Synchronous RF Pulsing for Plasma Etching Charge Control
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Solution Overview
Problem
Conventional plasma etching of dielectric structures faces issues such as reactive ion etch lag, etch stop, and feature twisting due to polymer deposition and positive charging, leading to selectivity and damage problems, especially in soft films, which existing synchronization methods fail to effectively address.
Innovation Solution
Generating a plasma using a first RF signal with a specific frequency and duty cycle, applying a second RF signal with the same frequency but a different duty cycle to bias the plasma, and adjusting the phase variance between the signals to control ion energy distribution and reduce ion bombardment damage and charge-up on substrates.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If synchronous pulsing of RF source and bias signals is used to dissipate charge from the material surface, then charging damage is reduced, but plasma uniformity deteriorates and etch rate control becomes poor
Solution Approach 1:
The patent applies asymmetry by using different duty cycles for the source RF signal and bias RF signal. The source signal has a first duty cycle while the bias signal has a second duty cycle that is different from the first, creating an asymmetric pulsing pattern that prevents plasma density non-uniformity while still dissipating charge accumulation on dielectric surfaces.
Solution Approach 2:
The patent implements dynamic control by independently adjusting the duty cycles of source and bias RF signals. This dynamic parameter control allows the system to optimize both charge dissipation and plasma uniformity by varying the temporal characteristics of each RF signal separately, rather than using fixed synchronous pulsing.
2Productivity
If conventional RIE process is used for dielectric etching, then etching capability is achieved, but aspect ratio dependent etching and feature twisting occur
Solution Approach 1:
The patent employs periodic pulsing of RF signals to alternate between etching phases and charge dissipation phases. This periodic action allows the etch process to proceed while periodically removing accumulated charge that would otherwise cause aspect ratio dependent etching and feature twisting, thereby improving etch uniformity in high aspect ratio structures.
Solution Approach 2:
The patent uses dynamic duty cycle control to optimize the balance between etching rate and charge management. By independently controlling the temporal characteristics of source and bias RF signals, the system can maintain high etching capability while dynamically managing charge accumulation to prevent distortion in high aspect ratio features.
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 method improves plasma uniformity, reduces ion bombardment damage, and enhances etch rate control, benefiting both low and high aspect ratio etching, particularly in dielectric materials, while preventing charging damage.
Implementation Method 1
generating a plasma by providing only a first RF signal having a first frequency and a first duty cycle
Implementation Method 2
applying only a second RF signal to bias the plasma towards the substrate
Data Source
AI summary
Methods for etching a substrate are provided herein. In some embodiments, a method of etching a substrate may include generating a plasma by providing only a first RF signal having a first frequency and a first duty cycle; applying only a second RF signal to bias the plasma towards the substrate, wherein the second RF signal has the first frequency and a second duty cycle different than the first duty cycle; adjusting a phase variance between the first and second RF signals to control an ion energy distribution in the plasma; and etching the substrate with the plasma.