Stair-Step Structure Formation Using Segmented Hardmask and Organic Mask
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Solution Overview
Problem
The existing methods for forming stair-step structures in semiconductor devices face limitations due to the reduction in mask height during lateral trimming, which restricts the number of steps that can be etched before requiring a new mask, making it challenging to achieve the desired packing density and electrical contact in 3D flash memory devices.
Innovation Solution
A method involving the formation of a hardmask with a top layer and sidewall layer over an organic mask, where the sidewall layer is removed while preserving the top layer, followed by trimming the organic mask and etching the substrate, with the process repeated multiple times to create multiple stair-steps, utilizing a plasma processing chamber with controlled gas sources and power to maintain precision and efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the organic mask is trimmed laterally to expose more substrate for etching, then more stair-steps can be formed, but the mask height is reduced making it vulnerable to damage in subsequent cycles
Solution Approach 1:
The mask system is segmented into two distinct components: a hardmask layer and an organic mask layer. The hardmask provides structural support and maintains height during the process, while the organic mask performs the lateral trimming function. This segmentation allows the organic mask to be trimmed without compromising overall mask integrity, enabling multiple etching cycles to form numerous stair-steps.
Solution Approach 2:
The hardmask acts as an intermediary protective layer between the organic mask and the substrate. During lateral trimming of the organic mask, the hardmask remains intact and provides mechanical support, preventing the organic mask from becoming too thin or damaged. This intermediary structure enables repeated trimming and etching cycles.
2Productivity
If the organic mask is used for multiple etching cycles, then packing density increases, but the mask becomes progressively thinner and eventually fails
Solution Approach 1:
The mask system is divided into a hardmask layer (providing structural support) and an organic mask layer (providing patterning). This segmentation allows the organic mask to be repeatedly trimmed for high packing density while the hardmask maintains sufficient height to prevent mask failure across multiple etching cycles.
Solution Approach 2:
The mask structure uses composite materials combining the hardmask (typically inorganic material like silicon oxide or silicon nitride) and organic mask (photoresist or other organic polymer). This composite structure combines the advantages of both materials: the hardmask provides mechanical strength and height retention, while the organic mask provides ease of patterning and trimming.
3Device complexity
If a single organic mask is used for forming multiple stair-steps, then process complexity is reduced, but precision of each step deteriorates due to mask thinning
Solution Approach 1:
The mask system is segmented into hardmask and organic mask layers, where the hardmask maintains consistent thickness and structural integrity across multiple etching cycles. This segmentation preserves manufacturing precision for each stair-step while allowing a single organic mask to be reused, reducing process complexity compared to applying new masks for each cycle.
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 formation of a large number of stair-steps without significant mask thinning, enabling increased packing density and effective electrical contact in 3D memory structures, with the potential for up to thirty-two steps using a single organic mask process.
Implementation Method 1
A plasma processing chamber is provided, comprising a chamber wall forming a plasma processing chamber enclosure
Implementation Method 2
The substrate is etched. The forming the hardmask, removing the sidewall layer, trimming the organic mask, removing the hardmask, and etching the substrate are repeated a plurality of times
Data Source
AI summary
A method for forming a stair-step structure in a substrate is provided. An organic mask is formed over the substrate. A hardmask with a top layer and sidewall layer is formed over the organic mask. The sidewall layer of the hard mask is removed while leaving the top layer of the hardmask. The organic mask is trimmed. The hardmask is removed. The substrate is etched. The forming the hardmask, removing the sidewall layer, trimming the organic mask, and etching the substrate are repeated a plurality of times.