Material Reliability of Low-Temperature Boron Deposition for PureB Silicon Photodiode Fabrication

Abstract

The chemical-vapor deposition conditions for the growth of pure boron (PureB) layers on silicon at temperatures as low as 400°C were investigated with the purpose of optimizing photodiodes fabricated with PureB anodes for minimal B-layer thickness, low dark current and chemical robustness. The B-deposition is performed in a commercially-available Si epitaxial reactor from a diborane precursor. In-situ methods commonly used to improve the cleanliness of the Si surface before deposition are tested for a deposition temperature of 450°C and PureB layer thickness of 3 nm. Specifically, high-temperature baking in hydrogen, and exposure to HCl are tested. Both material analysis and electrical diode characterization indicate that these extra cleaning steps degrade the properties of the PureB layer and the fabricated diodes.

Nanometer-thin pure boron CVD layers as material barrier to Au or Cu metallization of Si

“…However, for a similar 400°C deposition, we found considerable etching of the Si in the implanted p ? -regions, but none at all in the nonimplanted regions [29]. Such a difference was also observed on samples with 700°C B-deposition if the Si had been exposed to non-optimal surface treatments before deposition.…”

“…Moreover, previous experiments using the same type of PureB diode test structures have shown that depositing on the implanted p ? -regions sometimes led to a weakening of B bonds [29]. This was seen in tests where the devices were exposed to the Si wet-etchant tetra-methyl ammonium hydroxide (TMAH).…”

“…The B-deposition was performed on a whole 100-mm test wafer by CVD in an ASM Epsilon 2000 Si/SiGe epitaxy system equipped with diborane (B 2 H 6 ) gas as precursor and nitrogen as carrier gas, following the recommendations given in previous work [1,29] to achieve a clean Si surface. Therefore, the wafer was given an HF dip to remove native oxide and kept in the load lock for 1 h before depositing at a temperature of 450°C using low flow rates that ensured B-deposition selectively on the open Si regions.…”

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

“…For B deposited below 250℃, the growth of the layer appears to stagnate at around 1 nm to 1.5 nm, as determined by in-situ ellipsometry. As opposed to higher temperature deposition [130], possibly the conditions at 250℃ resulted in a preference for the B to adsorb on Si sites rather than Bsites, leading to an almost self-limiting deposition [21]. SIMS analysis of these samples was carried out and the resulting B concentration is shown in Fig.…”

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

“…In contrast, for the PureB capping of detectors for SEM systems there has been no indication that the B surface is prone to oxidation, something which would negatively impact the signal gain of the photodiodes. Nevertheless, experiments have shown that contamination of the CVD system will readily lead to incorporation of oxygen in the B-layer [38], a danger that increases as the deposition temperature, and thus the deposition rate, is reduced. For synthesis of borophene, such contamination has been reported to be devastating.…”