Silicon Nitride Film Selective Etching Using Hydrogen Fluoride Gas
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Solution Overview
Problem
Existing methods for removing silicon nitride films from substrates often damage the underlying thermally-oxidized films due to lack of selective etching, as both films are etched during wet or dry etching processes.
Innovation Solution
A substrate processing method involving heating the substrate to at least 60°C and supplying hydrogen fluoride gas without plasma formation, which selectively etches the silicon nitride film without affecting the thermally-oxidized film, by maintaining the substrate temperature below 200°C and controlling the etch rate through temperature management and gas exposure time.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If wet etching using hot phosphoric acid or dry etching using plasma is used to remove the silicon nitride film, then the silicon nitride film can be removed, but the thermally-oxidized film is also etched and damaged
Solution Approach 1:
The patent changes the temperature parameter to 60°C or higher, which fundamentally alters the etching behavior. At this temperature, hydrogen fluoride gas selectively etches silicon nitride film while sparing the thermally-oxidized film, achieving both high productivity and reliable selectivity without the damage caused by conventional methods
Solution Approach 2:
The patent utilizes the phase transition of hydrogen fluoride from liquid to gas form. By supplying hydrogen fluoride gas instead of using it in liquid form or as plasma, the process achieves selective etching of silicon nitride while preventing damage to the thermally-oxidized film, resolving the contradiction between etching efficiency and film protection
2Speed
If the substrate temperature is increased to accelerate the etching rate, then the etching speed increases, but the selective ratio decreases and the thermally-oxidized film becomes damaged
Solution Approach 1:
The patent identifies and exploits a critical temperature threshold of 60°C. By maintaining the substrate at this specific temperature or higher (but controlled), the etching rate of silicon nitride is dramatically enhanced while the thermally-oxidized film remains protected, achieving both high speed and high selectivity simultaneously
3Productivity
If plasma is used to enhance the etching process, then the etching efficiency improves, but the thermally-oxidized film is damaged by plasma exposure
Solution Approach 1:
The patent uses hydrogen fluoride gas as an intermediary substance that enables selective etching without the harmful effects of plasma. The gas phase hydrogen fluoride provides the necessary chemical reactivity for efficient etching while avoiding the physical damage caused by plasma, thus resolving the contradiction between productivity and harm reduction
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 ensures the selective removal of silicon nitride films without damaging the thermally-oxidized films, maintaining a reliable etch ratio and preventing plasma-induced damage to the thermally-oxidized films.
Implementation Method 1
hydrogen fluoride gas is supplied toward the substrate. When the substrate reaches a temperature of not less than 60° C., the silicon nitride film is suddenly etched by the hydrogen fluoride gas although the thermally-oxidized silicon film is not etched by the hydrogen fluoride gas
Implementation Method 2
a heating step of heating the substrate to a temperature of not less than 60° C.
Implementation Method 3
When the temperature of the substrate rises, the etch rate at which the silicon nitride film is etched by the hydrogen fluoride gas decreases, and when the temperature of the substrate reaches 200° C., the etch rate of the silicon nitride film becomes nearly zero
Data Source
AI summary
A substrate processing method that can remove a silicon nitride film without damaging a thermally-oxidized film. A substrate having at least a thermally-oxidized film and a silicon nitride film formed on the thermally-oxidized film is heated to a temperature of not less than 60° C. Then, hydrogen fluoride gas is supplied toward the substrate.