Perpendicular Sidewall Etching for Semiconductor Openings
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Solution Overview
Problem
Conventional methods for forming openings in semiconductor devices often result in inaccurate critical dimensions due to sloped sidewall profiles, affecting the functionality and reliability of conductive contacts and the overall yield of semiconductor devices.
Innovation Solution
A method involving a semiconductor substrate with sequential silicon oxide, polysilicon, and silicon nitride layers, where a patterned silicon nitride layer is used to form an initial opening, followed by etching processes using hydrogen bromide, oxygen, and fluorocarbons to create openings in the polysilicon and oxide layers with perpendicular sidewalls, ensuring uniform critical dimensions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If a conventional photolithographic process is used to form a patterned photoresist layer, then the photoresist layer can be formed with a pattern, but the critical dimension of the opening transferred to the dielectric layer becomes inaccurate due to sloped sidewall profile
Solution Approach 1:
The patent segments the opening formation process into multiple stages: first forming an opening in the silicon nitride layer, then using that opening as a mask to etch the polysilicon layer, and finally removing the silicon nitride layer to complete the opening in the oxide layer. This segmentation allows each layer to be processed independently with optimized etching parameters, ensuring perpendicular sidewalls and accurate critical dimensions throughout the structure.
Solution Approach 2:
The patent performs preliminary patterning of the silicon nitride layer before etching the underlying polysilicon layer. This preliminary action creates a precise mask structure that defines the opening geometry, ensuring that the critical dimension is established early in the process and maintained through subsequent etching steps with perpendicular sidewalls.
2Ease of manufacture
If a photoresist layer with sloped sidewalls is used as an etching mask, then the etching process can proceed, but the critical dimension of the opening in the dielectric layer differs from the photoresist layer
Solution Approach 1:
The patent introduces silicon nitride layer as an intermediary mask structure between the photoresist and the polysilicon layer. This intermediary layer can be etched with perpendicular sidewalls using optimized gasous etchants, serving as a precise template that accurately transfers the critical dimension to the underlying layers without the sloped sidewall problem of photoresist.
Solution Approach 2:
The patent changes the etching parameters by using gasous etchants comprising hydrogen bromide, oxygen, and fluorocarbons specifically for etching the polysilicon layer through the silicon nitride mask. These parameter changes enable formation of perpendicular sidewalls and accurate critical dimension transfer, overcoming the limitations of photoresist-based masking.
3Productivity
If conventional etching methods are used to form openings, then the process can be completed, but the sidewall profile becomes sloped affecting subsequent conductive contact formation
Solution Approach 1:
The patent replaces conventional mechanical or plasma etching methods with a chemically-driven etching process using gasous etchants (hydrogen bromide, oxygen, and fluorocarbons). This substitution enables precise control of the etching reaction to produce perpendicular sidewalls while maintaining high productivity through efficient material removal rates.
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 ensures that the critical dimensions of the openings are accurately transferred across layers, meeting design specifications and enhancing the reliability and yield of semiconductor devices by maintaining consistent conductive contact dimensions.
Implementation Method 1
performing a first etching process, using gasous etchants comprising hydrogen bromide (HBr), oxygen (O2), and fluorocarbons (CxFy), forming a second opening in the polysilicon layer
Data Source
AI summary
A method for forming an opening in a semiconductor device is provided, including: providing a semiconductor substrate with a silicon oxide layer, a polysilicon layer and a silicon nitride layer sequentially formed thereover; patterning the silicon nitride layer, forming a first opening in the silicon nitride layer, wherein the first opening exposes a top surface of the polysilicon layer; performing a first etching process, using gasous etchants including hydrogen bromide (HBr), oxygen (O2), and fluorocarbons (CxFy), forming a second opening in the polysilicon layer, wherein a sidewall of the polysilicon layer adjacent to the second opening is substantially perpendicular to a top surface of the silicon oxide layer, wherein x is between 1-5 and y is between 2-8; removing the silicon nitride layer; and performing a second etching process, forming a third opening in the silicon oxide layer exposed by the second opening.