  The process $e^+e^-\to H t\bar t$ can be used at the Next Linear Collider to
measure the Higgs-top Yukawa coupling. In this paper, we compute $2\to 8$
processes of the form $e^+e^-\to b\bar b b\bar b W^+W^-\to b\bar b b\bar b
\ell^\pm\nu_\ell q\bar q'$, accounting for the Higgs-top-antitop signal as well
as several irreducible backgrounds in the semi-leptonic top-antitop decay
channel. We restrict ourselves to the case of a light Higgs boson in the range
100 GeV $\le M_H \le$ 140 GeV. We use helicity amplitude techniques to compute
exactly such processes at tree level in the framework of the Standard Model.
Total rates and differential spectra of phenomenological interest are given and
discussed
