Epitaxial Silicon Wafer Gettering via Controlled Oxygen
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Solution Overview
Problem
In semiconductor device fabrication, low-temperature thermal processes hinder the growth of oxygen precipitate nuclei, leading to reduced gettering capability and increased epitaxial defects, while existing methods either increase production costs or compromise gettering effectiveness.
Innovation Solution
An epitaxial silicon wafer with a specific composition and production process, including a Czochralski-grown silicon single crystal with controlled oxygen, nitrogen, and carbon concentrations, and a COP region, which allows for reduced oxygen precipitate nuclei formation and enhanced gettering capability without pre-annealing, ensuring minimal epitaxial defects at low temperatures.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If low-temperature thermal process is used for circuit pattern miniaturization, then device fabrication is enabled for advanced nodes, but oxygen precipitate nuclei cannot grow and gettering capability is reduced
Solution Approach 1:
The patent applies preliminary action by forming oxygen precipitate nuclei in the silicon substrate before the low-temperature device fabrication process. These pre-formed nuclei serve as gettering sites that will capture metal contaminants during subsequent processing steps, ensuring gettering capability is maintained even when the device process temperature is too low for new precipitate formation.
Solution Approach 2:
The patent changes the oxygen concentration parameter in the silicon substrate to a specific range (5×10^18 to 2×10^19 atoms/cm³) to enable oxygen precipitate nuclei formation. This parameter adjustment ensures that sufficient nuclei are available for gettering during low-temperature processing without requiring high-temperature pre-treatment.
2Reliability
If nitrogen or carbon is doped to promote precipitate growth at low temperatures, then gettering capability is improved, but concentration variation between upper and lower portions reduces usable substrate amount
Solution Approach 1:
The patent extracts the nitrogen and carbon doping step from the process by using high-oxygen silicon substrates instead. This eliminates the segregation problem that occurs during crystal pulling with dopants, while still achieving the desired oxygen precipitate nuclei formation for gettering. The solution removes the harmful element (doping-induced concentration variation) while preserving the beneficial effect (precipitate growth).
Solution Approach 2:
The patent changes the approach from doping with nitrogen or carbon to using high-oxygen silicon substrates. By adjusting the oxygen concentration parameter to 5×10^18 to 2×10^19 atoms/cm³, the patent achieves uniform precipitate nuclei distribution throughout the substrate without the concentration variation problems associated with dopant segregation.
3Reliability
If pre-annealing is performed to form oxygen precipitate nuclei, then gettering capability is maintained at low temperatures, but production costs increase
Solution Approach 1:
The patent applies preliminary action by selecting silicon substrates that are pre-formed with high oxygen concentration during the crystal growth process. This preliminary preparation of the substrate eliminates the need for separate pre-annealing steps, as the oxygen precipitate nuclei are already present and ready to function as gettering sites during device fabrication.
Solution Approach 2:
The patent replaces the expensive and time-consuming pre-annealing process with a simpler, more cost-effective approach using high-oxygen silicon substrates. This substitution eliminates additional processing steps and associated costs while achieving the same gettering functionality.
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 sufficient gettering capability and prevents epitaxial defects during low-temperature device processes, maintaining wafer strength and reducing production costs by eliminating the need for pre-annealing.
Implementation Method 1
a silicon single crystal grown by a Czochralski method
Implementation Method 2
growing a silicon single crystal by a Czochralski method
Implementation Method 3
a time required to cool every part of the silicon single crystal during the growth from 800° C. down to 600° C. is set to 450 minutes or less
Implementation Method 4
forming an epitaxial layer on a surface of the silicon wafer
Data Source
AI summary
An epitaxial silicon wafer cut from a silicon single crystal grown by the Czochralski method, and having a diameter of 300 mm or more. In this epitaxial silicon wafer, the time required to cool every part of the silicon single crystal during the growth from 800° C. down to 600° C. is set to 450 minutes or less, the interstitial oxygen concentration is from 1.5×1018 to 2.2×1018 atoms/cm3 (old ASTM standard), the entire surface of the cut silicon wafer is composed of a COP region, and the BMD density in the bulk of the epitaxial wafer after a heat treatment at 1000° C. for 16 hours is 1×104/cm2 or less. In this epitaxial silicon wafer, even if the thermal process in a semiconductor device fabrication process is a low temperature thermal process, epitaxial defects do not occur, as well as sufficient gettering capability being obtainable.