Selective Blocking Dielectric Removal in 3D NAND Strings
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Solution Overview
Problem
Existing methods for forming monolithic three-dimensional NAND strings face challenges in selectively removing blocking dielectric materials without damaging the device, particularly with materials like aluminum oxide, which are resistant to etching, leading to over-etching and damage to control gates and substrates.
Innovation Solution
The method involves forming a stack of alternating layers over a substrate, etching to create openings, and using selective etching processes to form backside and frontside recesses, blocking dielectrics, and control gates, with oxidized metal portions protecting the control gates during etching and wet chemical etching to remove the blocking dielectric, ensuring precise removal without damaging the device.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If conventional etching methods are used to remove blocking dielectric materials like aluminum oxide, then the blocking dielectric can be removed, but the control gates and substrates are damaged due to over-etching
Solution Approach 1:
A protective coating is applied to the control gates before the etching process. This preliminary protective action prevents the control gates from being damaged by the etchant, allowing selective removal of the blocking dielectric material without harming the underlying structures.
Solution Approach 2:
The protective coating acts as an intermediary layer between the etchant and the control gates. It selectively allows the etchant to remove the blocking dielectric while preventing the etchant from reaching and damaging the control gates and substrates.
2Ease of manufacture
If repeated formation of sidewall spacers and etching is used to form the active region, then the active region can be formed, but the process becomes time-consuming and complex
Solution Approach 1:
The fabrication process is divided into distinct sequential steps: forming the active region first, then forming sidewall spacers, and finally etching the blocking dielectric. This segmentation allows each step to be optimized independently and reduces the need for repeated iterations of the same process.
Solution Approach 2:
The active region is formed in advance before the blocking dielectric is removed. This preliminary formation of the active region simplifies subsequent processing steps and eliminates the need for repeated sidewall spacer formation and etching cycles.
3Reliability
If blocking dielectric material is not selectively removed, then the control gates are protected, but the NAND string structure cannot be completed
Solution Approach 1:
The protective coating serves as an intermediary that enables selective removal of the blocking dielectric. It allows the etchant to access and remove the blocking dielectric in specific regions while preventing damage to the control gates, thus completing the NAND string structure without compromising device integrity.
Solution Approach 2:
The protective coating is applied selectively to specific regions where control gate protection is needed. This local application allows the blocking dielectric to be removed in other regions where it is not needed, simplifying the overall fabrication process while maintaining device reliability.
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 allows for the selective removal of blocking dielectric materials without causing unwanted damage, maintaining the integrity of the NAND string structure and improving etching precision, thereby enhancing the fabrication process of monolithic three-dimensional NAND memory arrays.
Implementation Method 1
etching the back side opening using a wet chemical etch to remove the blocking dielectric from the sidewalls and the bottom surface of the backside opening
Implementation Method 2
oxidizing a portion of the metal material of the control gates adjacent to the second side surfaces of the control gates
Data Source
AI summary
Methods of making a monolithic three dimensional NAND string may enable selective removal of a blocking dielectric material, such as aluminum oxide, without otherwise damaging the device. Blocking dielectric may be selectively removed from the back side (e.g., slit trench) and/or front side (e.g., memory opening) of the NAND string. Also disclosed are NAND strings made in accordance with the embodiment methods.