Johnny,

Is your question regarding etching oxide (SiO2) without affecting Aluminum,
I have a small list of different etchants both wet and dry compiled from
various sources which are listed below. The same list is also included as a
pdf file.

Hope this helps,
Sunil Kumar

MuSquared, Inc
[email protected]

Oxide Etch without etching Aluminum

      Etchant
     Oxide Etch Rate (nm/min)[*]
     Aluminum Etch Rate (nm/min)
     Selectivity

      Wet etching




      73% HF [1], [2]
     1500
     2.2
     680

      73% HF:IPA (1:1)
     833
     12
     69

      73% HF:IPA (1:2)
     167
     18
     9






      49% HF [3]
     2300
     4.2
     547






      40% HF [2]
     844
     68
     12

      40% HF:IPA (1:1)
     400
     122
     3

      40% HF:IPA (1:2)
     233
     145
     1.6






      BHF/Glycerol [4]
     95
     .55
     170






      Olin 777 Etch, NH4F based [5]
     Olin



      Pad Etchant [6], [7]
     Pad Etch IV from Ashland



      BOE, Transene [8]

     45-50 (BOE)


      NH4F + CH3COOH+H2O
     Add propylene glycol to save Al








      Dry etching [8]




      RIE in CF4 plasma




      RIE in SF6, CHF3, CF4, 10% O2




















[1]. Micromachined Transducers Sourcebook, Gregory Kovacs, Section 6.1.2,
88-89



[2]. Sacrificial Oxide etching compatible with Aluminum metallization, P.T.J
Gennisen, P.J French, Transducer’s 97

[3].
http://mail.mems-exchange.org/pipermail/mems-talk/2001-November/005515.html,
Kirt Williams, [email protected]

[4]. CMOS foundry based micromachining, Harrie A C Tilmans, Kris Baert,
Agnes Verbist and Robert Puers, MME’ 95 & J. of Micromechanics and
Microengineering, 6(1996) 122-127

[5].
http://mail.mems-exchange.org/pipermail/mems-talk/2001-November/005528.html

Olin makes something called 777 Etch, which contains acetic acid, ammonium
fluoride, ethylene glycol, and water.  It is intended for use in etching
SiO2 to open up bond pads. It supposedly doesn't attack the aluminum as HF
based etches do.[6].
http://mail.mems-exchange.org/pipermail/mems-talk/2001-November/005523.html

[7]. Double pass metallization for CMOS Aluminum, Johannes B¨uhler, J¨org
Funk, Jan G. Korvink, Franz-Peter Steiner,  Pasqualina M. Sarro, and Henry
Baltes, Transducers’ 95 360-363

[8]. http://mail.mems-exchange.org/pipermail/mems-talk/1999-June/002533.html

Isotropic etch recipe for silicon dioxide without attacking aluminum.


----------------------------------------------------------------------------
----

[*] Etch rates are for thermal oxide, which etches 12 times slower than
PECVD oxide in dilute HF [1]



----- Original Message -----
From: "HE,Han(Johnny)" 
To: 
Sent: Tuesday, February 25, 2003 6:26 PM
Subject: [mems-talk] Wet etchant not attack Al and SiO2


Hi,
Just wondering if there is any special wet etchant recipe (Such as TMAH+Si
powder+NH4S2O8) will not attack Al and SiO2 respectively.
Thanks.
Johnny
===========================================
Johnny H.HE,  Ph.D. Candidate
Division of Electrical Engineering, Engineering
Department,Cambridge University,CB2 1PZ, UK
or Downing College, Cambridge, CB2 1DQ ,UK
Email: [email protected]
Tel:+44 1223 332605 Fax:+44 1223 332662
===========================================



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