The investigation aims to reveal and confirm the phosphorus
(P)–oxygen
(O) bonds formed in the poly-Si (n+) film of the TOPCon
device, which is beneficial for reducing the resistivity and the potential
barriers of grain boundaries (GBs) due to further passivation of GBs
within the film. To overcome the difficulty of gaining the chemical
components in the interface and bulk of the n-Si/SiO
x
/poly-Si (n+) materials, we undertake X-ray photoelectron
spectroscopy (XPS) with the depth profile by means of argon ion milling,
in which the collision damage of ion with target surface has been
neglected because of an effective detectable depth and longer mean
escape depth of the optoelectron in the ionized state in the sampling
point of the subsurface. High-resolution transmission electron microscopy
(HR-TEM) has been employed to check the atomic lattice morphology
of the multi-layer stacks for further distinguishing the crystallographic
plane orientation of crystallites and ultrathin SiO
x
layer feature distribution in the interfacial region and bulk
of SiO
x
/poly-Si (n+) films.
The results of XPS-P 2p fitting peaks at 133.4 and 136.2 eV and −O
1s satellite peak at 535.3 eV, respectively, manifesting that the
P–O bonds or derivatives (PO
x
)
may be present in the poly-Si (n+) film and localized in
the GBs, through the heavily P dopants that induce tensile stress
within crystallites and compress stress in GBs. The conclusion has
been supported by the variation of thermodynamic functions, such as
molar enthalpy, reaction entropy, Gibbs energy, and formation energy
of silicon and phosphorus oxides, at the temperatures of 298 and 1173
K in terms of the minimum principle of energy.
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