Silicon Oxide Spacer Formation in DRAM Peripheral Circuits
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Solution Overview
Problem
Void formation in the spacer material layer within the memory cell region of DRAMs can cause damage to the gate structure of peripheral transistors during the formation of spacers, due to incomplete cleaning and uneven deposition of the silicon oxide layer.
Innovation Solution
A method using diluted hydrofluoric acid to clean both the memory cell and peripheral circuit regions, which preferentially removes residues and native oxide from the silicon nitride layer, allowing for faster deposition of the silicon oxide layer on the bottom of recesses than on the sidewalls, ensuring the oxide layer fills voids before sealing, thus preventing damage to the gate structure.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a spacer material layer is formed to cover both cell transistors and peripheral transistors, then the peripheral transistors can be protected, but voids are formed in the spacer material layer within the memory cell region which can cause damage to the gate structure
Solution Approach 1:
A silicon nitride layer is deposited on the substrate before forming the oxide layer. This preliminary layer serves as a foundation that enables selective removal of residues and controls subsequent oxide deposition, ensuring uniform spacer formation without voids while protecting the peripheral transistor gate structure.
Solution Approach 2:
The patent changes the chemical composition and deposition parameters by using diluted hydrofluoric acid to clean the silicon nitride layer, removing residues and native oxide selectively. This parameter change ensures uniform surface preparation for subsequent oxide deposition, eliminating void formation while maintaining structural integrity.
2Manufacturing precision
If the substrate is cleaned before forming the oxide layer, then deposition uniformity is improved, but incomplete cleaning leaves residues that cause void formation
Solution Approach 1:
Diluted hydrofluoric acid is used as an intermediary cleaning agent that selectively removes residues and native oxide from the silicon nitride layer. This intermediary substance enables complete cleaning without damaging the underlying structure, ensuring uniform oxide deposition without void formation.
Solution Approach 2:
The patent changes the cleaning parameters by using diluted hydrofluoric acid with specific concentration and exposure time, which optimally removes residues and native oxide while preserving the silicon nitride layer integrity, thereby achieving complete cleaning without void formation.
3Manufacturing precision
If the silicon oxide layer is deposited conformally, then the sidewalls are covered uniformly, but the recess remains unfilled creating voids
Solution Approach 1:
The silicon nitride layer is prepared in advance with selective residue removal, creating an optimal surface that promotes uniform oxide deposition. This preliminary preparation ensures that the oxide layer fills the recess completely while maintaining uniform sidewall coverage, preventing void formation.
Solution Approach 2:
The deposition parameters are changed by controlling the oxide layer formation process to achieve complete recess filling. The combination of proper surface preparation and deposition parameter optimization ensures both uniform sidewall coverage and complete recess filling without voids.
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
The method ensures a void-free silicon oxide layer, maintaining the integrity of the gate structure in the peripheral circuit region and preventing damage during subsequent processing steps, while ensuring efficient cleaning and deposition without using mixed acid solutions.
Implementation Method 1
a cleaning process is performed to clean the memory cell region and the peripheral circuit region using diluted hydrofluoric acid
Implementation Method 2
an oxide layer is formed to cover the memory cell region, the peripheral circuit region, the conductive lines and the gate structure
Data Source
AI summary
A method of changing a formation rate of silicon oxide includes providing a substrate, wherein two conductive lines are disposed on the substrate and a recess is between the conductive lines. Later, a cleaning process is performed to clean the substrate and the conductive lines using diluted hydrofluoric acid. After the cleaning process, a silicon oxide layer is formed to cover a sidewall and a bottom of the recess, wherein a formation rate of the silicon oxide layer at the bottom of the recess is greater than a formation rate of the silicon oxide layer at the sidewall of the recess.