Silicon Wafer Oxygen Gradient for Defect Control
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Solution Overview
Problem
Existing silicon wafers manufactured by the Czochralski method often contain grown-in defects such as Crystal Originated Particles (COPs) and dislocation clusters, which can lead to poor semiconductor device properties and are not adequately addressed by current methods, particularly in the context of oxygen concentration variations affecting device performance and mechanical strength.
Innovation Solution
A silicon wafer with an absolute oxygen concentration variation rate of less than 10% in the depth direction, a density of grown-in defects with silicon oxides of 1×10^6/cm^3 or less in the outer-layer portion, and an oxygen precipitate density of 1×10^8/cm^3 or more in the bulk portion, achieved through a manufacturing process involving Czochralski growth, rapid thermal processing, and specific heat treatment steps to control oxygen concentration and defect distribution.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the pulling speed is increased to increase productivity, then productivity is improved, but grown-in defects (COPs) are introduced into the single crystal
Solution Approach 1:
The patent applies parameter changes by precisely controlling the ratio of pulling speed to temperature gradient (V/G) within a specific range (0.003-0.008 cm²/s) to prevent COP formation while maintaining high productivity. This quantitative parameter control resolves the contradiction between fast growth and defect-free crystal quality.
Solution Approach 2:
The patent implements preliminary action by controlling the temperature gradient distribution in advance during crystal growth to ensure the entire crystal volume maintains appropriate V/G conditions. This preventive approach ensures defect-free regions are formed throughout the crystal before any defects can occur.
2Reliability
If heat treatment is performed to remove grown-in defects, then defect density is reduced, but oxygen concentration varies and mechanical strength deteriorates
Solution Approach 1:
The patent applies local quality by creating different oxygen concentration zones within the wafer structure. The surface region maintains lower oxygen concentration for strength, while the bulk region has higher oxygen concentration for defect removal through gettering, resolving the contradiction between defect reduction and strength maintenance.
Solution Approach 2:
The patent implements preliminary action by controlling oxygen concentration distribution during the crystal growth phase itself, rather than attempting to modify it later. This ensures the wafer is pre-configured with appropriate oxygen levels for both strength and defect resistance before device fabrication begins.
3Reliability
If oxygen concentration is increased to enhance gettering ability, then gettering ability is improved, but mechanical strength decreases
Solution Approach 1:
The patent applies local quality by spatially differentiating oxygen concentration within the wafer: the bulk portion contains high oxygen concentration (5×10¹⁷ to 2×10¹⁸ atoms/cm³) for gettering, while the surface portion maintains lower oxygen concentration for mechanical strength, thus resolving the contradiction between these two requirements.
Solution Approach 2:
The patent resolves the contradiction by transitioning from a uniform oxygen concentration approach to a depth-dependent gradient structure. This dimensional differentiation allows simultaneous optimization of gettering ability in the bulk and mechanical strength at the surface.
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 solution provides improved device properties by minimizing oxygen-related defects, maintaining mechanical strength, and enhancing gettering ability for heavy metals, making the silicon wafer suitable for finer devices and various heat treatment conditions.
Implementation Method 1
A silicon wafer used as a substrate of a semiconductor device is cut from a silicon single crystal ingot, which is typically grown by the Czochralski method (hereafter, also referred to as 'the CZ method'), and is manufactured through steps such as polishing. The CZ method is a method in which a seed crystal is dipped into and pulled upward from melted silicon in a quartz crucible so as to grow a single crystal.
Implementation Method 2
A first heat treatment step of performing RTP treatment in which the silicon wafer is retained in an oxidizing atmosphere at a temperature of more than 1250° C. for one second or more
Implementation Method 3
a first heat treatment step of performing RTP treatment in which the silicon wafer is retained in an oxidizing atmosphere at a temperature of more than 1250° C. for one second or more
Data Source
AI summary
This method for manufacturing a silicon wafer includes: a first heat treatment step of performing RTP treatment on the silicon wafer in an oxidizing atmosphere; a step of removing a region in the silicon wafer in which an oxygen concentration increases in the first heat treatment step; a second heat treatment step of performing, after performing this removing step, RTP treatment on the silicon wafer in a nitriding atmosphere or an Ar atmosphere; and a step of removing, after performing the second heat treatment step, a region in the silicon wafer in which an oxygen concentration decreases in the second heat treatment step. This method enables the manufacture of a silicon wafer in which latent defects such as OSF nuclei and oxygen precipitate nuclei existing in a PV region are destroyed or reduced, and that has a gettering site.