Deep Silicon Etch Mask Undercut Prevention
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Solution Overview
Problem
During semiconductor wafer processing, the etching process often results in silicon features with significant undercutting due to the removal of underlying material, which affects the thickness and integrity of the features formed.
Innovation Solution
A method involving the deposition of a polymer layer using a hydrogen-free C4F8 gas plasma over a silicon layer, followed by selective removal of the polymer on the bottoms of mask openings to prevent undercutting, allowing for controlled etching through the mask and deposited polymer layer using a different etching gas.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If a conventional etching process is used to remove underlying material through mask openings, then the etching depth can be achieved, but significant undercutting occurs causing silicon lines to be thinner than the original mask
Solution Approach 1:
A polymer layer is deposited as an intermediary material between the mask and the silicon layer. This polymer layer acts as a mediator that modifies the etching process by providing a protective cushion that prevents direct undercutting of the silicon layer, thereby maintaining silicon line thickness while achieving the required etching depth
Solution Approach 2:
The polymer layer is deposited in advance before the etching process begins. This preliminary deposition creates a protective barrier that prevents undercutting during the subsequent etching step, ensuring that the silicon lines maintain their intended thickness throughout the etching process
2Length of stationary object
If the etching depth is increased to achieve deeper features, then the desired deep etch profile is obtained, but the undercutting becomes more severe
Solution Approach 1:
The polymer layer serves as a protective intermediary that absorbs the undercutting effect during deep etching. As the etch progresses deeper into the silicon layer, the polymer cushion continues to protect the mask-silicon interface, preventing the undercut from propagating laterally and maintaining vertical etch profile precision even at increased depths
3Manufacturing precision
If a polymer layer is deposited to prevent undercutting, then undercut control is improved, but additional process steps are required
Solution Approach 1:
The polymer deposition process serves multiple functions: it acts as an anti-undercutting cushion during etching, provides a protective barrier for the mask, and can be integrated into existing plasma processing equipment. This multi-functionality justifies the additional process step by delivering multiple benefits from a single material deposition
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 effectively reduces or eliminates undercutting, improves etch profile control, and enables quicker processing by forming features with reduced thickness variations and enhanced precision.
Implementation Method 1
forming a plasma from the deposition gas, depositing a polymer from the plasma
Implementation Method 2
deposited polymer layer over the mask by flowing a hydrogen free deposition gas comprising C4F8, forming a plasma from the deposition gas, depositing a polymer from the plasma
Implementation Method 3
flowing an opening gas, forming a plasma from the opening gas which selectively removes the deposited polymer on bottoms of the plurality of mask openings with respect to deposited polymer on sides of the plurality of mask openings
Implementation Method 4
etching the silicon layer through the mask and deposited polymer layer by flowing an etching gas different from the opening gas and forming a plasma from the etching gas, which etches the silicon layer
Implementation Method 5
The silicon layer is etched through the mask and deposited polymer layer
Data Source
AI summary
A method for forming features in a silicon layer is provided. A mask is formed with a plurality of mask openings over the silicon layer. A polymer layer is deposited over the mask by flowing a hydrogen free deposition gas comprising C4F8, forming a plasma from the deposition gas, depositing a polymer from the plasma for at least 20 seconds, and stopping the depositing the polymer after the at least 20 seconds. The deposited polymer layer is opened by flowing an opening gas, forming a plasma from the opening gas which selectively removes the deposited polymer on bottoms of the plurality of mask openings with respect to deposited polymer on sides of the plurality of mask openings, and stopping the opening when at least some of the plurality of mask features are opened. The silicon layer is etched through the mask and deposited polymer layer.