Bubblers and Cylinders for CVD/ALD Precursor Handling

Chemical vapor deposition (CVD) is a process of deposition of a solid material, such as nanotubes, nanowires, particle, thin film, and much more, on a substrate by creating reactive species in the gaseous phase. The formation of reactive species occurs when precursor gases come in contact with or pass over the heated substrate. There are several types of CVD, including metal-organic chemical vapor deposition (MOCVD), low pressure chemical vapor deposition (LPCVD), and atmospheric pressure chemical vapor deposition (APCVD). In the MOCVD process, metal-organic species are utilized to form thin films of metals and metallic compounds such as metal nitrides and metal oxides.

Figure 1. Typical CVD Reactor.

A specific form of CVD is the atomic layer deposition (ALD) process, wherein control over deposition on atomic scale is possible. In the process, various precursors are alternatingly supplied into the reaction chamber separately and undergo self-limiting surface reactions so as to allow the deposition of the same amount of material in each reaction cycle. This creates very smooth, homogenously thick, alternating layers of high dense materials with fewer defects.

Applications of CVD/ALD Processes

CVD/ALD processes are gaining momentum as they can form thin films of high homogeneity and conformality with a precisely controlled thickness. The following are the applications of the CVD process:

• Fabrication of optical storage media
• Production of semiconductor devices
• Synthesis of exotic new powdered/fibrous materials
• Production of protective coatings, including high temperature-, corrosion-, and wear-resistance coatings
• Formation of ceramic composites, optical fibers and dense structural components.

Especially, the ALD process is gaining more interest thanks to its even better control over the formation of thin films. The following are the applications of the ALD process:

• Development of electroluminescent device technology
• Production of new high-k gate dielectrics that hold potential to serve as an alternative to silica in next generation of metal oxide semiconductor field effect transistors
• Fabrication of microelectronic devices, including thin-film capacitors, radiation detectors, switches, ferroelectric memories, integrated circuits, and microelectromechanical structures (MEMS).

Role of Bubblers and Cylinders in CVD/ALD Processes

Although majority of the precursors used in the CVD/ALD processes are liquid at room temperature, they are also used in powder form in certain cases. Most precursors are air and/or water sensitive and very flammable or pyrophoric in nature. Nevertheless, they exhibit good thermal stability and are storable for extended periods of time if well packed. For the CVD/ALD process, precursors are generally utilized directly from the package wherein they were supplied in order to avoid their handling issues. For this reason, the package must be considered as a component of the product.

Generally bubblers with internal dip tubes are utilized as a packaging option for liquids, while stainless steel cylinders with the suitable seals and fittings are utilized for gases. Typically, the transfer of liquid precursors into the reaction chamber is performed by bubbling a carrier gas via the container wherein they are stored at or less than room temperature.

Hydrogen is the most commonly used carrier gas; however, nitrogen or other inert gases can serve the purpose in certain cases. In order to avoid the condensation of the precursor in the tubing that connects the cylinder to the reaction chamber, the likely temperature of the cylinder or bubbler is below the room temperature, if the vapor pressure of the precursor allows. It is possible to avoid condensation by heating the tubing above room temperature if cooling cannot be done.

Bubblers and Cylinders from Strem Chemicals

Strem Chemicals, a provider of high-purity specialty chemicals, offers an extensive range of bubblers and cylinders for the CVD/ALD processes.

CVD/ALD Electropolished Stainless Steel Bubblers

Figure 2. Electropolished stainless steel bubblers.

Strem Chemicals offers CVD/ALD electropolished stainless steel bubblers with the following features:

• Vertical and horizontal configurations
• Different volumes are available: 150 ml, 300 ml. 600 ml, 1000 ml, 1200 ml, 2000 ml, 2500 ml, and 3000 ml
• Selection between in-line valves or valves that are turned 90 degrees away from the fill port
• Available with and without dip tubes, and with dip tubes of various lengths
• Available with diaphragm sealed valves
• Available with valves that are specified for high temperature operation (315°C).

CVD/ALD Stainless Steel Cylinders

Figure 3. Stainless steel standard assembly.

Figure 4. Stainless steel cylinders.

Strem Chemicals offers CVD/ALD stainless steel cylinders with the following features:

• Volume: 50 ml
• Choice of 1/4" VCR Male Ball Valve and Female Nut; 1/4'' VCR Male DP Valve (Ultra High Purity) and Female Nut; or 1/4" VCR Male Bellows-Sealed Valve (High Temp) and Female Nut
• Swagelok Cylinder Assemblies.

This information has been sourced, reviewed and adapted from materials provided by Strem Chemicals.

For more information on this source, please visit Strem Chemicals.