UV absorption spectra of adlayers of MOCVD source gases

Submicron selective organometallic vapor phase epitaxy growth using tunable deep UV excitation

“…The spectrum of the TMG/AsH 3 co-chemisorbed adlayer, however, was shown to extend to longer wavelengths, suggesting that adlayer photolysis without significant gas phase absorption should be possible around 250 nm. 6 In agreement with the absorption spectra, growth enhancement for 193 nm ͑ArF͒ excimer-laser stimulation was shown to arise from gas phase photolysis 2 and growth rate enhancements at higher wavelengths ͑308 nm XeCl, 351 nm XeF͒ are caused by laser-induced heating with no evidence of photolysis. 3,7 Direct comparison of 193 nm ͓ArF͔, 254 nm ͓low-pressure Hg lamp͔, and 351 nm ͓XeF͔ excitation suggested a surface or near surface stimulation process for 254 nm irradiation.…”

“…Thus, the photochemical pathway of the adlayer reaction must differ significantly from the gas phase photolysis of TMG and TMA, since different dissociation rates would be expected from the gas phase absorption spectra. 6 Varying the excitation wavelength, we found an abrupt drop to zero enhanced growth for wavelengths greater than 252 nm. Figure 3 displays the feature heights of the selectivity grown AlGaAs spots as a function of excitation wavelength between 235 and 255 nm.…”

Wavelength tunable UV laser stimulated growth of Al/sub x/Ga/sub 1-x/ by OMVPE

“…Exposure times less than 15 minutes resulted in a constant stimulated growth rate of 2.6 p d h r . Sasaki et al [6] investigated the UV absorption spectra of TMG, TMA and arsine, as well as the spectral changes upon adsorption on synthesized silica. Although all spectra exhibit their absorption tail around 250 nm, that of the TMG/AsH, co-chemisorbed adlayer extends greatly to longer wavelengths than the vapor phase or physisorbed species.…”

“…Among these, adlayer stimulation is most desirable, since it allows for the highest resolution patteming. Several studies have investigated the absorption spectra of gas phase and adsorbed OMVPE precursors [6], and their laser-induced decomposition when adsorbed on GaAs [7] or silica substrates [8]. Although the energy of a single UV photon is sufficient to break bonds of typical precursor molecules, the exact photochemical pathways of both, single molecule dissociation and adlayer reaction stimulation are still poorly understood.…”

Photoassisted physical vapor epitaxial growth of semiconductors: a review of light-induced modifications to growth processes

“…Many metal alkyls strongly absorb photons with wavelengths below 250 nm, allowing this method to be carried out with ArF (λ = 193 nm) excimer lasers. 65,66,67,68 Photons from KrF (248 nm) excimer lasers and low-pressure Hg mercury lamps (λ = 250 nm) can also be absorbed, although with a much lower cross section. A single photon can initiate cleavage of a valence bond in the molecule, resulting in multi-step dissociation of the excited radicals.…”