  The annual modulation of scintillation event rate observed by the DAMA/LIBRA
experiment has been a long-standing controversy in the quest of the direct
detection of dark matter. The effort to definitively confirm or refute the
annual modulation has turned out to be challenging due to the lack of NaI(Tl)
crystals with high enough radio-purity. Most recently, we successfully grew a
6-kg ingot free from contamination during growth, from which a 3.4-kg crystal
scintillator was made. The $^{39}$K concentration in the final crystal is
estimated to be 4.3$\pm$0.2~ppb, unprecedented for NaI(Tl) crystals. The
$^{210}$Pb activity is estimated to be 0.34$\pm$0.04~mBq/kg via $\alpha$
counting of $^{210}$Po, among the lowest of currently-running NaI-based dark
matter experiments except DAMA/LIBRA. More importantly, the techniques and
protocols we have developed will further contribute to the growth of higher
purity NaI(Tl) crystals for dark matter searches.
