Multi-Zone Aperture Plate Ion Filtering for Bosch DRIE
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Solution Overview
Problem
Existing plasma processing technologies face challenges in achieving an optimal ratio of ions to neutral radicals for effective etching and deposition, particularly at higher pressures, where prior methods become less effective due to electron trapping issues and lack of flexibility in adjusting ion to radical ratios across the wafer or over time.
Innovation Solution
The use of an aperture plate with multiple zones, each connected to separate electrical bias sources, allows for adjustable bias voltages to control ion filtering, enabling precise adjustment of ion numbers reaching the substrate during plasma processing, either spatially or temporally, to match varying plasma source conditions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If gas flow and power are increased to achieve faster etching rates, then productivity is improved, but the ratio of ions to neutral radicals becomes unbalanced with excessive ions causing damage
Solution Approach 1:
An aperture plate is introduced as an intermediary component between the plasma source and substrate. The plate with controlled aperture openings filters the plasma flux, selectively allowing neutral radicals to reach the substrate while blocking excess ions. This mediator enables high etching rates by maintaining sufficient neutral radical flux while removing the harmful effect of excessive ions that would otherwise cause damage to etched structures.
Solution Approach 2:
The invention changes the physical parameters of plasma transport by introducing an aperture plate with specific geometric characteristics (aperture size, spacing, pattern). By controlling the physical dimensions and arrangement of apertures, the plate modifies the mean free path and scattering angles of plasma particles, preferentially transmitting neutral radicals while deflecting ions. This parameter control allows optimization of the ion-to-neutral ratio independent of gas flow and power settings.
2Quantity of substance
If magnetic fields are used to direct ions to loss surfaces, then ion numbers are reduced, but the technique becomes less effective at pressures above 10 to 20 mTorr due to electron collision
Solution Approach 1:
The invention replaces the magnetic field-based ion control mechanism with a purely mechanical/physical aperture plate structure. Instead of relying on electromagnetic fields to guide and trap electrons for indirect ion loss, the aperture plate uses geometric constraints and physical scattering to directly filter ions from the plasma flux. This mechanical approach is pressure-independent because it does not rely on electron mean free path or magnetic confinement, which degrade at higher pressures due to increased neutral gas collisions.
Solution Approach 2:
The aperture plate is segmented into multiple discrete aperture openings rather than using a continuous structure. This segmentation creates multiple independent filtering paths, increasing the probability that ions will encounter plate material and be scattered or absorbed. The segmented structure also allows optimization of aperture size and distribution to match specific plasma conditions and substrate requirements.
3Object-affected harmful factors
If a simple perforated plate is used to reduce ion numbers, then ion damage is reduced, but there is no flexibility to adjust ion to radical ratios across the wafer or over time
Solution Approach 1:
The aperture plate is designed with multiple independently controllable aperture zones that can be dynamically adjusted. Each zone can be selectively opened or closed, or have its aperture dimensions modified, allowing real-time control of plasma flux distribution across different regions of the substrate. This dynamic capability enables adjustment of ion-to-neutral ratios both spatially (across the wafer surface) and temporally (over time during the process), providing versatility for different process requirements.
Solution Approach 2:
Different regions of the aperture plate are designed with locally optimized aperture characteristics (size, shape, density, orientation) to achieve specific plasma filtering functions in different zones. This local quality variation allows different areas of the substrate to receive tailored plasma flux compositions, enabling simultaneous optimization of etching in some regions while protecting other regions, or creating intentional gradients in ion-to-neutral ratios across the wafer surface.
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 provides greater control over ion flux, enhancing the selectivity and efficiency of the Bosch DRIE process by reducing ion damage and maintaining uniform ion density across the wafer, while allowing for flexible adjustments in ion to radical ratios as needed.
Implementation Method 1
The use of an aperture plate with multiple zones, each connected to separate electrical bias sources, allows for adjustable bias voltages to control ion filtering
Implementation Method 2
plasma is generated in a source region from appropriate precursor gases forming positive ions of the gas, electrons and neutral radicals
Data Source
AI summary
The present invention provides a method for using ion filtering to adjust the number of ions delivered to a substrate. The method comprising a process chamber being provided that is operatively connected to a plasma source. The substrate is provided on a substrate support that is provided within the process chamber. An electrical bias source is provided that is operatively connected to an aperture plate that is provided in the process chamber. The substrate on the substrate support is processed using a plasma generated using the plasma source. A variable bias voltage from the electrical bias source is applied to the aperture plate during the plasma processing of the substrate. The plasma processing of the substrate can further comprise exposing the substrate to a plasma time division multiplex process which alternates between deposition and etching on the substrate.