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3D inspection algorithm
An envelope of interference signal acquired from the interferometer is calculated
using a four-bucket algorithm [3]. The general expression of the interference pattern
acquired by interferometry is shown in Figure 4.
The light intensity of the shifted interference pattern is defined as follows:

where D is the mean intensity, γ is the visibility, is the phase of the
interferogram, and δ 0 is the phase shift.
The light intensity of each phase in the case of a 90 degree phase shift is given by: Figure 4: Interference pattern calculation using a
four-bucket algorithm.
on a 99.73% probability that the standard
deviation for any given bump height
Using a four-bucket algorithm, the amplitude is calculated as follows, result will be less than σ worst . The results
where u is the amplitude. of σ RPT for three chips are 0.714μm,
0.708μm, and 0.724μm. An example of
Finally, the envelope peak of the interference signal is detected by a centroid 3σ for one sample is shown in Figure
algorithm [4]. 5a.
We have also compared results of
Measurement results three samples measured by WSI and
In order to evaluate the WSI system, the bump height repeatability based on 30 a reference system using the confocal
measurements is calculated for every bump. Because each chip comprises tens of principle [5]. A comparison of the
thousands of interconnects, we focus on the distribution of standard deviations for bump height measurement using two
every bump measured. Following this principle, σ RPT is represented by the statistical systems is shown in Figure 5b. The
upper three-sigma limit of the sigma distribution. The repeatability sigma is assessed bump height process specification is
based on σ RPT ≡σ worst =ave σi +3σ σi where σ worst is the worst-case standard deviation based equal to 45μm±4.5μm. Correlation of
measured data has the bump height
2
R =0.89 with a mean difference less
than 1μm, which shows measurement
matching of the two systems.
WSI is sensitive to vibration, so it is
necessary to correct the scan steps by
using an anti-vibration system during
scanning. To overcome this issue, we
are now working on dispersive white-
light interferometry (DWI), which
uses spectral imaging to extract high
vertical resolution without vertical
For over a decade, Technic’s Elevate scanning. For a DWI system, the Z
®
Chemistry has risen to meet the accuracy depends on the spectrometer
greatest challenges of our industry se n sit iv it y a nd t he fa st Fou r ie r
with innovation, expertise, exceptional transform (FFT) method. Therefore,
analytical support, and the best DW I w i l l p r ov id e h ig he r s p e e d
customer service in the industry. and accuracy for in-line inspection
as applied to the sem iconductor
• Electroplating Solutions for mounting process.
Copper
Nickel & Tin 3D interconnect inspection
Precious Metals parameters
In this section, inspection parameters
• Photoresist Strippers o f i n t e r c o n n e c t / bu m p h e i g h t ,
• Metal Etchants coplanarity, and CAW are explained
• Post Etch Residue Removers to overcome challenges of large form
factor multi-chip packaging. One main
challenge is how to assure successful
die bonding conditions before silicon
die attach to the expensive multi-chip
package. Three key parameters are
Learn more at www.technic.com defined as follows:

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