Silicon carbide single crystal substrate and process for producing same

Abstract

Provided are: a silicon carbide single crystal substrate which is cut out from a silicon carbide bulk single crystal grown by the Physical Vapor Transport method; and a process for producing the same. The number of screw dislocations in one of the semicircle areas of the substrate is smaller than that in the other thereof, namely, the number of screw dislocations in a given area of the substrate is reduced. The semicircle areas of the substrate correspond respectively to the halves of the substrate. The present invention pertains to: a silicon carbide single crystal substrate which is cut out from a silicon carbide bulk single crystal grown by the Physical Vapor Transport method and which is characterized in that the average value of the screw-dislocation densities observed at multiple measurement points in one of the semicircle areas, which correspond respectively to the halves of the substrate, is 80% or less of the average value of screw-dislocation densities observed at multiple measurement points in the other of the semicircle areas; and a process for producing the same.

1 . A silicon carbide single crystal substrate cut from a bulk silicon carbide single crystal grown by a physical vapor transport method, wherein an average value of screw dislocation densities observed at a plurality of measurement points in one semicircular region which is one-half of the substrate is not more than 80% of an average value of screw dislocation densities observed at a plurality of measurement points in one semicircular region which is the other one-half of the substrate. 
     
     
         2 . The silicon carbide single crystal substrate according to  claim 1 , wherein the substrate has a main surface having an angle θ w  of more than 0° and not more than 12°, the angle θ w  being formed by the normal penetrating center point O of the substrate and the [0001] direction; when two semicircular regions bounded by a diameter R ⊥  of the substrate are defined, the diameter R ⊥  being perpendicular to the virtual direction V obtained by projecting the [0001] direction axis on the main surface from the center point O, the average value of screw dislocation densities observed at a plurality of measurement points in a first semicircular region which is one of the semicircular regions is not more than 80% of the average value of screw dislocation densities observed at a plurality of measurement points in a second semicircular region which is the other semicircular region. 
     
     
         3 . The silicon carbide single crystal substrate according to  claim 2 , wherein the average value of screw dislocation densities observed at a plurality of measurement points in the first semicircular region is not more than 60% of the average value of screw dislocation densities observed at a plurality of measurement points in the second semicircular region. 
     
     
         4 . The silicon carbide single crystal substrate according to  claim 2 , wherein the average value of screw dislocation densities observed at a plurality of measurement points in the first semicircular region is not more than 50% of the average value of screw dislocation densities observed at a plurality of measurement points in the second semicircular region. 
     
     
         5 . The silicon carbide single crystal substrate according to  claim 2 , wherein when a sectoral region having a central angle of ±45° from a radius r ∥  which equally divides the first semicircular region is defined, the average value of screw dislocation densities observed at a plurality of measurement points in the sectoral region is not more than 40% of the average value of screw dislocation densities observed at a plurality of measurement points in the second semicircular region. 
     
     
         6 . The silicon carbide single crystal substrate according to  claim 2 , wherein when a sectoral region having a central angle of ±45° from a radius r ∥  which equally divides the first semicircular region is defined, the average value of screw dislocation densities observed at a plurality of measurement points in the sectoral region is not more than 30% of the average value of screw dislocation densities observed at a plurality of measurement points in the second semicircular region. 
     
     
         7 . The silicon carbide single crystal substrate according to  claim 2 , wherein the substrate has an off angle corresponding to the angle θ w  of which off direction d w  is <11-20> direction. 
     
