Method of manufacturing annealed wafer
Annealed wafers having reduced residual voids after annealing and reduced deterioration of TDDB characteristics of an oxide film formed on the annealed wafer, while extending the range of nitrogen concentration contained in a silicon single crystal, are prepared by a method wherein crystal pulling conditions are controlled such that a ratio V/G between a crystal pulling rate V and an average axial temperature gradient G is ≧0.9×(V/G) crit and ≦2.5×(V/G) crit , and hydrogen partial pressure is ≧3 Pa and ≦40 Pa. The silicon single crystal has a nitrogen concentration of >5×10 14 atoms/cm 3 and ≦6×10 15 atoms/cm 3 , a carbon concentration of ≧1×10 15 atoms/cm 3 and ≦9×10 15 atoms/cm 3 , and heat treatment is performed in a noble gas atmosphere having an impurity concentration of ≦5 ppma, or in a non-oxidizing atmosphere.
1. A method of manufacturing an annealed wafer, comprising the steps of:
a) growing a silicon single crystal by the Czochralski method from a silicon melt to which nitrogen, carbon, and hydrogen are added in a crystal pulling furnace;
b) cutting out a substrate from said silicon single crystal; and
c) heat treating said substrate, wherein, during growth of the silicon single crystal in step a),
a)i) the ratio of a crystal pulling rate V (mm/min) and an average temperature gradient G (° C./mm) in a crystal growth axial direction is defined as V/G, and V/G in a case where nitrogen, hydrogen, and carbon are not added to a silicon single crystal is defined as (V/G) crit , crystal pulling conditions are controlled such that V/G is not less than 0.9×(V/G) crit and not more than 2.5×(V/G) crit (where V represents the pulling rate [mm/min], G represents the average temperature gradient [° C./mm] in the crystal growth axial direction from a melting point to 1350° C., and (V/G) crit is the V/G value of a portion corresponding to a boundary between an I region and a V region in the silicon single crystal to which nitrogen, hydrogen, and carbon are not added, said V region being a region into which excessive vacancies are introduced from a solid-liquid interface during crystal growth, and said I region being a region into which excessive interstitials are introduced from the solid-liquid interface during the crystal growth),
a)ii) a hydrogen partial pressure within the crystal pulling furnace is set to not less than 3 Pa and not more than 40 Pa,
a)iii) and the silicon single crystal grown in the step of growing the silicon single crystal is a silicon single crystal having a nitrogen concentration of more than 5×10 14 atoms/cm 3 and not more than 6×10 15 atoms/cm 3 , and a carbon concentration of not less than 1×10 15 atoms/cm 3 and not more than 9×10 15 atoms/cm 3 , and
during heat treating in step c), heat treatment is performed in a noble gas atmosphere having an impurity concentration of not more than 5 ppma, or in a non-oxidizing atmosphere in which a film thickness of an oxide film to be formed on a surface of said substrate after the heat treatment is suppressed to not more than 2 nm, at a heating temperature of not less than 1150° C. and not more than 1250° C., for a heating time period of not less than 10 minutes and not more than two hours.
2. The method of manufacturing an annealed wafer of claim 1 , wherein, in step a) of growing the silicon single crystal, nitrogen and carbon are added to the silicon melt.
3. The method of manufacturing an annealed wafer of claim 1 , wherein, in the step of growing the silicon single crystal, the rate of cooling from 1100 ° C. to 1000° C. is not more than 2.5° C./min.
4. The method of manufacturing an annealed wafer of claim 2 , wherein, in the step of growing the silicon single crystal, the rate of cooling from 1100° C. to 1000° C. is not more than 2.5° C./min.