DRAM Landing Pad Test Structure for Early WAT Detection
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Solution Overview
Problem
There is a need for a test structure in dynamic random access memory (DRAM) manufacturing that can effectively detect the quality of landing pads early in the process to ensure reliable electrical connections between MOS transistors and cell capacitors, as existing methods lack efficient means for assessing the electrical performance of these pads during the wafer acceptance test (WAT).
Innovation Solution
A test structure comprising a semiconductor substrate with gate structures, source/drain regions, bit lines, dielectric layers, landing pads, and a conductive layer, where the conductive layer is electrically connected to the landing pads and covers their upper surfaces, allowing for the detection of electrical performance through wafer acceptance tests, and optionally includes a barrier layer for enhanced adhesion and contact.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If traditional test structures are used without dedicated landing pad detection, then the manufacturing process remains simple, but the quality of landing pads cannot be effectively detected early in the process
Solution Approach 1:
The test structure is segmented into distinct functional components: MOS transistor region with gate and source/drain, landing pads, contact plugs, and bit line structures. This segmentation allows independent detection of landing pad quality while maintaining overall test structure functionality, resolving the contradiction between detection precision and structural simplicity.
Solution Approach 2:
The patent introduces intermediate test elements including contact plugs connecting landing pads to bit lines, and dedicated bit line structures that serve as intermediaries to detect landing pad electrical properties. These intermediaries enable indirect but effective measurement of landing pad quality without requiring direct access to the pads themselves, balancing detection capability with structural elegance.
2Reliability
If comprehensive test structures with multiple components are implemented, then landing pad quality can be detected, but the manufacturing process becomes more complex and time-consuming
Solution Approach 1:
The test structure employs universal components that serve multiple functions: the MOS transistor serves both as a functional element and as part of the test structure; bit lines serve both as signal transmission lines and as test elements for detecting landing pad quality; contact plugs serve both as electrical connections and as test vias. This multi-functionality ensures reliable electrical connection detection while avoiding the need for separate dedicated test structures that would reduce manufacturing efficiency.
3Loss of time
If landing pad quality is not detected early, then the manufacturing process remains fast, but potential issues like necking cannot be identified until later stages
Solution Approach 1:
The test structure is designed to be formed concurrently with the actual DRAM cell structures during the same manufacturing steps. Landing pads, contact plugs, and bit line structures are created in advance as part of the normal fabrication process, enabling early detection of quality issues like necking before subsequent processing steps. This preliminary formation of test elements allows detection timing to be advanced without requiring additional manufacturing steps.
Data Source
AI summary
A test structure for use in a dynamic random access memory is provided. A first gate structure is disposed in a semiconductor substrate. First and second source/drain regions are disposed in the semiconductor substrate and at two sides of the first gate structure. A bit line structure is disposed on the first source/drain region. A dielectric layer is disposed on the semiconductor substrate. First and second landing pads are disposed on the dielectric layer. A first contact plug is disposed in the dielectric layer and is electrically connected to the second source/drain region and the first landing pad. A conductive layer is disposed on and electrically connected to the first landing pad and the second landing pad, in which the conductive layer covers upper surfaces of the first and second landing pads and has a portion between the first landing pad and the second landing pad.