High Resistivity CZ Silicon via Thermal Donor Control
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Solution Overview
Problem
Current methods for producing high resistivity CZ silicon wafers face challenges such as boron contamination, thermal donor formation due to interstitial oxygen, and the difficulty in achieving high resistivity decoupled from acceptor atom concentration, particularly in large diameters and commercial environments.
Innovation Solution
A thermal treatment process that controls the ratio of thermal donors to acceptors in CZ silicon wafers, adjusting boron and oxygen concentrations and annealing temperatures to achieve a resistivity significantly higher than calculated based on boron concentration, using the equation [B]=1e14([Oi]/[Oi]ref)nexp(E/kT−E/kTref) to optimize the thermal donor and acceptor balance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If CZ silicon is grown with low boron concentration to achieve high resistivity, then resistivity increases, but thermal donor formation during processing reduces the effective resistivity
Solution Approach 1:
The patent applies preliminary action by growing CZ silicon with controlled interstitial oxygen concentration and specific dopant levels before device processing. This pre-conditioning of the silicon material ensures that when thermal processing occurs during normal fabrication, the thermal donors form in a controlled manner that compensates for acceptors, maintaining high resistivity throughout the device manufacturing process rather than requiring resistivity control after processing begins
Solution Approach 2:
The patent changes the parameters of the silicon crystal growth process, specifically controlling the interstitial oxygen concentration and dopant concentration ratios during CZ growth. By adjusting these parameters to specific ranges, the material is prepared to achieve the desired thermal donor/acceptor balance during subsequent thermal processing, thereby achieving high and stable resistivity
2Manufacturing precision
If thermal treatments are applied to precipitate interstitial oxygen to suppress thermal donors, then thermal donor formation is reduced, but the process becomes costly and time-consuming
Solution Approach 1:
The patent extracts the problematic interstitial oxygen from the silicon crystal structure during the growth phase by controlling the CZ growth conditions to achieve specific oxygen concentration ranges. Rather than attempting to remove oxygen after growth through lengthy thermal treatments, the method extracts and controls oxygen incorporation at the source during crystal formation, eliminating the need for subsequent time-consuming oxygen precipitation steps
Solution Approach 2:
The patent performs the oxygen control action preliminarily during the crystal growth stage rather than during or after device processing. By establishing the correct oxygen concentration and dopant balance before device fabrication begins, the method avoids the need for lengthy thermal treatments that would otherwise be required to precipitate oxygen and suppress thermal donor formation
3Manufacturing precision
If FZ silicon is used to achieve high resistivity, then resistivity increases, but mechanical stability decreases and size is limited
Solution Approach 1:
The patent changes the growth method parameters from FZ to CZ and adjusts the CZ growth parameters to achieve specific interstitial oxygen and dopant concentrations. This parameter change allows the use of CZ silicon with controlled properties that provide both high resistivity and the mechanical stability inherent to CZ-grown crystals, which contain more oxygen and have better mechanical properties than FZ silicon
4Manufacturing precision
If CZ silicon is grown with controlled purity to achieve high resistivity, then resistivity increases, but manufacturing difficulty and cost increase
Solution Approach 1:
The patent changes the approach from attempting to grow extremely pure silicon with very low dopant concentrations to growing silicon with controlled, moderate dopant concentrations and specific interstitial oxygen levels. This parameter change makes the manufacturing process more feasible for commercial production while achieving high resistivity through the thermal donor/acceptor compensation mechanism that occurs during standard thermal processing
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 process effectively decouples resistivity from boron concentration, achieving resistivities up to tens of thousands of ohm-cm with uniformity across the wafer diameter and depth, suitable for high-frequency applications.
Implementation Method 1
Thermal donors are produced during the thermal treatments employed as part of the integrated circuit manufacturing process, as a result of the presence of interstitial oxygen in the CZ silicon
Implementation Method 2
subjecting a silicon structure, which comprises a CZ single crystal silicon substrate having an initial resistivity of at least about 50 ohm-cm, to a heat-treatment for a duration and at a temperature such that the resulting substrate of the heat-treated structure has a concentration of thermal donors
Data Source
AI summary
The present invention generally relates to a high resistivity CZ silicon wafer, or a high resistivity silicon structure derived therefrom, and a process for the preparation thereof. In particular, the high resistivity silicon structure comprises a large diameter CZ silicon wafer as the substrate thereof, wherein the resistivity of the substrate wafer is decoupled from the concentration of acceptor atoms (e.g., boron) therein, the resistivity of the substrate being substantially greater than the resistivity as calculated based on the concentration of said acceptor atoms therein.