Single Crystal Silicon Wafer for IGBT Gate Oxide Integrity
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Solution Overview
Problem
The production of large-diameter single crystal silicon wafers for insulated gate bipolar transistors (IGBTs) using the Czochralski method faces challenges such as crystal defects, resistivity variation, and oxygen excess, which affect gate oxide integrity and recombination lifetime, leading to high production costs and reduced yield.
Innovation Solution
The method involves controlling crystal originated particles (COP) density and interstitial oxygen concentration within specific ranges, using neutron irradiation and phosphorus doping to achieve stable resistivity and recombination lifetime, while applying a magnetic field to suppress oxygen precipitation and maintain low COP sizes, thereby enhancing gate oxide integrity and yield.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If single crystal silicon wafers are grown by the Czochralski method to increase wafer diameter and reduce cost, then production cost decreases and wafer diameter increases, but crystal defects increase and gate oxide integrity deteriorates
Solution Approach 1:
The patent applies parameter changes by precisely controlling the interstitial oxygen concentration within 5×10^17 to 2×10^18 atoms/cm³ and COP density within 1×10^5 to 1×10^6 cm⁻³. These specific parameter ranges resolve the contradiction by enabling large-diameter CZ wafer production while maintaining gate oxide integrity through optimized oxygen content that prevents both excessive defect formation and oxygen precipitation.
Solution Approach 2:
The patent implements feedback control through systematic measurement and adjustment of interstitial oxygen concentration and COP density during crystal growth. By monitoring these parameters and adjusting growth conditions accordingly, the method ensures that wafers meet the required specifications for both cost-effectiveness and reliability, closing the loop between manufacturing parameters and product quality.
2Manufacturing precision
If interstitial oxygen concentration is increased to suppress crystal defects, then crystal defect density decreases, but oxygen precipitation increases and recombination lifetime decreases
Solution Approach 1:
The patent resolves this contradiction through precise parameter control of interstitial oxygen concentration within the narrow range of 5×10^17 to 2×10^18 atoms/cm³. This optimized oxygen level is sufficient to suppress crystal defect formation during growth but remains below the threshold that triggers oxygen precipitation and carrier recombination, thereby simultaneously achieving high manufacturing precision and extended recombination lifetime.
3Reliability
If COP density is reduced to improve gate oxide integrity, then gate oxide breakdown is suppressed, but crystal growth stability deteriorates
Solution Approach 1:
The patent maintains crystal growth stability while achieving low COP density (1×10^5 to 1×10^6 cm⁻³) by optimizing the interstitial oxygen concentration to 5×10^17 to 2×10^18 atoms/cm³. This parameter optimization creates a balanced growth environment where the oxygen content is sufficient to suppress excessive COP formation but not so high as to cause growth instability or oxygen precipitation, thereby resolving the contradiction between reliability and compositional stability.
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 single crystal silicon wafers with improved gate oxide integrity, reduced resistivity variation, and extended recombination lifetime, achieving a yield of 90% or more and maintaining resistivity within narrow tolerance limits, thus addressing the limitations of existing methods.
Implementation Method 1
wherein the single crystal silicon is doped with phosphorus by being subjected to neutron irradiation
Implementation Method 2
by applying a magnetic field to suppress oxygen precipitation
Data Source
AI summary
A single crystal silicon wafer for use in the production of insulated gate bipolar transistors is made of single crystal silicon grown by the Czochralski method and has a gate oxide with a film thickness of from 50 to 150 nm. The wafer has an interstitial oxygen concentration of at most 7.0×1017 atoms/cm3, a resistivity variation within the plane of the wafer of at most 5% and, letting tox (cm) be the gate oxide film thickness and S (cm2) be the electrode surface area when determining the TZDB pass ratio, a density d (cm-3) of crystal originated particles (COP) having a size at least twice the gate oxide film thickness which satisfies the formula d ≤ -ln(0.9)/(S·tox/2). The wafers have an increased production yield and a small resistivity variation.