Plasma Processing Apparatus Duty Ratio Modulation for Stable Ignition
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Solution Overview
Problem
Conventional capacitively coupled plasma processing apparatuses face challenges in reliably igniting plasma under low duty ratio or high pulse frequency conditions, leading to unstable plasma processes and potential charging damage during semiconductor manufacturing.
Innovation Solution
A plasma processing method and apparatus that modulate high frequency power in a pulse shape, with an initial high duty ratio for ignition followed by a gradual reduction to a set value, ensuring stable plasma ignition and operation under preset conditions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If high frequency power is modulated in a pulse shape with low duty ratio or high pulse frequency, then charging damage is suppressed and etching selectivity is improved, but plasma ignition becomes unreliable and plasma process stability deteriorates
Solution Approach 1:
The patent applies preliminary action by implementing a warm-up period before the actual plasma etching process. During this warm-up period, the plasma is generated at a higher duty ratio (first duty ratio) to ensure stable plasma ignition and establishment. After the plasma is stabilized, the duty ratio is then reduced to the target lower value (second duty ratio) for the etching process. This preliminary high duty ratio operation prevents ignition failures that would occur if the low duty ratio were applied from the start.
2Manufacturing precision
If pressure and ion energy are reduced to improve etching selectivity and uniformity, then charging damage increases, but etching performance is maintained
Solution Approach 1:
The patent applies periodic action by modulating the high frequency power in a pulse shape with a specific duty ratio. The plasma is generated intermittently rather than continuously, with the duty ratio controlling the ratio of plasma generation time to total cycle time. This periodic plasma generation reduces the cumulative charge accumulation on the substrate while maintaining the low pressure and ion energy conditions needed for good etching uniformity and selectivity.
3Object-affected harmful factors
If duty ratio is reduced to suppress charging damage, then plasma ignition becomes difficult, but etching quality is improved
Solution Approach 1:
The patent implements preliminary action by using a higher first duty ratio during a warm-up period to ensure easy plasma ignition and stabilization. Only after the plasma is firmly established does the system transition to the lower second duty ratio for the actual etching process. This two-stage approach eliminates the ignition difficulties that would occur if the low duty ratio were applied from the beginning.
Solution Approach 2:
The patent applies dynamics by making the duty ratio time-dependent rather than fixed. The duty ratio dynamically changes from an initial higher value (first duty ratio) during the warm-up period to a lower target value (second duty ratio) during the etching process. This dynamic adjustment allows the system to adapt to different operational phases, ensuring easy ignition initially and then achieving charging damage suppression during steady-state operation.
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
Enables secure and stable plasma ignition and processing even with low duty ratios or high pulse frequencies, reducing the risk of charging damage and improving process reliability.
Implementation Method 1
A high frequency power having a frequency (typically, about 13.56 MHz or higher) suitable for plasma generation is applied to the upper electrode or the lower electrode. Electrons are accelerated by a high frequency field generated between the two facing electrodes by applying the high frequency power
Implementation Method 2
plasma is generated as a result of ionization by collision between the electrons and a processing gas
Implementation Method 3
a high frequency power for plasma generation is modulated in a pulse shape... a plasma generation state in which plasma of a processing gas is being generated and a plasma non-generation state in which plasma is not being generated are alternately repeated at a preset cycle
Implementation Method 4
the non-uniformity of the plasma potential in the entire surface of the substrate may easily cause the charging damage on a gate oxide film
Data Source
AI summary
At a time point T0 when starting a process, a duty ratio of a high frequency power RF1 to which power modulation is performed is set to be an initial value (about 90%) which allows plasma to be ignited securely under any power modulating conditions. At the substantially same time of starting the process, the duty ratio of the high frequency power RF1 is gradually reduced from the initial value (about 90%) in a regular negative gradient or in a ramp waveform. At a time point t2 after a lapse of a preset time Td, the duty ratio has an originally set value Ds for an etching process. After the time point t2, the duty ratio is fixed or maintained at the set value Ds until the end (time point T4) of the process.