ICMCTF1998 Session HP: H - Posters

Wednesday, April 29, 1998 5:00 PM in Room Atlas Foyer

Wednesday Posters

Time Period WeP Sessions | Topic H Sessions | Time Periods | Topics | ICMCTF1998 Schedule

HP-1 The Interface Chemistry of Au/GaAs Dependent on the Surface Treatment Using HCI and (NH4)2) Ssub x
H.H. Park, M.G. Kang, S.H. Sa (Yonsei University, Korea)
In application of GaAs to device integration, the surface preparation of GaAs plays an important role on the performance and reliability of the device because the electrical properties of GaAs based device highly depend on the surface state. In particular, Schottky contact property at gate line is most sensitive to the nature of the prepared GaAs surface before the deposition of gate metal.Prior to gate metallization, the GaAs surface was passivated with sulfur ion using (NH4)2S-vapor, (NH4)2S-, (NH4)2Sx-, and Na2S-solutions and was characterized using X-ray photoelectron spectroscopy. With solution treatments the thickness of S-passivation layer was limited to mono-atomic layer or less than that due to the competition between etching and passivation, while (NH4)2S-vapor treatment showed the effective control of the thickness of S-passivation layer to several atomic layer. The composition of passivation layer was also highly dependent on the precleaned GaAs surface state, especially on elemental state. The GaAs surfaces with various composition and thickness of S-passivation layer were introduced into the gate metallization of GaAs MESFET, which forms AuGe/Ti/S/GaAs. The interaction between GaAs and metals was greatly influenced by the thickness and bonding states in the S-passivation layer, and made a significant influence on the Schottky barrier height, ideality factor, and transconductance.
HP-2 A study of the NiSi to NiSi2Transition in the Ni-Si Binary System
B.A. Julies, D. Knoesen (University of the Western Cape, South Africa); R. Pretorius (National Accelerator Centre, South Africa); D. Adams (University of the Western Cape, South Africa)

In this study an investigation into the Ni-Si binary system was made. Several techniques namely Rutherford Backscattering Spectrometry (RBS), Transmission Electron Microscopy (TEM), Scanning Electron Microscopy (SEM), Auger Electron Spectroscopy (AES) and X-ray Diffraction (XRD) were employed in the characterization of nickel thin films on silicon and the > respective silicides which were formed. Special attention was given > to the phase transition from NiSi to NiSi2.

Final > phase formation (NiSi2) was mainly examined at 750°C. A > SEM investigation showed that after 5 minutes of annealing islands of > NiSi2 was observed in a NiSi matrix. With longer annealing > times these islands grow laterally and eventually join up with > others. SEM shows that after the coalescence of individual > NiSi2 islands, holes appear on the grain boundaries. > As the NiSi2 phase continues to grow, these holes increase > in size and later take on the same crystal structure as the > surrounding cubic NiSi2 grains.

A model has been proposed to explain the NiSi to NiSi2 transition process.
HP-3 Effect of O2 Plasma Treatment on the Properties of SiO2 Aerogel Film
H.H. Park, H.R. Kim, M.H. Jo, J.K. Hong (Yonsei University, Korea)

In the down-scaling trend of ultra large scaled integration, SiO 2 aerogel film can be a promising material for intermetal dielectric with the inherent low dielectric constant. A TEOS-derived SiO 2 aerogel film by spin-coating and supercritical drying method shows a three dimensional network structure which results in a low density and large surface area. And due to the large internal surface area, the material and electrical properties of SiO 2 aerogel are closely related to the porous nature of the film and also the chemical species of surface coverage, such as organic groups, hydroxyl groups and adsorbed water.

