Source Line Formation in NAND Flash Memory
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Solution Overview
Problem
The challenge in forming NAND flash memory contacts is the microloading effect during etching, which leads to deeper trench etching and non-uniformity, making it difficult to achieve accurate exposure of both source and drain contact areas without under-etching or over-etching as device sizes scale to smaller dimensions.
Innovation Solution
A method involving an initial etch to form a trench and individual openings in the dielectric layer, followed by filling with conductive material and subsequent patterning to maintain the bottom surface area, and further etching to extend these features uniformly, allowing for the formation of a common source line and individual bit line contacts with alternating conductive and non-conductive areas along the trench.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If a trench and individual openings are formed in the same etch process, then both source and drain contacts can be formed in a single process step, but the microloading effect causes deeper etching in the trench leading to non-uniform etch depth
Solution Approach 1:
The patent applies local quality by forming a filler material specifically in the trench region (but not in individual openings) to create a localized structural difference. This filler material modifies the etch environment locally, causing the etch rate in the trench to match the etch rate in the individual openings, thereby achieving uniform etch depth across different feature types despite their geometric differences.
Solution Approach 2:
The patent implements preliminary action by depositing the filler material into the trench before performing the unified etch process. This pre-placement of filler material ensures that when the etch process occurs, the trench already has the modified structure needed to achieve uniform etching, preventing the microloading effect from causing depth variations.
2Quantity of substance
If device sizes are scaled to smaller dimensions, then memory capacity increases, but achieving accurate exposure of contact areas becomes more difficult due to enhanced microloading effects
Solution Approach 1:
The filler material creates a localized structural modification in the trench that compensates for the microloading effect, which becomes more pronounced at smaller dimensions. This local quality change ensures that the etch front progresses uniformly across both trench and individual openings even as feature sizes decrease, maintaining contact area exposure accuracy despite scaling.
Solution Approach 2:
The patent changes the physical parameters of the trench by introducing filler material, which alters the etch rate characteristics locally. This parameter change (adding filler material) compensates for the scaling-induced microloading effects, allowing accurate contact area exposure to be maintained even as device dimensions are reduced to increase memory capacity.
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 ensures uniform etch depth and accurate exposure of contact areas, preventing under-etching or over-etching, and allows for the formation of reliable source and drain contacts in NAND flash memory structures.
Implementation Method 1
performing an initial etch, thereby forming a trench in the dielectric layer over first contact areas of a plurality of NAND strings, the trench extending along a second direction that is perpendicular to the first direction, the initial etch also forming a plurality of individual openings in the dielectric layer over second contact areas of the plurality of NAND strings
Implementation Method 2
subsequently adding material in the trench to reduce an area of exposed bottom surface of the trench while maintaining the plurality of individual openings without substantial reduction of bottom surface area
Data Source
AI summary
An initial etch forms a trench over first contact areas of a plurality of NAND strings, the initial etch also forming individual openings over second contact areas of the plurality of NAND strings. Material is added in the trench to reduce an area of exposed bottom surface of the trench while maintaining the individual openings without substantial reduction of bottom surface area. Subsequent further etching extends the trench and the plurality of individual openings.