Floating Gate Void Prevention via Two-Step Etching
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Solution Overview
Problem
The existing methods for fabricating floating gates in flash memories often result in voids due to high depth-to-width ratios and small filling openings, leading to reduced product yield.
Innovation Solution
A defect relieving method involving a two-step etching process using phosphoric acid and hydrofluoric acid to remove the mask layer, forming a controlled opening that prevents voids during floating gate filling, ensuring a uniform and adequate space for the floating gate.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If phosphoric acid is used to remove silicon nitride by one step, then the mask layer removal is simplified, but the opening becomes small and tapered leading to voids in the floating gate
Solution Approach 1:
The single-step etching process is segmented into two distinct steps: first using phosphoric acid to remove the silicon nitride mask layer, then using hydrofluoric acid to remove the oxide layer and enlarge the opening. This segmentation allows each step to be optimized independently, preventing the opening tapering problem while maintaining process simplicity.
Solution Approach 2:
The phosphoric acid etching is performed as a preliminary action to remove the mask layer and create an initial opening structure. This preliminary action prepares the structure for the subsequent hydrofluoric acid treatment, which then enlarges and uniformizes the opening to prevent void formation during floating gate filling.
2Productivity
If the opening is made small to achieve high integration, then the device density increases, but voids occur during floating gate filling reducing product yield
Solution Approach 1:
The chemical parameters of the etching process are changed by introducing a second etching step with hydrofluoric acid. This parameter change transforms the opening geometry from tapered and small to uniform and adequately sized, enabling reliable floating gate filling while maintaining high device integration density.
3Manufacturing precision
If the mask layer is completely removed to form adequate opening, then the floating gate can be filled properly, but the process becomes complex with multiple etching steps
Solution Approach 1:
The oxide layer serves as an intermediary that is selectively removed by hydrofluoric acid after the phosphoric acid removes the silicon nitride mask. This intermediary layer enables the transformation from a tapered opening to a uniform opening without requiring direct complex etching of the mask layer itself, simplifying the overall process while achieving the desired opening geometry.
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 method effectively prevents voids and ensures a desired shape and structure for the floating gate, enhancing product yield by maintaining a uniform opening width and completely removing the mask layer for proper filling.
Implementation Method 1
performing a first etching process to remove a first thickness of the mask layer between adjacent ones of the plurality of trenches
Implementation Method 2
performing a second etching process to remove a remaining thickness of the mask layer between the adjacent ones of the plurality of trenches, and reducing a width of a portion of the filler that exceeds a top surface of the gate oxide layer
Data Source
AI summary
A defect relieving method for a floating gate is disclosed, which includes: providing a front-end structure, including an active region, a gate oxide layer on the active region, a mask layer on the gate oxide layer, a plurality of trenches penetrating through the mask layer, the gate oxide layer, and at least part of the active region, and a filler that is filled in the trenches; performing a first etching process to remove a first thickness of the mask layer between adjacent ones of the trenches; performing a second etching process to remove a remaining thickness of the mask layer between the adjacent trenches, and reducing a width of a portion of the filler that exceeds a top surface of the gate oxide layer, thereby an opening is formed; and filling the opening with a floating gate. The method increases the diameter of the opening, thus avoiding occurrence of voids.