Process for production of silicon single crystal, and highly doped N-type semiconductor substrate

A producing method of a silicon monocrystal, comprising:

• adding phosphorus (P) and germanium (Ge) into a silicon melt or adding phosphorus into a silicon/germanium melt;
• and
• growing a silicon monocrystal from the silicon melt by a Czochralski method, wherein:
• a phosphorus concentration [P]L (atoms/cm3) in the silicon melt, a Ge concentration [Ge] (atoms/cm3) in the silicon monocrystal, an average temperature gradient Gave (K/mm) and a pull speed V (mm/min) are controlled to satisfy a formula (1) as follows,
• a phosphorus concentration [P] (atoms/cm3) in the silicon monocrystal is 4.84×1019 atoms/cm3 or more and 8.49×1019 atoms/cm3 or less, and
• the phosphorus concentration [P] (atoms/cm3) and the Ge concentration [Ge] (atoms/cm3) in the silicon monocrystal satisfy a relationship according to a formula (2) as follows while growing the silicon monocrystal
• [P]L+(0.3151×[Ge]+3.806×1018)/1.5<0.5×(Gave/V+43)×1019 (1)
• [Ge]←6.95×[P]+5.90×1020 (2).