Showerhead Electrode Layer Stack for RF Parasitic Plasma Control
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Solution Overview
Problem
In semiconductor processing chambers, parasitic plasma formation due to RF fields is not effectively reduced by existing methods, particularly when using ceramic pedestals, as they require impractically thick solid dielectric layers to achieve low RF impedance paths to ground.
Innovation Solution
A system comprising multiple dielectric layers with alternating gaps is used between an electrode and a grounded conducting structure, which reduces parasitic plasma by creating a high impedance path to ground and attenuating RF fields, thereby preventing plasma formation between the electrode and the substrate or showerhead.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a solid dielectric layer is used between ground and the electrode to prevent excessive RF coupling to ground, then RF coupling to ground is reduced, but the required thickness of the dielectric layer becomes impractically large
Solution Approach 1:
The patent divides a single thick dielectric layer into multiple thinner dielectric layers separated by conductive shielding layers. This segmentation achieves the same RF blocking function as a thick dielectric layer while maintaining a compact overall thickness, as the alternating dielectric and conductive layers create multiple reflection and absorption interfaces for RF fields.
Solution Approach 2:
The patent creates a composite structure combining dielectric materials and conductive shielding materials in alternating layers. This composite approach leverages the RF blocking properties of dielectrics and the RF reflection/absorption properties of conductors to achieve effective RF coupling prevention in a compact thickness.
2Object-affected harmful factors
If an RF shield is used to reduce parasitic plasma by lowering electric fields, then parasitic plasma is reduced, but the RF shield may create a low RF impedance path to ground if not designed properly
Solution Approach 1:
The RF shield is segmented into multiple thin dielectric layers separated by conductive shielding layers. This segmentation prevents the creation of a continuous low-impedance path to ground while still providing RF field attenuation to reduce parasitic plasma, as each conductive layer is separated by dielectric barriers that block current flow.
Solution Approach 2:
The dielectric layers act as intermediaries between the conductive shielding layers, preventing direct electrical connection while allowing the conductive layers to provide RF field attenuation. This intermediary structure reduces parasitic plasma through RF field control without creating a low-impedance ground path.
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 solution significantly reduces parasitic plasma density by a factor of about 5, providing effective RF shielding while maintaining practical layer thicknesses, and can be retrofitted into existing systems.
Implementation Method 1
A number of the plurality of dielectric layers and sizes of the first gap, the second gap and the third gap are selected to prevent parasitic plasma between the first surface and the electrode during the semiconductor process
Implementation Method 2
A plurality of dielectric layers that are arranged between an electrode and the first surface... selected to prevent parasitic plasma
Implementation Method 3
The plurality of dielectric layers defines a first gap between the electrode and one of the plurality of dielectric layers, a second gap between adjacent ones of the plurality of dielectric layers, and a third gap between a last one of the plurality of dielectric layers and the first surface
Data Source
AI summary
A system includes an electrode. The electrode includes a showerhead having a first stem portion and a head portion. A plurality of dielectric layers is vertically stacked between the electrode and a first surface of a conducting structure. The plurality of dielectric layers includes M dielectric layers arranged adjacent to the head portion and P dielectric portions arranged around the first stem portion. The plurality of dielectric layers defines a first gap between the electrode and one of the plurality of dielectric layers, a second gap between adjacent ones of the plurality of dielectric layers, and a third gap between a last one of the plurality of dielectric layers and the first surface. A number of the plurality of dielectric layers and sizes of the first gap, the second gap, and the third gap are selected to prevent parasitic plasma between the first surface and the electrode.