Bit Line Contact Opening Undercut to Prevent Misalignment Shorts
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Solution Overview
Problem
The challenge in semiconductor memory device manufacturing is the occurrence of short circuits due to misalignment during the formation of bit line contact openings, which narrows the process window and reduces manufacturing yield.
Innovation Solution
The implementation of an under-cut structure at the edge of the bit line contact opening, achieved through a specific etching process that forms a wider bottom than top, enhances alignment precision and prevents short circuits by ensuring adequate removal of active region portions, thereby increasing the process window.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a conventional bit line contact opening is formed without under-cut structure, then the manufacturing process is simpler, but misalignment occurs leading to short circuits
Solution Approach 1:
The bit line contact opening is designed with an asymmetric under-cut structure where the bottom width is greater than the top width. This asymmetric geometry ensures that even when misalignment occurs during fabrication, the wider bottom portion maintains proper electrical contact while the narrower top provides alignment tolerance, preventing short circuits between adjacent contact openings.
Solution Approach 2:
The solution transitions from a simple vertical contact opening to a three-dimensional under-cut structure. By modifying the contact opening geometry in the horizontal dimension (creating wider bottom and narrower top), the design gains additional spatial tolerance that prevents short circuits while maintaining manufacturing feasibility through controlled etching processes.
2Manufacturing precision
If the process window is narrow, then the manufacturing precision requirements are tighter, but misalignment leads to short circuits
Solution Approach 1:
The under-cut structure acts as a pre-designed cushion or buffer zone that compensates for potential misalignment. The wider bottom portion of the contact opening provides a tolerance buffer that absorbs alignment errors, allowing the manufacturing process to operate with a wider process window without sacrificing precision.
Solution Approach 2:
The contact opening geometry is changed from a uniform cylindrical shape to a tapered shape with different top and bottom dimensions. This parameter change (creating width variation through the depth of the opening) fundamentally alters the alignment sensitivity, enabling larger process windows while maintaining manufacturing precision.
3Ease of manufacture
If the bit line contact opening has uniform width, then the fabrication process is easier, but misalignment causes short circuits
Solution Approach 1:
The contact opening employs asymmetric dimensions with a wider bottom and narrower top, created through controlled etching processes. This asymmetric design maintains ease of manufacture using standard semiconductor fabrication techniques while simultaneously preventing short circuits by ensuring proper spacing between adjacent contacts.
Solution Approach 2:
Different portions of the contact opening have different widths tailored to specific functional requirements: the wider bottom provides spacing tolerance to prevent short circuits, while the narrower top facilitates precise alignment and connection. This local differentiation of geometric properties optimizes both manufacturability and reliability.
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 effectively reduces the risk of short circuits and enhances the process window of the bit line contact opening, leading to improved manufacturing yield and product reliability.
Implementation Method 1
a specific etching process that forms a wider bottom than top
Data Source
AI summary
A semiconductor memory device and a manufacturing method thereof are provided in the present invention. An under-cut structure is formed at an edge of a bit line contact opening in the process of forming the bit line contact opening for avoiding short problems caused by alignment shifting, and the process window of the process of forming the bit line contact opening may be improved accordingly.