Diluted Hydrofluoric Acid Etching of Nitride Spacers
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Solution Overview
Problem
Conventional etching processes using phosphoric acid for nitride films are inefficient due to high viscosity, poor stability, and high costs, requiring lengthy preheating and multiple dummy etching cycles, with limited selectivity over oxide films.
Innovation Solution
The use of a diluted hydrofluoric acid solution at temperatures between 65° C. and 85° C., with a water-to-HF volume ratio of 1000:1 to 2500:1, to selectively remove sacrificial nitride spacers and form stress-inducing electrically insulating layers in integrated circuit devices, offering improved selectivity and stability over phosphoric acid.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If phosphoric acid is used to etch nitride films, then nitride-to-oxide selectivity is achieved (26 to 27), but processing time increases due to lengthy preheating and multiple dummy etching cycles
Solution Approach 1:
The patent changes the chemical composition parameter by substituting phosphoric acid with hydrofluoric acid-based etching solution. This parameter change achieves comparable nitride-to-oxide selectivity (exceeding 26:1) while eliminating the need for lengthy preheating and dummy etching cycles, thereby reducing processing time without sacrificing etching precision
Solution Approach 2:
The patent employs a fresh hydrofluoric acid-based etching solution for each processing cycle rather than requiring multiple dummy cycles to stabilize phosphoric acid. This approach treats the etching solution as a reliable, single-use medium that delivers consistent performance immediately, eliminating waste of time and resources associated with conditioning phosphoric acid
2Reliability
If phosphoric acid is used for etching, then nitride film removal is achieved, but cost increases and stability decreases
Solution Approach 1:
The patent replaces expensive and unstable phosphoric acid with a more cost-effective hydrofluoric acid-based etching solution. The new solution provides comparable etching performance with improved stability and lower cost, making the manufacturing process more economically viable without compromising reliability
Solution Approach 2:
The patent modifies the chemical parameters of the etching solution by using hydrofluoric acid with specific concentration ratios (e.g., 1:1000 to 1:2500 dilution in water) and controlled temperatures (65°C to 85°C). These parameter changes achieve the desired etching performance while improving process stability and reducing costs compared to phosphoric acid
3Manufacturing precision
If phosphoric acid is used to etch nitride, then selectivity of 26 to 27 is achieved, but viscosity is high requiring lengthy preheating
Solution Approach 1:
The patent changes the chemical composition from high-viscosity phosphoric acid to lower-viscosity hydrofluoric acid-based solution. This parameter change maintains high etching selectivity (exceeding 26:1) while reducing the temperature and preheating requirements to a manageable range (65°C to 85°C), thereby improving manufacturing precision without excessive thermal processing
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 provides enhanced selectivity for nitride-to-oxide etching, reduces processing time and costs, and allows for efficient formation of field effect transistors with improved stress-inducing layers, comparable to phosphoric acid selectivity while being more stable and cost-effective.
Implementation Method 1
The sacrificial nitride spacers are selectively removed using a diluted hydrofluoric acid solution having a nitride-to-oxide etching selectivity in excess of one
Data Source
AI summary
Methods of forming integrated circuit devices include forming a field effect transistor having a gate electrode, sacrificial nitride spacers on opposing sidewalls of the gate electrode and source/drain regions, which are self-aligned to the sacrificial nitride spacers, on a semiconductor substrate. The sacrificial nitride spacers are selectively removed using a diluted hydrofluoric acid solution having a nitride-to-oxide etching selectivity in excess of one. In order to increase charge carrier mobility within a channel of the field effect transistor, a stress-inducing electrically insulating layer is formed on opposing sidewalls of the gate electrode. This insulating layer is configured to induce a net tensile stress (NMOS) or compressive stress (PMOS) in the channel.