Buried Isolation Layer via Thermal Oxidation
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Solution Overview
Problem
Integrated circuits formed on silicon-on-insulator wafers are costly, and methods to create buried silicon dioxide layers for dielectric isolation are problematic, leading to dimension control issues and stress on the wafer during photolithographic operations.
Innovation Solution
An isolation recess is formed in a single-crystal silicon substrate with sidewall insulators and a buried thermal oxide layer, preventing oxide growth on sidewalls, allowing a single-crystal semiconductor layer to be formed laterally separated from the substrate, which is then planarized to be coplanar with the substrate.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If silicon-on-insulator wafers are used to form integrated circuits, then dielectric isolation is achieved, but production cost increases
Solution Approach 1:
The patent replaces expensive commercial SOI wafers with a cost-effective alternative: forming buried oxide layers in-situ on standard silicon wafers through controlled thermal oxidation. This eliminates the need to purchase and process expensive pre-fabricated SOI substrates, directly addressing the cost issue while maintaining the dielectric isolation function.
Solution Approach 2:
The patent introduces sidewall insulators as intermediary structures that control oxide growth during thermal processing. These sidewall insulators act as masks to prevent oxide formation on vertical surfaces while allowing controlled oxidation at the bottom of isolation recesses, enabling precise formation of buried isolation layers without requiring expensive SOI wafers.
2Reliability
If oxygen implantation is used to form buried silicon dioxide layers, then dielectric isolation is achieved, but lateral and vertical dimension control deteriorates
Solution Approach 1:
The patent replaces the oxygen implantation process with thermal oxidation. Instead of using ion implantation to deposit oxygen atoms, the method uses controlled thermal oxidation where oxygen diffuses through the silicon lattice under heat treatment. This substitution provides superior dimensional control because thermal oxidation is a well-established process with precise control over oxide thickness through temperature, time, and atmosphere parameters.
Solution Approach 2:
The patent performs preliminary formation of isolation recesses and sidewall insulators before the thermal oxidation step. The sidewall insulators are deposited and patterned in advance to define the precise boundaries where oxide growth should occur. This preliminary structuring ensures that subsequent thermal oxidation produces buried isolation layers with accurate lateral and vertical dimensions.
3Reliability
If oxygen implantation is used to form buried silicon dioxide layers, then dielectric isolation is achieved, but wafer stress increases
Solution Approach 1:
The patent replaces the high-energy oxygen implantation process with gentle thermal oxidation. Oxygen implantation requires high-energy ion bombardment that can create lattice damage and induce wafer stress. In contrast, thermal oxidation occurs under milder conditions with oxygen molecules diffusing into the silicon lattice, avoiding the mechanical stress and damage associated with ion implantation while still achieving dielectric isolation.
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 reduces the cost of integrated circuit production by avoiding expensive SOI wafers and minimizes stress during photolithography, enabling precise control over lateral and vertical dimensions of the buried oxide layer.
Implementation Method 1
Thermal oxide is formed at a bottom surface of the isolation recess to provide a buried isolation layer
Data Source
AI summary
An integrated circuit may be formed by forming an isolation recess in a single-crystal silicon-based substrate. Sidewall insulators are formed on sidewalls of the isolation recess. Thermal oxide is formed at a bottom surface of the isolation recess to provide a buried isolation layer, which does not extend up the sidewall insulators. A single-crystal silicon-based semiconductor layer is formed over the buried isolation layer and planarized to be substantially coplanar with the substrate adjacent to the isolation recess, thus forming an isolated semiconductor layer over the buried isolation layer. The isolated semiconductor layer is laterally separated from the substrate.