On the Many Applications of Nanometer-Thin Pure Boron Layers in IC and Microelectromechanical Systems Technology.

An overview is given of the many applications that nm-thin pure boron (PureB) layers can have when deposited on semiconductors such as Si, Ge, and GaN. The application that has been researched in most detail is the fabrication of nm-shallow p+n-like Si diode junctions that are both electrically and chemically very robust. They are presently used commercially in photodiode detectors for extremeultraviolet (EUV) lithography and scanning-electron-microscopy (SEM) systems. By using chemicalvapor deposition (CVD) or molecular beam epitaxy (MBE) to deposit the B, PureB diodes have been fabricated at temperatures from an optimal 700 °C to as low as 50 °C, making them both front- and back-end-of-line CMOS compatible. On Ge, near-ideal p+n-like diodes were fabricated by covering a wetting layer of Ga with a PureB capping layer (PureGaB). For GaN high electron mobility transistors (HEMTs), an Al-on-PureB gate stack was developed that promises to be a robust alternative to the conventional Ni-Au gates. In MEMS processing, PureB is a resilient nm-thin masking layer for Si micromachining with tetramethyl ammonium hydroxide (TMAH) or potassium hydroxide (KOH), and low-stress PureB membranes have also been demonstrated.

Modular microreactor with integrated reflection element for online reaction monitoring using infrared spectroscopy.

We report on the fabrication of an internal reflection element (IRE) combined with a modular polymer microfluidic chip that can be used for attenuated total reflection (ATR) infrared spectroscopy. The IRE is fabricated from a silicon wafer. Two different polymers are used for the fabrication of the two types of modular microfluidic chips, namely polydimethylsiloxane (PDMS) and cyclic olefin copolymer (COC). The microfluidic chip is modular in the sense that several layers of mixing channels, using the herringbone mixer principle, and reactions chambers, can be stacked to facilitate the study of the desired reaction. A model Paal-Knorr reaction is carried out to prove that the chip works as intended. Furthermore, we highlight the strength of IR spectroscopy as a tool for reaction monitoring by identifying the peaks and showing the different reaction orders at the different steps of the Paal-Knorr reaction. The reduction of the aldehyde groups indicates a (pseudo) first order reaction whereas the vibrational modes associated with the ring formation indicate a zero order reaction. This zero order reaction can be explained with literature, where it is suggested that water acts as a catalyst during the dehydration step, which is the final step in the pyrrole ring formation.