     
         8 . The silicon carbide single crystal substrate according to  claim 2 , wherein 24 radii r 1  to r 24  extending radially from the center point O of the substrate set to 0 are regarded as axes, each scaled from 0 to 1, the 24 radii r 1  to r 24  existing in 12 diameters dividing the circumference of the substrate into 24 equal parts, respectively, the average value of the screw dislocation densities observed in the first semicircular region is an average of values measured at all of 27 measurement points of i) to iii) below and the average value of the screw dislocation densities observed in the second semicircular region is an average of values measured at all of 22 measurement points of iv) to v) below:
 i) center point O   ii) a 1  to a 13      iii) b 1  to b 13      iv) a 14  to a 24      v) b 14  to b 24      (wherein numerals appended to symbols a and b correspond to numerals of the radii r 1  to r 24  and, for example, a 1  and b 1  represent measurement points present on the radius r 1 ; among the measurement points, “a” represents measurement points present within a range of from more than 0 and not more than 0.5 in each radius, and “b” represents measurement points present within a range of from more than 0.5 and not more than 1; and 24 measurement points having the same symbol are present on the same circle of each of the symbols a and b; one of the two radii existing in the diameter R ⊥  is r 1  and the radius adjacent to r 1  and located in the first semicircular region is defined as r 2 , and the reference numbers of radii are serially allocated along the direction of the circumference).   
     
     
         9 . The silicon carbide single crystal substrate according to  claim 8 , wherein the average value of screw dislocation densities observed in the first semicircular region is not more than 600/cm 2 . 
     
     
         10 . The silicon carbide single crystal substrate according to  claim 5 , wherein 24 radii r 1  to r 24  extending radially from the center point O of the substrate set to 0 are regarded as axes, each scaled from 0 to 1, the 24 radii r 1  to r 24  existing in 12 diameters dividing the circumference of the substrate into 24 equal parts, respectively, the average value of the screw dislocation densities observed in the sectoral region is an average of values measured at all of 15 measurement points of i), vi) and vii) below and the average value of the screw dislocation densities observed in the second semicircular region is an average of values measured at all of 22 measurement points of iv) to v) below:
 i) center point O   vi) a 4  to a 10      vii) b 4  to b 10      iv) a 14  to a 24      v) b 14  to b 24      (wherein numerals appended to symbols a and b correspond to numerals of the radii r 1  to r 24  and, for example, a 1  and b 1  represent measurement points present on the radius r 1 ; among the measurement points, “a” represents measurement points present within a range of from more than 0 and not more than 0.5 in each radius, and “b” represents measurement points present within a range of from more than 0.5 and not more than 1; and 24 measurement points having the same symbol are present on the same circle of each of the symbols a and b; one of the two radii existing in the diameter R ⊥  is r 1  and the radius adjacent to r 1  and located in the first semicircular region is defined as r 2 , and the reference numbers of radii are serially allocated along the direction of the circumference).   
     
     
         11 . The silicon carbide single crystal substrate according to  claim 10 , wherein the average value of screw dislocation densities observed in the sectoral region is not more than 400/cm 2 . 
     
     
         12 . The silicon carbide single crystal substrate according to  claim 3 , wherein when a sectoral region having a central angle of ±45° from a radius r ∥  which equally divides the first semicircular region is defined, the average value of screw dislocation densities observed at a plurality of measurement points in the sectoral region is not more than 40% of the average value of screw dislocation densities observed at a plurality of measurement points in the second semicircular region. 
     
     
         13 . The silicon carbide single crystal substrate according to  claim 4 , wherein when a sectoral region having a central angle of ±45° from a radius r ∥  which equally divides the first semicircular region is defined, the average value of screw dislocation densities observed at a plurality of measurement points in the sectoral region is not more than 40% of the average value of screw dislocation densities observed at a plurality of measurement points in the second semicircular region. 
     
     
         14 . The silicon carbide single crystal substrate according to  claim 3 , wherein when a sectoral region having a central angle of ±45° from a radius r ∥  which equally divides the first semicircular region is defined, the average value of screw dislocation densities observed at a plurality of measurement points in the sectoral region is not more than 30% of the average value of screw dislocation densities observed at a plurality of measurement points in the second semicircular region. 
     
     
         15 . The silicon carbide single crystal substrate according to  claim 4 , wherein when a sectoral region having a central angle of ±45° from a radius r ∥  which equally divides the first semicircular region is defined, the average value of screw dislocation densities observed at a plurality of measurement points in the sectoral region is not more than 30% of the average value of screw dislocation densities observed at a plurality of measurement points in the second semicircular region.