Atomic Layer Deposition (ALD)-Technology

© Fraunhofer IMS
Picosun R-200: Single wafer processes (200 mm)

Advanced process technology for new MEMS and NEMS devices

Media-resistant protective coatings for sensors, optical coatings, high-capacity trench capacitors, new NEMS devices for gas sensors, biosensors with nanowires, ultra-thin free-standing membranes: all this can be realized with modern ALD technology (Atomic Layer Deposition).

ALD is a deposition process based on the surface chemical reaction of at least two precursors. The process enables layer-by-layer growth of high-quality films with thicknesses in the range of 1-100 nm. A steadily growing selection of ALD materials enables new innovative sensor applications. As a member institute of the Forschungsfabrik Mikroelektronik Deutschland (FMD) the Fraunhofer IMS acts as ALD competence center. ALD technology for 200 mm wafers is available at the Fraunhofer IMS.

Application areas of ALD technology

Since the process temperature of ALD deposition is low compared to conventional CVD processes, ALD films can be deposited especially on integrated circuit substrates, i.e., CMOS wafers. Thus, ALD technology can be used for various MEMS, NEMS or CMOS-related applications, such as:

Cost-effective 3D NEMS technologies for the generation of free-standing nanostructures on CMOS surfaces with highest reproducibility have been developed and patented by Fraunhofer IMS
Media-resistant coatings for sensor applications such as pressure sensors or for encapsulating medical implants. Aluminum oxide (Al2O3) and tantalum pentoxide (Ta2O5) are available as ALD passivation. Upon request, further ALD materials can be implemented at Fraunhofer IMS
Electrical or optical shielding can be produced by metallic layers such as ruthenium (Ru). In addition, ALD layers can be used as transparent conductive electrode layers, e.g. for optical sensors or solar cell applications
Due to the high conformality of the ALD process, dielectrics can be ideally used as insulation in trench capacitors. High- and medium-k dielectrics are available for trench capacitors. Fraunhofer IMS has experience in the development of trench capacitors for high temperature applications (more than 250 °C) based on ALD layers.

ALD technology offers the possibility to realize free-standing 3D MEMS or NEMS structures with wall thicknesses in the nanometer range on CMOS surfaces. The combination of different ALD materials enables the exact tuning of the physical and chemical parameters of the free-standing structure. Due to the nanoscale wall thickness and a low mechanical as well as thermal mass, the 3D structures are ideally suited for advanced sensor applications in gas or biosensing. Furthermore, nanowires, ultrathin membranes and cantilevers are fabricated at Fraunhofer IMS using ALD technology.

Special solutions for arbitrarily shaped components, such as packaged sensors or coatings with special materials, can be realized on request.

ALD Processes which are available

Material	Type Temperature	Homogeneity	Resistance	Max. Film Thickness	Applications
Al₂O₃	200 °C - 300 °C	98 %		50 - 100 nm	Protective layer, Medium-k dielectric
Ta₂O₅	275 °C	90 %		15 nm	Protective Layer, High-k dielectric
ZnO	200 °C	96 %	5240 µΩcm	75 nm	Transparent conductive layer
AZO	200 °C	96 %	2075 µΩcm	75 nm	Transparent conductive layer
TiAlCN	400 °C	80 %	560 µΩcm	100 nm	Conductive layer, barrier
TiN	400 °C	75 %	140 µΩcm	30 nm	Conductive layer, barrier
Ru	350 °C	85 %	20 µΩcm	50 nm	Conductive layer, electrical or optical shielding

ALD advantages at a glance

Very high conformality of deposited layers. Very good sidewall coverage of ALD layers in high aspect ratio cavities enables applications in the field of 3D technologies.
Precise layer thicknesses due to monolayer growth.
The deposited layers are of high quality and almost free of pinholes.
A growing variety of materials is available: Metals, insulators, high-k dielectrics, functional materials for sensors (e.g. metal oxides), optical materials as well as transparent conductive oxides are provided by Fraunhofer IMS.