Semiconductor wafer made of monocrystalline silicon, and method for producing same
A semiconductor wafer comprising single-crystal silicon has defined concentrations of oxygen, nitrogen and hydrogen; the semiconductor wafer further contains BMD seeds having a density averaged over the radius of not less than 1×10 5 cm −3 and not more than 1×10 7 cm −3 ; surface defects having a density averaged over the radius of not less than 1100 cm −2 ; and BMDs, whose density is not lower than a lower limit of 5×10 8 /cm 3 . The semiconductor wafers are produced by a process which enables obtention of the required ranges of concentrations of oxygen, nitrogen, hydrogen, BMD seeds, and BMD's.
1. A semiconductor wafer comprising single-crystal silicon with a center, an edge and a radius R between the center and the edge,
an oxygen concentration of not less than 4.9×10 17 atoms/cm 3 and not more than 5.85×10 17 atoms/cm 3 ;
a nitrogen concentration of not less than 5×10 12 atoms/cm 3 and not more than 1.0×10 14 atoms/cm 3 ;
a hydrogen concentration of not less than 3×10 13 atoms/cm 3 and not more than 8×10 13 atoms/cm 3 ;
bulk micro defect (“BMD”) seeds whose density averaged over the radius of the semiconductor wafer, as determined by infrared (“IR”) tomography, is not less than 1×10 5 cm −3 and not more than 1×10 7 cm −3 ;
surface defects whose density averaged over the radius is not less than 1100 cm′ as determined by optical microscopy after heat treatments of the semiconductor wafer at a temperature of 900° C. over a period of 8 h in an atmosphere of nitrogen and at a temperature of 1100° C. over a period of 2 h in an atmosphere of oxygen and hydrogen; and
bulk micro defects (“BMDs”), whose density is not lower than a lower limit of 5×10 8 /cm 3 determined by IR tomography along the radius from a radial position r=R/3 to a radial position r=R/1.15 after heat treatments of the semiconductor wafer at a temperature of 780° C. over a period of 3 h and at a temperature of 1000° C. over a period of 16 h.
2. The semiconductor wafer of claim 1 , wherein a frontside of the semiconductor wafer is covered with an epitaxial layer comprising silicon.
3. The semiconductor wafer of claim 2 , wherein the density of BMDs is not less than 3×10 8 /cm 3 and not more than 5×10 9 /cm 3 , determined from the center to the edge of the semiconductor wafer for an edge exclusion of 1 mm and evaluated by IR tomography after heat treatments of the semiconductor wafer at a temperature of 780° C. over a period of 3 h and at a temperature of 1000° C. over a period of 16 h.
4. The semiconductor wafer of claim 2 , wherein the density of BMDs varies by not more than 80% based on a mean density, determined along the radius from a radial position r=R/1.0791 to a radial position r=R/1.0135 and evaluated by IR tomography after heat treatments of the semiconductor wafer at a temperature of 780° C. over a period of 3 h and at a temperature of 1000° C. over a period of 16 h.
5. The semiconductor wafer of claim 3 , wherein the density of BMDs varies by not more than 80% based on a mean density, determined along the radius from a radial position r=R/1.0791 to a radial position r=R/1.0135 and evaluated by IR tomography after heat treatments of the semiconductor wafer at a temperature of 780° C. over a period of 3 h and at a temperature of 1000° C. over a period of 16 h.
6. A process for producing a semiconductor wafer of claim 1 from single-crystal silicon, comprising:
pulling a single crystal from a melt by the CZ method at a pulling velocity V, wherein the melt is doped with oxygen, nitrogen and hydrogen and the single crystal grows at a crystallization interface;
controlling the incorporation of oxygen, nitrogen and hydrogen in a section of the single crystal having a uniform diameter in such a way that the oxygen concentration is not less than 4.9×10 17 atoms/cm 3 and not more than 5.85×10 17 atoms/cm 3 , the nitrogen concentration is not less than 5×10 12 atoms/cm 3 and not more than 1.0×10 14 atoms/cm 3 and the hydrogen concentration is not less than 3×10 13 atoms/cm 3 and not more than 8×10 13 atoms/cm 3 ;
controlling the pulling velocity V such that it is within a span ΔV within which the single crystal in the section having a uniform diameter grows in a P v region, wherein the pulling velocity V is in a subrange of the span which comprises 39% of the span and a lowest pulling of velocity of the subrange is 26% greater than a pulling velocity V Pv/Pi at the transition from the P v region to a P i region; and
separating the semiconductor wafer from the section of the single crystal having a uniform diameter.
7. The process of claim 6 , further comprising pulling the single crystal in an atmosphere comprising hydrogen, wherein the partial pressure of the hydrogen is not less than 5 Pa and not more than 18 Pa.
8. The process of claim 6 , further comprising increasing the partial pressure of the hydrogen once the section of the single crystal having a uniform diameter has reached an axial length greater than 50% of an intended axial length of this section.
9. The process of claim 6 , further comprising increasing the partial pressure of the hydrogen once the section of the single crystal having a uniform diameter has reached an axial length greater than 50% of an intended axial length of this section.
10. The process of claim 6 , wherein an epitaxial layer of silicon is deposited on a frontside of the semiconductor wafer.
11. The process of claim 6 , wherein an epitaxial layer of silicon is deposited on a frontside of the semiconductor wafer.
12. The process of claim 6 , wherein an epitaxial layer of silicon is deposited on a frontside of the semiconductor wafer.