Planarisation
The test wafers were measured for flatness; Figure 2: Lapping
surface roughness and starting thickness before machine fitted with
processing. The wafers were then split into two abrasive cylinder and
sets where set a) were put through a pre-CMP lapping plate.
lapping stage and an identical set b) were
processed directly by CMP. The results were then
analysed and compared in section 4.
Process
The process stages were followed as listed:
ring6 Measurement and analysis of the start
Issue III 2009
conditions
square4
ring6 Pre-CMP lap of the wafer surface to
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remove the bulk of the material and
leave sufficient thickness to CMP
process to remove the subsequent
lapping surface and surface damage optimized by empirical trials and are contained
ring6 After cleaning all lapping debris the in Table 3.
wafer was then CMP processed to the The CMP process was carried out on a
final thickness and surface conditions as bench top CMP tool as highlighted in figure 3.
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detailed on the results section 4. The flatness interferograms are captured
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ring6 The results were tabulated and from a Grazing Incidence Interferometer (See
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compared to the start value data figure 4).
By initially measuring the start conditions of the
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wafers, the total thickness of the blanket layers Results
and the substrate material was recorded below. Flatness images are showing Newton’s rings,
See table 1 and the final values added in the light bands or fringes of interference. The source
results section 4. is from a grazing incidence interferometer which
The wafer was mounted into a lapping has the advantages of allowing the capture of
chuck ,(Figure 1). interferograms from non polished surfaces. The
The lapping machine (Fgure 2) was prepared negative consequence of this reduces the
with appropriate slurry before placing the accuracy of the fringe spacing from 0.335um to
lapping chuck on the lapping plate of the 2um per fringe.
machine. As the flatness of the wafers is greater than
The key factors which dictate the speed of 1um then this does not affect the quality of the
material removal and final surface results are measured results.
split into machine parameters and process
variables and are displayed in Table 2 a and b.
The lapping process variables were
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