Protection Diode Oxide Thickness for Gate Reliability
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Solution Overview
Problem
The challenge in semiconductor device manufacturing is the thin base oxide film of poly-silicon diodes, which leads to rectification failures due to electric potential influence, and the need for long high-temperature thermal treatment for thick oxide films, causing substrate deformation and increasing manufacturing steps, while also affecting the flatness and reliability of the device.
Innovation Solution
A semiconductor device with a protection diode having a plurality of PN-junctions in a poly-silicon layer, formed on a thicker silicon oxide film with a higher impurity content than the gate insulating film, connected between the gate electrode and source, using ion-implanted layers and anisotropic etching to maintain reliability and reduce manufacturing complexity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a thin base oxide film is used for the poly-silicon diode, then the device size is reduced and manufacturing is simplified, but the rectification function fails due to electric potential influence from the base
Solution Approach 1:
The patent applies local quality by creating different oxide film thicknesses in different regions: a thin oxide film (30-150 nm) under the MOS transistor gate for proper transistor operation, and a thick oxide film (>150 nm) in the field region under the poly-silicon diode to ensure rectification function. This spatial differentiation allows each component to have the optimal oxide thickness for its specific function.
2Reliability
If a thick oxide film is formed by long high-temperature thermal treatment, then the poly-silicon diode rectification function is ensured, but the semiconductor substrate deforms and manufacturing steps increase
Solution Approach 1:
The patent applies preliminary action by forming the thick oxide film in the field region before forming the MOS transistor gate structure. The thick oxide film is prepared in advance as a base layer, which prevents substrate deformation during subsequent processing and eliminates the need for long high-temperature thermal treatments later in the manufacturing process.
Solution Approach 2:
The patent segments the oxide film formation process into distinct steps: first forming a thin oxide film across the entire surface, then selectively thickening the oxide film only in the field region using plasma oxidation. This segmentation allows precise control of oxide thickness in different regions without requiring uniform high-temperature treatment across the entire substrate.
3Reliability
If a thick oxide film is formed on the active region, then the poly-silicon diode base is sufficiently thick, but the flatness of the semiconductor substrate is reduced causing misalignment and reduced lithography margin
Solution Approach 1:
The patent applies local quality by restricting the thick oxide film formation to only the field region where the poly-silicon diode will be formed, while maintaining a thin oxide film in the active region containing the MOS transistor. This localized thickening ensures the diode has sufficient base thickness without creating flatness issues in the active region that would affect lithography alignment.
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 solution enhances the reliability of the protection diode, prevents degradation, and reduces manufacturing steps by forming a thicker silicon oxide film without requiring long high-temperature treatments, maintaining device flatness and enabling miniaturization of MOS transistors.
Implementation Method 1
These oxide films are formed by thermally oxidizing a surface of a semiconductor substrate
Implementation Method 2
forming a first ion-implanted layer by selectively implanting impurities into the second area of the semiconductor substrate
Data Source
AI summary
A semiconductor device comprises an insulated gate field effect transistor and a protection diode. The insulated gate field effect transistor has a gate electrode formed on a gate insulating film, a source and a drain. The source and the drain are formed in a first area of a semiconductor substrate. A first silicon oxide film is formed on a second area of the semiconductor substrate adjacent to the first area. The first silicon oxide film is thicker than the gate insulating film and contains larger amount of impurities than the gate insulating film. A poly-silicon layer is formed on the first silicon oxide film. The protection diode has a plurality of PN-junctions formed in the poly-silicon layer. The protection diode is connected between the gate electrode and the source so as to prevent breakdown of the gate insulating film.