Pulsed Voltage Feedback Loop for Single-Peak IEDF Etching
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Solution Overview
Problem
In semiconductor manufacturing, maintaining a consistent sheath voltage in plasma processing chambers is challenging due to real-time changes in plasma density, chamber conditions, and substrate temperature, leading to difficulties in controlling the Ion Energy Distribution Function (IEDF) and feature profile precision, especially in high aspect ratio etch applications.
Innovation Solution
A closed feedback loop system is implemented, using a data acquisition system with conditioning circuits and a fast data acquisition module to analyze and adjust pulsed voltage waveforms in real-time, ensuring a nearly constant sheath voltage and a single-peak IEDF through a pulsed voltage waveform generator connected to a biasing electrode in the plasma processing chamber.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stress or pressure
If a lower frequency RF bias generator is used to achieve higher self-bias voltages, then the self-bias voltage increases, but the ion energy distribution becomes bimodal causing bowing of etched feature walls
Solution Approach 1:
The patent applies periodic pulsed voltage waveforms at frequencies significantly higher than the RF bias frequency (e.g., >100 MHz versus 2 MHz) to reshape the ion energy distribution. The pulsed nature creates a single-peak IEDF by delivering ions in synchronized bursts, eliminating the bimodal distribution caused by low-frequency RF bias while maintaining high self-bias voltages for deep etching applications
2Manufacturing precision
If real-time feedback control is implemented to maintain predetermined voltage waveform, then waveform control precision improves, but system complexity increases due to high amplitude measurements
Solution Approach 1:
The patent introduces an intermediary voltage divider network that scales down the high amplitude voltage waveform (tens of kV) to a measurable range while preserving waveform characteristics. This intermediary device enables standard measurement equipment to accurately capture the pulsed voltage waveform without requiring specialized high-voltage measurement systems, thus reducing overall system complexity
3Manufacturing precision
If pulsed voltage waveform is used to maintain constant sheath voltage, then etch anisotropy improves, but difficulty in measuring and analyzing high amplitude waveform increases
Solution Approach 1:
The voltage divider acts as an intermediary that makes the high amplitude waveform measurable by scaling it to safe voltage levels for standard oscilloscopes and measurement equipment. The divider maintains the pulsed waveform shape and timing characteristics while reducing amplitude from tens of kV to manageable levels, enabling real-time verification of the constant sheath voltage condition
Solution Approach 2:
The patent replaces direct high-voltage measurement with an electrical transformation approach using the voltage divider network. Instead of using complex high-voltage probes or specialized measurement systems, the solution transforms the measurement problem into a low-voltage domain where standard electronic measurement tools can be used effectively
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 precise control of the IEDF and feature profiles, maintaining a consistent sheath voltage for up to 90% of the processing time, resulting in repeatable and desirable mono-energetic ion distributions for improved etch anisotropy and feature control.
Implementation Method 1
a plasma is formed in an RIE processing chamber and ions from the plasma are accelerated towards a surface of a substrate
Implementation Method 2
The application of RF voltage to the power electrode causes an electron-repelling plasma sheath (also referred to as the 'cathode sheath') to form over a processing surface of a substrate
Implementation Method 3
a data acquisition system with conditioning circuits and a fast data acquisition module to analyze and adjust pulsed voltage waveforms in real-time
Data Source
AI summary
Embodiments of this disclosure describe a feedback loop that can be used to maintain a nearly constant sheath voltage and thus creating a mono-energetic IEDF at the surface of the substrate. The system described herein consequently enables a precise control over the shape of IEDF and the profile of the features formed in the surface of the substrate.