Kinetics of Copper Drift in Lowk

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Kinetics of Copper Drift in Low-k Polymer
Interlevel Dielectrics
Standford University Alvin L. S. Loke, Student
Member, IEEE IEEE Trans. On Electron Devices
(1999)
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Introduction
For reliable integration with existing backend
oxide dielectrics, Cu must be encapsulated with
barrier materials. Although thermal diffusion of
Cu in oxide may be negligible at metallization
process temperatures(lt400?), positive Cu
ions drift rapidly through oxide in the presence
of an electric field even at low temperatures.
During BTS (150?275? up to 1.5MV/cm) current-ti
me(I-t), current-voltage(I-V), time-to-failure(TTF
) measurement
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Experiments
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Results
Interface-related C-V instabilities
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Oxide-sandwiched
Al does not drift into oxide
Oxide capping layer, SiH4/N2O rather than SiH4.O2
Poly(arylene ether), aromatic hydrocarbon, Fluorin
ated polyimide, benzocyclobutene, Parylene-F
1000? to form a stable, high-quality
interface with the Si substrate
All BTS experiments and C-V measurements are
conducted without breaking The N2 ambient. ? This
ensures that the exposed Cu electrodes do
not Oxidize during heating and that the polymer
films do not take up moisture Throughout the
testing sequence. Increase polarization in the
dielectric and Give rise to anomalous C-V
hysteresis and increased capacitance.
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At 200? for 1h under various gate biases
Cu ions
Alkali ions
PAE k2.8
polymer/oxide
FPI k2.6
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BCB k2.6
At 300? using SiH4/NH3
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Model of copper drift kinetics
Singly ionized Cu ions(CU) are Assumed to be
injected since the Product of diffusivity and
solid solubility Of Cu in oxide is
insignificant Compared to that of Cu in oxide.
At 200?
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Thermal-oxide
Low-k
Thermal-oxide
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Extraction of copper drift rates
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Time-dependent dielectric breakdown(TDDB)
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Discussion
Cu drift barrier property fluorinated polyimide
lt poly(arylene ether) lt SiLKTM lt parylene-F lt
benzocyclobutene

• Among the polymers, the differences in observed
  Cu drift rates reflect interactions
• between Cu ions and the local chemical
  environments of the polymers.
• Crosslinking by minimizing the free volume in the
  polymer
• Polarity in the polymer -gt The mobility of Cu
  ions should be enhanced by
• polar groups in the polymer behaving as centers
  of strong partial charge(?-) that
• can attract Cu ions electrostatically.(Consider
  the oxygen atoms incorporated
• in various polymers.)
• ? The carbonyl (CO) oxygen in FPI-136M is very
  polar and may be responsible
• for the poor Cu barrier property. The poor
  barrier performance of PAE-2 and
• ALCAP-E may also be attributed to the ether
  oxygen linkages whose bonds are
• not diametrically opposed.
• ? Strong partial negative charges also exist in
  phenyl(benzene) rings.
• Polymers with relatively strong aromatic
  character, such as PAE and SiLKTM
• polymer exhibit poorer Cu barrier property
  than polymers with weaker aromatic
• character.
• ? The concentration and inhomogeneity of defects
  in the polymer matrix, such as
• polymer chain ends, are also likely to
  affect Cu drift kinetics.

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