Floating Focus Ring Voltage Control for Plasma Etching
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Solution Overview
Problem
In plasma etching processes for semiconductor manufacturing, achieving a balance between reducing deposits on the peripheral substrate and improving the etching profile is challenging due to the deformation of the plasma sheath caused by the potential difference between the mounting table and the focus ring, which requires frequent replacement of focus rings and complex voltage adjustments.
Innovation Solution
A plasma processing apparatus with a focus ring configured in a floating state on a dielectric ring, where a conductive ring is connected to a voltage sensor and DC power supply to detect and adjust the floating voltage, allowing for the determination of an optimum application voltage without changing the focus ring's shape, thereby maintaining an optimal state despite erosion or changes in plasma conditions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-generated harmful factors
If the mounting table and focus ring are insulated from each other via a dielectric member to generate a potential difference, then deposits on the rear surface of the peripheral portion of the substrate are reduced, but the plasma sheath is deformed and the incident angle of ions becomes inclined, resulting in inclination of holes or trenches formed in the peripheral portion
Solution Approach 1:
The patent applies a DC voltage to the focus ring to change the electrical potential parameter, creating a potential difference between the focus ring and mounting table. This parameter change generates an electric field that directs ions vertically onto the rear surface of the peripheral portion, reducing deposits while maintaining proper etching profile through controlled voltage adjustment
2Manufacturing precision
If the height of the top surface of the focus ring is increased to improve the incident angle of ions to the peripheral portion, then the inclination of holes or trenches is improved, but it becomes difficult for ions to reach the rear surface of the peripheral portion, reducing the effect of reducing deposits
Solution Approach 1:
The patent replaces the mechanical adjustment of focus ring height with an electrical field approach. Instead of physically positioning the focus ring at different heights, a DC voltage is applied to create an electric field that directs ions vertically onto the rear surface, achieving the same effect as height adjustment without the mechanical constraints and erosion issues
3Manufacturing precision
If the focus ring is replaced frequently to maintain optimal height, then the plasma sheath deformation is prevented and manufacturing precision is maintained, but the downtime and costs increase
Solution Approach 1:
The patent enables the focus ring to serve dual functions: maintaining its mechanical position for plasma sheath uniformity while simultaneously having DC voltage applied to create the electric field for vertical ion direction. This self-service approach eliminates the need for frequent replacements based on height erosion, as the electrical field compensation works regardless of minor height changes
4Manufacturing precision
If different focus rings with various heights are prepared and tested to find the optimum, then the optimal plasma sheath configuration is achieved, but the device complexity and time required increase
Solution Approach 1:
The patent uses DC voltage as a controllable parameter to achieve optimal plasma sheath configuration without needing multiple physical focus rings. By adjusting the DC voltage applied to the focus ring, the electric field strength can be optimized to direct ions vertically onto the rear surface while maintaining plasma sheath uniformity, eliminating the need for multiple focus ring variants and extensive testing
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 allows for accurate and simple adjustment of the optimum application voltage, reducing the frequency of focus ring replacement, decreasing downtime and costs, and improving the uniformity of the etching process by maintaining an optimal etching profile and reducing deposits on the substrate.
Implementation Method 1
a voltage sensor configured to detect a floating voltage of the conductive ring
Implementation Method 2
a DC power supply configured to apply a DC voltage to the conductive ring
Implementation Method 3
ions in the plasma are attracted to and introduced into the peripheral portion of the substrate by such an electric field
Implementation Method 4
plasma is generated by applying a high frequency voltage to electrodes placed to face each other within a depressurizable processing chamber of a plasma processing apparatus, and an etching process is performed on the substrate mounted on a mounting table by using the plasma
Data Source
AI summary
An optimum application voltage for reducing deposits on a peripheral portion of a substrate as well as improving a process result in balance is effectively found without changing a height of a focus ring. A plasma processing apparatus includes a focus ring which includes a dielectric ring provided so as to surround a substrate mounting portion of a mounting table and a conductive ring provided on the dielectric ring; a voltage sensor configured to detect a floating voltage of the conductive ring; a DC power supply configured to apply a DC voltage to the conductive ring. An optimum voltage to be applied to the conductive ring is obtained based on a floating voltage actually detected from the conductive ring, and the optimum application voltage is adjusted based on a variation in the actually detected floating voltage for each plasma process.