Air-Gap Dielectric Etching for High SiO2/SiN Selectivity
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Solution Overview
Problem
Existing etching methods for silicon nitride in dynamic random-access memory (DRAM) fabrication fail to achieve the required etching selectivity ratio of SiO2/SiN, with conventional methanol and ammonia catalytic processes only achieving selectivity ratios of 30:1 and 20:1 respectively, which is insufficient for precise film removal in deep groove structures.
Innovation Solution
An etching method that divides the process into a surface layer removal step and an etching step, using a combination of hydrogen fluoride and ammonia gases at specific pressures and flow rates to selectively etch silicon oxide films, ensuring the surface modification layer is removed without excessive etching of silicon nitride, thereby achieving a high etching selectivity ratio.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If conventional methanol or ammonia catalytic processes are used to etch silicon nitride, then the etching process can be performed, but the etching selectivity ratio of SiO2/SiN is too low (30:1 or 20:1)
Solution Approach 1:
The etching process is divided into two distinct stages: a first etching stage using CF4/O2 plasma to remove silicon oxide and a second etching stage using CHF3/NH3 plasma to etch silicon nitride. This segmentation allows each stage to be optimized independently, achieving high selectivity (500:1 or 1000:1) by preventing SiN etching in the first stage and then efficiently removing SiO2 in the second stage.
Solution Approach 2:
The invention changes multiple process parameters including gas composition (CF4/O2 followed by CHF3/NH3), pressure conditions, and power settings between stages. These parameter changes enable the first stage to selectively etch SiO2 while protecting SiN, and the second stage to efficiently remove remaining SiO2 with high selectivity.
2Manufacturing precision
If a single etching process is used to remove silicon oxide, then the process is simple, but the selectivity cannot prevent silicon nitride etching in deep groove structures
Solution Approach 1:
The etching process is divided into two distinct stages: a first etching stage using CF4/O2 plasma to remove silicon oxide and a second etching stage using CHF3/NH3 plasma to etch silicon nitride. This segmentation allows each stage to be optimized independently, achieving high selectivity (500:1 or 1000:1) by preventing SiN etching in the first stage and then efficiently removing remaining SiO2 in the second stage.
Solution Approach 2:
The invention changes multiple process parameters including gas composition (CF4/O2 followed by CHF3/NH3), pressure conditions, and power settings between stages. These parameter changes enable the first stage to selectively etch SiO2 while protecting SiN, and the second stage to efficiently remove remaining SiO2 with high selectivity.
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 significantly improves the etching selectivity ratio of SiO2/SiN, ensuring precise film removal and high etching efficiency, with selectivity ratios exceeding 500:1, enhancing the performance of air-gap dielectric layers and dynamic random-access memory (DRAM) devices.
Implementation Method 1
Another method uses a hydrogen fluoride (HF) gas supplemented by alcohols (e.g., methanol) or an alkaline gas (e.g., NH3) to perform a catalytic etching, commonly known as methanol catalytic process or ammonia catalytic process.
Implementation Method 2
The dry etching method uses chemical reaction gases and catalysts to chemically interact with a film layer directly
Implementation Method 3
The dry etching method uses chemical reaction gases and catalysts to chemically interact with a film layer directly, through a process integration control to remove bottom portions of holes and/or groves accurately and efficiently with no substrate damage (no plasma)
Data Source
AI summary
An etching method for selectively etching a silicon oxide film on a wafer surface that includes the silicon oxide film and a silicon nitride film includes: a surface layer removal process including: etching the silicon oxide film at a first etching rate and removing a surface modification layer covering on the silicon nitride film; and an etching process including: etching the silicon oxide film at a second etching rate. The first etching rate is smaller than the second etching rate.