Electron Beam Etching Using NF3 Precursor at Cryogenic Temperatures
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Solution Overview
Problem
Current beam-induced etching technologies face issues with precursor gases like XeF2, which are toxic, corrosive, and cause instability in electron beam systems, and struggle with low temperature limitations that reduce etching efficiency.
Innovation Solution
Cooling the substrate to a temperature near the boiling point of a precursor gas, such as NF3, to maximize surface coverage without condensation, allowing for efficient desorption of reaction products and improved etching precision.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If XeF2 is used as precursor gas for beam-induced etching, then etching capability is improved, but toxicity and corrosiveness increase
Solution Approach 1:
The patent replaces persistent, hazardous XeF2 gas with a system using NF3 gas at controlled low temperatures. The NF3 is introduced only when needed for etching and can be rapidly removed by warming the substrate, effectively making the hazardous gas presence temporary and controllable rather than persistent
Solution Approach 2:
The patent creates an inert environment by cooling the substrate to cryogenic temperatures (near liquid nitrogen temperature), which suppresses spontaneous chemical reactions between the precursor gas and substrate. This allows safe handling of reactive gases like NF3 without unwanted side reactions, reducing harmful effects
2Quantity of substance
If substrate temperature is lowered to prevent precursor condensation, then precursor coverage is improved, but reaction product desorption becomes difficult
Solution Approach 1:
The patent employs periodic temperature cycling: cooling the substrate to near liquid nitrogen temperature during precursor exposure to maximize surface coverage, then rapidly warming to room temperature during the etching phase to enable reaction product desorption. This periodic action between cold and warm states resolves the contradiction
Solution Approach 2:
The patent performs preliminary cooling of the substrate before introducing the precursor gas, ensuring maximum precursor surface coverage is achieved before the actual etching reaction begins. This preliminary action at low temperature sets up the optimal condition for subsequent high-temperature etching
3Quantity of substance
If gas pressure is increased to improve precursor delivery, then beam path interference increases
Solution Approach 1:
The patent creates a local high-pressure environment only at the substrate surface where precursor delivery is needed, while the rest of the vacuum chamber maintains low pressure to preserve beam quality. This is achieved through localized gas introduction and confinement near the cold substrate
Solution Approach 2:
The patent separates the pressure dimensions: the substrate chamber operates at higher pressure to enable adequate precursor gas delivery, while the beam path region maintains vacuum conditions. This dimensional separation of pressure zones allows both requirements to be satisfied simultaneously
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 method enhances etching rates and image quality by maintaining precursor gas coverage while preventing condensation, using NF3 as a safer and more effective precursor that allows for precise pattern removal and reliable imaging.
Implementation Method 1
An electron beam is directed at the work piece, and the electrons dissociate the adsorbates, generating reaction products
Implementation Method 2
Cooling the substrate to a temperature near the boiling point of a precursor gas, such as NF3, to maximize surface coverage without condensation
Implementation Method 3
Cooling the substrate to a temperature near the boiling point of a precursor gas, such as NF3, to maximize surface coverage without condensation
Data Source
AI summary
Beam-induced etching uses a work piece maintained at a temperature near the boiling point of a precursor material, but the temperature is sufficiently high to desorb reaction byproducts. In one embodiment, NF3 is used as a precursor gas for electron-beam induced etching of silicon at a temperature below room temperature.