Silicon Nitride Etching with Temperature-Staged Ammonia Desorption
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Solution Overview
Problem
Existing etching methods for silicon nitride films adjacent to silicon oxide or polysilicon films face challenges as ammonia produced by the etching reaction does not easily desorb at low temperatures, leading to unintended etching of the silicon oxide or polysilicon films.
Innovation Solution
An etching method involving the supply of hydrogen fluoride gas at a controlled temperature range, followed by active radicals generated from a radical generation gas, maintains the etching subject at a predetermined temperature to facilitate selective etching of silicon nitride films while minimizing etching of adjacent silicon oxide or polysilicon films.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If the temperature of the wafer is maintained at a relatively low temperature during etching, then the etching reaction of hydrogen fluoride and silicon nitride can proceed, but ammonia produced by the etching reaction does not easily desorb from the surface of the wafer, leading to unintended etching of the silicon oxide film
Solution Approach 1:
The patent applies parameter changes by transitioning from low temperature to high temperature (400°C or higher) during the etching process. This temperature parameter change enables ammonia desorption from the wafer surface, preventing the formation of etching gas that would otherwise cause unintended etching of the silicon oxide film while maintaining selective etching of the silicon nitride film.
2Object-generated harmful factors
If the temperature of the wafer is increased to promote ammonia desorption, then unintended etching of adjacent films is reduced, but the etching reaction rate may be affected
Solution Approach 1:
The patent implements periodic action by dividing the etching process into distinct stages: first supplying hydrogen fluoride gas at low temperature for selective etching, then increasing the temperature to promote ammonia desorption, and finally supplying inert gas radicals to enhance the etching reaction. This periodic sequence of temperature and gas supply changes optimizes both ammonia removal and etching efficiency.
Solution Approach 2:
The patent applies preliminary action by first supplying hydrogen fluoride gas to adsorb on the silicon nitride film surface before increasing the temperature. This preliminary adsorption step ensures that the etching reaction is already initiated and positioned, so that when the temperature is raised for ammonia desorption, the etching process can continue efficiently without interruption.
3Manufacturing precision
If hydrogen fluoride gas is supplied to etch the silicon nitride film, then the silicon nitride film can be selectively removed, but the produced ammonia remains on the wafer surface and causes etching of the silicon oxide film
Solution Approach 1:
The patent applies the extraction principle by removing ammonia from the wafer surface through temperature increase to 400°C or higher. This extraction of the harmful byproduct (ammonia) from the reaction zone prevents it from participating in unintended etching reactions with the silicon oxide film, while the selective etching of silicon nitride is maintained through the controlled sequence of gas supply and temperature management.
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
The method enhances the selectivity of etching silicon nitride films by ensuring even adsorption and reaction of hydrogen fluoride, promoting ammonia desorption and reducing unintended etching of adjacent films, thereby improving the silicon nitride to silicon oxide or polysilicon film ratio.
Implementation Method 1
first, the hydrogen fluoride gas is supplied to the wafer so that hydrogen fluoride is adsorbed on the surface of the silicon nitride film
Implementation Method 2
supplying a hydrogen fluoride gas to the etching subject while heating the etching subject so that a temperature of the etching subject is maintained at a predetermined temperature
Implementation Method 3
the inert gas radicals are supplied to the wafer so that the wafer receives energy that is greater than or equal to an activation energy for etching reaction of hydrogen fluoride and silicon nitride
Data Source
AI summary
A method for selectively etching a silicon nitride film can include supplying a hydrogen fluoride gas to an etching subject while heating the etching subject so that a temperature of the etching subject is maintained at a predetermined temperature included in a range of a first temperature to a second temperature, inclusive. The method can include supplying active radicals generated from a radical generation gas to the etching subject while heating the etching subject so that the temperature of the etching subject after being supplied with the hydrogen fluoride gas is maintained at the predetermined temperature.