Laser-Assisted Processes

Laser beams can also be used to drive chemical reactions in a technique known as laser-assisted chemical etching. Much higher local etch rates can be achieved with this method than are possible with RIE. Similarly, a laser beam can supply energy to drive a deposition the method is called laser-driven deposition. An example is depositing W onto specific areas of a substrate from tungsten hexacarbonyl [W(CO)J. Laser-assisted processes can be used to create interesting three-dimensional structures. However, the processes are intrinsically serial, not parallel, meaning that a beam must be scanned across the areas to be processed spot by spot instead of simultaneously. 

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In addition to the three basic microfabrication steps discussed above, other fabrication techniques are quite useful. We will briefly discuss a few of them, namely lift-off, annealing, liquid phase photopolymerization, micromolding, soft lithography, electroplating, sacrificial processes, bonding, surface modification, laser-assisted processes, planarization, and fabrication on flexible substrates and curved surfaces. Some of these techniques do not necessarily belong to the traditional repertoire of microfabrication of ICs. However, they have proved very useful for the creation of other types of microdevices and systems such as MEMS, microfluidics, and labs on chips. 

Discusses many microfabrication techniques, including deposition, photolithography, etching, annealing, liquid-phase photopolymerization, micromolding, electroplating, laser-assisted processes, and more... 

Fast screening techniques, such as temperature-resolved in-source filament pyrolysis and laser-assisted pyrolysis, benefit from the high cycle time and mass accuracy of FUCR-MS [214]. An additional advantage of FUCR-MS in the study of pyrolysis processes is that MS can be readily used for structural identification of desorption and pyrolysis products. 

There are numerous materials, both metallic and ceramic, that are produced via CVD processes, including some exciting new applications such as CVD diamond, but they all involve deposition on some substrate, making them fundamentally composite materials. There are equally numerous modifications to the basic CVD processes, leading to such exotic-sounding processes as vapor-phase epitaxy (VPE), atomic-layer epitaxy (ALE), chemical-beam epitaxy (CBE), plasma-enhanced CVD (PECVD), laser-assisted CVD (LACVD), and metal-organic compound CVD (MOCVD). We will discuss the specifics of CVD processing equipment and more CVD materials in Chapter 7. 

In laser-assisted thermal CVD by gas-phase heating, the laser is used to vibrationally excite the gas (e.g., SiH4) and active film precursors (e.g., SiH2). The modeling of these processes revolves around the transport phenomena that control the access of the film precursors to the surface, as exemplified by the finite-element analysis by Patnaik and Brown of amorphous silicon deposition (228). 

Vacuum deposition techniques, such as sputtering, electron beam evaporation, and plasma deposition are common. Photopolymerization and laser-assisted depositions are used for preparation of specialized layers, particularly in the fabrication of sensing arrays. Most commercial instruments have thickness monitors (Chapter 4) that allow precise control of the deposition process. 

Page, J. S., and Sweedler, J. V. (2002). Sample depletion of the matrix-assisted laser desorption process monitored using radionuclide detection. Anal. Chem. 74 6200-6204. 

Abstract. We address the question of the importance of relativity in selected non-linear radiative processes to be observed when an atomic system is submitted to an intense radiation field. To this end, we report on recent results obtained in the theoretical analysis of the following processes i) two-photon transitions in high-Z hydrogenic systems, ii) laser-assisted Mott scattering of fast electrons, and iii) two-colour photoionisation spectra of atoms in the simultaneous presence of two ultra-intense laser fields. In each case, the signature of relativistic effects is evidenced. 

B. A. Mamyrin, Laser assisted reflectron time of flight mass spectrometry, Int. J. Mass Spectrom. Ion Process., 131 (1993) 1-19. 

The study of reactive excited states of van der Waals complexes is the link between the laser-assisted collision and the photodissociation approach it brings the collisional problem into a much simpler photodissociation problem. Here, a cold complex which has a defined geometry is formed between the collision partners and optically excited to trigger the reactive process. This creates the photodissociation of a molecule with very weakly bound ground state. The van der Waals spectroscopy has already allowed the accurate determination of the interatomic potential [Na-Ar (Smalley et al. 1977 Tellinghuisen et al. 1979), HgAr (Breckenridge et al. 1985, 1994 Fuke et al. 1984)]. More complex collisional... 

It can be pointed out that the van der Waals technique is the equivalent of the excitation of the collision pair or the laser-assisted collision, and we will discuss the differences and similarities between the excitation of the complex and the collisional process. 

Laser-induced chemical hquid deposition of copper fihns on qnartz and glass from Cn(acac)2 (7a) as precnrsor was reported by Onchi and collaborators 2. The process is realized throngh the interaction of copper coUoids with the appropriate snrfaces. It was fonnd that, depending on whether the laser irradiation is discontinnons (ArF laser) or continnons (KrF laser), closed copper fihns or nano-islands were formed. This method differs from the laser-assisted liqnid-phase metallization of polymers, wherein a laser beam was nsed to enhance chemical rednction of copper(II) salts. ... 

A relatively unexplored extension of the Kramers theory is the escape of a Brownian particle out of a potential well in the presence of an external periodic force. Processes such as multiphoton dissociation and isomerization of molecules in high-pressure gas or in condensed phases/ laser-assisted desorption/ and transitions in current-driven Josephson junctions under the influence of microwaves " may be described with such a model, where the pieriodic force results from the radiation field. 

A combined aerosol-assisted/laser-assisted technique has been used to deposit Si3N4 from a single-source precursor. The precursor was silazane monomer having cyclic structure of (CHsSiHNH) , where x = 3 or 4. The chemistry of deposition is a straight pyrolysis process following the unbalanced equation ... 

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