DRAM Manufacturing Selective Nitride Removal for Defect Reduction
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Solution Overview
Problem
The increasing packing density in dynamic random access memory (DRAM) leads to a higher defect rate, which is not effectively addressed by simple hydrogen processing, especially when using a semiconductor substrate with single crystal silicon that has a lower dangling bond rate compared to polysilicon.
Innovation Solution
A method for manufacturing DRAM that involves eliminating the silicon nitride film in the peripheral circuit area and processing the substrate in a hydrogen gas atmosphere, allowing hydrogen to terminate dangling bonds and reduce defects, while maintaining or improving the packing density.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If the packing density of DRAM is increased, then the memory capacity per unit area is improved, but the defect rate increases
Solution Approach 1:
The patent applies different treatments to different regions of the semiconductor substrate. Specifically, the silicon nitride film is selectively removed from the peripheral circuit area while being maintained in the memory array area. This local differentiation allows hydrogen to reach the peripheral circuits for dangling bond termination without affecting the memory cells, thereby resolving the contradiction between increased packing density and reduced defect rate.
Solution Approach 2:
The semiconductor substrate is divided into distinct functional regions: memory array areas where silicon nitride film is retained, and peripheral circuit areas where the film is removed. This segmentation enables targeted hydrogen processing in peripheral regions to reduce defects while maintaining the integrity and low defect rate characteristics of the memory array regions, thus allowing higher overall packing density without proportionally increasing defect rates.
2Loss of time
If simple hydrogen processing is applied to single crystal silicon substrate, then the processing time is reduced, but the defect reduction effect is insufficient
Solution Approach 1:
The patent extracts or removes the silicon nitride film from the peripheral circuit area to enable hydrogen access. This extraction is necessary because the silicon nitride film acts as a barrier that prevents hydrogen from reaching and terminating dangling bonds in the peripheral circuits. By selectively removing this barrier in specific regions, the patent achieves effective defect reduction without requiring prolonged processing times across the entire substrate.
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 method significantly reduces the defect rate in DRAM even with increased packing density, enhancing the reliability and performance of the memory cells by effectively terminating dangling bonds and reducing leak current.
Implementation Method 1
The dangling bond is terminated by hydrogen. In view of this, there has been proposed a method of terminating dangling bond contained in the polysilicon with use of hydrogen contained in the plasma nitride film used in the polysilicon.
Implementation Method 2
a step (2) of processing in an atmosphere of a hydrogen gas a substrate-to-be-processed obtained by the step (1)
Data Source
AI summary
The present invention has an object to provide a method for manufacturing a dynamic random access memory capable of reducing a defect rate even if the memory has a large packing density. The method of the present invention is a method for manufacturing a dynamic random access memory having memory array areas and a peripheral circuit area arranged in a semiconductor substrate and a silicon nitride film provided over the memory array areas and the peripheral circuit area, the method having at least a step (1) of eliminating the silicon nitride film provided in the peripheral circuit area; and a step (2) of processing in an atmosphere of a hydrogen gas a substrate-to-be-processed obtained by the step (1).