Plasma Etch Gas Distribution for Wafer Profile Uniformity
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Solution Overview
Problem
Capacitively coupled plasma etch processes for semiconductor wafers face challenges with non-uniform etch rates and profiles due to variations in gas residency time across the wafer surface, leading to issues like etch stop and taper profiles, particularly at the wafer center, which are exacerbated by high aspect ratios and specific gas mixtures.
Innovation Solution
A plasma etch process that injects a polymerizing etch gas through an annular zone of gas injection orifices and evacuates gas through a pumping annulus, using VHF source power and/or HF and/or LF bias power to generate plasma, while injecting oxygen or nitrogen through a center gas injection orifice to slow polymer deposition and adjust flow rates to minimize etch stop and profile differences between the center and periphery.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If process gas flow rate is increased to improve etch rate, then etch rate increases, but gas residency time decreases leading to non-uniform dissociation and worsening etch profile non-uniformity
Solution Approach 1:
The gas distribution system is segmented into multiple independent zones (center, inner, outer) with separate gas injection orifices and flow control. This allows different gas flow rates to be applied to different radial regions of the wafer, enabling optimization of etch rate and profile uniformity independently in each zone
Solution Approach 2:
Different gas flow rates are applied to different radial zones of the wafer based on local requirements. The center zone receives higher flow rates to compensate for shorter residency time, while outer zones receive lower flow rates to maintain polymer deposition. This local differentiation resolves the contradiction between overall etch rate improvement and profile uniformity
2Productivity
If process gas flow rate is increased to improve etch rate, then etch rate increases, but polymer deposition increases causing etch stop at wafer center
Solution Approach 1:
The gas flow rate parameter is changed differently across radial zones. Higher flow rates are applied to the center zone to improve etch rate, while the system controls polymer deposition through the specific gas composition and flow distribution pattern, preventing etch stop despite increased overall flow rates
3Stability of the object's composition
If high aspect ratio reactor geometry is used to achieve uniform plasma distribution, then plasma uniformity improves, but gas residency time variation across wafer surface increases leading to non-uniform etch profiles
Solution Approach 1:
The gas distribution is segmented into radial zones with independent flow control, allowing compensation for the residency time variations inherent in high aspect ratio geometries. Each zone can be optimized independently to achieve uniform etch profiles across the entire wafer surface
4Productivity
If gas flow rate is decreased at wafer periphery to improve center etch rate, then center etch rate improves, but gas residency time increases at periphery worsening etch rate non-uniformity
Solution Approach 1:
The system applies different gas flow rates to different radial zones based on local requirements. The center zone receives higher flow rates to improve etch rate, while outer zones receive lower flow rates to maintain appropriate polymer deposition and etch profiles, achieving both goals simultaneously through local optimization
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 achieves uniform etch rates and profiles across the wafer by increasing etch rates at the center and reducing etch stop, with the ability to adjust gas flow rates to optimize etch performance, resulting in more uniform dielectric and photoresist etch rates.
Implementation Method 1
capacitively coupled plasma reactor
Implementation Method 2
the residency time of the gas increases with wafer radius, so that the minimum residency time (and hence the minimum gas dissociation) occurs at the wafer center
Implementation Method 3
Formation of such a protective polymer layer enhances etch selectivity
Implementation Method 4
by generating a plasma in the reactor by applying VHF source power and/or HF and/or LF bias power to the electrodes
Data Source
AI summary
A plasma etch process etches high aspect ratio openings in a dielectric film on a workpiece in a reactor having a ceiling electrode overlying the workpiece and an electrostatic chuck supporting the workpiece. The process includes injecting a polymerizing etch process gas through an annular zone of gas injection orifices in the ceiling electrode, and evacuating gas from the reactor through a pumping annulus surrounding an edge of the workpiece. The high aspect ratio openings are etched in the dielectric film with etch species derived from the etch process gas while depositing a polymer derived from the etch process gas onto the workpiece, by generating a plasma in the reactor by applying VHF source power and/or HF and/or LF bias power to the electrodes at the ceiling and/or the electrostatic chuck. The process further includes slowing the deposition rate of the polymer, minimizing etch stop and/or increasing the etch rate in a region of the workpiece typically the center by injecting oxygen or nitrogen and/or high-fluorine containing gas through gas injection orifice in the corresponding region of the ceiling electrode, and adjusting the flow rate of the oxygen or nitrogen and/or high-fluorine containing gas through the gas injection orifice to minimize the difference between profiles and etch depths at the workpiece center and the workpiece periphery.