Wednesday, January 15, 2020

Metal mask coating by ALD for reliable plasma process in PECVD

The PECVD method with metal masks has, in general, been used to deposit inorganic layers like SiNx and SiO2 for manufacturing LCD and OLED displays.

However, this plasma process has severe problems like plasma arcing or particle generation due to instability of electrical isolation between the metal mask and the showerhead as an RF electrode. Therefore it is required to deposit dielectric materials such as Al2O3, Y2O3, TiO2, MgO, ZrO2, etc. on the metal mask to prevent plasma damage.

Typically, the dielectric layer is coated by a sputtering method, also known as physical vapor deposition (PVD). However, this method is difficult to coat the metal mask uniformly with large area and complex structure as well as it has the disadvantage of requiring a thick deposition of several µm and multiple processes.

To obtain excellent electrical isolation properties of metal masks in the PECVD process, the atomic layer deposition (ALD) of Al2O3 thin film might be the best solution which enables getting uniform deposition on them with large area and complex structure. 

ALD Al2O3 layers could give them remarkable electric isolation and great protection, even if the thickness is less than one ㎛. When 50nm ~ 200nm layers of Al2O3 deposited by NCD large-area demo tool on metal masks were applied to the PECVD process, there was no issues like plasma arcing or damage. 

Images of metal mask coated by ALD with Al2O3 a) before (b) after

In fact, even though ALD Al2O3 has lots of advantages, the end customer has to consider of low throughput using general large-area ALD equipment. However, NCD’s Lucida GD Series for large-area ALD applications might be the most suitable equipment with superb productivity to provide superior protective layers to the metal masks from plasma issues in the PECVD process.

NCD has steadily developed large area and high throughput ALD equipment and technology. The applications for display, solar cell, and semiconductor fields have been already commercialized, and also NCD has worked hard to find use in special markets like excellent plasma protective coating on metal masks. NCD will aggressively respond to the development and then supply of ALD equipment, which customers would need for various industries in the future.

LucidaTM ALD system for metal mask coating.

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