3D NAND Silicon Nitride Etching Silica Deposition Control
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Solution Overview
Problem
High etch rates in wet etching processes for 3D NAND structures lead to re-deposition of etch products on multilayer structures, hindering the selective removal of silicon nitride layers and potentially blocking etching of silicon oxide layers, especially as the number of alternating layers increases.
Innovation Solution
A method involving controlled etching solution temperature, concentration, and flow, where the etch rate is adjusted based on monitored silica concentration to prevent deposition on silicon oxide surfaces, using techniques such as reduced bath temperature, diluted acid mixtures, and active feedback control to maintain silica concentration below threshold values.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If high etch rate is used to shorten etch process time, then productivity is improved, but re-deposition of etch products occurs on multilayer structures
Solution Approach 1:
The patent applies dynamics by making the etch rate variable rather than constant. The etch rate is dynamically adjusted based on the depth of the trench being etched: higher etch rates are used in shallower regions, and lower etch rates are used in deeper regions. This dynamic adjustment prevents re-deposition of etch products while maintaining overall productivity, as the etch process adapts to local conditions rather than using a fixed high rate throughout.
Solution Approach 2:
The patent changes the etch rate parameter during the etching process. By modifying the etch rate based on trench depth and silica concentration, the process optimizes between productivity and quality. The etch rate is reduced when silica concentration increases or trench depth increases, preventing re-deposition while still achieving complete etching of silicon nitride layers.
2Productivity
If high etch rate is used to improve productivity, then etch process time is reduced, but etching precision deteriorates due to re-deposition blocking trenches
Solution Approach 1:
The patent changes the etch rate parameter dynamically during the process to maintain both productivity and precision. By reducing the etch rate when silica concentration reaches critical levels or when trench depth increases, the process prevents re-deposition that would block trenches and compromise etching selectivity. This parameter adjustment ensures complete removal of silicon nitride without blocking the trench channels.
Solution Approach 2:
The patent implements feedback control by monitoring silica concentration in the etching solution and adjusting the etch rate accordingly. When silica concentration increases to levels that risk re-deposition, the etch rate is reduced to maintain etching precision. This feedback mechanism ensures that productivity gains do not compromise the selective etching of alternating layers.
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 effectively reduces silica deposition on silicon oxide surfaces, ensuring complete etching of silicon nitride layers without blocking the trench channels, even in structures with higher numbers of alternating layers, by maintaining silica concentration within acceptable limits throughout the etching process.
Implementation Method 1
wet etch processes are important steps for selectively removing different material layers
Implementation Method 2
The etching solution includes a first acid that etches the first material, and initiating etching of the first material at a first etch rate, etching of the first material resulting in an etch product
Implementation Method 3
the etch processing system configured to control temperature of the etching solution
Implementation Method 4
In the past, the general trend has been to make the temperature of the etch bath as high as possible in order to make the etch rate high
Implementation Method 5
the etch processing system configured to control temperature of the etching solution, a concentration of the etching solution, and flow of the etching solution within the tank
Implementation Method 6
monitoring a concentration of the etch product within the etching solution
Data Source
AI summary
A method of etching a substrate includes providing an etching solution in a tank of an etch processing system, where the etch processing system is configured to control temperature of the etching solution, a concentration of the etching solution, and flow of the etching solution within the tank. The substrate contains micro-fabricated structures that have alternating layers of a first material and a second material, and the etching solution including an acid that etches the first material and results in an etch product to be moved from the substrate. The method further includes monitoring a concentration of the etch product within the etching solution, and maintaining the concentration of the etch product within the etching solution below a predetermined value to prevent deposition of the etch product on the second material in an amount that blocks etching of the first material by the etching solution.