Polysilicon Etch Selectivity via Remote Plasma
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Solution Overview
Problem
Plasma-based etching of polysilicon in integrated circuits faces challenges with low throughput and selectivity in wet etching, and high costs and damage to surrounding structures in dry reactive-ion-etching processes.
Innovation Solution
A method involving a remote plasma etching process using a hydrogen-based species and a fluorine-based species, such as hydrogen or ammonia and nitrogen trifluoride or carbon tetrafluoride, to selectively remove polysilicon layers at high etch rates while minimizing damage to exposed nitride and oxide structures, achieving selectivity greater than 500:1 and etch rates exceeding 1000 Å per minute.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If wet etching process is used to remove polysilicon, then the process is simple and low cost, but the etch rate is low leading to low throughput and selectivity over other materials is insufficient
Solution Approach 1:
The patent changes the chemical parameters of the etching process by using a remote plasma source to generate highly reactive fluorine species from CF4 or NF3 gas. This parameter change transforms the etching mechanism from a slow wet chemical process to a fast plasma-enhanced process, achieving etch rates exceeding 1000 Å/min while maintaining simplicity by avoiding complex RIE hardware modifications.
2Manufacturing precision
If dry RIE process is used to achieve high selectivity, then selectivity over surrounding structures is improved, but hardware complexity increases due to external bias requirements and damage to surrounding structures occurs
Solution Approach 1:
The patent extracts the plasma generation function from the reaction chamber and places it in a remote source chamber. This separation allows the reaction chamber to remain simple without external bias hardware, while still achieving high selectivity (greater than 500:1) through the controlled delivery of reactive fluorine species to the polysilicon surface.
Solution Approach 2:
The patent introduces an intermediary transport chamber that carries the plasma-generated fluorine species from the source to the reaction chamber. This intermediary system allows high-selectivity etching without requiring complex bias control hardware in the reaction chamber, as the selectivity is achieved through chemical specificity of the fluorine species rather than physical ion bombardment control.
3Manufacturing precision
If dry RIE process is used to achieve high selectivity, then selectivity over surrounding structures is improved, but damage to surrounding nitride and oxide structures occurs due to ion and photon flux exposure
Solution Approach 1:
The patent converts the potentially harmful ion flux into a beneficial effect by using it only for polymer formation on sidewalls (protective layer), while the actual etching is performed by neutral fluorine radicals that do not cause damage. This separation of functions achieves high selectivity without the harmful ion bombardment damage to surrounding nitride and oxide structures.
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 provides high selectivity and efficiency in removing polysilicon layers with minimal loss to surrounding materials, reducing costs and damage, and optimizing process conditions for temperature, pressure, and gas concentrations to achieve optimal etch rates.
Implementation Method 1
exposing the etchant to a remote plasma to activate the hydrogen-based species and the fluorine-based species
Data Source
AI summary
Provided are methods and systems for removing polysilicon on a wafer. A wafer can include a polysilicon layer and an exposed nitride and/or oxide structure. An etchant with a hydrogen-based species, such as hydrogen gas, and a fluorine-based species, such as nitrogen trifluoride, can be introduced. The hydrogen-based species and the fluorine-based species can be activated with a remote plasma source. The layer of polysilicon on the wafer can be removed at a selectivity over the exposed nitride and/or oxide structure that is greater than about 500:1.