Hi Inge,
Regarding the various elements seen with EDX analysis: small amounts of C are unavoidable - too high an amount would obviously indicate an organic contaminant; Cu is commonly present in Al bond pads at up to 2%; O is the unavoidable indicator of Al2O3 or an aluminum hydroxide; Cl is clearly undesirable but common at very low levels; Fe is not expected; F could be the source of your problem. F contamination of bond pad surfaces, and formation of aluminum fluoride species (stoichiometrically AlF3, or possibly a hydrate form of aluminum fluoride) could be a real problem. Fluorinated plasmas are often used to create passivation openings to expose the Al bond pad. The fluorine / fluoride has a bad effect on formation of the desired Al-Au intermetallics needed for adhesion of the ball bond. So my first guess is that you have a fluorine problem, but knowledge about the quantity of the contaminants is key. Regarding the unusual microstructure of the pad, the Cu added to the Al pad metallurgy can concentrate at intersections of 3 Al grains in the pad microstructure. The etch rate of the Al and Cu can be different with plasma resulting in etch pits. Another source of possible etch problems is at the wafer dicing operation. The cooling water can cause some pad surface etching if it is not maintained properly. CO2 is commonly bubbled through the water making it slightly acidic to help avoid ESD and other problems. Sometimes a dicing surfactant is used to help clean the wafer after dicing to remove Si particles. The surfactants should not impede good wire bonding, but if an excessively thick organic surfactant layer formed, it may be a problem. The surfactant layer thickness should be quite stable with surfactant content in the water but it may be worth considering. The cooling water is also a potential factor since some chill the water and others do not. I suggest you perform some scanning Auger electron analysis and get depth profiles of the contaminants to see if you learn more.
Best regards,
Leo
Leo M. Higgins III, Ph.D.
Sr. Vice President, Engg and Technology
ASAT, Inc.
13809 Research Blvd., Suite 635
Austin, Texas 78750
office phone 512-249-4758
mobile 512-423-2002
[log in to unmask]
www.asat.com
-----Original Message-----
From: TechNet [mailto:[log in to unmask]]On Behalf Of Hernefjord Ingemar
Sent: Thursday, September 06, 2007 9:01 AM
To: [log in to unmask]
Subject: [TN] Semi guys, need support
25 micron gold ball bonding bad yield, ball lifts, poor adhesion on Al
pads. Triple diff line tranceiver chip. Weird micrographic exteriour,
EDAX gives C,F,O, Cl,Cu,Al,Fe. Cu can be ppm alloy but the others
unwanted on semi chip bond pads I think. 1kV SEI SEM reveals strange
superficial structure. Chip not contaminated by us, fresh opened chip
trays show this face. Question: what semi manufacturing problem can this
be? Will post a few pics to Steve's gallery.
TrikeMan?
/Inge
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