I would like to know whether LTC3618 can generate 1.2v and 0.6V for DDR4.
Yes. The datasheet gives some example circuits. You need to adjust the feedback resistors for 1.2V output. The demo circuit DC1726A can be ordered from the Analog Devices website, and be modified (for instance change R3) for 1.2V output. http://www.analog.com/media/en/technical-documentation/eval-board-schematic/1726asch.pdf