Pulsed Bias Plasma Etch for High Aspect Ratio Distortion
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Solution Overview
Problem
Plasma etching processes face challenges in achieving high aspect ratio features on semiconductor wafers due to twisting and distortion, particularly at ultra-high aspect ratios, caused by asymmetric etching and differential charging, leading to reduced etch rates and increased aspect ratio dependent etching.
Innovation Solution
A plasma processing chamber with a high frequency RF power source and a bias power system that provides a bias of at least 500 volts to the upper electrode to create secondary electrons and a pulsed bias to the lower electrode, intermittently collapsing the plasma sheath, which helps in reducing distortion and aspect ratio dependent etching by controlling ion flux and charge balance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Length of moving object
If conventional plasma etching is used to etch deeper features, then feature depth increases, but aspect ratio increases leading to twisting and distortion
Solution Approach 1:
The patent applies dynamic control by pulsing the bias power to the lower electrode, intermittently collapsing the plasma sheath. This dynamic adjustment of plasma sheath collapse timing and duration optimizes ion flux delivery to the feature bottom, maintaining etch rate consistency and reducing twisting/distortion in ultra-high aspect ratio features while accommodating increasing feature depth
Solution Approach 2:
The patent changes critical plasma process parameters including applying at least 500 volts bias to the lower electrode, using specific gas flow rates (CHF3 at 50-200 sccm, O2 at 50-200 sccm), and controlling pressure (10-100 mTorr). These parameter changes optimize the plasma chemistry and ion flux to maintain etch rate consistency throughout ultra-high aspect ratio features, preventing the twisting and distortion that occurs with conventional parameters
2Productivity
If feature width decreases to increase density, then device density increases, but aspect ratio increases causing twisting and distortion
Solution Approach 1:
The patent modifies plasma process parameters including bias voltage (at least 500 volts), gas composition (CHF3 and O2), pressure (10-100 mTorr), and power delivery to optimize ion flux and etch rate consistency. These parameter changes enable successful etching of ultra-high aspect ratio features with aspect ratios greater than 10:1, maintaining feature shape accuracy even as feature width decreases to increase device density
3Productivity
If ultra-high bias is applied to increase ion flux, then etch rate increases, but differential charging increases causing twisting
Solution Approach 1:
The patent employs periodic action by pulsing the bias power to the lower electrode, creating periodic plasma sheath collapse. This periodic collapse timing and duration are optimized to deliver ion flux effectively to the feature bottom while preventing excessive charge accumulation. The pulsed nature allows charge dissipation between pulses, reducing differential charging and twisting while maintaining high etch rates
Solution Approach 2:
The patent implements feedback control by monitoring plasma parameters and adjusting bias power delivery accordingly. The system responds to plasma conditions to optimize ion flux delivery and prevent excessive charge accumulation at the feature bottom, maintaining etch rate consistency and reducing twisting/distortion through real-time parameter adjustment
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 solution effectively reduces twisting and distortion in high aspect ratio features, maintaining etch rate consistency and preventing aspect ratio dependent etching, even at ultra-high aspect ratios greater than 10-to-1, by ensuring efficient ion delivery and charge balance.
Implementation Method 1
the bias to the upper electrode creates secondary electrons
Implementation Method 2
the bias to the lower electrode is pulsed to intermittently collapse a generated plasma sheath
Implementation Method 3
A plasma is formed in the plasma processing chamber, between the upper electrode and the lower electrode
Data Source
AI summary
An apparatus for etching high aspect ratio features is provided. A plasma processing chamber is provided, comprising a chamber wall forming a plasma processing chamber enclosure, a lower electrode, an upper electrode, a gas inlet, and a gas outlet. A high frequency radio frequency (RF) power source is electrically connected to at least one of the upper electrode or lower electrode. A bias power system is electrically connected to both the upper electrode and the lower electrode, wherein the bias power system is able to provide a bias to the upper and lower electrodes with a magnitude of at least 500 volts, and wherein the bias to the lower electrode is pulsed to intermittently. A gas source is in fluid connection with the gas inlet. A controller is controllably connected to the gas source, the high frequency RF power source, and the bias power system.