Tungsten Recess Etching Micro-Loading Mitigation
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Solution Overview
Problem
The surface roughness of tungsten layers in DRAM device manufacturing leads to micro-loading effects during recess etching, causing uneven upper surfaces of buried word line trenches, which negatively impacts electrical performance.
Innovation Solution
A method involving blanket deposition of a tungsten layer, followed by planarization using a polymer layer formed with specific plasma etching conditions, and subsequent etching steps to achieve a smooth surface and ensure even trench levels, with etching selectivity of 1:1 between the planarization layer and tungsten layer.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If blanket deposition of tungsten layer is performed, then the tungsten layer can be formed in trenches and on substrate, but the surface roughness becomes too large causing micro-loading effect
Solution Approach 1:
The etching process is segmented into two distinct steps: a first etching step that etches the planarization layer and tungsten layer with 1:1 selectivity, and a second etching step that continues etching the tungsten layer. This segmentation allows separate optimization of each etching step to address surface roughness and micro-loading effects independently
Solution Approach 2:
A planarization layer is introduced as an intermediary layer between the deposited tungsten layer and the etching process. This planarization layer has 1:1 etching selectivity with tungsten in the first etching step, allowing it to serve as a mediator that removes surface irregularities while protecting the underlying tungsten structure during planarization
2Productivity
If recess etching is performed directly on rough tungsten layer, then the etching process can proceed, but the upper surfaces of tungsten layer in trenches are not at the same horizontal level
Solution Approach 1:
A planarization layer is formed on the tungsten layer before etching as a preliminary action. This planarization layer pre-compensates for surface roughness and creates a uniform starting surface for the subsequent etching steps, ensuring that the final tungsten surfaces are at the same horizontal level
Solution Approach 2:
The etching process parameters are changed between two steps: the first etching step uses parameters optimized for 1:1 selectivity between planarization layer and tungsten, while the second etching step uses parameters optimized for continuing tungsten etching. This parameter change allows precise control over etching depth and surface uniformity
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
The method effectively reduces surface roughness and ensures that the top surfaces of the tungsten layer within trenches are at the same horizontal level, improving the micro-loading effect and electrical performance of DRAM devices.
Implementation Method 1
A first etching step is performed to completely etch away the planarization layer and a portion of the tungsten layer. The etching selectivity of the planarization layer and the tungsten layer in the first etching step is 1:1.
Data Source
AI summary
A method of improving micro-loading effect when recess etching a tungsten layer. A substrate having trenches thereon is provided. A tungsten layer is deposited on the substrate and in the trenches. A planarization process is performed to form a planarization layer on the tungsten layer. A first etching process is performed to etch the planarization layer and the tungsten layer with an etch selectivity of planarization layer:tungsten layer=1:1 until the planarization layer is completely removed. A second etching process is performed to etch the remainder of the tungsten layer to recess the tungsten layer within the trenches.