A new ion implanter has been designed for high‐dose predeposition in a semiconductor production line. It incorporates a microwave ion source, a 90° magnetic mass separator, and a rotating disk target chamber. Mass peak variations of PH3gas are shown as a function of the incident microwave power. The ion energy level can be varied from 10 to 50 keV. It makes 10 mA P+implantation (maximum 15 mA) possible. After beam adjustment, implantation is automatically carried out with a microcomputer. The operation rate of the implanter is remarkably improved due to the long lifetime of the modified microwave ion source and the low gas consumption. The dose nonuniformity of a 3‐in. wafer implanted with this implanter has a standard deviation (&sgr;) of 0.5%. This small nonuniformity results in a small &sgr; in the transistor current gain (less than 3.5%).