Edge Ring Voltage Waveform Control for Wafer Edge Etch Uniformity
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Solution Overview
Problem
Plasma etching processes in semiconductor fabrication often result in ion angular spread at the extreme edge of wafers, leading to non-uniformity of features due to ions forming incidence angles other than normal to the surface.
Innovation Solution
A tailored edge ring voltage waveform is applied to the plasma processing chamber, comprising an additive direct current (DC) bias and a radio frequency (RF) component, ensuring the plasma sheath along the edge ring is coplanar with the wafer sheath, thereby reducing ion angular spread by making ion incidences substantially normal to the wafer.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If a standard RF voltage waveform is applied to the edge ring, then the plasma processing is simple and straightforward, but ion angular spread occurs at the extreme edge of the wafer causing non-uniformity of features
Solution Approach 1:
The patent applies a tailored voltage waveform to the edge ring that modifies the plasma sheath height through controlled voltage parameters. By adjusting the voltage waveform parameters (amplitude, frequency, phase), the plasma sheath along the edge ring is made coplanar with the wafer sheath, ensuring normal ion incidence angles and uniform feature etching at the extreme edge.
Solution Approach 2:
The patent applies a specific voltage waveform treatment only to the edge ring region, while the rest of the plasma chamber operates with standard conditions. This localized application of tailored voltage waveform to the edge ring area addresses the ion angular spread problem specifically at the wafer periphery without affecting the overall plasma processing uniformity across the entire wafer surface.
2Manufacturing precision
If the plasma sheath along the edge ring is made coplanar with the wafer sheath, then ion incidences become substantially normal to the wafer reducing ion angular spread, but this requires precise voltage waveform control
Solution Approach 1:
The patent employs a control system that monitors plasma sheath conditions and adjusts the voltage waveform applied to the edge ring in real-time. By measuring the plasma sheath height and ion incidence angles, the system provides feedback to optimize the voltage waveform parameters, ensuring the plasma sheath along the edge ring remains coplanar with the wafer sheath for consistent normal ion incidence.
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 improves etch uniformity and yield at the extreme edge of the wafer by reducing ion tilt angles, ensuring consistent plasma behavior across the wafer and edge ring.
Implementation Method 1
when ions are accelerated through the plasma sheath, the ion incidences will be substantially normal to the wafer
Implementation Method 2
a radio frequency (RF) signal provides power and is applied to at least one of the electrodes of the plasma processing chamber to form an electric field between the electrodes. The process gas is turned into plasma by the RF signal
Data Source
AI summary
A system for etching a wafer is provided. In one example, the system includes a lower electrode and an upper electrode disposed above the lower electrode. The system further includes an edge ring surrounding the lower electrode. The system includes a first radio frequency (RF) generator electrically coupled to the lower electrode and a second radio frequency (RF) generator electrically coupled to the edge ring. The system also includes a direct current (DC) bias generator for electrically supplying an additive DC bias to the edge ring. The system includes a controller interfaced with the first and second RF generators and the DC bias generator. The first RF generator is configured to produce a wafer voltage (V w) waveform at the lower electrode. The produced Vw waveform includes an induced direct current (DC) component and a first RF component produced by the first RF generator. The controller is configured to produce an edge ring voltage (VER) waveform for application to the edge ring. The VER waveform includes the additive DC bias and a second RF component produced by the second RF generator. The VER waveform is programmed by the controller to have a substantially same frequency and phase as the Vw waveform, a DC offset from the Vw waveform, and an amplitude variation relative to an amplitude of the Vw waveform.