Epitaxial Silicon Wafer Boron Diffusion Control
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Solution Overview
Problem
Boron diffusion in silicon substrates during device fabrication processes leads to degraded semiconductor device characteristics due to changes in impurity profiles and increased resistance uniformity, even without oxidizing heat treatments, as oxygen precipitates grow and promote kick-out diffusion of boron atoms.
Innovation Solution
An epitaxial silicon wafer with a boron-doped p-type silicon substrate is developed, where the boron concentration is between 2.7×10^17 and 1.3×10^19 atoms/cm^3, and the initial oxygen concentration is 11×10^17 atoms/cm^3 or less, ensuring the density of oxygen precipitates remains below 1×10^10/cm^3, thereby suppressing boron diffusion through interstitial silicon atoms.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If boron concentration in the silicon substrate is increased to secure gettering ability and lower electrical resistance, then the electrical resistivity and gettering ability are improved, but boron diffusion to the epitaxial layer is enhanced which degrades the uniformity of in-plane electrical resistivity
Solution Approach 1:
The patent applies parameter changes by precisely controlling the oxygen concentration in the silicon substrate (5×10^17 to 2×10^18 atoms/cm³) and the density of oxygen precipitates (1×10^8 to 1×10^9/cm³). These parameter adjustments suppress kick-out diffusion of boron atoms while maintaining the required boron concentration for gettering ability and low electrical resistance, thereby resolving the contradiction between reliability and manufacturing precision.
2Reliability
If boron concentration is increased to lower electrical resistance, then the electrical resistivity is improved, but the width of the transition region of boron concentration is increased which reduces the effective thickness of the epitaxial layer
Solution Approach 1:
The patent utilizes parameter changes by optimizing the oxygen concentration (5×10^17 to 2×10^18 atoms/cm³) and oxygen precipitate density (1×10^8 to 1×10^9/cm³) in the silicon substrate. These controlled parameters suppress boron diffusion into the epitaxial layer, thereby maintaining a narrow transition region and preserving the effective thickness of the epitaxial layer while achieving the desired electrical resistivity.
3Reliability
If oxygen concentration in the silicon substrate is increased, then the density of oxygen precipitates is increased which enhances boron diffusion, but reducing oxygen concentration may affect the gettering ability
Solution Approach 1:
The patent applies parameter changes by precisely controlling two key parameters: oxygen concentration (5×10^17 to 2×10^18 atoms/cm³) and oxygen precipitate density (1×10^8 to 1×10^9/cm³). This dual-parameter control creates an optimal balance where sufficient oxygen precipitates exist to maintain gettering ability, while the concentration is limited to suppress kick-out diffusion of boron atoms, thereby resolving the contradiction between reliability and harmful boron diffusion.
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 effectively limits boron diffusion to near baseline levels, even during heat treatments, maintaining the integrity of the epitaxial layer thickness and device performance by controlling oxygen precipitate density, thus enhancing the manufacturing yield of semiconductor devices.
Implementation Method 1
oxygen precipitates grow and promote kick-out diffusion of boron atoms
Implementation Method 2
density of oxygen precipitates remains below 1×10^10/cm^3
Data Source
AI summary
A method of manufacturing an epitaxial silicon wafer that includes growing a silicon single crystal ingot doped with a boron concentration of 2.7×1017 atoms/cm3 or more and 1.3×1019 atoms/cm3 or less by the CZ method; producing a silicon substrate by processing the silicon single crystal ingot; and forming an epitaxial layer on a surface of the silicon substrate. During growing of the silicon single crystal ingot, the pull-up conditions of the silicon single crystal ingot are controlled so that the boron concentration Y (atoms/cm3) and an initial oxygen concentration X (×1017 atoms/cm3) satisfy the expression X≤−4.3×10−19Y+16.3.