Planarisation
The flatness
In figure 3a) the initial flatness is not uniform
due to the stress ‘bow’ or ‘warp’ created by the
of the
deposition process. Approximate shape is
~10um convex with concave valleys running
wafer top
between 3 main high points.
After lapping the surface exhibits a more
layer can
uniform and flat curvature with only 2 fringes
visible (some background aberrations which can
be
be ignored from the internal reflections)
measured as 2 fringes = Ï (wavelength) = 4um
significantly
convex. Final CMP flatness is improved
by adding the pre-CMP lapping stage as in
improved
figure 4.
Figure 4 shows the result of a pre-CMP lap
to reduce
to improve the final CMP surface flatness
(above). The flatness above shows less than 1
‘bow’ and
fringe = λ/2 (wavelength) = 2um convex
The roughness generated by the lapping stage Above: Figure 3 shows a typical bench top CMP
‘warp’
also has the negative impact of degrading the tool at the Logitech laboratories.
original surface and so the CMP stage restores
effects
and improves upon the start condition. See
figure 5 a), b) and c). choice of pad/plate and abrasive type
The roughness profiles taken reflect the ring6 The surface roughness can be improved
stages of a typical p-type Silicon wafer pre and upon over the original surface by
post CMP using a Dektak 3ST surface profiler removing the original surface and any
24
and AFM to measure the Ra and RMS values. underlying damage
ring6 The flatness of the wafer top layer can
www
Conclusions: be significantly improved to reduce
.eur From the combined data on flatness, roughness, ‘bow’ and ‘warp’ effects.
oasiasemiconductor
uniformity and material removal it can be seen
that:
ring6 The material removal rates can be
significantly improved over standard
CMP processes
ring6 The WIWNU across the wafer can be
.com
Figure 4: A Grazing significantly improved while removing
Incidence microns of material
Interferometer with ring6 The ‘relief’ between hard/soft materials
square4
Issue III 2009
phase shift in one layer can be minimized due to the
analysis options
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