Resistivity stabilization measurement of fat neck slabs for high resistivity and ultra-high resistivity single crystal silicon ingot growth

Abstract

Methods for forming single crystal silicon ingots with improved resistivity control are disclosed. The methods involve growth of a sample rod. The sample rod may have a diameter less than the diameter of the product ingot. The sample rod is cropped to form a center slab. The resistivity of the center slab may be measured directly such as by a four-point probe. The sample rod or optionally the center slab may be annealed in a thermal donor kill cycle prior to measuring the resistivity, and the annealed rod or slab is irradiated with light in order to enhance the relaxation rate and enable more rapid resistivity measurement.

What is claimed is: 
     
         1 . A method comprising:
 contacting a silicon seed crystal with a silicon melt, wherein the silicon melt is contained within a crucible and comprises molten silicon;   withdrawing the silicon seed crystal from the silicon melt to form a sample rod comprising single crystal silicon, the sample rod having a main body and comprising a central axis, a circumferential edge, and a diameter;   slicing a slab from the sample rod, the slab comprising a longitudinal plane encompassing at least a portion of the central axis of the sample rod and having a thickness;   annealing the slab to annihilate thermal donors;   lapping the slab;   after annealing and lapping the slab, irradiating the slab with light to enhance a resistivity relaxation rate of the slab, wherein the light has a wavelength between 0.75 micrometers to 1000 micrometers or between 400 nanometers to 4.5 micrometers; and   after irradiating the slab, measuring a resistivity of the slab.   
     
     
         2 . The method of  claim 1  further comprising growing a single crystal silicon ingot from the silicon melt. 
     
     
         3 . The method of  claim 2  wherein the single crystal silicon ingot has a resistivity of at least 500 Ω-cm. 
     
     
         4 . The method of  claim 1  further comprising, after measuring the resistivity of the slab:
 adding a dopant to the silicon melt; and 
 growing a single crystal silicon ingot from the silicon melt having a resistivity different from the resistivity of the sample rod. 
 
     
     
         5 . The method of  claim 4  wherein the single crystal silicon ingot has a resistivity of at least 500 Ω-cm. 
     
     
         6 . The method of  claim 4  wherein the single crystal silicon ingot is a p-type single crystal silicon ingot and the added dopant is selected from the group consisting of phosphorus, arsenic, and antimony and wherein the dopant is added to increase the resistivity of the p-type single crystal silicon ingot. 
     
     
         7 . The method of  claim 6  wherein the single crystal silicon ingot has a resistivity of at least 500 Ω-cm. 
     
     
         8 . The method of  claim 4  wherein the single crystal silicon ingot is a p-type single crystal silicon ingot and the added dopant is selected from the group consisting of boron, gallium, and aluminum and wherein the dopant is added to decrease the resistivity of the p-type single crystal silicon ingot. 
     
     
         9 . The method of  claim 8  wherein the single crystal silicon ingot has a resistivity of at least about 500 Ω-cm. 
     
     
         10 . The method of  claim 4  wherein the single crystal silicon ingot is a n-type single crystal silicon ingot and the added dopant is selected from the group consisting of boron, gallium, and aluminum and wherein the dopant is added to increase the resistivity of the n-type single crystal silicon ingot. 
     
     
         11 . The method of  claim 10  wherein the single crystal silicon ingot has a resistivity of at least 500 Ω-cm. 
     
     
         12 . The method of  claim 4  wherein the single crystal silicon ingot is a n-type single crystal silicon ingot and the added dopant is selected from the group consisting of phosphorus, arsenic, and antimony and wherein the dopant is added to decrease the resistivity of the n-type single crystal silicon ingot. 
     
     
         13 . The method of  claim 12  wherein the single crystal silicon ingot has a resistivity of at least 500 Ω-cm. 
     
     
         14 . The method of  claim 1  wherein the central axis of the sample rod is between 100 millimeters to 500 millimeters in length. 
     
     
         15 . The method of  claim 1  wherein the diameter of the sample rod is less than 150 millimeters. 
     
     
         16 . The method of  claim 1  wherein the thickness of the slab is between 1 millimeter to 3 millimeters. 
     
     
         17 . The method of  claim 1  wherein annealing the slab to annihilate thermal donors comprises annealing the slab at a temperature of at least 500° C. for no more than 60 minutes. 
     
     
         18 . The method of  claim 1  wherein the slab is irradiated with light having the wavelength between 0.75 micrometers to 1000 micrometers. 
     
     
         19 . The method of  claim 1  wherein the slab is irradiated with light having the wavelength between 400 nanometers to 4.5 micrometers. 
     
     
         20 . The method of  claim 1 , wherein the slab is irradiated with infrared light for between 10 minutes to 2 hours. 
     
     
         21 . The method of  claim 1 , wherein, after irradiating, the slab is cooled to below 30° C. before measuring the resistivity of the slab.