Shallow Trench Isolation Fabrication Using Cap Layer Implant Mask
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Solution Overview
Problem
The existing methods for fabricating isolation shallow trenches in deep trenches are complex, have a small process window, and high process difficulty, especially at advanced levels below 90 nanometers, affecting cost and yield.
Innovation Solution
A cap layer is filled in the upper portion of the deep trench, followed by a tilt angle implant process to form an etching mask, allowing for a single etching process to create the shallow trench, increasing the process window and simplifying the fabrication.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If a tilt angle implant process is performed with a small angle to reduce the size of the isolation shallow trench, then the trench size is reduced, but the process window becomes small and process difficulty increases
Solution Approach 1:
The patent applies preliminary action by forming a cap layer in the upper portion of the deep trench before performing the tilt angle implant process. This pre-formed cap layer serves as a stop layer that allows the use of a larger tilt angle (thereby improving process window and ease of manufacture) while still achieving precise control over the isolation shallow trench size through the controlled implantation into the cap layer.
2Manufacturing precision
If sequential wet etching and oxidation processes are performed to form the isolation shallow trench, then the trench can be formed, but the process becomes complex and productivity decreases
Solution Approach 1:
The patent merges multiple sequential processes (wet etching and oxidation processes) into a single tilt angle implant process followed by a single etching process. The cap layer is formed as a unified structure that serves multiple functions: it acts as a mask for the implant process and as a stop layer for subsequent etching, thereby eliminating the need for separate wet etching and oxidation steps and improving productivity.
3Adaptability or versatility
If the element integration is increased and memory cell sizes are reduced, then high integration is achieved, but the process window for implant processes becomes even smaller
Solution Approach 1:
The patent introduces a cap layer as an intermediary structure in the upper portion of the deep trench. This cap layer acts as a mediator that decouples the relationship between trench size and implant angle. By providing this intermediate layer, the process can use a larger, more robust tilt angle for implantation while still achieving the precise dimensional control required for high integration levels, thereby maintaining both adaptability and ease of manufacture.
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 a larger tilt angle implantation, reducing process difficulty and improving yield by eliminating the need for sequential wet etching and oxidation processes, while maintaining control over trench size even at advanced levels.
Implementation Method 1
a tilt angle implant process is performed to form a crust layer on the surface of a portion of the cap layer
Implementation Method 2
an etching process is performed to the substrate 12 to remove portions of the nitride layer 26 and the conductive layer 22 not covered by the oxidation mask layer 34
Data Source
AI summary
A method of fabricating an isolation shallow trench contains providing a substrate with at least a deep trench, forming a cap layer on the upper portion of the deep trench, forming a crust layer on a portion of the cap layer, defining a trench extending through the cap layer and the conductive layer, and forming an isolation layer in the shallow trench.