Flash Memory Select Gate Protection via Selective Oxidation
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Solution Overview
Problem
The fabrication of split-gate memory cells in flash memory is prone to etch damage during the removal of the nitride mask layer, leading to breakdown voltage issues and current leakage, while tuning the etching process to prevent damage results in incomplete nitride removal affecting electrical properties.
Innovation Solution
A method involving the formation of a memory gate, a hard mask layer, and a select gate with a selective oxidation process creating an oxide layer of varying thickness, allowing for the selective removal of the hard mask layer without damaging the select gate, using a dry oxidation process and specific etching steps with diluted hydrofluoric and phosphoric acids.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If a common etching process is used to remove the nitride mask layer on the memory gate, then the etching process is simple and fast, but the oxide-nitride spacer and select gate are damaged leading to breakdown voltage issues and current leakage
Solution Approach 1:
An oxide layer is grown on the select gate and hard mask layer as an intermediary protective barrier before etching. This oxide layer prevents the etching plasma from directly contacting and damaging the select gate, while allowing the nitride mask to be removed. The oxide layer acts as a mediator that protects sensitive structures during the necessary etching process.
Solution Approach 2:
The oxide layer is grown in advance before the etching process to pre-protect the select gate. This preliminary action ensures that when the etching process subsequently removes the nitride mask, the select gate is already shielded and cannot be damaged by the etching plasma.
2Reliability
If the etching process is tuned to prevent over-etching on the ON spacer and select gate, then the select gate is protected from damage, but nitride residue remains on the memory gate affecting electrical properties
Solution Approach 1:
The oxide layer serves as a sacrificial intermediary that enables complete nitride removal. By growing the oxide layer first, the etching process can proceed aggressively to remove all nitride mask material without fearing select gate damage. The oxide layer absorbs the full etching attack, allowing 100% nitride removal while the select gate remains protected underneath.
Solution Approach 2:
The oxide layer provides beforehand cushioning protection to the select gate, enabling the etching process to be tuned for maximum nitride removal efficiency. The cushioning oxide layer absorbs all etching damage that would otherwise affect the select gate, allowing the process to be optimized for complete mask removal without compromising gate integrity.
3Reliability
If the oxide layer on the select gate is made thicker to provide better protection, then the select gate is better protected from etch damage, but more material must be removed afterward and the process becomes more complex
Solution Approach 1:
The oxidation parameters (time, temperature, atmosphere) are optimized to grow an oxide layer of precisely the right thickness for protection. By controlling the oxidation parameters, the process achieves adequate protection without excessive oxide growth, maintaining process simplicity while ensuring select gate integrity.
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 etch damage to the select gates, ensuring complete removal of the hard mask layer without residue, maintaining electrical performance and reliability of the flash memory device.
Implementation Method 1
performing a selective oxidation process to form an oxide layer on the hard mask layer and the select gate, wherein a portion of the oxide layer on the select gate is thicker than a portion of the oxide layer on the hard mask layer
Implementation Method 2
using a dry oxidation process
Implementation Method 3
removing the oxide layer on the hard mask layer and the hard mask layer to expose a top surface of the memory gate
Implementation Method 4
specific etching steps with diluted hydrofluoric and phosphoric acids
Data Source
AI summary
A method of fabricating a semiconductor device includes forming a memory gate and a hard mask layer on the memory gate, forming a select gate on a sidewall of the memory gate and the hard mask layer, performing a selective oxidation process to form an oxide layer on the hard mask layer and the select gate, wherein a portion of the oxide layer on the select gate is thicker than a portion of the oxide layer on the hard mask layer, and removing the oxide layer on the hard mask layer and the hard mask layer to expose a top surface of the memory gate.