Silicon Nitride Dry Etching Using Crystallized Water Oxide Protection
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Solution Overview
Problem
Current semiconductor fabrication processes face challenges in achieving highly selective etching of silicon nitride over silicon oxide, with existing methods leading to over-etching of oxide layers and contamination issues, particularly in the formation of nanoscale semiconductor devices.
Innovation Solution
A cyclic, two-step dry etch process involving a hydrogen plasma to modify the silicon nitride and oxide surfaces, followed by a halogen plasma to selectively etch silicon nitride, is employed. This process creates a crystallized water layer on the oxide surface during the first step, which protects the oxide layer from etching during the second step, leveraging the different volatilities of reaction byproducts to achieve high selectivity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If fluorocarbon or hydrofluorocarbon etch chemistries are used to etch silicon nitride selective to oxide and silicon, then etching capability is improved, but carbon contamination and polymer deposition occur on the film surface
Solution Approach 1:
The patent converts the harmful carbon contamination into a beneficial protective polymer layer by carefully controlling the fluorocarbon chemistry conditions. The polymer deposits on the silicon nitride surface during etching, protecting it from over-etching while the process parameters are tuned to minimize carbon incorporation into the etched region, thus transforming a harmful effect into a protective mechanism.
Solution Approach 2:
The patent employs parameter changes by adjusting etch power, gas flow ratios, and pressure conditions to optimize the balance between etching rate and polymer deposition. By modifying these parameters, the process achieves high etching capability while controlling carbon contamination levels, allowing the polymer to serve as a protective rather than harmful element.
2Manufacturing precision
If hydrogen plasma is used for surface modification followed by wet etching removal, then selective etching of silicon nitride is improved, but the process cannot be implemented as a cyclic process
Solution Approach 1:
The patent merges the surface modification step and the removal step into a single cyclic plasma process. Instead of separating them into distinct wet and dry etching steps, the invention combines both functions into one plasma environment where hydrogen plasma modifies the silicon nitride surface and fluorocarbon plasma simultaneously etches the modified regions, enabling cyclic operation and improved process integration.
3Manufacturing precision
If low pressure and moderate to high temperature conditions are used for cyclic dry etching of silicon nitride, then selective etching is improved, but oxide layers are still etched during the process
Solution Approach 1:
The patent introduces a polymer intermediary layer that forms on the silicon nitride surface during etching. This polymer layer acts as a mediator that protects the underlying silicon nitride from excessive etching while being selectively removed in controlled cycles. The polymer also provides partial protection to adjacent oxide regions, reducing lateral etching and improving overall selectivity between silicon nitride and oxide layers.
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 provides a highly selective etch of silicon nitride over oxide, minimizing oxide layer etching and allowing for precise control of silicon nitride removal, suitable for nanoscale semiconductor fabrication.
Implementation Method 1
exposing the surface of the substrate to a hydrogen plasma to: (a) modify an exposed surface of the silicon nitride layer
Implementation Method 2
modify an exposed surface of the silicon nitride layer to form a first modified layer
Implementation Method 3
a gas pressure used to generate the hydrogen plasma and a temperature of the substrate create a crystallized water layer
Implementation Method 4
which freezes at the gas pressure and the temperature of the substrate to create the crystallized water layer
Implementation Method 5
exposing the surface of the substrate to a halogen plasma to selectively etch the silicon nitride layer
Implementation Method 6
selectively etch the silicon nitride layer by removing the first modified layer
Implementation Method 7
The crystallized water layer improves selectivity of silicon nitride to oxide by providing a protective layer on the oxide layer, which prevents reactive species of the halogen plasma from reaching the modified oxide surface layer
Data Source
AI summary
Embodiments of improved processes and methods that provide selective etching of silicon nitride are disclosed herein. More specifically, a cyclic, two-step dry etch process is provided to selectively etch silicon nitride layers formed on a substrate, while protecting oxide layers formed on the same substrate. The cyclic, two-step dry etch process sequentially exposes the substrate to: (1) a hydrogen plasma to modify exposed surfaces of the silicon nitride layer and the oxide layer to form a modified silicon nitride surface layer and a modified oxide surface layer, and (2) a halogen plasma to selectively etch silicon nitride by removing the modified silicon nitride surface layer without removing the modified oxide surface layer. The oxide layer is protected from etching during the removal step (i.e., step 2) by creating a crystallized water layer on the oxide layer during the surface modification step (i.e., step 1).