This invention describes the deposition of boron and silicon carbide films using a novel fabrication method. Prior to this invention, deposition of boron containing materials via charged particle induced dissociation of boron precursor molecules had not been demonstrated. In industry, the main process is chemical vapor deposition (CVD), which relies on thermal dissociation of the precursor molecule to produce film growth. CVD has been used be produce a vast variety of boron containing materials and can be used to direct-write material using a laser beam. Techniques that rely on thermal heating for precursor dissociation such as CVD also involve heating of the substrate to processing temperature. Heating can induce thermally induced effects in the fabricated film and substrate, introducing material degradation and material distortion. This problem is also overcome in this described technology, which is critical in many fabrication environments.
The LLNL charged particle deposition technology enables fabrication of material via the charged particle induced dissociation of precursor molecules. For the case electron beam induced fabrication of boron carbide, gaseous boron precursor is delivered to a substrate in a vacuum chamber. Surface adsorbed molecules are dissociated by a beam of electrons. Non-volatile fragments remain on the substrate leading to formation of a boron containing deposit.
The vacuum chamber and beam of charged particles are provided by a scanning electron/ion microscope or a large area flood irradiation system. The scanning electron microscope can provide a focused nanoscale beam of electrons or ions which is used to control the deposit feature size down to tens of nanometers. The beam can be scanned over the substrate to pattern features. A motorized stage can be used for patterning larger features across the substrate. The use of a large area flood irradiation system allows deposition of material with feature sizes on the order of hundreds of microns to a few millimeters under current designs and larger with further optimization.
The typical work method entails:
- The substrate is placed in the system and pumped to high-vacuum.
- Precursor is delivered to the substrate by a gas injection system.
- Focused charged particles (electrons or ions) are directed at the area where material is to be deposited.
- Particles irradiate the area until the desired amount of material has been deposited.
- Films deposited by charged particle induced dissociation of precursor gas do not suffer thermally induced effects, greatly reducing the film stress that results in cracking.
- Conventional precursors used in chemical vapor deposition such as BCl3 and B2H6 are highly toxic, pyrophoric gases which are too dangerous to handle in most facilities.
- This technology uses precursors which do not pose a significant health and safety risk to personnel or the instrument.
The ability to deposit boron and silicon carbide at multiple length scale is advantageous in many systems including protective material coatings, optical components and MEMS technology. This is the first demonstrated technology which can rapidly prototype nanosized boron carbide material via the additive approach, giving large advantages over existing techniques.
Potential uses include fabrication of ultra-hard and low-Z coatings. Further applications exist in the areas of solid-state neutron detectors, low-κ dielectrics for ultra-large-scale integrated circuits, and other unique semiconductor devices. Given the large application space of boron and silicon carbide coatings and devices the applications span multiple areas and length scales.
The technology has been demonstrated in a laboratory environment with scaling to desired industrial application requiring optimization for the specific task. This work was carried out at LLNL utilizing a prototype system implemented for the fabrication of millimeter sized boron carbide and silicon carbide films. Scaling the films to smaller or larger sizes can be implemented based on desired film requirements. Deposition rates are on the order of that found with similar techniques such as laser chemical vapor deposition.