Plasma Etching Stage Bias Waveform for Vertical Trench Profiles
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Solution Overview
Problem
In plasma etching processing, the verticality of trench side walls is compromised due to charged particles on the wafer surface, leading to increased damage to metal layers that should not be etched, and existing methods are inadequate for timely removal of these charges.
Innovation Solution
A plasma processing apparatus with a DC power supply applying a DC voltage having a periodically repeated waveform with a changing amplitude, superimposed on a radio frequency power supply, to generate a current that effectively removes charged particles on the wafer surface, ensuring high verticality of trench shapes and minimizing damage to non-etched films.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If radio frequency voltage is applied to the wafer mounting table to achieve anisotropic etching, then etching rate and verticality are improved, but charged particles accumulate on the wafer surface causing trajectory bending and side wall charging
Solution Approach 1:
A periodic voltage is applied to the wafer mounting table that reverses polarity at regular intervals. During the negative half-cycle, ions are accelerated toward the wafer for etching. During the positive half-cycle, the polarity reverses creating an electric field that extracts accumulated charged particles from the wafer surface and dielectric layer, preventing trajectory bending and side wall charging while maintaining etching effectiveness during the negative cycle.
Solution Approach 2:
The system dynamically switches the voltage polarity on the wafer mounting table between negative and positive states. This dynamic voltage reversal creates time-varying electric fields that alternately accelerate ions toward the wafer for etching and then extract accumulated charged particles, adapting the electric field direction to the instantaneous charge accumulation state on the wafer surface.
2Object-generated harmful factors
If continuous current is generated by applying opposite polarity voltage to remove charged particles, then charged particles can be removed, but the process takes milliseconds which is too slow for high frequency radio frequency processing
Solution Approach 1:
Instead of using slow continuous current extraction, the system applies periodic voltage reversal at radio frequency intervals. The positive half-cycles occur frequently enough to continuously clear charged particles before they can significantly affect etching accuracy, while the entire process completes within fractions of a millisecond, maintaining compatibility with high-speed plasma processing.
Solution Approach 2:
The system changes the voltage parameter from static or slowly varying to rapidly oscillating at radio frequency. This parameter change enables charged particle removal to occur on the same timescale as the etching process itself, eliminating the time delay between etching and charge removal that plagues slower methods.
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 apparatus achieves trench shapes with enhanced verticality and reduces damage to non-etched films by effectively removing charged particles on the wafer surface, improving the precision of plasma etching processes.
Implementation Method 1
A DC power supply that applies a DC voltage, that is changed according to a periodically repeated waveform, to the sample stage
Implementation Method 2
gas supplied to the inside of a processing chamber whose pressure is reduced to a predetermined degree of vacuum is turned into plasma by an electric field or the like formed inside a vacuum vessel
Implementation Method 3
since a sheath generated between the plasma and the mounting table has a rectifying action, the time-averaged voltage of the mounting table becomes negative due to self-bias. Therefore, positive ions are accelerated
Data Source
AI summary
A plasma processing apparatus includes a processing chamber in which a sample is subjected to plasma processing, a first radio frequency power supply that supplies radio frequency power for generating plasma, a sample stage on which the sample is mounted, and a second radio frequency power supply that supplies radio frequency power to the sample stage, the plasma processing apparatus further includes a DC power supply that applies a DC voltage, that is changed according to a periodically repeated waveform, to the sample stage, and the waveform of one cycle has a period in which amplitude changes by a predetermined amount or more during a predetermined time. Accordingly, charged particles on a wafer surface are removed, a trench shape with high verticality can be obtained, and damage to a film that is not to be etched inside a trench can be reduced.