Plasma Etching Selectivity for 3D Memory Stacks
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Solution Overview
Problem
In the etching process for 3D stacked semiconductor memory, the photoresist layer is often lost before reaching the base film, and it becomes difficult to maintain a desired critical dimension (CD) at the bottom of deep holes or trenches, especially as the number of layers increases.
Innovation Solution
A manufacturing method using a dual-frequency plasma etching process with specific high-frequency power settings and gas mixtures, including CF-based gases and bromine-containing gases, to increase photoresist layer selectivity and ensure a desired CD by gradually adjusting etching depths and applying pulsed biasing power.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Length of moving object
If the etching process is extended to increase depth, then the hole or trench can reach the base film, but the photoresist layer disappears before the hole reaches the base film
Solution Approach 1:
The etching process is divided into multiple steps with different gas mixtures and parameters. The first step uses a gas mixture optimized for photoresist etching, while subsequent steps use different mixtures for the stacked film, allowing selective removal at different depths without compromising photoresist integrity
Solution Approach 2:
The patent changes etching parameters including gas flow rates, power settings, and pressure conditions across different etching steps. By adjusting these parameters, the etching selectivity is controlled to match the photoresist removal rate with the stacked film removal rate, preventing premature photoresist disappearance
2Length of moving object
If the hole depth increases, then more layers are etched, but ions cannot reach the bottom portion of the hole
Solution Approach 1:
The patent employs periodic pulsing of the bias power applied to the substrate electrode. This periodic action creates oscillating ion bombardment that helps ions reach the bottom of deep holes by periodically clearing charge accumulation and enhancing ion acceleration, thereby maintaining critical dimension precision at the hole bottom
Solution Approach 2:
The etching process uses dynamic adjustment of process parameters including power levels and gas flows during the etching sequence. This dynamic control allows optimization of ion transport to the hole bottom while maintaining vertical sidewalls and consistent critical dimensions throughout the deep etching process
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 method effectively increases photoresist layer selectivity and maintains a desired CD at the bottom of deep features, preventing photoresist loss and ensuring accurate etching even in multi-layered structures.
Implementation Method 1
etching a multilayer film using a plasma
Implementation Method 2
it becomes increasingly difficult for ions to reach the bottom portion of the hole or trench
Data Source
AI summary
A plasma processing method is provided for etching a multilayer film having a first film and a second film with differing dielectric constants alternatingly stacked on a substrate, and forming a hole with a predetermined shape in the multilayer film. The plasma processing method includes a first step of etching the multilayer film to a first depth using a gas mixture containing a CF based gas at a first flow rate and a bromine-containing gas, a chloride-containing gas, and/or an iodine-containing gas; a second step of etching the multilayer film to a second depth after the first step using a gas mixture containing the CF based gas at a second flow rate and the bromine-containing gas, the chloride-containing gas, and/or the iodine-containing gas; and a third step for over etching the multilayer film after the second step until the hole reaches a base layer.