Sang-Bae Jung

Adhesion enhancement of ion beam mixed Cu/Al/polyimide

Cu (400 A)/polyimide was mixed with 80 keV Ar+ and N2+ from 1.0×1015 to 2.0×1016 ions/cm2. The same processes were repeated for the Cu (400 A)/Al (50 A)/polyimide system which has Al as a buffer layer. The quantitative adhesion strength was measured by a standard scratch test. X-ray photoelectron spectroscopy was employed to investigate the change in the chemical bonds of the ion beam mixed polyimide substrate and the intermediate effects for the adhesion enhancement in Cu/Al/polyimide. Two distinct tendencies are observed in the adhesion strength: Cu/Al/polyimide is more adhesive than Cu/polyimide after ion beam mixing, and N2+ ions are more effective in the adhesion enhancement than Ar+. The formation of an interlayer compound of CuAl2O4 accounts for the former, while the latter is understood by the fact that N2+ ions produce more pyridinelike moiety, amide group and tertiary amine moiety which are known as adhesion promoters.

The effects of pre-aging and concentration of surface modifying agent on the microstructure and dielectric properties of SiO2 xerogel film

Abstract Surface modification is a key process for the preparation of porous SiO 2 xerogel film by ambient pressure drying. The microstructure and surface terminal bonds which determine the properties of the film are closely related with the surface modification. Two kinds of pre-aged film were prepared to investigate the effect of wet-gel microstructure on the surface modification of film. The concentration of surface modifying agent (tetramethylchlorosilane; TMCS) in solvent ( n -hexane) was also varied. As concentration of TMCS increased, surface morphology was obtained from a two-dimensional structure to a three-dimensional network structure with pre-aged film for 1 h at 70°C. This is due to the increase in methyl groups as surface terminal bonds and the suppression of condensation reaction. Variation in film thickness, porosity, dielectric constants, and I – E characteristic according to the TMCS concentration in n -hexane modifying solution was explained in the view-point of the nature of wet-gel structure. However, because of the additional increase in the strength of network and the effective exchange of surface terminal –OH groups with –OSi(CH 3 ) 3 groups even with low concentration of TMCS, there were no serious changes in the properties of SiO 2 xerogel film pre-aged for 12 h at 70°C.

Investigation of the properties of organically modified ordered mesoporous silica films.

Organically modified, ordered mesoporous silica films, which can provide hydrophobicity and low polarizability to the framework, were prepared using Brij-76 block copolymer as a template. Due to a fast condensation reaction of the silica precursor, mesostructured silica films were not properly synthesized. To circumvent this problem, a synthesis procedure was modified to provide an enhancement of pore periodicity through the incorporation of methyl ligands on the framework. The micropore volume was reduced, and the pore size was enlarged, as the concentration of the methyl ligands on the framework was increased. A mesophase transition from a two-dimensional hexagonal structure to a body-centered cubic (BCC) structure was observed according to the concentration of incorporated methyl ligands. The mechanical properties of the fabricated films were investigated according to the pore ordering and film density. The mechanical properties of the films with random pore geometry show a positive correlation between film density and elastic modulus. Meanwhile, the mechanical behavior of organically modified mesoporous silica films with periodic pore distribution represents a negative correlation within a certain density range, which is advantageous to the low-k materials. Especially, film with a low micropore volume fraction and BCC pore ordering is more applicable to a low-k material due to low dielectric constant and high mechanical strength.

Control of surface residual OH polar bonds in SiO2 aerogel film by silylation

SiO2 aerogel film was effectively silylated with n-hexane solution containing 6 vol.% of trimethylchlorosilane (TMCS). Through the silylation, hydrophilic polar OH bond was exchanged with hydrophobic non-polar Si(CH3)3 bond. Approximately 12% of reduction in dielectric constant and almost 2 orders of improvement in leakage current were observed after the silylation. Silylation behavior was examined with various volume concentrations of TMCS. The silylation of SiO2 aerogel film with 70% porosity was maximized when using 6 vol.% of TMCS. The fully silylated film showed an excellent moisture-resistant behavior. Even after 5 days of exposure to an air atmosphere with 45–50% of controlled humidity, an increase in dielectric constant due to the generation of polar OH bond through moisture absorption was not observed. It was clearly revealed that the improved film properties such as low dielectric constant, low leakage current and high resistance to moisture absorption could be obtained by exchanging terminal polar OH bond with non-polar Si(CH3)3 bond by the silylation with TMCS.

Roughness and pore structure control of ordered mesoporous silica films for the enhancement of electrical properties

Mesostructured silica films with a well-ordered Im3m structure and enhanced surface properties can be synthesized by means of cosolvent addition and the optimization of sol aging time. Mesostructured silica films fabricated using ethanol, a commercial solvent, result in wavy surface properties induced by the Marangoni effect irrespective of rotation speed during spin coating. In order to improve the surface roughness, we used an ethanol-acetone mixture as a solvent with a certain molar ratio. Wavy and rough films could be avoided when the acetone molar ratio was optimized. The simultaneous increase of unit cell size and thickness of the film was observed when the amount of cosolvent was increased. The unit cell was also enlarged with sol aging time, and well-ordered mesoporous silica films could be synthesized by controlling the silica sol aging. The dielectric property could be improved by means of cosolvent addition only after the development of a highly ordered mesoporous nature of the film by calcinat...

