DRAM Buried Word Line Trench Fabrication Using Composite Mask
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Conventional methods for forming buried word lines in DRAMs often result in fractures and inconsistent trench widths, leading to electrical issues due to defects in the word line trench.
Innovation Solution
A method involving the formation of a hydrogen-containing silicon nitride layer with a specific chemical formula (SixNyHz) followed by a silicon oxide layer, which is patterned to create a smooth surface for accurate word line trench formation, preventing defects and ensuring consistent trench widths.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If a conventional method is used to form the word line trench, then the fabrication process is simple, but the word line trench has fractures and inconsistent width leading to electrical problems
Solution Approach 1:
The mask layer is divided into multiple distinct layers: a first mask layer (hydrogen-containing silicon nitride) and a second mask layer (silicon oxide). This segmentation allows each layer to perform its specific function - the first mask layer defines the trench pattern while the second mask layer protects the trench walls during etching, resulting in consistent trench width without fractures
Solution Approach 2:
The patent uses a composite mask structure combining hydrogen-containing silicon nitride and silicon oxide materials. This composite approach leverages the complementary properties of both materials - the etch selectivity of silicon nitride and the protective qualities of silicon oxide - to achieve precise trench formation with uniform width and no fractures
2Manufacturing precision
If the word line trench is formed with conventional methods, then the process is fast, but the surface is rough causing lithographic inaccuracies
Solution Approach 1:
The first mask layer is formed with a controlled hydrogen content (specific ratio of H to Si atoms) before the etching process begins. This preliminary control of the mask layer composition ensures that the subsequent etching produces a smooth trench surface, enabling accurate lithographic patterning without requiring additional surface treatment steps
3Reliability
If the word line trench width is inconsistent, then material usage is flexible, but electrical performance deteriorates
Solution Approach 1:
The patent implements a controlled etching process where the second mask layer (silicon oxide) is deposited to a specific thickness (50-200 nm) after the first mask layer is formed. This controlled deposition acts as a feedback mechanism that ensures consistent trench width by protecting the trench walls uniformly during etching, guaranteeing reliable electrical performance
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 prevents fractures and ensures consistent word line trench widths, thereby improving the reliability and performance of buried word lines by maintaining a smooth surface for precise lithographic processes, reducing electrical problems in DRAMs.
Implementation Method 1
forming a hydrogen-containing silicon nitride layer (24) to cover the substrate (10)
Implementation Method 2
forming a silicon oxide layer (26) to cover and contact the hydrogen-containing silicon nitride layer (24)
Implementation Method 3
the substrate is etched by taking the first patterned mask layer as a mask to form a word line trench
Data Source
AI summary
A method of fabricating a DRAM includes providing a substrate. Later, a first mask layer is formed to cover the substrate. The first mask layer includes a hydrogen-containing silicon nitride layer and a silicon oxide layer. The hydrogen-containing silicon nitride layer has the chemical formula: SixNyHz, wherein x is between 4 and 8, y is between 3.5 and 9.5, and z equals 1. After that, the first mask layer is patterned to form a first patterned mask layer. Next, the substrate is etched by taking the first patterned mask layer as a mask to form a word line trench. Subsequently, the first patterned mask layer is removed entirely. Finally, a word line is formed in the word line trench.