  In this study, assuming the Type-Y (flipped) 2HDM at the SM-like scenario as
the theoretical framework, observability of the additional heavy neutral Higgs
bosons $H$ and $A$ is investigated through the signal process chain $e^- e^+
\rightarrow AH \rightarrow b\bar{b}b\bar{b}$ at a linear collider operating at
the center-of-mass energy of 1.5 TeV. The assumed signal process is highly
motivated by the enhancements in the $A/H\rightarrow b\bar{b}$ decays at
relatively high $\tb$ values. Such enhancements result in the dominance of the
mentioned decay modes even for Higgs masses above the threshold of the on-shell
top quark pair production. Taking advantage of such a unique feature, several
benchmark scenarios are studied. Simulating the detector response based on the
SiD detector at the ILC, simulated events are analyzed to reconstruct the $H$
and $A$ Higgs bosons. The top quark pair production and $Z/\gamma$ production
are the main SM background processes and are well under control. Results
indicate that, the $H$ and $A$ Higgs bosons are observable with signals
exceeding $5\sigma$ with possibility of mass measurement in all the tested
scenarios. Specifically, the parameter space region enclosed with the mass
ranges $m_H$=150-500 GeV and $m_A$=230-580 GeV with the $A/H$ mass splitting of
80 GeV is observable at the integrated luminosity of 500 $fb^{-1}$.
