Laser CVD

Laser CVD involves essentially the same deposition mechanism and chemistry as conventional thermal CVD and theoretically the same wide range of materials can be deposited. Some examples of materials deposited by laser CVD are listed in Table 5.2.h Hi8] 

Examples of Materials Deposited by Thermal Laser CVDP P h 1 

Experimental applications include the direct deposition of patterns as small as 0.5 im in semiconductor applications using holographic methods, and the production of rods and coreless boron and silicon carbide fibers (see Ch. 19). 

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PF3A11CI, prepared from Au2C16 and PF3 in SOCl2 has a vapour pressure of 10 4mbar at room temperature and has been suggested as a laser CVD precursor [80],... 

AuMe2(acac) is being studied as a vehicle for laser CVD of gold films it has the expected square planar structure in the gas phase (Au—C 2.054 A Au-O 2.085 A) [168],... 

Figure 5.13. Schematic of laser-CVD growth mechanism (stripe deposition).

In photo CVD, the chemical reaction is activated by the action of photons, specifically ultraviolet (UV) radiation, which have sufficient energy to break the chemical bonds in the reactant molecules. In many cases, these molecules have a broad electronic absorption band and they are readily excited by UV radiation. Although UV lamps have been used, more energy can be obtained from UV lasers, such as the excimer lasers, which have photon energy ranging from 3.4 eV (XeF laser) to 6.4 eV (ArF laser). A typical photo-laser CVD system is shown schematically in Fig. 5.14.117]... 

In addition to thermal MOCVD, laser CVD hasbeen successfully demonstrated. 0... 

Crystalline deposits are obtained with Reaction (2) in the temperature range of 350-400°C at low pressure (< 1 Torr).P9] At still lower temperature (< 330°C) and moderate pressure (20-50 Torr), an amorphous germanium deposit is obtained. With Reaction (2), germanium is obtained by plasma CVD at 450°C and by laser CVD at 340°C.[31][32]... 

Plasma CVD and thermal laser CVD are also used particularly in the deposition of GaAs. The formation of epitaxial GaAs at 500°C and polycrystalline GaAs at 185°C has been reported,... 

A new process based on laser CVD does not require a core material and is able to produce fibers with a much smaller diameter. Deposition rate is up to 1 mm/sec. The process is still experimental and is presently being developed for the production of boron, SiC, and Si3N4.1 1 The core-less deposition may be accomplished by impinging the laser beam on the growing end of a retreating fiber in a CVD atmosphere. 

Si3N4 powder by laser CVD from halogenated silane and ammonia with an inert sensitizer such as SFg.P l... 

Gate Oxide Tunnel Oxide f SiH4/N20 PECVD Microwave Plasma Anodisation Laser CVD... 

Figure 13.3 Schematic arrangement of Laser CVD systems. Left photolytic LCVD right pyrolytic LCVD.

In a pyrolytic or thermal LCVD experiment, the gas is transparent and the substrate absorbs the laser energy. This creates a so - called hot - spot on which a normal thermal CVD process occurs. Pyrolytic LCVD allows a very precise localization of the coating. In a sense, this technique may be compared to the cold - wall CVD technique in which the substrate may be heated by passing an electric current through it (resistance heating), or by induction, where the substrate itself acts as a susceptor. In these cases, the gas volume is not heated significantly (hence the name cold - wall CVD). The main difference between the cold-wall CVD and the pyrolytic laser CVD is that in the latter, the heated area can be localized and scanned very precisely. 

In general, several possible chemical reactions can occur in a CVD process, some of which are thermal decomposition (or pyrolysis), reduction, hydrolysis, oxidation, carburization, nitridization and polymerization. All of these can be activated by numerous methods such as thermal, plasma assisted, laser, photoassisted, rapid thermal processing assisted, and focussed ion or electron beams. Correspondingly, the CVD processes are termed, thermal CVD, plasma assisted CVD, laser CVD and so on. Among these, thermal and plasma assisted CVD techniques are widely used, although polymer CVD by other techniques has been reported. ... 

If nitrogen is used, the ideal deposition temperature is 1000°C. The deposition temperature is lower for the ammonia reaction (575 700°C). Plasma processing can be used to reduce the processing temperature to 500°C . Thermal laser CVD has also been used to deposit TiN at reduced temperature . In an alternate approach, titanium tetraiodide is the precursor (with no plasma) at a deposition temperature under 450°CT... 

Lehmann O, Stuke M (1995) Laser-CVD 3D rapid prototyping of laser driven moveable micro-objects. J Phys IV5 C5-601-606... 

Duty CE, Jean DL, Lackey WJ (1999) Design of a laser CVD rapid prototyping system. Ceram Eng Sci Proc 20 347-354... 

Thermal laser CVD involves the same chemical deposition processes that occur in thermal CVD. It, therefore, is applicable to depositing the same types of materials that the thermal CVD process does. Its major application is the direct writing of thin films in semiconductor processing. 

In the Chemical Vapor Deposition (CVD) methods, the starting material undergoes specific chemical reactions at the hot surface of the substrate to form thin layers of the desired material. The reaction can be stimulated by various energy sources, e.g. plasma, giving plasma enhanced CVD (PECVD), or a laser, giving laser CVD. 

Oliveira J.C., Conde O. Deposition of Boron Carbide by Laser CVD a Comparison with... 

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