Surface analysis of bond pad flower-like defects in wafer fabrication
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Date
2004-04
Authors
Lim, Boon Hoe
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Abstract
The flower-like defects (FLD) at integrated circuit (Ie) bond pads will cause yield
and reliability problems in wire bonding process such as non-stick bond pad and bond
pad corrosion. The objec.ti ve of this research is to perform in-depth surface and profile
characterization on the FLD so that its root cause and mechanism of formation are
understood in order to recommend possible preventions and solutions. The FLD were
analysed with optical microscopy and surface analytical techniques such as SEM,
quantitative EDS, FIB cross sectioning and grain imaging contrast and its potential to
grow was closely monitored. The EDS analysis result revealed high fluorine and
oxygen content on FLD. Fluorine residual from plasma etch process gases on bond
pads and wet cleaning inefficiency are the root causes. Aluminium reacts with
fluorine and then with water or moisture to gradually and progressively form
compounds mixture of AIF3 (aluminium fluoride), AI(OF)x (aluminium oxy-fluoride),
AI(OH)3 (aluminium hydroxide) and AIF3.xH20 (aluminium fluoride hydrate) on
bond pads that eventually delaminate from the surface. Possible preventions and
solutions employed were cleaning efficiency improvement, stringent wafer storage
conditions li!<e vacuum-sealed with moisture barrier bag and kept in nitrogen-purged
cabinet and environmental factors (relative humidity, temperature and air-flow)
controlled. With these measures, no FLD were seen on bond pads after 10 1 days in
nitrogen-purged cabinet.
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Keywords
The flower-like defects (FLD) at integrated circuit (Ie) bond pads , will cause yield and reliability problems in wire bonding process