Capacitively-Coupled Plasma Focus Ring for Uniform Etching
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Solution Overview
Problem
In semiconductor substrate processing, high aspect ratio pattern structures and larger substrates lead to etch defects and reduced yield due to non-uniform plasma distribution, particularly at the edge regions, necessitating improved plasma etching apparatus for enhanced uniformity.
Innovation Solution
A capacitively coupled plasma substrate processing apparatus is designed with a focus ring and cover ring structure, where the focus ring has a two-layer structure with a doped silicon upper layer and an Al2O3 lower layer, and the cover ring is positioned to support the focus ring, reducing impedance differences and RF phase differences, thereby achieving uniform plasma distribution across the substrate.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If a conventional plasma etching apparatus is used, then the etching process can be performed, but non-uniform plasma distribution occurs particularly at the edge region of the substrate, leading to etch defects and reduced yield
Solution Approach 1:
The focus ring is designed with non-uniform thickness (varying from 3mm to 6mm) to create different electrical properties at different locations. This local variation in the focus ring structure modifies the RF impedance distribution across the substrate surface, thereby achieving uniform plasma density distribution and eliminating edge-related etch defects while maintaining high substrate yield
Solution Approach 2:
The focus ring is constructed using composite materials with specific electrical properties (resistivity between 10-1000 Ω·cm). The combination of the focus ring and cover ring with different material properties creates an optimized impedance matching system that distributes plasma uniformly across the substrate, resolving the contradiction between manufacturing precision and productivity
2Productivity
If the plasma density is increased to improve process speed, then productivity increases, but plasma uniformity deteriorates due to edge effects
Solution Approach 1:
The focus ring parameters (thickness varying from 3mm to 6mm, resistivity between 10-1000 Ω·cm) are optimized to control RF impedance and plasma distribution. By adjusting these parameters, the system achieves both high process speed and uniform plasma density, eliminating the trade-off between productivity and manufacturing precision
3Device complexity
If a simple ring structure is used, then device complexity is reduced, but plasma uniformity control is insufficient
Solution Approach 1:
The ring structure is segmented into two distinct components: the focus ring with non-uniform thickness and the cover ring with uniform thickness. This segmentation allows each component to perform its specific function - the focus ring controls plasma distribution through its variable geometry, while the cover ring provides structural support and electrical grounding, achieving plasma uniformity without excessive complexity
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
The apparatus generates a high density plasma region outside the substrate edge, ensuring uniform etching across the entire substrate, thereby increasing production yield and process speed.
Implementation Method 1
the focus ring has a two-layer structure that includes a doped silicon layer as an upper layer having a first thickness and an Al2O3 layer as a lower layer having a second thickness, and the ratio of the first thickness to the second thickness is between 3:1 and 3:2
Implementation Method 2
reducing impedance differences and RF phase differences, thereby achieving uniform plasma distribution across the substrate
Implementation Method 3
applying a high frequency RF power to one of the electrostatic chuck and the shower head while injecting gas into the chamber from the shower head to generate a plasma inside the chamber
Implementation Method 4
One of the lower electrode and the upper electrode is connected to a high frequency power supply
Implementation Method 5
The electrostatic chuck is connected to the housing and includes a lower electrode, and is for mounting a semiconductor substrate thereon
Implementation Method 6
The shower head includes an upper electrode mounted on the fixing ring, and includes injection holes passing through part of the upper electrode and configured to inject gas into the chamber
Implementation Method 7
etching the semiconductor substrate using the plasma to form a pattern on a surface of the semiconductor substrate
Data Source
AI summary
According to some embodiments, a semiconductor substrate processing apparatus includes a housing, a plasma source unit, an electrostatic chuck, and a ring unit. The housing encloses a process chamber. The plasma source unit is connected to the housing, and includes a shower head and a fixing ring positioned to support the shower head. The shower head includes an upper electrode mounted on the fixing ring, and includes injection holes passing through part of the upper electrode and configured to inject gas into the chamber. The electrostatic chuck is connected to the housing and includes a lower electrode, and is for mounting a semiconductor substrate thereon. The ring unit is mounted on an edge portion of the electrostatic chuck, and includes a focus ring and a cover ring surrounding the focus ring. One of the lower electrode and the upper electrode is connected to a high frequency power supply, and the other of the lower electrode and the upper electrode is connected to ground. The focus ring has an inner side surface, and an opposite outer side surface that contacts the cover ring, and a width between the inner side surface and the outer side surface of the focus ring is a first width. The cover ring has an inner side surface that contacts the outer side surface of the focus ring, and an outer side surface, and a width between the inner side surface and the outer side surface of the cover ring is a second width. The first width is between 2 and 10 time the second width.