Epi_wafer: 在single crystal wafer上再dep一層single crystal Si ,Improve the performance of bipolar transistor, with high breakdown voltage of the collector-substrate junction and low collector resistance. Lightly doped epiwafer minimizes latch-up effect, accurately controlled doing concentration.是在原本Heavily doped substrate上，以的方式成長一層Lightly doped Epi-layer，以作為CMOS製程的底材。因此CMOS是直接建立在Lightly doped Epi-layer上，而Heavily doped substrate則作為接地。此可使CMOS中直立式pnp雙載子寄生電晶體的電流不易橫向地流往寄生的npn電晶體，而流向Heavily doped substrate。因為底材接地，寄生pnp與npn的閉鎖(Latch up)現象可被抑制，但相對使用Epi-Wafer會提高成本。
