Laser-Induced Deposition of Gold
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LASER-INDUCED DEPOSITION OF GOLD
THOMAS H. BAUM,
IBM Almaden Research Center, San Jose, California 95120-6099
ABSTRACT The laser-induced, vapor-phase deposition of gold metal from dimethyl-(2,4-pentanedionato) gold (III) and two fluorinated derivatives was examined by both photopyrolytic (LCVD) and photochemical modes of decomposition. High purity gold deposits are formed by LCVD with the rates of deposition being extremely vapor pressure dependent and thus, gold complex dependent. Photochemical deposition of gold patterns with 2 pm resolution can be achieved by irradiation of these complexes in the UV, but the deposited material is contaminated with carbon impurities.
INTRODUCTION The laser-induced deposition of gold has been reported from plating solutions (1], spin-on organogold films [2], and from the vapor phase decomposition of volatile organometallic complexes 13,41. The latter approach is a completely dry, single-step process with rates of gold film formation which are competitive to the other deposition methods as mentioned above. Laser chemical vapor deposition (LCVD) is a modification of conventional CVD, In which a focused laser is absorbed by the substrate and used as a localized heat source. An organometallic, adsorbed or colliding with the surface, undergoes pyrolytic decomposition to metal with the liberation of volatile reaction products. The spatially-resolved surface temperature profile, induced by laser heating of the substrate, defines the reaction zone and controls the decomposition reaction. The optical and thermo-physical properties of the substrate and deposited metal are thus important process parameters. Alternatively, photochemical deposition occurs when the organometallic complex, adsorbed on the substrate or in the gas phase, is electronically excited by the laser radiation and undergoes dissociation to form metal atoms: This process often requires UV radiation, with the reaction zone being defined by the incident light. A critical component to all laser-induced depositions is the organometallic complex used as the metal precursor. The precursor's chemical and physical properties will profoundly affect the rates of metal deposition, the purity of the metal deposit and the overall parameters necessary for deposition. Dimethyl-(Z,4-pentandionato) gold (III) and two fluorinated derivatives [5] undergo clean thermal decomposition to gold with the subsequent liberation of volatile reaction products [6]. The incorporation of fluorine substituents, as depicted in Figure 1, results in increased volatility of the gold complex [[7at room temperature. All three gold compounds (ia, lb and 1c) undergo exothermic decomposition beginning at -160 °C, as determined by differential scanning calorimetry. These same complexes are also photoactive in the UV and undergo photochemical dissociation to produce gold-containing films.
Mat. Res. Soc. Symp. Proc. Vol. 75. ý 1987 Materials Research Society
142
R
/0
CH 3 \ Au CH
Complex la lb 1c
3
Structure R=R'=CH3 R=CH3 R'=CF3 R=R'=CF3
0-
R T(O°C) 8
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