Edge Ring Assembly for Wafer Feature Profile Tilting Control
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Solution Overview
Problem
Feature profile tilting at the extreme edge of semiconductor wafers during plasma etch processes renders the edge region unusable, particularly affecting MEMS devices like silicon gyroscopes, leading to yield decreases due to quadrature errors and ion focusing issues.
Innovation Solution
A passively powered edge ring assembly with capacitive coupling to the electrostatic chuck (ESC) is introduced, which modifies the plasma sheath boundary to control ion trajectories and reduce tilting, utilizing an upper edge ring made of insulating material, a lower inner edge ring of conductive material with anodized aluminum for insulation, and a lower outer edge ring of insulating material, extending the plasma sheath continuity over the wafer edge.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If plasma etch process is carried out on wafer, then etching of features is achieved, but feature profile tilting occurs at extreme edge of wafer
Solution Approach 1:
The patent applies local quality by creating a non-uniform electric field distribution through the edge ring assembly. The ring structure generates localized electric field enhancement at the wafer edge region, which specifically addresses the tilting problem only at the extreme edge while maintaining normal etching conditions in the central wafer area. This localized intervention corrects the plasma sheath bending effect precisely where it occurs without affecting the overall etch process.
Solution Approach 2:
The patent changes the electric field parameter distribution by introducing the edge ring assembly with specific geometric parameters (radius, thickness, positioning). By adjusting these parameters, the electric field strength and distribution at the wafer edge are modified to counteract the plasma sheath bending effect, thereby correcting the feature profile tilting through parameter optimization rather than fundamental process change.
2Manufacturing precision
If passively powered edge ring electrode is used, then plasma sheath boundary control is improved, but device complexity increases
Solution Approach 1:
The edge ring electrode is passively powered, meaning it derives its operating voltage from the existing plasma potential without requiring an independent power supply or control system. The ring automatically adjusts to the plasma conditions and provides the necessary electric field correction, making the system self-regulating and eliminating the need for additional active control components that would increase device complexity.
Solution Approach 2:
The edge ring assembly acts as an intermediary element between the plasma source and the wafer surface. It mediates the interaction by providing a controlled electric field that modifies the plasma sheath boundary and ion trajectories indirectly, rather than requiring direct control of the entire plasma process. This intermediary approach simplifies the control architecture while achieving the desired precision.
3Area of stationary object
If edge region of wafer is used, then usable area is increased, but feature profile tilting renders it unusable
Solution Approach 1:
The edge ring assembly provides preliminary anti-action by establishing the corrective electric field before the plasma etching process begins. The pre-biased ring creates an opposing electric field that counteracts the plasma sheath bending effect as the plasma is introduced, preventing feature profile tilting from occurring in the first place rather than attempting to correct it after the fact. This allows the extreme edge region to be used effectively.
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 effectively reduces feature profile tilting and ion focusing at the wafer edge, increasing the usable wafer area and improving the yield of fabricated devices by enabling precise control over ion trajectories and the ion to neutral flux ratio, thus enhancing the fabrication of MEMS devices.
Implementation Method 1
a passively powered edge ring electrode is provided that exhibits a capacitive coupling to the electrostatic chuck (ESC) when RF power is applied to the ESC
Implementation Method 2
The passive powering of the edge ring does not require the additional expense or added complexity of a separate RF power supply, yet still provides for improvement in the profile tilt of features etched at the wafer edge
Implementation Method 3
Achieving control over ion trajectory and minimizing the resulting ion focusing effects caused due to sheath bending near the wafer edge can not only manipulate the ion trajectories to the wafer but also the ion to neutral flux ratio
Implementation Method 4
The plasma sheath boundary in the vicinity of the extreme wafer edge can be modified by enabling a sheath continuity over the edge ring assembly. The presence of the modified sheath boundary due to the passively powered edge ring electrode reduces ion tilting and ion focusing at the wafer edge
Data Source
AI summary
An edge ring assembly is provided, including: an upper edge ring configured to surround an electrostatic chuck (ESC), the ESC having a top surface for supporting a substrate and an annular step surrounding the top surface, the annular step defining an annular shelf that is lower than the top surface, the upper edge ring being disposed above the annular shelf; a lower inner edge ring disposed below the upper edge ring in the annular step and disposed over the annular shelf, the lower inner edge ring being defined from an electrically conductive material, the lower inner edge ring being electrically insulated from the ESC; a lower outer edge ring surrounding the inner edge ring, the lower outer edge ring being disposed below the upper edge ring in the annular step and disposed over the annular shelf, the lower outer edge ring being defined from an electrically insulating material.