NOVELTY - The method involves carrying out unidirectional solidification of melt (1) of metallic silicon in casting-mold (5) of solidification purifier. The impurity element in metallic silicon is removed. The melt is heated and/or cooled so that constitutional-super-cooling index is represented using solidification rate. The impurity element concentration with respect to critical value of super-cooling is represented using gradient of liquidus line and diffusion coefficient of impurity element read from state diagram of silicon impurity element in metallic silicon.    USE - Solidification purification method of metallic silicon for manufacturing silicon substrate for solar cell.    ADVANTAGE - Since the impurity element concentration with respect to critical value of constitutional super-cooling is represented using gradient of liquidus line and diffusion coefficient of impurity element read from state diagram of silicon impurity element in metallic silicon, the optimization of solidification rate can be attained. The production efficiency of the silicon substrate can be improved and silicon substrate for solar cell can be manufactured at low cost.    DETAILED DESCRIPTION - The method involves insulating side surface of the casting-mold when unidirectional solidification of melt within casting-mold heats by radiation from level upper portion of melt. The super-cooling index is carried out based on physical-property value information of metallic silicon. The melt side temperature gradient in solidification interface and product of solidification rate are calculated with respect to solidification advancing direction. An INDEPENDENT CLAIM is included for metallic silicon solidification purifier has solidification surface height calculating unit which calculates time solidification surface height by accumulation calculation from computed time solidification rate. The temperature measuring unit measures temperature of heater in time series. The heater temperature control unit adjusts temperature of heater according to advancing of solidification of melt. The time-sequential information of solidification surface height calculated by solidification surface height measurement unit is replaced with the time-sequential information of solidification surface height and input into constitutional-super-cooling index calculating unit.    DESCRIPTION OF DRAWING(S) - The drawing shows a longitudinal cross-sectional view of solidification purifier illustrating process for manufacturing highly purified silicon crystal for manufacturing silicon substrate for solar cell.    Melt (1)    Casting-mold (5)    Electrothermal-heater (6)    Water cooled jacket (7)    Cooling water (8)