Plasma Grid Assembly for Selective Semiconductor Etching
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Solution Overview
Problem
Plasma etching processes for advanced semiconductor structures like FinFET gates face challenges in achieving precise and uniform etching, particularly in maintaining selectivity, profile angle, and uniformity across the substrate, especially due to variations in feature density and local loading effects.
Innovation Solution
An apparatus with a plasma chamber divided by a grid assembly into upper and lower sub-chambers, where the grid assembly prevents induced current and allows for distinct plasma zones with controlled electron temperature and density, producing an ion-ion plasma in the lower sub-chamber for improved etching precision and uniformity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a conventional plasma etching process is used, then the etching can be performed, but the selectivity between etched material and retained material deteriorates
Solution Approach 1:
The plasma chamber is divided into two separate plasma zones by a grid assembly: an upper plasma generation zone and a lower plasma treatment zone. This segmentation allows independent control of plasma parameters in each zone, enabling the upper zone to generate sufficient plasma density while the lower zone maintains conditions for high selectivity and vertical profiles through controlled electron temperature and density.
2Productivity
If the plasma density is increased to improve etching rate, then the productivity improves, but the uniformity across the substrate deteriorates due to local loading effects
Solution Approach 1:
The grid assembly creates distinct plasma zones that decouple the plasma generation function from the plasma treatment function. The upper zone can operate at high power to generate high plasma density for fast etching, while the lower zone maintains lower electron temperature and controlled density to ensure uniform etching across the substrate, eliminating the trade-off between productivity and uniformity.
Solution Approach 2:
Different plasma conditions are created in different spatial zones: the upper zone has high electron temperature and high plasma density for efficient plasma generation, while the lower zone has controlled electron temperature and controlled density for uniform substrate treatment. This local differentiation of plasma quality allows simultaneous achievement of high etching rate and high uniformity.
3Use of energy by moving object
If the electron temperature is increased to improve plasma generation efficiency, then the energy efficiency improves, but the uniformity of etching across the substrate deteriorates
Solution Approach 1:
The grid assembly separates the plasma generation zone (upper) from the plasma treatment zone (lower), allowing high electron temperature in the upper zone for efficient plasma generation while maintaining lower, controlled electron temperature in the lower zone for uniform etching across the substrate.
Solution Approach 2:
High electron temperature is localized to the upper plasma generation zone where it improves plasma generation efficiency, while the lower plasma treatment zone maintains controlled electron temperature to ensure uniform etching. This spatial separation of thermal conditions resolves the contradiction between energy efficiency and uniformity.
4Device complexity
If a simple plasma chamber design is used, then the device complexity is reduced, but the ability to control plasma parameters for high precision etching deteriorates
Solution Approach 1:
The grid assembly provides a relatively simple structural addition that divides the chamber into two independently controllable plasma zones. This segmentation enables precise control of plasma parameters (electron temperature, density, composition) in each zone without requiring complex multi-component systems, achieving high etching precision with moderate device complexity.
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 solution enables superior selectivity, profile angle control, and uniformity across the substrate, reducing undesirable byproduct dissociation and local loading effects, resulting in high-quality etched features with improved center-to-edge uniformity and selectivity.
Implementation Method 1
In etching conducted with an inductively coupled plasma source, a chamber coil performs a function analogous to that of a primary coil in a transformer, while the plasma performs a function analogous to that of a secondary coil in the transformer.
Implementation Method 2
the grid assembly includes two or more grids having a plurality of slots that substantially prevent formation of induced current in the grid when the plasma is produced within the chamber
Implementation Method 3
Typically, a plasma contains electrons, as well as positive and negative ions, and some radicals. The radicals, positive ions, and negative ions interact with a substrate to etch features, surfaces and materials on the substrate.
Data Source
AI summary
The embodiments disclosed herein pertain to improved methods and apparatus for etching a semiconductor substrate. A plasma grid assembly is positioned in a reaction chamber to divide the chamber into upper and lower sub-chambers. The plasma grid assembly may include one or more plasma grids having slots of a particular aspect ratio, which allow certain species to pass through from the upper sub-chamber to the lower sub-chamber. Where multiple plasma grids are used, one or more of the grids may be movable, allowing for tenability of the plasma conditions in at least the lower sub-chamber. In some cases, an electron-ion plasma is generated in the upper sub-chamber. Electrons that make it through the grid to the lower sub-chamber are cooled as they pass through. In some cases, this results in an ion-ion plasma in the lower sub-chamber.