Silicon Oxide Etching via Low-Temperature Plasma
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Solution Overview
Problem
The high reactivity of nitrogen trifluoride (NF3) with mask materials in the high aspect ratio contact (HARC) process for forming deep holes in silicon oxide films leads to expansion of critical dimensions (CDs), necessitating an improvement in etching rate while suppressing CD expansion.
Innovation Solution
An etching method using a plasma processing system that sets the substrate temperature to 0° C. or less and generates plasma from a gas mixture containing fluorine, nitrogen, and carbon, with a fluorine-to-nitrogen ratio (F/N) between 0.5 and 10, employing HF/N2 gas to etch silicon oxide films through a carbon-containing mask, thereby improving etching rates and preventing CD expansion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If nitrogen trifluoride (NF3) is used for etching silicon oxide films, then the etching rate is improved, but the critical dimensions (CDs) expand due to high reactivity with mask materials
Solution Approach 1:
The patent changes the chemical composition parameters of the etching gas from pure NF3 to a mixed gas containing CF4, N2, and CO2 with specific ratios. This parameter change maintains high etching rate while reducing mask reactivity and CD expansion by introducing carbon-containing CO2 to passivate mask surfaces and adjust the chemical environment.
Solution Approach 2:
The patent uses a composite gas mixture (CF4-N2-CO2) instead of a single gas (NF3). The composite gas combines the benefits of CF4 for silicon oxide etching, N2 for inert atmosphere, and CO2 for mask protection, achieving both high productivity and precision simultaneously.
2Productivity
If the etching rate is increased to form deep holes efficiently, then the productivity is improved, but the aspect ratio control and CD uniformity deteriorate
Solution Approach 1:
The patent optimizes multiple process parameters including gas flow ratios (CF4: 30-70 sccm, N2: 70-30 sccm, CO2: 5-20 sccm), pressure (10-100 mTorr), and power (50-200 W) to achieve the desired balance between etching rate and profile control, demonstrating that parameter optimization can resolve the contradiction between speed and precision.
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 enhances the etching rate while effectively suppressing the expansion of critical dimensions, achieving a high aspect ratio in silicon oxide films while maintaining process control.
Implementation Method 1
the silicon oxide film is etched through the mask by generating plasma from a gas containing fluorine, nitrogen, and carbon
Data Source
AI summary
An etching method includes: providing, on a stage, a substrate including an etching film containing a silicon oxide film, and a mask formed on the etching film; setting a temperature of the stage to be 0° C. or less; and generating plasma from a gas containing fluorine, nitrogen, and carbon, and having a ratio of the number of fluorine to the number of nitrogen (F/N) in a range of 0.5 to 10, thereby etching the silicon oxide film through the mask.