Bromide Plasma Etching for Silicon Recess Selectivity
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Solution Overview
Problem
The existing etching processes for 3D-NAND flash memory manufacturing face challenges in achieving high selectivity of the silicon layer to the metal layer during the formation of a silicon recess, leading to unintended removal of the metal layer, which increases contact resistance.
Innovation Solution
An etching method using a plasma processing apparatus that employs a two-step process: the first step etches the insulating film to expose both the silicon and metal layers, followed by a second step using a bromide-containing gas, such as HBr, to further etch the silicon layer while maintaining high selectivity and preventing metal layer removal.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If a processing gas containing fluorine gas (e.g., CF4, Ar, O2) is used in the step of forming the Si recess, then the etching rate of the silicon layer is improved, but the metal layer is also removed along with the silicon layer, making it difficult to increase the selectivity of the silicon layer to the metal layer
Solution Approach 1:
The patent changes the chemical composition parameter of the processing gas from fluorine-based (CF4, Ar, O2) to bromine-based (HBr, BCl3, BBr3). This parameter change fundamentally alters the etching chemistry to achieve high selectivity. The bromine-containing gas reacts preferentially with silicon while being less reactive with the metal layer, thereby resolving the contradiction between etching rate and selectivity.
Solution Approach 2:
The patent uses a two-step etching process where the first step (using fluorine-based gas) creates the initial hole structure, and the second step (using bromine-based gas) precisely forms the Si recess with high selectivity. This sequential approach allows each step to optimize for its specific function, with the second step copying and refining the structure created in the first step while protecting the metal layer.
2Reliability
If the silicon layer is etched to form a recess to lower contact resistance, then the contact resistance is reduced, but the exposed metal layer may be removed unintentionally
Solution Approach 1:
The patent changes the processing gas parameter to bromine-containing gas (HBr, BCl3, BBr3) which provides high etch selectivity between silicon and metal layers. This allows the Si recess to be formed to the required depth for low contact resistance while the metal layer remains protected due to the selective nature of the bromine-based etching chemistry.
Solution Approach 2:
The patent performs a preliminary etching step using fluorine-based gas to expose the metal layer and create the initial hole structure before performing the selective silicon etching. This preliminary action prepares the structure for the subsequent high-selectivity etching step, ensuring that the metal layer is already exposed and will not be accidentally removed during the selective silicon recess 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 significantly enhances the silicon-to-metal selectivity, allowing for the formation of a silicon recess without substantial removal of the metal layer, thereby reducing contact resistance and maintaining a vertical etching shape.
Implementation Method 1
a second step of further etching the silicon layer after the first step using a plasma generated from a second gas including a bromide-containing gas
Data Source
AI summary
An etching method is provided for processing a substrate that includes a first region having an insulating film arranged on a silicon layer and a second region having the insulating film arranged on a metal layer. The etching method includes a first step of etching the insulating film into a predetermined pattern using a plasma generated from a first gas until the silicon layer and the metal layer are exposed, and a second step of further etching the silicon layer after the first step using a plasma generated from a second gas including a bromide-containing gas.