Nonvolatile Memory Element Etching with Receding Photoresist Mask
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Solution Overview
Problem
Conventional variable resistance nonvolatile memory elements experience variations in resistance values due to etch damage during dry etching, which are influenced by the thickness, composition, and shape of the variable resistance layer and electrode layers, as well as the photoresist mask used in photolithography.
Innovation Solution
The method involves forming a nonvolatile memory element using a hard mask with a photoresist mask having receding corner portions and an etching gas containing an oxygen deficiency-suppressing gas, such as bromine compounds, to reduce etch damage and oxygen content variations in the variable resistance layer, resulting in a more uniform etching process and reduced resistance value variations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If conventional dry etching is used to form the nonvolatile memory element, then the etching process can be completed, but etch damage occurs causing variation in resistance values
Solution Approach 1:
A hard mask layer is introduced as an intermediary between the photoresist mask and the variable resistance layer. This hard mask layer protects the variable resistance layer from direct etch damage while allowing precise pattern transfer, thereby reducing resistance value variation without compromising etching effectiveness.
Solution Approach 2:
The photoresist mask is designed with receding corner portions before the etching process begins. This preliminary design modification prevents excessive etching at corner regions, ensuring uniform etching depth and reducing etch damage across the entire variable resistance layer, which directly improves resistance value uniformity.
2Ease of manufacture
If the photoresist mask has standard rectangular corners, then the patterning process is simple, but non-uniform etching occurs at corner portions
Solution Approach 1:
The photoresist mask is designed with asymmetric receding corner portions rather than standard rectangular corners. This asymmetric design ensures that all corner regions receive uniform etching treatment, eliminating the non-uniform etching that would otherwise occur at sharp corners while maintaining manufacturing simplicity.
3Shape
If the variable resistance layer has sharp corners, then the device structure is well-defined, but etch damage varies significantly at different regions
Solution Approach 1:
The photoresist mask is pre-designed with receding corner portions that anticipate and compensate for etching variations. This preliminary action ensures that the etching process produces uniform results across the variable resistance layer, maintaining well-defined device structure while eliminating regional etch damage differences.
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 leads to a high-quality nonvolatile memory element with reduced resistance value variations and improved operational characteristics, suitable for applications in electronic devices like digital home appliances, memory cards, and personal computers.
Implementation Method 1
a component included in the oxygen deficiency-suppressing gas adheres to sides of the variable resistance layer as a result of the etching using the etching gas that contains the oxygen deficiency-suppressing gas
Implementation Method 2
forming a photoresist mask on the hard mask layer; forming a hard mask by performing etching on the hard mask layer, using the photoresist mask
Data Source
AI summary
The method includes: forming a lower electrode layer above a substrate; forming a variable resistance layer on the lower electrode layer; forming an upper electrode layer on the variable resistance layer; forming a hard mask layer on the upper electrode layer; forming a photoresist mask on the hard mask layer; forming a hard mask by performing etching on the hard mask layer using the photoresist mask; and forming a nonvolatile memory element by performing etching on the upper electrode layer, the variable resistance layer, and the lower electrode layer, using the hard mask. In the forming of a photoresist mask, the photoresist mask is formed to have corner portions which recede toward the center portion in planar view.