Silicon Wafer RTP for Low Oxygen and Heavy Metal Gettering
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Solution Overview
Problem
Silicon wafers grown by the Czochralski method contain high oxygen concentrations and oxygen precipitates, leading to current leakage in power devices, and existing methods like FZ and epitaxial wafers are costly and inefficient for large-diameter crystals.
Innovation Solution
Silicon wafers with low oxygen concentration (1×10^16 to 7×10^17 atoms/cm^3) and high vacancy-based complex defect concentration (1×10^12 atoms/cm^3 or more within 100 μm from the surface) are treated using rapid thermal processing at 1250°C or higher with controlled oxygen partial pressure to reduce BMD density and enhance gettering capability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If silicon wafers are grown by the Czochralski method, then large-diameter single crystals can be produced efficiently, but the oxygen concentration increases to at least 5×10^17 atoms/cm³ causing BMD formation and current leakage
Solution Approach 1:
The patent applies preliminary action by performing rapid thermal processing (RTP) at 1250°C or higher on silicon wafers before device fabrication. This pre-treatment reduces oxygen concentration from at least 5×10^17 atoms/cm³ to below 5×10^17 atoms/cm³ and suppresses BMD formation, thereby eliminating the harmful effects of high oxygen content before the wafers are used in device manufacturing
Solution Approach 2:
The patent changes the physical parameters of the silicon wafers through rapid thermal processing. By heating to 1250°C or higher and controlling the thermal conditions, the oxygen concentration is reduced and the crystal structure is modified to suppress BMD formation, transforming the wafer properties to achieve both low oxygen content and low BMD density
2Reliability
If silicon wafers are treated to reduce oxygen concentration, then BMD formation is suppressed, but the gettering capability for heavy metals decreases
Solution Approach 1:
The patent simultaneously optimizes multiple parameters through rapid thermal processing: reducing oxygen concentration to below 5×10^17 atoms/cm³ to suppress BMD formation, while maintaining or enhancing vacancy-based complex defect concentration to preserve gettering capability. This multi-parameter optimization resolves the contradiction between reducing oxygen-related defects and maintaining heavy metal gettering
3Reliability
If FZ method is used to grow large-diameter single crystals, then oxygen concentration is reduced, but the crystal growth becomes difficult and device yield is insufficient
Solution Approach 1:
The patent extracts the oxygen removal function from the crystal growth process itself. Instead of relying on the FZ method to grow low-oxygen large-diameter crystals, the patent uses the MCZ method to grow crystals and then extracts excess oxygen through rapid thermal processing, thereby achieving low oxygen concentration without the manufacturing difficulties of the FZ method
4Ease of operation
If epitaxial layers are thickened to manufacture vertical devices, then device functionality is improved, but the epitaxial layer perfectness deteriorates and current leakage increases
Solution Approach 1:
The patent applies preliminary action by treating the silicon wafers with rapid thermal processing before epitaxial layer formation or device fabrication. This pre-treatment creates a substrate with reduced oxygen concentration and suppressed BMD formation, providing a high-quality foundation that allows thick epitaxial layers to be grown without the usual deterioration in perfectness or increase in current leakage
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
The method produces silicon wafers with low oxygen concentration and low BMD density, effectively inhibiting current leakage and improving the gettering of heavy metals, making them suitable for high-grade power devices.
Implementation Method 1
when rapid thermal processing (RTP) is subjected to silicon wafers having a low oxygen concentration for a time scale of a few tens of seconds or less at a high temperature of 1250° C. or higher
Implementation Method 2
the concentration of vacancy-based complex defect gradually increases as it goes deeper from the surface
Data Source
AI summary
To provide a method of manufacturing silicon wafers having a low oxygen concentration and being provided with the gettering capability of heavy metals even when the density of BMD is low. The method includes a step of placing wafers sliced from a silicon single crystal and having an oxygen concentration in the range of 1×1016 atoms/cm3 to 7×1017 atoms/cm3, in a chamber and a step of performing rapid thermal processing at a maximum temperature reached of not less than 1250° C. or not more than 1350° C. after introducing a mixed gas having an oxygen partial pressure in the range of 1% to 10% of oxygen and an inert gas.