Deep Trench Capacitor Scalloped Profile Etching Without Undercut
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Solution Overview
Problem
The existing manufacturing methods for deep trench capacitors face challenges in forming a uniform scalloped profile, which limits the capacitance due to undercut issues and non-constant trench slopes, especially as trench depth increases beyond 60-100 um.
Innovation Solution
A method involving multiple etching cycles with varying bias powers and plasma source gases, such as C4F8 for passivation and SF6 for etching, is employed to form a deep trench capacitor with a scalloped profile, optimizing the etching process to maintain a vertical trench profile and increase surface area.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If a deep trench is formed with increased depth to increase capacitance, then the capacitance increases, but the trench profile becomes non-vertical with undercut issues and non-constant slope
Solution Approach 1:
The etching process is segmented into multiple alternating steps: a first etching step that etches the trench deeper, followed by a second etching step that removes lateral undercut. This segmentation allows independent control of vertical depth and lateral profile, enabling deep trenches to be formed while maintaining vertical sidewalls and uniform scalloped profiles throughout the trench depth.
Solution Approach 2:
The patent employs periodic alternation between two etching modes with different bias powers. The first etching uses a first bias power to create vertical etching with scalloped profile, then switches to a second bias power to remove lateral undercut. This periodic switching continues throughout the deep trench formation process, maintaining consistent profile control even as trench depth increases beyond 60-100 micrometers.
2Ease of manufacture
If a single etching process is used to form deep trenches, then the process is simple, but the sidewall profile becomes balloon-shaped or scallop-shaped with undercut issues
Solution Approach 1:
The etching process dynamically adjusts the bias power between two distinct levels during the etching sequence. The bias power is switched from a first level during the first etching step to a second level during the second etching step. This dynamic adjustment enables the process to adapt the etching characteristics in real-time, forming vertical sidewalls with scalloped profiles while preventing undercut, all within a single programmable etching cycle.
3Productivity
If higher bias power is used to etch deeper trenches faster, then the etching speed increases, but the trench profile control deteriorates with increased undercut and non-vertical sidewalls
Solution Approach 1:
The etching process is divided into two segmented steps with different bias power levels. The first etching step uses a first bias power optimized for vertical etching speed to advance the trench depth. The second etching step uses a second bias power optimized for profile control to remove lateral undercut. This segmentation allows each step to operate at its optimal bias power without compromising the other, achieving both high productivity and precise profile control in deep trench formation.
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 enhances the capacitance of deep trench capacitors by forming a uniform scalloped profile, maximizing the capacitor's capacity while preventing undercut and ensuring a vertical trench shape, thus improving the manufacturing process efficiency.
Implementation Method 1
A plasma source gas of the passivation operation may be different from the first and second plasma source gases
Implementation Method 2
The first and second etchings may be conducted with a reactively ionized etching process and an isotropic etching process, respectively
Data Source
AI summary
A manufacturing method for a deep trench, the method includes forming a first trench in a substrate and performing a first cycle and a second cycle. Each comprising performing a passivation operation forming a passivation film on a sidewall and a bottom surface of the first trench, performing a first etching with a first bias power to remove the passivation film formed on the bottom surface of the first trench to expose the bottom surface of the first trench, and performing a second etching with a second bias power etching the exposed bottom surface of the first trench to form a second trench disposed below the first trench. The first bias power and the second bias power in the second cycle is greater than the first bias power and the second bias power in the first cycle, respectively.