3D Memory Etching via Multi-Step Hot Phosphoric Acid Process
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
The challenge in fabricating three-dimensional memory devices is the precipitation of silicon-containing materials, such as silica, in the lower parts of backside trenches during the removal of silicon nitride sacrificial layers, which clogs access to lateral recesses and prevents the formation of control gate electrodes, leading to defective memory devices.
Innovation Solution
A method involving multiple hot phosphoric acid wet etch processes is used to selectively remove silicon nitride layers, controlling the silicon concentration in the etching solution to prevent precipitation, with etch mask spacers and conformal silicon oxide liners employed to manage the etching process and maintain selectivity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If a single hot phosphoric acid wet etch process is used to remove silicon nitride sacrificial layers, then the etching process is simple and fast, but silicon-containing materials precipitate in the lower parts of backside trenches causing clogging
Solution Approach 1:
The single etching process is divided into multiple sequential etching steps with different conditions. The first etching step uses hot phosphoric acid to remove upper silicon nitride layers, while the second etching step uses a different solution or modified conditions to remove lower silicon nitride layers without causing precipitation. This segmentation resolves the contradiction by maintaining etching effectiveness while preventing harmful precipitation in different regions.
Solution Approach 2:
The etching process employs periodic alternation between different etching solutions or conditions. After the first etching step removes certain layers, the process pauses to allow solution replacement or condition modification before proceeding to the second etching step. This periodic action prevents continuous precipitation while maintaining overall etching productivity.
2Ease of manufacture
If silicon nitride layers are removed to form lateral recesses, then control gate electrodes can be formed, but silicon-containing material precipitation clogs access to lateral recesses
Solution Approach 1:
Etch mask spacers are formed on the sidewalls of trenches before the etching process begins. These spacers serve as protective barriers that prevent silicon-containing material precipitation from clogging the lateral recesses during etching. The preliminary placement of these protective structures ensures that subsequent etching operations can proceed without harmful clogging.
Solution Approach 2:
Conformal silicon oxide liners are deposited as intermediary protective layers on specific surfaces during the etching process. These liner layers act as mediators that prevent direct contact between the etching solution and certain surfaces, thereby preventing precipitation and clogging while allowing the etching to proceed in desired regions.
3Manufacturing precision
If multiple etching steps are used to prevent precipitation, then etching precision is improved, but process complexity increases
Solution Approach 1:
The etch mask spacers and conformal silicon oxide liners serve multiple functions simultaneously: they protect against precipitation, define etching boundaries, and maintain structural integrity during processing. This multi-functionality reduces the need for additional separate process steps, thereby limiting the increase in overall process complexity despite the use of multiple etching steps.
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 prevents silicon-containing material precipitation, ensuring the formation of functional lateral recesses and enabling the creation of operational three-dimensional memory devices by maintaining the desired silicon concentration in the etching solution.
Implementation Method 1
employing a first hot phosphoric acid wet etch process
Implementation Method 2
precipitation of silicon-containing materials, such as silica
Data Source
AI summary
At least one alternating stack of insulating layers and silicon nitride layers is formed over a substrate. Memory stack structures are formed through the at least one alternating stack. A trench and an etch mask spacer are formed such that the trench extends through the entirety of the alternating stack while the etch mask covers upper layers of the at least one alternating stack. Lower silicon nitride layers are removed employing a first hot phosphoric acid wet etch process. After removal of the etch mask spacer, upper silicon nitride layers are removed employing a second hot phosphoric acid wet etch process. Electrically conductive layers are formed in the lateral recesses formed by removal of the silicon nitride layers.