Investigation of the effect of calcination temperature on HMDS-treated ordered mesoporous silica film.

To reduce signal delay in ultra-large-scale integrated circuits, an intermetal dielectric with low dielectric constant is required. Ordered mesoporous silica film is appropriate for use as an intermetal dielectric due to its low dielectric constant and superior mechanical properties. To reduce the dielectric constant, an ordered mesoporous silica film prepared by a tetraethoxysilane/methyltriethoxysilane silica precursor and Brij-76 block copolymer was surface-modified by hexamethyldisilazane (HMDS) treatment. HMDS treatment substituted OH with Si(CH(3))(3) groups on the silica surface. After treatment, ordered mesoporous silica films were calcined at various calcination temperatures, and the calcination temperature to obtain optimal structural, electrical, and mechanical properties was determined to be approximately 300 degrees C.

Atomic transport in thermal spike induced ion mixing

A simple relationship between the ratio of atomic transport induced by ion mixing and the activation energies for the impurity diffusion of constituents in a bilayer is presented to describe quantitatively the symmetric and asymmetric atomic transport in the thermal spike induced ion mixing. The model predicts fairly satisfactorily the trend of experimental observations in the bilayer systems which have near zero heats of mixing and relatively high spike activation energies. For instance, the Pd/Co bilayer system shows nearly symmetric atomic transport, since its constituents have similar activation energies for the impurity diffusion.

Effect of solvent on the preparation of ambient pressure-dried SiO 2 aerogel films

SiO2 aerogel film has a promising property as intermetal dielectrics (IMD) for its low dielectric constant. However, a stable and porous SiO2 aerogel film was not properly synthesized due to the rapid evaporation of solvent during spin coating even in a solvent saturated atmosphere. So less evaporative solvent, 2-methoxyethanol (2MeEtOH), was introduced and the properties of film were compared with films using conventional solvent, ethanol (EtOH). It was found that gelation was faster with 2MeEtOH than EtOH. Highly porous and three-dimensionally well microstructured SiO2 aerogel film could be fabricated with 2MeEtOH. The maximum porosity of the films using 2MeEtOH and EtOH was 85 and 71%, respectively. The amount of residual -OR, and -OH groups was smaller in the former. The compositional ratios of Si:O:C in the films were 1:2.1:0.2 for the former and 1:2.4:1.1 for the latter. And corresponded dielectric constants were 1.6 and 2.2, respectively.

Modification of GaAs and copper surface by the formation of SiO2 aerogel film as an interlayer dielectric

Abstract For the application of SiO2 aerogel film to GaAs based devices, the changes of interfacial chemical bonding state of HCl-cleaned (or S-passivated) GaAs surface were investigated using monochromatic X-ray photoelectron spectroscopy after immersing the GaAs in each constituent of SiO2 sol. A large amount of oxide was formed on the HCl-cleaned GaAs after the treatment using tetraethoxysilane and de-ionized water due to hydroxyl group in SiO2 sol, while the S-passivated GaAs was not oxidized. The interfacial surface of GaAs was also investigated after the removing SiO2 aerogel film formed by supercritical drying. The aerogel film showed 80% of porosity and low dielectric constant of 1.8. Normally the oxidation of GaAs was successfully suppressed with S-passivation, however during the supercritical drying due to the high temperature and pressure, S-passivation layer was completely decomposed, and GaAs-oxides and elemental As were generated somewhat, but less than the case of HCl-treated GaAs. Furthermore, the formation of SiO2 aerogel film on copper metal substrate was revealed to induce a modification of metal surface. The modified and oxidized state of copper surface formed during the formation of the aerogel film was found to be not greatly influenced on the leakage current behavior of SiO2 aerogel/Cu system.

Investigation on the interface formation of ambient-pressure-dried SiO2 aerogel film deposited on GaAs

The interfacial state between ambient-pressure-dried aerogel and GaAs has been examined with specific emphasis on the solvent of modification. Trimethylchlorosilane (TMCS), being widely used to modify aerogel, was shown to be inadaptable due to its constitutional chlorine, which formed HCl and then etched GaAs oxides on GaAs surface. The interface of GaAs with aerogel was roughly etched from the reflection of surface microstructure of aerogel. Therefore, surface modification of aerogel with TMCS induced a great damage to interfacial GaAs surface, resulted in the change of surface characteristics of GaAs, and finally induced cracks and a collapse of aerogel fractal structure. On the contrary, hexamethyldisilazane, another modifying agent for aerogel surface, represented a relatively good interfacial state, while aerogel could be successfully formed on GaAs substrate.