Shallow Trench Isolation Height Control for NAND Memory
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Solution Overview
Problem
Existing fabrication techniques for high-density semiconductor devices, such as NAND flash memory, face challenges in reducing feature sizes and preventing process-related failures like gouging and polysilicon residue formation due to the narrow window for etching processes, which can result in either over-etching or under-etching issues.
Innovation Solution
The implementation of a shallow trench isolation trench with a controlled height difference between its top surfaces in the peripheral region of the substrate, which helps prevent gouging of active areas and polysilicon residue formation by allowing more precise etching and reducing the risk of exposure during the formation of transistors and capacitors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If conventional etching processes are used to reduce feature sizes, then manufacturing density is improved, but process control precision deteriorates due to the narrow etching window causing over-etching or under-etching
Solution Approach 1:
The patent applies preliminary action by forming a mandrel structure and applying a first sacrificial layer before the actual trench formation. This preparatory structure guides the subsequent etching process, ensuring precise trench depth and width control. The mandrel and sacrificial layer are removed after defining the trench geometry, having served their preliminary purpose of enabling precise feature size reduction without compromising etching process control.
Solution Approach 2:
The patent uses an intermediary approach by introducing a second sacrificial layer that fills the trench and acts as a mediator during the etching process. This intermediate material layer helps control the etching front, preventing both over-etching and under-etching by providing a controlled interface for the etchant to interact with the underlying structure, thus maintaining manufacturing precision while achieving high density.
2Manufacturing precision
If aggressive etching is used to prevent polysilicon residue formation, then manufacturing precision is improved, but harmful factors increase due to gouging of active areas
Solution Approach 1:
The patent converts the potential harm of aggressive etching into a benefit by using the sacrificial layers as protective elements. The first and second sacrificial layers are specifically designed to be removed selectively, and their presence during etching actually protects the active areas from gouging while allowing aggressive etching conditions to be used to prevent polysilicon residue. The sacrificial materials essentially turn the aggressive etching process into a controlled operation that achieves precision without damage.
Solution Approach 2:
The sacrificial layers serve as intermediary protective elements between the aggressive etchant and the active areas. These intermediate layers absorb the harsh etching conditions, preventing direct contact with and damage to the active areas, while still allowing the etching process to proceed aggressively enough to prevent polysilicon residue formation in the trench regions.
3Object-affected harmful factors
If conservative etching is used to prevent active area gouging, then harmful factors are reduced, but manufacturing precision deteriorates due to polysilicon residue formation
Solution Approach 1:
The patent applies the extraction principle by removing the problematic polysilicon material through the sacrificial layer mechanism. The first sacrificial layer is applied over the polysilicon, and the second sacrificial layer fills the trench. During processing, these sacrificial layers are selectively removed, taking the polysilicon residue problem with them. This extraction approach allows conservative etching conditions to be used while still achieving clean removal of polysilicon without residue formation.
Solution Approach 2:
The sacrificial layers are applied in preliminary action before the final trench formation and polysilicon processing. This preliminary application of sacrificial materials creates a protective and removable framework that enables conservative etching to proceed without leaving polysilicon residue. The preliminary structure is designed to be removed afterward, having served its purpose of enabling precise polysilicon removal under gentle etching conditions.
Data Source
AI summary
A NAND memory is provided that includes a memory cell region and a peripheral region. The peripheral region includes a shallow trench isolation trench disposed in a substrate. The shallow trench isolation trench includes a first top surface, and a second top surface. A difference between a height of the second top surface and a height of the first top surface is less than a predetermined value ΔMAX.