  Half-Heusler alloy topological semimetal YPtBi is a promising candidate for
an efficient spin source material having both large spin Hall angle
${\theta}$$_{SH}$ and high thermal stability. However, high-quality YPtBi thin
films with low bulk carrier density are usually grown at 600${\deg}$C, which
exceeds the limitation of 400${\deg}$C for back end of line (BEOL) process.
Here, we investigate the crystallinity and spin Hall effect of YPtBi thin films
grown at lower growth temperature down to 300${\deg}$C. Although
${\theta}$$_{SH}$ degraded with lowering the growth temperature to 300${\deg}$C
due to degradation of the crystallinity, it was recovered by reducing the
sputtering Ar gas pressure. We achieved a giant ${\theta}$$_{SH}$ up to 8.2 and
demonstrated efficient spin-orbit torque magnetization switching by ultralow
current density of ~10$^5$ A/cm$^2$ in YPtBi grown at 300${\deg}$C with the Ar
gas pressure of 1 Pa. Our results provide the recipe to achieve giant
${\theta}$$_{SH}$ in YPtBi grown at lower growth temperature suitable for BEOL
process.
