Phosphorus Doped Silicon Crystal Radial Resistivity Control
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Solution Overview
Problem
Existing methods for producing large-diameter phosphorus doped silicon single crystals face challenges in achieving an even distribution of phosphorus dopant atoms across the crystal cross-section, leading to variations in resistivity values, particularly for high-power electronics applications.
Innovation Solution
Combining gas doping and neutron transmutation doping (NTD) processes, using specific constants (K2 and K3) to control the radial distribution of phosphorus atoms, ensuring a consistent target resistivity and reduced radial resistivity variation (RRV) in silicon wafers cut from large-diameter crystals.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If neutron transmutation doping (NTD) is used to dope large-diameter silicon crystals, then phosphorus dopant atoms are introduced into the silicon, but the distribution of phosphorus atoms becomes uneven across the crystal cross-section due to neutron absorption
Solution Approach 1:
The patent applies preliminary action by first performing gas doping to introduce phosphorus atoms into the silicon crystal before neutron irradiation. This pre-doping step establishes a baseline phosphorus distribution that can be subsequently modified by NTD. The gas doping phase allows phosphorus to be introduced uniformly or with a predetermined profile before the non-uniform neutron irradiation occurs, enabling better control over the final dopant distribution.
Solution Approach 2:
The patent employs parameter changes by varying the phosphorus concentration introduced during gas doping across different radial positions of the silicon crystal. By adjusting the phosphorus concentration profile during the gas doping phase, the patent compensates for the expected non-uniform neutron absorption during subsequent NTD. This allows the final phosphorus distribution after both processes to achieve the desired uniformity despite the inherent non-uniformity of neutron irradiation.
2Quantity of substance
If gas doping is used to dope silicon crystals, then phosphorus dopant atoms are introduced into the silicon, but systematic variations in phosphorus distribution occur across the crystal
Solution Approach 1:
The patent merges two doping processes - gas doping and neutron transmutation doping (NTD) - into a combined approach. The gas doping phase introduces phosphorus atoms with a controlled distribution, and the subsequent NTD phase adds additional phosphorus atoms through neutron irradiation. By carefully designing the phosphorus concentration profile during gas doping, the combined effect of both processes achieves a more uniform final phosphorus distribution than either process alone could provide.
3Area of stationary object
If large-diameter silicon crystals (above 150 mm) are produced, then more silicon wafers can be cut, but neutron irradiation will not be even through the cross-section due to neutron absorption
Solution Approach 1:
The patent applies preliminary action by performing gas doping before neutron irradiation to establish an initial phosphorus distribution that accounts for the large crystal diameter. This pre-doping step allows the introduction of phosphorus atoms throughout the entire cross-section of the large-diameter crystal uniformly, preparing the crystal for subsequent NTD. The preliminary gas doping ensures that even regions of the large crystal receive adequate phosphorus before the non-uniform neutron irradiation occurs.
Solution Approach 2:
The patent employs parameter changes by adjusting the phosphorus concentration profile during gas doping as a function of radial position in the large-diameter crystal. By varying the phosphorus introduction rate or concentration across different radial zones, the patent compensates for the expected non-uniform neutron absorption in large crystals. This allows the final phosphorus distribution to achieve the required uniformity despite the challenges posed by the large crystal diameter and associated non-uniform neutron irradiation.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach results in silicon wafers with RRV values of 2% or less for at least 75% of wafers, achieving a normalized average resistivity close to the target value, enhancing the homogeneity and quality of silicon wafers for high-power electronics.
Implementation Method 1
gas doping and neutron transmutation doping (NTD) processes
Implementation Method 2
silicon atoms in solid silicon can be converted to phosphorus atoms by irradiating the material with neutrons
Implementation Method 3
annealing the silicon at a temperature in the range of 800°C to 1300°C
Data Source
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Figure 2
Figure 3~4
AI summary
The present invention relates to a phosphorus doped silicon single crystal having a diameter of at least 175 mm and an axial length in the range of 50 mm to 1000 mm, the phosphorus doped silicon single crystal in a transverse plane having a density of dopant atoms providing a target resistivity (ρNTD) in the range of 5 Ωcm to 2000 Ωcm for a wafer cut from the phosphorus doped silicon ingot, wherein a RRV value of 3% or less as determined according to the SEMI standard SEMI MF81 is obtained for at least 75% of wafers cut from the phosphorus doped silicon single crystal when the resistivity is measured after annealing the silicon at a temperature in the range of 800°C to 1300°C, to a wafer and to a plurality of wafers cut from the phosphorus doped silicon single crystal and to a method of producing a phosphorus doped silicon single crystal. The products of the invention are particularly suited for use in high power electronics.