Plasma Etching Mask Selectivity Pit Formation Control
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Solution Overview
Problem
The existing silicon etching process using SF6/O2/SiF4 gas often results in pit formation on the oxide film mask, which can lead to adverse effects on semiconductor devices due to insufficient mask selectivity and the formation of undercuts beneath the mask.
Innovation Solution
A plasma etching method involving a two-step process where the initial etching uses a resist layer as a mask, followed by a second etching step using the silicon oxide layer as a mask after the resist layer is completely removed, with the SF6/O2/SiF4 gas, to prevent pit formation and control etching profiles.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If SF6/O2/SiF4 gas is used as etching gas to improve mask selectivity and prevent undercuts, then etching selectivity is improved, but pit formation occurs on the oxide film mask
Solution Approach 1:
A deposit removal process is performed before the silicon etching process to remove organic deposits from the oxide film mask surface. These deposits would otherwise serve as nuclei for pit formation during subsequent etching. By removing them in advance, the harmful pit formation is prevented while maintaining the benefits of using SF6/O2/SiF4 etching gas for high selectivity and undercut prevention.
2Shape
If resist layer is used as mask for high aspect ratio trench etching, then etching profile control is improved, but mask selectivity deteriorates compared to oxide film mask
Solution Approach 1:
The masking function is segmented into two distinct layers: the resist layer provides mechanical support and defines the etching pattern for high aspect ratio trenches, while the oxide film mask layer provides the necessary etching selectivity. This segmentation allows each layer to fulfill its optimal function without compromise.
Solution Approach 2:
The masking system uses a composite structure combining resist material and oxide film material. The resist layer (organic polymer) and oxide film mask (inorganic ceramic) have complementary properties that together solve both the profile control and selectivity requirements that neither material could achieve alone.
3Manufacturing precision
If oxide film mask is used for silicon etching, then mask selectivity is improved, but undercuts are formed beneath the mask
Solution Approach 1:
The etching gas composition is changed from conventional SF6/O2 to SF6/O2/SiF4. The addition of SiF4 modifies the etching chemistry to reduce undercut formation while maintaining the high mask selectivity provided by the oxide film mask. This parameter change in the etching process allows simultaneous achievement of both selectivity and profile control.
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 pit formation and ensures high mask selectivity, allowing for precise control of etching profiles, thereby enhancing the reliability and miniaturization capabilities of semiconductor devices.
Implementation Method 1
a plasma generating process of generating a plasma from a processing gas containing SF6, O2 and SiF4 in a processing chamber of a plasma processing apparatus
Implementation Method 2
a second silicon etching process of etching the target layer by the plasma while using the silicon oxide layer as a mask after the resist layer is completely removed
Data Source
AI summary
A processing method includes a silicon oxide etching process of performing a plasma etching on a target layer mainly made up of silicon, a silicon oxide layer formed on the target layer and a target object having a previously patterned resist layer formed on the silicon oxide layer, the plasma etching of the silicon oxide layer being performed by using the resist layer as a mask; a deposits removing process of removing deposits generated in the silicon oxide etching process and stuck to the target object; and a silicon etching process of performing a plasma etching on the target layer by a plasma generated from a processing gas containing SF6, O2 and SiF4 while using the silicon oxide layer as a mask.