Silicon Etching Selectivity via Periodic Plasma Deposition
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Solution Overview
Problem
Conventional etching methods for forming deep trenches in silicon layers face challenges in achieving sufficient selectivity and etching depth due to the increased etching rate of the oxide mask layer, limiting the formation of high-aspect ratio trenches.
Innovation Solution
A substrate processing method involving the alternation of etching and deposition steps using a plasma generated from a mixed gas of fluorine-based, bromine-based, and oxygen-based gases, with SiCl4 gas, to enhance selectivity and control the thickness of the oxide mask layer, allowing for the formation of deep trenches with stable opening shapes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Length of moving object
If the etching rate of the silicon layer is increased to achieve sufficient etching depth, then the etching depth is improved, but the etching rate of the oxide mask layer also increases, reducing the selectivity and causing the mask layer to be consumed prematurely
Solution Approach 1:
The patent employs periodic alternation between etching steps and deposition steps. During etching steps, the silicon layer is etched with fluorine-based plasma. During deposition steps, oxide material is deposited to replenish the mask layer. This periodic action maintains the mask layer thickness throughout the process, allowing continuous etching at high rates without mask consumption, thereby achieving both deep etching depth and sustained selectivity
Solution Approach 2:
The patent changes process parameters by switching between different gas compositions and plasma conditions. Fluorine-based gases (SF6, CF4) are used during etching steps to achieve high silicon etching rates. Oxygen-based gases (O2, CO) are introduced during deposition steps to promote oxide formation on the mask layer. This parameter change allows optimization of etching rate and mask protection separately in different time periods
2Productivity
If conventional etching methods are used with fluorine-based gases, then the etching rate is improved, but the selectivity with respect to the oxide mask layer deteriorates due to simultaneous etching of the mask layer
Solution Approach 1:
The patent uses periodic alternation between pure etching steps (fluorine-based plasma only) and deposition steps (oxygen-based plasma for oxide replenishment). During etching steps, high fluorine concentration provides high silicon etching rates. During deposition steps, oxygen is introduced to deposit oxide on the mask layer surface. This periodic action decouples the trade-off between etching rate and selectivity, allowing high productivity while maintaining mask integrity
Solution Approach 2:
The patent maintains continuous progress toward the etching goal by alternating etching and deposition steps. The etching step removes silicon at high rates, and the deposition step replenishes the mask layer, ensuring the etching process can continue without interruption or mask failure. This continuity allows sustained high etching rates throughout the entire deep trench formation process
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 improves the selectivity and etching rate of the silicon layer, enabling the formation of high-aspect ratio deep trenches with controlled opening shapes and secure mask layer thickness, overcoming the limitations of conventional techniques.
Implementation Method 1
a plasma generated from a mixed gas of a fluorine-based gas, a bromine-based gas, O2 gas, and SiCl4 gas
Implementation Method 2
depositing a deposit on a surface of the oxide layer by a plasma generated from a mixed gas
Implementation Method 3
an etching step of etching the silicon layer by a plasma generated from a mixed gas of a fluorine-based gas, a bromine-based gas, and O2 gas
Data Source
AI summary
In a substrate processing method of processing a substrate that includes an oxide layer as a mask layer and a silicon layer as a target layer to be processed, the silicon layer is etched while depositing a deposit on a surface of the oxide layer by a plasma generated from a mixed gas of a fluorine-based gas, a bromine-based gas, O2 gas, and SiCl4 gas to secure a thickness of the mask layer.