Self-Aligned Twin Well Region Formation via Dopant Holding Layer
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Solution Overview
Problem
Conventional processes for forming twin well regions in semiconductor wafers are costly and result in a non-planar silicon substrate surface due to large surface step artifacts, complicating shallow trench isolation and lithography processes.
Innovation Solution
A method involving implanting a first well type doping species into a dopant holding layer, etching away a portion of the layer using a photoresist mask, implanting a second well type doping species into the exposed substrate, and redistributing the first well type species into the substrate, reducing the number of processing steps and eliminating the surface step artifact.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If separate masking and implant steps are used for each well type, then precise doping control is achieved, but processing cost increases
Solution Approach 1:
The patent combines multiple separate masking and implant steps into a single unified process. A dopant holding layer is formed once, and both n-type and p-type dopants are introduced through this single layer using sequential implantation without removing the mask between steps. This merging of operations reduces processing complexity while maintaining doping precision through the selective etching of the dopant holding layer.
Solution Approach 2:
The dopant holding layer is formed in advance before any doping operations. This preliminary structure serves as a template that guides both n-type and p-type dopant placement. By preparing this holding layer beforehand, the patent enables subsequent dopants to be implanted through the same mask structure, eliminating the need for multiple masking steps and reducing overall processing complexity.
2Manufacturing precision
If multiple photoresist masks are applied sequentially, then selective doping regions are defined, but processing time increases
Solution Approach 1:
The patent merges multiple sequential masking operations into a single masking step. One photoresist mask is applied and maintained throughout the process, serving as a template for both n-type and p-type dopant introduction. The dopant holding layer is selectively removed in different regions to allow different dopants to reach the substrate, achieving the selectivity of multiple masks with the simplicity of a single mask, thereby reducing processing time.
Solution Approach 2:
The single photoresist mask is applied in advance and used as a permanent template throughout the doping sequence. Rather than removing and reapplying masks between n-type and p-type doping steps, the preliminary mask structure remains in place, and the dopant holding layer is selectively removed through the mask in different regions. This preliminary action eliminates the time-consuming cycle of multiple mask applications and removals while maintaining precise doping selectivity.
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 processing costs and eliminates the large surface step artifact, simplifying the formation of self-aligned twin well regions and improving the planarity of the silicon substrate surface.
Implementation Method 1
implanting a first well type doping species into the DHL such that its distribution remains stopped in the DHL above the silicon substrate
Implementation Method 2
etching away a portion of the DHL using a photoresist mask
Implementation Method 3
implanting a second well type doping species into the portions of the silicon substrate exposed by the etching
Implementation Method 4
moving a portion of the first well type doping species into the silicon substrate
Data Source
AI summary
A method for forming a self-aligned twin well region is provided. The method includes implanting a first well type doping species into the DHL such that its distribution remains stopped in the DHL above the silicon substrate, etching away a portion of the DHL using a photoresist mask, implanting a second well type doping species into the portions of the silicon substrate exposed by the etching, and moving a portion of the first well type doping species into the silicon substrate.