LOCOS Isolation Structure with CVD Oxide for High Voltage Stability
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Solution Overview
Problem
The manufacturing process for semiconductor devices with both high voltage and low voltage elements is inefficient due to the need for different silicon oxide film thicknesses, leading to complex processes, stress on edge portions, and deterioration of device characteristics.
Innovation Solution
A semiconductor device with a high voltage element region and a low voltage element region, utilizing a first LOCOS isolation structure with a CVD oxide film on the LOCOS oxide film in the high voltage region and a second LOCOS isolation structure in the low voltage region, allowing for simplified manufacturing and reduced stress on edge portions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a thick LOCOS oxide film is formed in the high voltage element region to relax electric field intensity, then high voltage characteristic stability is improved, but chip size is enlarged which goes against finer topography and higher integration level
Solution Approach 1:
The isolation structure is segmented into two distinct parts: a first LOCOS isolation structure with a thick oxide film in the high voltage element region, and a second LOCOS isolation structure with a thin oxide film in the low voltage element region. This segmentation allows each region to have optimized oxide thickness for its specific requirements, enabling high voltage stability without unnecessarily increasing overall chip size.
Solution Approach 2:
Different oxide film thicknesses are applied to different regions based on their specific requirements. The high voltage element region receives a thick oxide film for electric field relaxation, while the low voltage element region receives a thin oxide film to minimize chip area. This local quality differentiation resolves the contradiction between reliability and chip size.
2Reliability
If two thermal oxidation steps are performed to form LOCOS oxide films of different thicknesses, then high voltage and low voltage element requirements are met, but manufacturing process complexity increases
Solution Approach 1:
The manufacturing process is segmented into two sequential oxidation steps with different conditions. The first oxidation step forms a thin oxide film uniformly across both regions. The second oxidation step selectively forms additional oxide thickness only in the high voltage element region through selective masking. This segmentation allows meeting different regional requirements while maintaining a systematic, manageable process flow.
Solution Approach 2:
The thin oxide film is formed in advance as a base layer before the selective thickening step. This preliminary action ensures that both regions have a minimum isolation oxide layer, and then only the high voltage region receives additional oxidation. This approach simplifies process control compared to attempting to form different thicknesses simultaneously.
3Manufacturing precision
If thermal oxidation is performed at high temperature for long hours to form thick LOCOS oxide film, then sufficient oxide thickness is achieved, but stress acts on edge portions and impurities diffuse causing characteristic deterioration
Solution Approach 1:
The oxide formation process is segmented into two thermal oxidation steps with different durations and temperatures. The first step forms a thin oxide layer under moderate conditions. The second step selectively thickens the oxide only in the high voltage region with controlled parameters. This segmentation avoids the need for a single long-duration high-temperature oxidation that would cause stress and impurity diffusion, while still achieving the required thickness in the high voltage region.
Solution Approach 2:
A thin oxide film is formed in advance as a protective and foundational layer before the selective thickening oxidation. This preliminary oxide layer reduces stress concentration during subsequent processing and prevents impurity diffusion into the semiconductor substrate, thereby protecting device characteristics while allowing the high voltage region to achieve sufficient oxide thickness.
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 enables semiconductor devices with favorable characteristics for both high voltage and low voltage elements, simplifying the manufacturing process and preventing impurity diffusion, thus maintaining device stability and performance.
Implementation Method 1
a CVD step of forming a CVD oxide film on the LOCOS oxide film in the high voltage element region
Implementation Method 2
a step of forming LOCOS oxide films on the high voltage element region and the low voltage element region
Data Source
AI summary
A semiconductor device including a high voltage element and a low voltage element, including: a semiconductor substrate having high voltage element region where the high voltage element is formed, and a low voltage element region where the low voltage element is formed; a first LOCOS isolation structure disposed in the high voltage element region; and a second LOCOS isolation structure disposed in the low voltage element region, wherein the first LOCOS isolation structure includes a LOCOS oxide film formed on a surface of the semiconductor substrate and a CVD oxide film formed on the LOCOS oxide film, and the second LOCOS isolation structure includes a LOCOS oxide film.