Pulsed Plasma Etching for Bowing Suppression
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Solution Overview
Problem
Conventional plasma etching methods for forming high aspect ratio contact holes in semiconductor manufacturing often result in bowing due to insufficient emission of secondary electrons, leading to poor etching shape and increased hole diameter.
Innovation Solution
A plasma etching method using a capacitively coupled parallel plate plasma etching apparatus with a processing gas containing CxFy and a rare gas like helium, where high frequency power is alternately switched on and off, and a negative DC voltage is applied to the upper electrode with a greater absolute value during the off period to enhance secondary electron emission and modify the protective film, reducing bowing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If high frequency power is continuously applied to maintain plasma for high etching rate, then productivity is improved, but secondary electron emission becomes insufficient causing bowing and poor etching shape
Solution Approach 1:
The patent applies periodic pulsed plasma generation by alternating between plasma on-state and plasma off-state. During the on-state, plasma is generated for etching; during the off-state, secondary electrons are emitted to modify the protective film and suppress bowing. This periodic action resolves the contradiction by separating the functions of high-rate etching and bowing suppression into different time periods.
2Manufacturing precision
If negative DC voltage with greater absolute value is applied during plasma off-period, then secondary electron emission increases suppressing bowing, but energy consumption increases
Solution Approach 1:
The negative DC voltage with greater absolute value is applied only during the plasma off-period, not continuously. This periodic application reduces overall energy consumption compared to continuous application, while still achieving sufficient secondary electron emission during the critical off-period when bowing suppression is needed.
3Productivity
If plasma is continuously maintained for high etching rate, then productivity is improved, but protective film modification becomes insufficient leading to increased hole diameter
Solution Approach 1:
The patent utilizes the plasma off-period to enable secondary electron emission that modifies the protective film, increasing its etching resistance. This periodic modification prevents excessive hole diameter increase during the etching process, maintaining precision while allowing high etching rates during the on-period.
4Manufacturing precision
If pulse width ratio of plasma on-state to off-state is optimized, then both etching rate and bowing suppression are improved, but device complexity increases
Solution Approach 1:
The patent optimizes specific parameters including pulse width ratio (on-period to off-period), negative DC voltage magnitude during off-period, and processing gas composition. By carefully controlling these parameters, the system achieves both high etching rate and effective bowing suppression without requiring fundamentally complex device modifications, only coordinated control of existing components.
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 effectively suppresses bowing and maintains a vertical sidewall shape by increasing the selectivity between the deposit and polysilicon, ensuring precise microprocessing and high etching rates even at high pressures.
Implementation Method 1
a high frequency power application unit configured to apply a high frequency power for plasma generation to at least one of the upper electrode and the lower electrode
Implementation Method 2
applying the negative DC voltage from the DC power supply such that an absolute value of the negative DC voltage of the second condition becomes greater than an absolute value of the negative DC voltage of the first condition
Data Source
AI summary
In a plasma etching method for forming a hole in an etching target film, a process of generating a plasma of a processing gas containing at least CxFy gas and a rare gas having a mass smaller than a mass of Ar gas into the processing chamber in the processing chamber by switching on a high frequency power application unit under a first condition and a process of extinguishing the plasma of the processing gas in the processing chamber by switching off the high frequency power application unit under a second condition are alternately repeated. A negative DC voltage from a DC power supply is applied such that an absolute value of the negative DC voltage of the second condition becomes greater than an absolute value of the negative DC voltage of the first condition.