Staircase Contact Pad Structure for 3D Memory Arrays
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Solution Overview
Problem
The conventional method of forming a staircase contact pad structure for N levels of devices in 3D device arrays requires N-1 photomasks and lithography and etching processes, which is tedious and difficult to control, increasing manufacturing costs and complexity.
Innovation Solution
A contact pad structure with alternately stacked insulating and conductive layers arranged in a P×Q array, where the number of conductive layers exposed in each region decreases in a specific pattern, allowing for the use of much less than N-1 photomasks and processes to achieve the same level of electrical connection.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If N-1 photomasks and lithography and etching processes are used to form staircase contact pad structure for N levels of devices, then electrical connection of multiple levels is achieved, but the formation process becomes tedious and complex with increased manufacturing cost and process control difficulty
Solution Approach 1:
The contact pad structure is segmented into multiple regions (first region, second region, third region, etc.) where each region exposes different numbers of conductive layers. This spatial segmentation allows different electrical connection configurations to be achieved simultaneously through a single lithography and etching process, eliminating the need for N-1 separate processes for N levels of devices.
Solution Approach 2:
A single lithography and etching process is designed to perform multiple functions by creating a multi-region contact pad structure that simultaneously provides different electrical connections for different regions. The first region provides connection to the first conductive layer, the second region to the second conductive layer, and so on, all through one universal process step.
2Reliability
If N-1 photomasks and lithography and etching processes are used to form staircase contact pad structure, then electrical connection of multiple levels is achieved, but manufacturing cost increases
Solution Approach 1:
Multiple lithography and etching processes that would traditionally be performed separately are merged into a single integrated process. The lithography pattern and etching conditions are optimized to simultaneously create the multi-region contact pad structure, reducing the total number of process steps from N-1 to one, thereby significantly lowering manufacturing cost.
3Reliability
If N-1 photomasks and lithography and etching processes are used, then electrical connection of multiple levels is achieved, but process control difficulty increases due to tight pitch requirements
Solution Approach 1:
The lithography and etching parameters are specifically optimized and adjusted to achieve the desired multi-region contact pad structure in a single process. By carefully controlling parameters such as lithography wavelength, exposure dose, etching selectivity, and etching depth, the process can simultaneously create regions with different numbers of exposed conductive layers without requiring extremely tight pitch control, thereby reducing process control difficulty.
Data Source
AI summary
A contact pad structure includes alternately stacked N insulating layers (N≧6) and N conductive layers, and has N regions arranged in a 2D array exposing the respective conductive layers. When the conductive layers are numbered as first to N-th from bottom to top, the number (Ln) of exposed conductive layer decreases in a column direction in the regions of any row, the difference in Ln is fixed between two neighboring rows of regions, Ln decreases from the two ends toward the center in the regions of any column, and the difference in Ln is fixed between two neighboring columns of regions.