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

Abstract

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.

Low temperature pure boron layer deposition for Si diode and micromachining applications

“…For example, graphene, a 2D sheet of well-organized honeycomb carbon atoms, has very promising properties such as high mobility and high material strength [1]. However, disappointments with respect to manufacturability and bandgap engineering have shifted much of the research efforts to a series of other, electronically promising, 2D materials, some of which have been successfully fabricated [2], such as silicene [3], germanene [4], monolayer molybdenum disulfide (MoS2) [5], phosphorene [6], and borophene [7][8][9][10][11]. Although the properties of these 2D materials are exciting, they all face major challenges as far as manufacturability is concerned [2].…”

“…However, disappointments with respect to manufacturability and bandgap engineering have shifted much of the research efforts to a series of other, electronically promising, 2D materials, some of which have been successfully fabricated [2], such as silicene [3], germanene [4], monolayer molybdenum disulfide (MoS2) [5], phosphorene [6], and borophene [7][8][9][10][11]. Although the properties of these 2D materials are exciting, they all face major challenges as far as manufacturability is concerned [2]. Mechanical exfoliation as a fabrication method only renders poor efficiency and small sample sizes [12].…”

“…Nevertheless, the desire to replace 3D doped regions by 2D layers with comparable electrical functionality is commanding. Therefore, attention is now also being directed towards the electrical properties of interfaces where 2D sheets of compounds are created with special bonding structures that do not occur in the bulk form [2]. For example, the newly discovered topological insulators, where the bulk behaves as an insulator but the surface has exotic metallic states [14], have aroused widespread research interest.…”

“…Bismuth selenide (Bi2Se3) is one of the most popular materials [16,17] but, as for the other electrically promising 2D materials, topological insulators are facing many practical challenges mostly due to their fragility. Thus, also for these materials, there is a growing interest in looking at interface layers [2] where (1) the 2D electrical functions are formed by inherently more stable interface bonding, and (2) the "2D bulk" material works naturally as a protection layer, making the interface less susceptible to damage from varying environmental conditions. This thesis puts focus on an example of a such an electrically interesting 2D interface layer, the boron-to-silicon interface, and presents a further investigation and development of what has been called PureB technology, including the "2D bulk" material itself.…”

Influence of Barrier Layers on ZrCoCe Getter Film Performance

“…Microelectromechanical system (MEMS) devices have been used in aerospace [ 1 ], biomedical [ 2 ], automotive [ 3 ], communications [ 4 ], as well as other high-tech fields [ 5 , 6 ], many of which use Ge as a substrate [ 7 , 8 , 9 ]. Getter films have attracted significant attention for their sorption performance in maintaining and improving the vacuum degree in MEMS vacuum devices for extended periods [ 10 , 11 , 12 , 13 ].…”