RF Bias Waveform Control for Plasma Etching Precision
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Solution Overview
Problem
Current plasma etching processes for integrated circuit fabrication face challenges in achieving precise control over ion bombardment energy, leading to limitations in etch selectivity, substrate damage, and profile control of high aspect ratio features, due to the broad ion energy distribution function (IEDF) resulting from standard sinusoidal RF bias voltage.
Innovation Solution
A method and system that utilize a fast Fourier transform (FFT) to automatically generate and adjust the RF bias voltage waveform at the substrate, comparing measured and desired waveforms to converge on target characteristics, enabling precise control of ion energy distribution.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If standard sinusoidal RF bias voltage is used, then the etching process is simple to implement, but the ion energy distribution is broad which limits etch selectivity and precision
Solution Approach 1:
The patent applies dynamics by transitioning from a static sinusoidal waveform to a dynamic, adjustable waveform that can be modified in real-time. The system uses an arbitrary waveform generator to create time-varying voltage profiles that dynamically control ion energy distribution, allowing optimization of etch selectivity and precision without fixed constraints.
Solution Approach 2:
The patent implements parameter changes by modifying the voltage waveform parameters (amplitude, frequency, duty cycle, shape) to control ion energy distribution. By adjusting these parameters, the system achieves precise control over ion bombardment energy, enabling improved etch selectivity and reduced substrate damage while managing system complexity through programmable control.
2Productivity
If high energy ion bombardment is used to increase etch rate, then productivity improves, but substrate damage increases
Solution Approach 1:
The patent applies periodic action by using pulsed or cyclic voltage waveforms to deliver ion bombardment in controlled intervals. This periodic approach allows high energy ions to etch at high rates during active phases while providing rest periods that reduce cumulative substrate damage, achieving a balance between productivity and substrate integrity through time-dependent control.
Solution Approach 2:
The patent implements partial action by delivering ion bombardment energy in controlled portions rather than continuous high energy exposure. The waveform modulation allows selective application of high energy ions only when needed for etching, while limiting exposure during other phases, thus achieving high etch rates with reduced overall substrate damage through controlled energy delivery.
3Measurement precision
If manual trial and error method is used to set voltage waveform, then device complexity is low, but time consumption and precision are high
Solution Approach 1:
The patent implements feedback by measuring the actual voltage waveform at the substrate and comparing it with the desired waveform. The system uses this feedback information to automatically adjust and refine the waveform parameters, achieving precise control without manual trial and error. This closed-loop approach eliminates time-consuming manual adjustments while maintaining high precision through automated optimization.
Solution Approach 2:
The patent replaces the manual mechanical adjustment process with an automated electronic control system. Instead of manually tuning waveform parameters through trial and error, the system uses computer-controlled arbitrary waveform generators and automated measurement systems to precisely set and optimize waveforms, substituting human operation with automated electronic control to reduce time while maintaining precision.
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 reproducible control of ion bombardment energy, enhancing etch selectivity and reducing substrate damage, while improving the profile control of high aspect ratio features by tailoring the ion energy distribution.
Implementation Method 1
A fast Fourier transform (FFT) of the measured substrate waveform is compared with the FFT of a desired waveform to determine adjustments for frequency components of the waveform input to a waveform generator
Implementation Method 2
An inverse FFT yields the output waveform for application to the waveform generator
Implementation Method 3
a plasma excitation source coupled to the chamber for exciting a plasma and forming a gas in the chamber
Implementation Method 4
the ion energy is coarsely controlled by varying the amplitude of a radio frequency (RF) sinusoidal bias voltage that is applied to the substrate electrode
Data Source
AI summary
A method of automating a process for controlling a voltage waveform applied to an object is provided. A first waveform for applying to the object is received. A first FFT of the first waveform is calculated. A second waveform for input to the waveform generator is determined based on the first waveform. The determined second waveform is sent to a waveform generator. A third waveform is received that is measured across the object based on a waveform generated by the waveform generator. A second FFT of the received third waveform is calculated. The third waveform is compared with the first waveform to determine a convergence status of the third waveform. If the determined convergence status is not converged, an updated waveform is calculated based on the first FFT and the second FFT and the process is repeated with the updated waveform as the determined second waveform.