%, 20%, 15% (Pyrex etch rate approx. 0.8um/min)

after Step (13)

(13) coat both sides of Pyrex with 3um thick resist to protect during diesawing
machine: coater (TRL)
pre-bake only, no need to postbake -- easier removal after diesawing done

after Step (14)

(14) diesaw wide lanes in Pyrex ~300um deep
machine: diesaw (ICL)
use special 1mm extra wide blade - Disco: P1A862 SDC320N50BR50 56x1.0x40

after Step (16)

(15) strip protective resist with acetone in red-dot solvent beaker
machine: photo-wet-Au (TRL)
use dirtiest red-dot beaker you can find
(16) double piranha clean after diesaw
machine: acid-hood (TRL)

after Step (17)

(17) align and anodically bond Pyrex and Si wafers
machine: EV501-620 (TRL)
need to do piranha before bonding each pair of wafers

after Step (18)

(18) saw borders of device dies, leaving 20-50um of glass uncut
(use regular-width glass blade 200um)
machine: diesaw (ICL)


after Step (19)

(19) release cantilevers by dissolving bulk Si
machine: ***KOH bath (Manalis Lab)***

Alignment Marks

Mask 1: KOH TIPS

All masks superimposed