SiC Etching Selectivity via Silicon Nitride Intermediary
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Solution Overview
Problem
The challenge in fabricating silicon carbide (SiC) devices lies in the lack of effective selective etching methods, particularly at temperatures above 600°C, where traditional wet etching processes are inefficient, and existing masking materials exhibit poor selectivity when exposed to etch gases like chlorine (Cl2) and hydrogen bromide (HBr).
Innovation Solution
A method involving the formation of a silicon nitride etch stop layer, a silicon carbide layer, a silicon dioxide hard mask layer, and a photoresist mask is used, where the silicon dioxide hard mask layer is etched through the photoresist mask, allowing for controlled etching of the silicon carbide layer with improved selectivity using etch gases like Cl2 and HBr.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If traditional photoresist etch masks are used with SiC etching gases (Cl2, HBr), then the etching process can be performed, but the photoresist material exhibits poor selectivity compared to SiC
Solution Approach 1:
A nitrogen-containing dielectric layer (silicon nitride) is introduced as an intermediary between the photoresist mask and the SiC layer. This intermediate layer provides the necessary selectivity barrier, allowing the photoresist to pattern the dielectric layer while the dielectric layer protects the SiC from excessive etching, thereby achieving both good pattern transfer and lateral dimension control.
Solution Approach 2:
The etching system uses a composite masking structure consisting of multiple materials (photoresist + nitrogen-containing dielectric layer) rather than a single material. This composite approach combines the patterning capability of photoresist with the etching resistance of the dielectric layer, solving the selectivity problem while maintaining manufacturing precision.
2Productivity
If wet etching processes are used at temperatures less than 600°C, then etching can proceed, but SiC is not etched significantly by most acids and bases
Solution Approach 1:
The etching process parameters are changed by introducing a nitrogen-containing dielectric layer that has different chemical reactivity compared to SiC. This layer can be etched by standard wet etchants at lower temperatures, while SiC remains resistant, thereby achieving both acceptable etching rates and high selectivity through parameter optimization.
Solution Approach 2:
The nitrogen-containing dielectric layer serves as an intermediary that enables wet etching at lower temperatures. It provides a pathway for etching to occur at temperatures below 600°C while maintaining selectivity, as the dielectric layer can be removed by wet etchants without significantly etching the SiC substrate.
3Reliability
If wet etching processes are used at temperatures greater than 600°C, then etching of SiC can be achieved, but most wet etching processes are not easily effected at temperatures greater than about 600°C
Solution Approach 1:
The nitrogen-containing dielectric layer acts as a mediator that enables selective etching without requiring high temperatures. It allows the process to proceed at standard temperatures using conventional wet etching equipment, thereby maintaining ease of manufacture while achieving the required selectivity.
Solution Approach 2:
The process replaces the need for high-temperature thermal etching with a chemical etching approach using the nitrogen-containing dielectric layer. This substitution allows standard wet etching equipment and procedures to be used, simplifying the manufacturing process while maintaining effective SiC etching capability through the intermediate layer's selective removal.
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 enhances the selectivity ratio between the SiC layer and the hard mask layer, enabling precise etching of SiC devices with improved lateral dimension control and efficiency, even at elevated temperatures.
Implementation Method 1
selective etching of SiC films or SiC bulk materials
Implementation Method 2
photoresist etch masks
Implementation Method 3
Primary etch gasses that are used in SiC etching include chlorine (Cl2) and hydrogen bromide (HBr)
Data Source
AI summary
A method of etching a device in one embodiment includes providing a silicon carbide substrate, forming a silicon nitride layer on a surface of the silicon carbide substrate, forming a silicon carbide layer on a surface of the silicon nitride layer, forming a silicon dioxide layer on a surface of the silicon carbide layer, forming a photoresist mask on a surface of the silicon dioxide layer, and etching the silicon dioxide layer through the photoresist mask.