IEC 62418 pdf download – Semiconductor devices – Metallization stress void test
1 Scope
This International Standard describes a method of metallization stress void test andassociated criteria.lt is applicable to aluminium (Al) or copper (Cu) metallization.
This standard is applicable for reliability investigation and qualification of semiconductorprocess.
2Test equipment
A calibrated hot chuck or thermal chamber is required to subject the wafers or packaged teststructures to the specified temperature (15 °C) for the specified time. For resistancemeasurements dedicated equipment is needed.For void inspection deprocessing equipmentis required to remove the scratch protection layer. The inspections are performed with ascanning electron microscope (SEM).
3Test structure
3.1 Test structure patterns
Test structures shall be used for all metal layers which have to be inspected and severaldifferent types of structure may be used. The following two types of test structures areapplicable for this test standard.
NOTE For metallization without refractory shunt layers reflective notching at steps can occur in test structureswith underlying topography, which will therefore tend to indicate a relatively worse stress-voiding behaviour.
3.2Line pattern
Parallel lines which are patterned at the minimum linewidth allowed by design form anappropriate test structure. Unless otherwise specified a minimum length of 500 um and a totallength of 1 cm to 1 000 cm are recommended condition. Single long isolated lines arerecommended because stress voiding is often sensitive to line-to-line separation.
NOTE 1 Narrow lines are susceptible for stress voiding because the stress in the metal is typically higher innarrower lines than in wider lines.
NOTE 2 The line length should be sufficient to insure that void nucleation sites will exist.3.3Via chain pattern
3.3.1 Pattern types
A via chain pattern is applicable as a test structure.For technology investigations a Kelvin-pattern for four-point measurements may also be used.
3.3.2 Pattern for aluminium (Al) process
Via chains need to consist of a pattern of vias connected by minimum linewidth. Therecommended number of vias is between 1 000 and 100 oo0. it is recommended to useisolated and long minimum linewidths.
3.3.3 Pattern for copper (Cu) process
For Cu metallization the following structures are applicable:
a) via chains with top and bottom metal segments with minimum allowed width;
b) via chains with either the top or the bottom metal segment at minimum allowed width, and
the other segment at the maximum width allowed for a single via;
c) vias chains with both top and bottom metal segments at the maximum width allowed for a
single via;
d) Kelvin via structures,with various widths for top and bottom metal.Chains with 1 0o0 – 100 ooo vias are recommended.
4stress temperature
To evaluate the impact of stress voiding on chip reliability under use conditions, acceleratedtesting is needed to generate voiding.The acceleration factor can be strongly affected by thefactors listed in Annex B and Annex C. Therefore, it is recommended to determine empiricallythe temperature range for accelerated testing which will maximize voiding.Recommendedtemperature ranges are given in 5.2 and 5.3.
5Procedure
5.1Stress void evaluation methods
Two methods are specified for the metallization stress void test: a resistance measurementmethod and a visual inspection method.
-The resistance measure method is the default method.
– The inspection method is applicable for use as a verification when no stress voiding is
expected. It cannot be used for lifetime extrapolations.This method is not applicable to cCumetallization.The inspection method shall not be used in case the visibility of voids isinsufficient (see Note 2.)
NOTE1 The test method most likely to detect sensitivity to stress voiding and the one most usually conducted isconstant temperature (isothermal) aging，i.e.，annealing or baking at temperatures between the passivationdeposition temperature and the intended use temperature of the product.
NOTE2 This is the case for e.g. metallization with multiple metal levels,where the lower levels are not clearlyvisible, masking of voids by other process features.
5.2Resistance measurement method
This method assumes the void growth and therefore resistance changes can be modelled, toobtain an acceleration factor for void growth [1，2] 1 . Unless otherwise specified，thetemperature condition shall be determined within the range of 150 °C to 275 C. Samplesneed to be separated into each temperature condition group and each group to be baked atthe specified temperature.The procedure for resistance measurement is the following.
a) Measure the resistance of the metal line or via chain.Resistance measurements shall be
made at currents that minimize joule heating.
IEC 62418 pdf download – Semiconductor devices – Metallization stress void test
