Rectangular Contact Plug Structure for DRAM
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Solution Overview
Problem
Conventional contact plugs in DRAMs are cone-shaped, resulting in minimal contact area and increased contact resistance, which hinders the reduction of memory cell size and memory storage capacity.
Innovation Solution
The method involves forming a conductive stack on a semiconductor substrate, creating a depression, and using a mask block to form both a tall rectangular contact plug for capacitors and a short rectangular contact plug for bit lines, increasing the contact area and reducing resistance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional cone-shaped contact plugs are used, then the fabrication process is simple, but the contact area is minimal and contact resistance increases
Solution Approach 1:
The patent transitions from conventional two-dimensional planar contacts to three-dimensional vertical contacts by forming tall contact plugs that extend through multiple dielectric layers. This vertical dimensionality change increases the contact area between the contact plug and the underlying doped region, thereby reducing contact resistance while maintaining fabrication simplicity
Solution Approach 2:
The contact plug structure is segmented into distinct functional regions: a wide base portion for optimal electrical contact with the doped region, a tall intermediate portion for navigating through dielectric layers, and a top portion for connection to upper conductive structures. This segmentation allows each region to be optimized for its specific function
2Productivity
If memory cell size is reduced to increase storage capacity, then more memory cells fit per chip, but contact resistance increases due to smaller contact area
Solution Approach 1:
As memory cell dimensions are scaled down in the planar direction to increase density, the patent compensates by extending the contact plug vertically into the third dimension. This vertical extension maintains adequate contact area with the doped region even as the cell footprint shrinks, thereby reducing contact resistance despite smaller cell size
Solution Approach 2:
The patent changes the geometric parameters of the contact plug, specifically increasing the height and base width of the contact structure. This parameter modification allows the contact area to be decoupled from the planar cell dimensions, enabling small cell size while maintaining low contact resistance through optimized vertical geometry
Data Source
AI summary
In a further embodiment of the present invention, a method for preparing a contact structure includes the steps of forming a conductive stack on the semiconductor substrate; forming a patterned mask on the conductive stack; forming a depression in an upper portion of the conductive stack; forming a spacer layer on the surface of the depression and the patterned mask; forming a mask block filling the depression; removing a portion of the spacer layer not covered by the mask block; and removing a portion of the conductive stack by using the mask block and the patterned mask to form the contact structure including at least one tall contact plug under the patterned mask and at least one the short contact plug under the mask block.