3D Memory Epitaxial Layer Uniformity via Mandrel Etching
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Solution Overview
Problem
In three-dimensional non-volatile memory devices, defects and native oxide layers formed during the anisotropic etching process lead to uneven epitaxial layer thicknesses, affecting device performance.
Innovation Solution
A semiconductor structure with epitaxial layers in openings having a top surface between the top and bottom surfaces of an insulating layer, where the aspect ratio of the opening's second portion is greater than 1, and a cleaning process using hydrofluoric acid and SiCoNi treatments to remove impurities and native oxide layers, ensuring the epitaxial layers are substantially coplanar.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If anisotropic etching process is performed to form openings, then openings are formed to penetrate through stacked structure, but defects and etching by-products remain on bottoms of openings and native oxide layers are generated
Solution Approach 1:
The patent applies preliminary action by forming a mandrel structure before etching the openings. The mandrel serves as a template that defines the opening geometry and protects the substrate bottom during etching, preventing defects and by-product accumulation. This preliminary structure enables cleaner opening formation without compromising the etching process efficiency.
Solution Approach 2:
The mandrel structure acts as an intermediary element between the etching process and the substrate. It mediates the etching process by providing a controlled interface that prevents direct contact between etching by-products and the substrate bottom, thereby reducing defect formation and native oxide generation while still allowing opening penetration.
2Productivity
If epitaxial growth process is performed, then epitaxial layers are formed in openings, but epitaxial layer thickness varies due to defects, residues and native oxide layers
Solution Approach 1:
The mandrel structure is formed preliminarily to establish a clean and uniform base for epitaxial growth. By preventing defect formation during opening creation, the mandrel ensures that the subsequent epitaxial growth occurs on a consistent surface, leading to uniform layer thickness across all openings.
Solution Approach 2:
The invention achieves homogeneity in epitaxial layer thickness by using the mandrel structure to create uniform opening conditions. The mandrel ensures that all openings have consistent geometry and clean bottoms, which results in homogeneous epitaxial growth rates and uniform final layer thickness across the entire array of openings.
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 solution ensures uniform epitaxial layer growth and improved device performance by minimizing defects and native oxide layers, resulting in a three-dimensional memory device with enhanced reliability and efficiency.
Implementation Method 1
a cleaning process using hydrofluoric acid and SiCoNi treatments to remove impurities and native oxide layers
Implementation Method 2
when the epitaxial layer is formed with an epitaxial growth process
Data Source
AI summary
A semiconductor structure for three-dimensional memory device and a manufacturing method thereof are provided. The semiconductor structure is disposed on the substrate and has a plurality of openings penetrating through the semiconductor structure and extending into the substrate. The semiconductor structure includes a substrate, a stacked structure and an epitaxial layer. The stacked structure includes insulating layers and gate layers stacked alternatively. Each of the plurality of openings includes a first portion located above the surface of the substrate and a second portion located below the surface of the substrate. The aspect ratio of the second portion is more than 1. The epitaxial layer is disposed in each of the plurality of openings. The top surface of the epitaxial layer is between the top surface and the bottom surface of the i-th insulating layer as counted upward from the substrate, wherein i≥2.