3D Memory Staircase Dummy Steps for Uniform Step Length Control
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Current methods for forming three-dimensional memory devices face challenges in achieving uniform step lengths and precise control over staircase regions, leading to variations in device performance and yield.
Innovation Solution
The method involves forming an alternating stack of insulating and sacrificial material layers, followed by the creation of stepped surfaces using a trimmable mask and multiple iterations of anisotropic etching and trimming processes, resulting in pad stacks with uniform lateral dimensions and vertical coincident sidewalls, which allows for precise control over the staircase region and uniform memory stack structures.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If conventional etching methods are used to form staircase regions, then the manufacturing process is simple, but the step length uniformity and manufacturing precision are poor
Solution Approach 1:
The patent applies preliminary action by forming dummy steps before the main etching process. These dummy steps serve as pre-established reference structures that guide the subsequent anisotropic etching to create uniformly spaced staircase steps. The dummy steps are formed in advance and used as masks or alignment references during the pattern transfer process, ensuring consistent step lengths without requiring complex real-time control mechanisms.
Solution Approach 2:
The patent uses dummy steps as intermediary structures that mediate between the lithographic pattern and the final staircase structure. These intermediate dummy steps transfer the dimensional information from the mask to the underlying layers with high precision, acting as a buffer that simplifies the overall process while maintaining manufacturing precision. The dummy steps are later removed after serving their purpose as precision transfer intermediaries.
2Manufacturing precision
If multiple iterations of anisotropic etching and trimming are performed, then the manufacturing precision of staircase region is improved, but the manufacturing time and process complexity increase
Solution Approach 1:
The patent implements periodic action through multiple iterations of the pattern transfer sequence, where each iteration consists of anisotropic etching followed by mask trimming. This periodic repetition of etch-trim cycles progressively refines the staircase structure, with each cycle removing material and adjusting the mask to achieve the desired step dimensions. The periodic nature allows systematic control of step length and uniformity across multiple processing stages.
Solution Approach 2:
The patent incorporates feedback mechanisms through the iterative process where the results of each etching cycle inform the subsequent trimming step. The mask is trimmed based on the actual dimensions achieved in the previous etching step, creating a closed-loop control system. This feedback approach allows real-time adjustment and correction of dimensional variations, ensuring high precision staircase formation despite process variations.
3Stability of the object's composition
If dummy steps are used to control step length, then the uniformity of memory stack structures is improved, but the device complexity and process steps increase
Solution Approach 1:
The patent uses dummy steps as copies or replicas of the desired final structure. These dummy steps replicate the dimensional characteristics of the intended staircase steps, allowing the actual memory structures to be formed by transferring the pattern from the dummy steps. This copying approach ensures that the uniformity and dimensional accuracy of the dummy steps are replicated in the final memory stack structures, maintaining compositional stability.
Solution Approach 2:
The patent applies the discarding principle to dummy steps, which are temporary structures formed to enable precise pattern transfer but are later removed after serving their purpose. The dummy steps are discarded after the main memory structures are formed, having transferred their dimensional information to the permanent structures. This approach allows the use of complex dummy step structures without permanently increasing device complexity, as the dummy elements are recovered (removed) after fulfilling their function.
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 ensures consistent step lengths across the staircase region, enhancing the uniformity and reliability of three-dimensional memory devices by maintaining uniform lateral terrace lengths, thereby improving process yield and device performance.
Implementation Method 1
unmasked portions of the alternating stack and the insulating strips are etched anisotropically by a respective anisotropic etch process
Data Source
AI summary
A three-dimensional memory device includes an alternating stack of insulating layers and electrically conductive layers. Stepped surfaces including vertical sidewalls of the insulating layers are present in a staircase region. Pad stacks are located on the stepped surfaces. Each of the pad stacks includes an insulating pad having a same material composition as the insulating layers, and a dielectric material pad having a different material composition than the insulating layers and having sidewalls that are vertically coincident with sidewalls of the insulating pad. Memory stack structures extend through the alternating stack. Each of the memory stack structures includes a vertical stack of memory elements and a vertical semiconductor channel.