Monday, August 3, 2020

BDEAS - a versaitile ALD precursor for high quality dilectric films in leading edge semiconductor applications

One of the most important reasons why Silicon (Si), in place of Germanium (Ge), was propelled to the front of the class in the semiconductor industry from the very beginning, is the fact that Si forms a very stable oxide-semiconductor interface with SiO2. A high-quality oxide interface is a key to making field-effect transistors (MOSFETs). Germanium oxide is water-soluble which rendered it useless for MOSFET fabrication in the early days (now the industry is advanced enough to possibly solve that).

Thermal oxidation of Si at temperatures > 800 °C yields SiO2. To avoid such high temperatures and long processing times and tune the material properties, (wet) chemical oxidation, (plasma-enhanced) chemical vapor deposition or sputtering and electron beam evaporation are also preferred methods to grow SiO2. The advantages of precise thickness control, optimal large-area uniformity, and the conformality over demanding substrate topologies of atomic layer deposition (ALD) based SiO2 films, all led to an expansion of target applications such as; spacer based self-aligned double/quadruple patterning (SADP or SAQP) in fabricating DRAM and logic chips (Link), interface engineering between Si and high-k materials (Link), moisture barrier or protective or insulator coatings (Link), nanolaminate structures with tailored optical and electronic properties (Link) and double layer surface passivation in Si photovoltaics (Link), etc. to name but a few.

Link for the image

Bis(diethylamino)silane (BDEAS) [SiH2[N(CH2CH3)2]2, also known as SAM-24[MP1] , is one of the most preferred Si precursors for ALD of SiO2 and other Si-containing films. It’s an air-sensitive, moisture-sensitive, flammable, colorless, and odorless liquid precursor (boiling point 70 °C (30mm), density 0.804), which exhibits a high vapor pressure, i.e. ~100 Torr at 100 °C.

The research group of Prof. W. M. M. Kessels, Department of Applied Physics, Eindhoven University of Technology, has reported that BDEAS is suited for low-temperature synthesis of high-quality SiO2 by ALD with the SiO2 properties being relatively insensitive to the substrate temperature for the temperature range of 100 – 300 °C; for temperatures reaching 400 °C thermal stability issues of the precursor and its ligands start to play a role. The process is also relatively fast as it combines a high growth-per-cycle (0.8 – 1.7 Å/cycle) with relatively short dosing and purge times. The ALD SiO2 processes with BDEAS precursors are therefore of interest for high-volume manufacturing applications, for instance, using ALD batch processes or inline (plasma) ALD equipment.

Link for the image

Strem Chemicals, Inc., a high purity specialty chemicals manufacturer and supplier, headquartered in Newburyport, Massachusetts, USA, boasts a vast variety of ALD/CVD precursors, including BDEAS for depositing Si-based films in different applications.

Since 1964, Strem Chemicals, Inc. has been serving its clients from academic, industrial, and government research and development laboratories as well as commercial scale businesses in the pharmaceutical, microelectronic, and chemical/petrochemical industries. Strem also provides custom synthesis (including high-pressure synthesis) and current good manufacturing practice (cGMP) services. With ISO 9001 certification for the Quality Management System (QMS) standard and documentation, Strem products are high purity materials, typically 99%, with some at 99.9999% metals purity. Strem utilizes a comprehensive range of analytical techniques tailored to each product to ensure quality because  researchers typically rely on the supplier's quality procedures and documentation, which if poorly conducted[MP1]  may kill a great research idea. All of Strem's catalogs, since inception, have listed “Color and Form” for every product as primary indicators of quality.

 [MP1]SAM-24 may be an Air liquide trademark.


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