Pulse-Modulated Plasma Etching for Vertical STI Trenches
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Solution Overview
Problem
Existing plasma etching methods, such as those using pulse discharge and radio frequency RF bias power, face challenges in achieving vertical etching for complex three-dimensional structures like Fin-FETs, due to insufficient process windows and lateral etching issues.
Innovation Solution
A plasma processing method involving multiple steps of etching and deposition, where plasma is generated by radio frequency power modulated by pulses, with specific pulse frequencies and duty ratios to control the etching process and prevent undercutting.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If plasma with high degree of dissociation is used for etching, then etching speed is improved, but the process window for controlling radical deposition is insufficient for vertical etching
Solution Approach 1:
The patent applies periodic action by using pulse-modulated radio frequency power to generate plasma intermittently. The plasma generation power is supplied in pulses with specific duty ratios (e.g., 10-90%), creating periodic plasma discharge cycles. This periodic plasma generation allows control over radical density and deposition characteristics, enabling vertical etching while maintaining adequate etching speed through optimized pulse parameters.
2Manufacturing precision
If RF bias power is applied to cause local charge, then etching control is improved, but side etching occurs and verticality is impaired
Solution Approach 1:
The patent eliminates continuous RF bias power and instead uses periodic plasma generation with controlled duty ratios. By turning plasma generation on and off periodically, the method prevents continuous local charge accumulation on side surfaces that causes side etching. The periodic nature allows charge dissipation during off-periods, maintaining verticality while providing etching control through duty ratio adjustment.
Solution Approach 2:
The patent changes the parameter of plasma generation power from continuous to pulsed mode, and adjusts the duty ratio parameter (e.g., 10-90%) to control the balance between etching control and verticality. By varying the duty ratio, the method optimizes the trade-off between maintaining adequate ion flux for control and preventing excessive side etching, achieving both control and verticality.
3Device complexity
If pulse discharge is used for etching, then etching process is simplified, but the process window for controlling radical amount is insufficient
Solution Approach 1:
The patent uses periodic plasma generation with adjustable duty ratios to control radical amount. By varying the duty ratio parameter, the method provides a flexible process window for radical control without complicating the etching process. The simple pulse modulation approach maintains process simplicity while achieving precise radical amount control through duty ratio 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
This method enables precise control of process conditions to achieve vertical etching, reducing undercut amounts and maintaining trench shape integrity, thus improving the manufacturing process for semiconductor devices.
Implementation Method 1
plasma is generated by radio frequency power modulated by a first pulse
Implementation Method 2
radio frequency power modulated by a first pulse
Implementation Method 3
depositing a deposited film containing a silicon element on a mask
Implementation Method 4
depositing a deposited film containing a silicon element on a mask
Implementation Method 5
depositing a deposited film containing SiO on the mask
Implementation Method 6
depositing a deposited film containing SiO on the mask
Data Source
AI summary
A method for forming shallow trench isolation, including a first step of etching silicon by plasma; a second step of depositing a film containing a silicon element on a mask; a third step of etching the silicon by plasma such that an etching shape becomes perpendicular; and a fourth step of depositing a film containing SiO on the mask, in which the first step to the fourth step are repeated a predetermined number of times, the plasma in the third step is generated by radio frequency power modulated by a first pulse, the third step is performed while radio frequency power modulated by a second pulse is supplied to a sample having the silicon as a substrate, and a frequency of the first pulse in the third step is higher than a frequency of the second pulse in the third step.