Trench Etching Depth Uniformity via Dynamic Ion Energy Control
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Solution Overview
Problem
Current methods for forming trenches with different widths in a silicon substrate face challenges such as RIE-lag, where etching rate dependence on mask opening width makes it difficult to achieve equal depths, and existing solutions like double-layer passivation layers increase manufacturing time and are ineffective for high aspect ratios, leading to issues like 'black silicon' formation.
Innovation Solution
A method involving a wafer with a mask having openings of varying widths, where a polymer passivation layer is alternately deposited and removed using plasma to control trench depth, with specific ion energy settings to ensure equal etching depths across different width trenches without increasing manufacturing time, employing a reverse RIE-lag etching process to prevent passivation layer removal and maintain anisotropic etching.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If a double-layer passivation layer structure is used to reduce RIE-lag, then trench depth uniformity is improved, but manufacturing time increases
Solution Approach 1:
The patent changes the key parameter from passivation layer structure (double-layer to single-layer) to passivation layer material composition and deposition conditions. By adjusting the polymer passivation layer's material properties and deposition parameters, the invention achieves effective RIE-lag reduction without the time penalty of multiple layer formation and removal steps
Solution Approach 2:
The invention extracts and eliminates the unnecessary oxide layer from the double-layer passivation structure, retaining only the essential polymer passivation layer. This simplification removes the need for forming and removing multiple layers while preserving the core function of reducing RIE-lag effect
2Length of moving object
If the aspect ratio of the trench is greater than 20, then deeper trenches can be formed, but RIE-lag reduction becomes ineffective and black silicon forms
Solution Approach 1:
The patent changes the passivation layer material parameters and deposition conditions to create a polymer-based passivation layer with specific properties that remain effective at high aspect ratios. By adjusting material composition and deposition parameters, the invention maintains RIE-lag reduction capability even when trench depth exceeds 20 times the width
Solution Approach 2:
The invention uses a polymer-based composite passivation layer with specific material composition that provides both protection during etching and effective RIE-lag reduction. The composite material properties are tailored to maintain effectiveness at high aspect ratios where conventional passivation layers fail
3Length of moving object
If reactive ion etching is applied to increase trench depth, then trench depth is improved, but RIE-lag effect causes non-uniform depths across different width trenches
Solution Approach 1:
The patent applies local quality by creating a polymer passivation layer with spatially varying thickness that adapts to different trench geometries. The passivation layer naturally forms with different thicknesses on different trench walls and bottoms, providing locally optimized protection that compensates for the RIE-lag effect at each location
Solution Approach 2:
The invention introduces dynamics by alternating between passivation deposition and etching steps in a controlled sequence. This dynamic process allows the passivation layer to be continuously updated and adjusted during the etching sequence, enabling real-time compensation for RIE-lag effects as trenches of different widths are etched
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 allows independent control of trench depths with different widths without prolonging manufacturing time, preventing 'black silicon' formation and reducing RIE-lag, enabling precise trench formation even at high aspect ratios.
Implementation Method 1
depositing a polymer passivation layer on a side wall and a bottom of the trenches by converting gas introduced in the chamber into plasma
Implementation Method 2
applying reactive ion etching to the exposed silicon layer to increase a depth of the trenches
Data Source
AI summary
In a process for forming trenches having M different widths in a substrate, a passivation step and an etching step are alternately performed. The passivation step includes depositing a passivation layer on a bottom of the trenches by converting gas introduced in a chamber into plasma. The etching step includes removing the passivation layer on the bottom of the trenches and applying reactive ion etching to the bottom to increase a depth of the trenches. The etching step further includes setting energy for the reactive ion etching to a predetermined value when the passivation layer on the bottom of the trench having the Nth smallest width is removed. The value allows the etching amount of the trench having the Nth smallest width to be equal to or greater than the etching amount of the trench having the (N+1)th smallest width.