Isotropic Atomic Layer Etch for Silicon Oxide Using Nitric Oxide Activation
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Solution Overview
Problem
Current methods for removing silicon and germanium oxide layers on semiconductor substrates lack precision and control, particularly at an atomic scale, leading to issues with uniformity and defectivity in integrated circuit fabrication.
Innovation Solution
A method using nitric oxide (NO) to activate the oxide surface, followed by a fluorine-containing gas for controlled etching, which is self-limiting and allows for precise removal of defined atomic layers with high selectivity and low defectivity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If conventional plasma etching processes are used to remove silicon oxide layers, then the etching can proceed continuously with high etch rate, but the etch rate cannot be precisely controlled at atomic scale and uniformity across the substrate surface deteriorates
Solution Approach 1:
The continuous etching process is segmented into discrete atomic layer cycles. Each cycle consists of: (1) NO exposure to activate oxide surface, (2) F-containing gas exposure to etch activated surface, (3) purge step. This segmentation allows precise control of etch depth at atomic scale (0.3-1.0 nm per cycle) while maintaining high productivity through repetitive cycling
Solution Approach 2:
The etching process uses periodic exposure to NO and F-containing gases in alternating cycles. Each periodic cycle activates a fresh layer of oxide surface with NO, then etches it with F species, creating a self-limiting process that automatically stops when the activated layer is consumed. This periodic action enables atomic-scale precision while maintaining continuous material removal
2Productivity
If plasma power and gas flow rates are increased to improve etching productivity, then etching speed increases, but etch rate uniformity across the substrate surface deteriorates
Solution Approach 1:
The process is self-regulating through surface saturation mechanics. NO exposure saturates the oxide surface with nitrate groups, and F-containing gas exposure saturates the activated surface with etch products. This self-saturation mechanism automatically limits the etch depth to uniform atomic layers across the entire substrate surface, preventing over-etching and ensuring uniformity regardless of gas flow rate variations
Solution Approach 2:
The process changes the fundamental etching mechanism from plasma-driven continuous removal to chemically-driven layer-by-layer removal. By using NO activation followed by F-atom etching in controlled atmospheric conditions rather than high-power plasma, the process achieves both high productivity and uniform etch rate across the substrate surface
3Manufacturing precision
If conventional etching processes are used to remove oxide layers, then material removal can be achieved, but atomic scale fidelity and isotropic removal are not achieved
Solution Approach 1:
NO acts as an intermediary substance that temporarily modifies the oxide surface by forming nitrate groups, making it susceptible to F-atom etching. This intermediary activation step enables precise atomic-scale removal without requiring complex plasma equipment, as the chemistry itself provides the necessary surface modification and etching control
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
Enables accurate and isotropic removal of silicon and germanium oxide layers with atomic-scale uniformity, suitable for sub-10 nm devices, improving the fabrication of integrated circuits by allowing precise control over the etching process.
Implementation Method 1
contacting the substrate housed in a process chamber with excess NO species to modify the surface of silicon or germanium oxide on the substrate by forming Si/Ge-O-N-O bonds
Implementation Method 2
contacting the substrate with an F etchant after the surface of the treated oxide is saturated with Si/Ge-O-N-O bonds
Implementation Method 3
Desorption of nitrogen oxide from the surface of the treated oxide then results in controlled etching of the oxide surface
Data Source
AI summary
Methods for controlled isotropic etching of layers of silicon oxide and germanium oxide with atomic scale fidelity are provided. The methods make use of NO activation of an oxide surface. Once activated, a fluorine-containing gas or vapor etches the activated surface. Etching is self-limiting as once the activated surface is removed, etching stops since the fluorine species does not spontaneously react with the un-activated oxide surface. These methods may be used in interconnect pre-clean applications, gate dielectric processing, manufacturing of memory devices, or any other applications where accurate removal of one or multiple atomic layers of material is desired.