Bentley J. Palmer

Molecular design for photo and electron beam lithography with thin films of coordination compounds

Abstract The photochemistry of coordination complexes in the solid state has been investigated with a view towards developing a new method for the photolithographic deposition of materials. Ultraviolet exposure of thin films of coordination complexes through an optical lithography mask results in the patterning of materials in the exposed regions. The development of this method requires photochemically active complexes which efficiently eject ligands upon photolysis to produce the desired material in a solid state thin film. A generic reaction for the production of metal films is M L n ( thin film ) → h v M ( thin film ) + n L ( g ) In this paper the photochemistry of thin films of inorganic complexes of Co, Cu, Ni, Pd, Pt and U is presented. These examples will be used to outline the approaches used to design suitable precursor molecules for film deposition. Mechanistic studies of the surface photochemical reactions along with evidence for submicron resolution lithography of materials derived from these complexes will be highlighted. The use of electron beams to induce similar chemistry will also be discussed.

Photoresist-free lithography of 3?m wide UO3 lines from amorphous films of uranyl complexes

The solid-state photochemistry of two uranyl complexes has been investigated with the purpose of developing methods for optical lithography of uranium oxide films. The complex, UO2(NCS)2(OP(C6H5)3)2, is photosensitive in the solid state, undergoing loss of both NCS ligands to yield UO2(OP(C6H5)3)2 as the final photoproduct. Films of this material were easily patterned by photolithography. The complex, UO2(OP(C5H7O2)2, was also photosensitive and decomposed with no apparent intermediate to yield films of uranium oxide (δ-UO3). This process was also shown to be compatible with optical lithography by the patterning of δ-UO3 on silicon surfaces.

Photolithography of amorphous films of (η5-C5H5)2Ti(N3)2 on silicon (111) resulting in TiO2: The mechanism of the photodeposition reaction

Photolithography to produce TiO2 patterns from amorphous films of (η5-C5H5)2Ti(N3)2 has been demonstrated. The efficiency of the reaction has been measured yielding a quantum yield of 0.025. The mechanism of the photoreactions of (η5-C5H5)2Ti(N3)2 has been studied using Fourier transform-infrared spectroscopy in both a low-temperature 1,2-epoxyethylbenzene glass and as surface films. In each case the primary photochemical process was found to be loss of a single azido group. The result of subsequent photolysis was found to be dependent upon medium and temperature. In the low-temperature glass no further photochemistry was observed. The exhaustive photolysis of films at 20 K, or room temperature, under a vacuum or in air led to loss of all ligands and the formation of TiO2.

Photochemistry of (η5-C5Me5)Re(CO)2Br2 on Si(III) surfaces at low temperature

Abstract The photolysis of (η5-C5Me5)Re(CO)2Br2 on Si(III) surfaces at 77 K results in cis to trans isomerism. The mechanism of the photoreaction involves CO loss to generate an isomer of (η5-C5Me5)Re(CO)Br2 which, upon warming, reacts thermally with CO to generate only trans-(η5-C5Me5)Re(CO)2Br2. The first isomer of (η5-C5Me5)Re(CO)Br2 is photosensitive and converts to a second isomer which upon reaction with CO yields exclusively cis-(η5-C5Me5)Re(CO)2Br2.

Photochemical reactions of [(η5-C5R5)Mn(CO)2(NO)]+ (R5≡H5, H4Me, Me5) as films and in low temperature glasses

Abstract The photolysis of [(η5-C5R5)Mn(CO)2(NO)]+ (R5  H5, H4Me, Me5) was studied by Fourier transform IR spectroscopy in a low temperature 1,2-epoxyethylbenzene glass and in surface films. In each case the primary photoproduct was found to be [(η5-C5R5)Mn(CO)(NO)]+. The result of subsequent photolysis was observed to be dependent on medium and temperature. In the low temperature glass, NO+ was photoextruded and the resultant organometallic was {(η5-C5R5)Mn(μ-CO)}2. In the film at 77 K, two competing processes were observed: loss of NO and loss of NO+. Unlike the result in the glass, both terminal and bridging CO groups were observed following NO+ loss. Exhaustive photolysis at room temperature in the film led to loss of NO+ and ultimately loss of CO and the cyclopentadienyl ring.

Solid state photochemistry of fac-Co(NH3)3(NO2)3 and mer-Co(NH3)3(N3)3 as thin films on Si(111) surfaces

Abstract The solid state photochemistry of fac-Co(NH3)3NO2)3 and mer-Co(NH3)3(N3)3 have been investigated on Si(111) surfaces. The complex fac-Co(NH3)3(NO2)3 undergoes linkage isomerism as the major observed photoreaction generating a film which contains Co(NH3)3(NO2)(ONO)2. Concomitant with this reaction is the inefficient loss of both NH3 and NO2. Photolysis of mer-Co(NH3)3(N3)3 led to loss of ammine and the formation of Co(μ-N3)2(N3)4 as the initial photoprocess. Further photolysis resulted in the loss of azide ligands, ultimately producing cobalt, through the intermediacy of species containing bridging azides formulated as oligomers of {Co(μ-N3)2}. The relevance of these results to lithography is discussed.

The low temperature photochemistry of (η5-C5H5)M(CO)3X (M Mo, W; X Cl, Br, I): structure and solvation of the CO loss products

Abstract The complexes (η 5 -C 5 H 5 )M(CO) 3 X (M  Mo, W; X  Cl, Br, I) all undergo photochemical loss of CO at 12 K in a styrene oxide glass. The product in each case is (η 5 -C 5 H 5 )M(CO) 2 SX where S represents solvation by the glass. Each of the unsaturated species undergoes thermal reaction with CO to form (η 5 -C 5 H 5 )M(CO) 3 X upon warming. Prolonged photolysis of (η 5 -C 5 H 5 )W(CO) 2 SI leads to the loss of a second molecule of CO and the formation of a monocarbonyl species. The nature of the solvation of the unsaturated species (η 5 -C 5 H 5 )M(CO) 2 SX has been investigated by applying Timneys method to analyse the spectra of these complexes. The ligand effect constants have been refined for a variety of ligands from a set of 85 four-legged piano-stool molecules with molybdenum, tungsten, vanadium and rhenium as the central metals. Using the derived constants, the styrene oxide was found to be coordinated through the oxygen atom in most cases, leading to the general formulation of the photoproducts as (η 5 -C 5 H 5 )M(CO) 2 (OCH 2 CHPh)X (M  Mo; X  Cl, I) (M  W; X  Cl, Br, I). In one case, namely (η 5 -C 5 H 5 )Mo(CO) 2 (η 2 -PhCHCH 2 O)Br, the styrene oxide appears to be coordinated through the phenyl ring.