Selective Etching

Selective SiGe etching for GAA, Forksheets, and
CFET Logic Devices

As the scaling down of transistor devices continues, problems such as increased leakage current, short-channel effect, and reduced electrostatic control are arising.
New transistor structures such as gate-all-around FET(GAAFET), forksheet, and complementary FET(CFET) are attracting significant attention as advanced transistors because they can provide superior electrostatic performance.
To fabricate the Si channel structures in these devices, SiGe must be selectively etched in SiGe/Si stacked multilayer structures.
High SiGe/Si etching selectivity and precise control of etching rates are required to minimize channel material loss and obtain precise post-etch profiles.
Solvent conditions and process parameters required to achieve highly selective SiGe etching in SiGe/Si stacked multilayer structures are under research.

Selective Si3N4 etching for 3D NAND Flash Memory Devices

3D NAND flash memory is non-volatile memory device which is used in storage devices such as solid-state drives and mobile phone memory.
To manufacture 3D NAND flash memory devices, it is necessary to deliver an etchant into the structures, where Si3N4 and SiO2 are repeatedly stacked through a slit formed by dry etching, and selectively etch the Si3N4 layers.
In the selective Si3N4 etching process, improving the Si3N4/SiO2 etching selectivity and etching rate of Si3N4 etching rate is important. Also, suppressing the oxide thinning, oxide regrowth and clogging in the Si3N4/SiO2 repeatedly stacked layer structure is significant.
These problems can be overcome by introducing various types of additives which can enhance etchant’s properties.
And optimizing the composition of etchant and process condition can also solve these problems.

Selective SiO2 etching for 3D Memory Devices

As the semiconductors are being miniaturized and complicated, research continues to fabricate smaller, faster, and more efficient devices.
To overcome this, complex 3D structure devices such as Fin field-effect transistor (FET) and gate all around FET are being developed.
In these various 3D semiconductor devices, there are many cases where SiO2 must be etched selectively over other materials such as Si3N4 and W.
Today, etching of SiO2 with HF is widely used but Si3N4 is also etched by HF solution. Therefore, HF-based etchants have to be controlled very precisely.
Therefore, optimization of etchant conditions is essential and various additives are being studied to maximize the SiO2/Si3N4 selectivity.

Selective IGZO etching for future Memory Devices

For fabricating high-peformance & low-power DRAM, compact size of device is required, which causes leakage current.
IGZO(Indium Gallium Zinc Oxide) is emerging material to reduce this problem, having wide-bandgap compared to Si.
To install IGZO channel in device, IGZO is deposited on lower layer and have to be selectively etched over other materials.
Fine IGZO etching selectivity and stable etching process are demanded to reduce the ununecessary destuction of device and performance degradation.
Etchant properties, additives for enhancing etching efficiency and etching mechanism in various etchants and additives are in study.