LOCOS Thickness Control Without a Mask Using Blanket Etch
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Solution Overview
Problem
Existing methods for forming local oxidation of silicon (LOCOS) structures with different thicknesses on a semiconductor substrate require a mask level, increasing production costs and cycle time.
Innovation Solution
A blanket etch of a sacrificial layer is used to protect a first LOCOS structure while exposing a second LOCOS structure, eliminating the need for a mask and allowing the second structure to grow to a greater thickness, facilitated by an oxygen diffusion barrier layer and a test database for process optimization.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If a mask level is used to form LOCOS structures with different thicknesses, then the manufacturing precision and selectivity are improved, but the device complexity and production cost increase
Solution Approach 1:
The patent extracts and removes the mask layer from the fabrication process. Instead of using a mask to define regions for different LOCOS thicknesses, the invention uses a sacrificial layer that is selectively removed by blanket etching, leaving the first LOCOS structure protected while exposing the second LOCOS structure for further oxidation. This eliminates the mask level entirely while maintaining the ability to create different thicknesses.
Solution Approach 2:
The patent introduces a sacrificial layer as an intermediary element. This sacrificial layer is formed over both LOCOS structures, then selectively removed by blanket etching to expose only the second LOCOS structure. The sacrificial layer acts as a temporary mediator that enables differential oxidation without requiring a mask, and is subsequently removed after serving its protective function.
2Manufacturing precision
If a mask level is used to form LOCOS structures with different thicknesses, then the selectivity is improved, but the production cycle time increases
Solution Approach 1:
The patent implements continuous useful action through blanket etching. Instead of performing patterned etching that requires mask alignment and multiple steps, the sacrificial layer is etched uniformly across the entire wafer surface. This continuous blanket etching process eliminates the time-consuming mask alignment and application steps while maintaining selective exposure of the second LOCOS structure through the sacrificial layer's strategic placement and controlled removal.
3Device complexity
If a blanket etch of sacrificial layer is used to eliminate mask level, then the device complexity is reduced, but the manufacturing precision may deteriorate
Solution Approach 1:
The patent applies local quality by creating spatial variations in the sacrificial layer configuration. The sacrificial layer is formed with different thicknesses or removal characteristics in different regions, allowing the first LOCOS structure to remain protected while the second LOCOS structure is exposed. This local differentiation in the sacrificial layer's properties enables precise control over which structures undergo further oxidation, maintaining manufacturing precision without requiring a mask.
Solution Approach 2:
The patent utilizes parameter changes in the blanket etch process. By controlling etch duration, etch rate, and sacrificial layer thickness parameters, the process achieves selective removal of the sacrificial layer to expose only the second LOCOS structure. These parameter adjustments enable precise control over the etching depth and exposure patterns, maintaining manufacturing precision while using a simplified blanket etch approach instead of mask-based methods.
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 method reduces production costs and cycle time by eliminating the mask level, enabling efficient fabrication of LOCOS structures with different thicknesses, thereby improving the manufacturability of integrated circuits.
Implementation Method 1
the first LOCOS structure can be covered by an oxygen diffusion barrier (ODB) layer, while a portion of the second LOCOS structure can be exposed
Implementation Method 2
A wafer on which the LOCOS structures are formed is then subjected to an oxidation process, allowing the second LOCOS structure to grow to a greater thickness
Data Source
AI summary
An integrated circuit includes a gate electrode over a silicon substrate and a local oxidation of silicon (LOCOS) structure between the gate electrode and the silicon substrate. The LOCOS structure has bird's beak portions, peripheral portions between the bird's beak portions, and a central portion between the peripheral portions. The peripheral portions have a first thickness, and the central portion has a greater second thickness.