In this work, O 2 plasma treatment using inductively coupled plasma at room temperature was conducted to control the surface chemical groups of SiO 2 aerogel films. Basic physical and chemical evolutions of films during O 2 plasma treatment were investigated by Rutherford backscattering spectroscopy, Fourier transformed infrared spectroscopy, and X-ray photoelectron spectroscopy and compared with the furnace annealed films. O 2 plasma treatment was effective to remove the surface organic groups and resulted the improvement of electrical characteristics. Because the temperature in O 2 plasma treatment was much lower than that in thermal annealing, O 2 plasma treatment is more suitable one for improving the properties of SiO 2 aerogel film.
HP-4 Microstructural and Compositional Investigation on Plasma Etching of SiO2 Aerogel Film
H.H. Park, S.J. Wang (Yonsei University, KOREA)
As an intermetal dielectric material, sol-gel derived SiO2 aerogel is a hopeful one in coming high speed device era. Porous structure by supercritical drying method plays a key role in low dielectric constant about 2. And this porous nature accompanies large surface area. But SiO2 aerogel is a sol-gel derived one, considerable amounts of C and H reside in SiO2 aerogel as the forms of hydroxyl(Si-OH) and organic (Si-OR : R = CH3, C2H5, etc). Because of these reasons, the etching of this material depends strongly on its microstructure and surface coverage.paragraphIn this work, the etching behavior of SiO2 aerogel was examined with the microstructural and surface chemical points of view. For this SiO2 aerogel and thermally grown SiO2 were etched with a magnetized inductively coupled plasma. CHF3, C2F6 and the mixture with H2 gas were used as etching gases. The plasma condition was monitored using optical emission spectroscopy. Surface morphology or inner structure were investigated using scanning electron microscopy. Surface bonding states were analyzed using Fourier transformed-infrared and angle-resolved X-ray photoelectron spectroscopy(XPS). XPS depth profile analysis was also conducted to monitor the transport of etching gases into the micropores of the film. Due to the porous structure and high C, H contents of the film unlike the other SiO2 materials, SiO2 aerogel showed the different etching behavior. The obtained results were compared with those of thermal SiO2 and the role of hydrogen during the etching was especially discussed.
HP-5 The Effect of Sol Viscosity on the Sol-Gel Derived Low Density SiO2 Xerogel Film for Intermetal Dielectric Application
H.H. Park, J.K. Hong, H.R. Kim (Yonsei University, KOREA)
In multilevel microelectronics, as feature size becomes much smaller, low dielectric constant film is of importance. SiO2 xerogel films have many excellent properties for intermetal dielectrics due to their unique porous structure formed during controlled drying process. Xerogel film with 50 % porosity shows dielectric constant 2.5 which is much lower than that of conventional CVD SiO2 film. Because the dielectric constant of SiO2 xerogel film mainly depends on its porosity, the control of film porosity is essential to lower the dielectric constant of xerogel film paragraphIn this work, the porosity of SiO2 xerogel film was controlled by varying the sol viscosity during the deposition of the films using spin coater. The density and porosity of xerogel film was deduced from refractive index measurement and RBS analysis. The network structure of xerogel film was evaluated using scanning electron microscope and transmission electron microscope. X-ray photoelectron spectroscopic and Fourier transformed - infrared spectroscopic analyses were also conducted to investigate the composition and surface bondings of the films. From the above analyses, it can be found that the dielectric property of the film mainly depends on the porosity but also on the surface bonding nature of the films.
HP-6 Chemical Mechanical Polishing of Hydrogen Silsesquioxane and Methyl Silsesquioxane Spin-On Polymers
M.-S. Tsai, T.C. Chang (National Nano Device Laboratory, Taiwan, ROC)

The incorporation of spin-on polymer (SOP) into multilevel interconnect necessitate the evaluation of chemical Mechanical polishing (CMP) compatibility of this thin film to achieve global planarization. Depending on the chemical composition of HSQ and MSQ silsesquioxane-based polymers which are partial substitutions of hydrogen and methyl groups, adequate slurry should be formulated for optimal polish results.

Slurry formulation for CMP of HSQ and MSQ SOPs is investigated in this study. Pre- and post-cured SOP thin films with various hydrogen or organic content are subjected to polish experiments using silica or CeO2-based slurry. Preliminary results show that, as the amount of hydrogen or organic content increase, CMP removal rate drops with conventional oxide-CMP slurries. A suitable oxidizer, such as hydrogen peroxide, is added to obtain enhanced removal rate of silsesquioxane SOP.
HP-7 Pad Chargeability in CMP
F.A Malik (EMMAY Associates/National College); M. Hassan (EMMAY Associates)

Polishing pad plays an important role in CMP. The dressability, chargeability and clean ability of the pad ensures manufacturability of the process. In order for the pad to deliver constant polish rate it has to be dressed, cleaned and then charged with slurry. Pad life is determined by its chargeability. Polish rate decay with use is a result of reduced chargeability of the pad. Almost all CMP users have incorporated pad dressing as an essential part of the process. Despite claims by vendors, dressing free pads have not been introduced successfully by IC manufacturers or silicon polishers.

Pad properties play an important role in its applications. In order to hold slurry the permeability of the pad is important. Pad density, hardness, roughness has to be considered as well. Pad development continues to be a challenge. Results of this investigation have been used to improve pad life and performance together with the development of a better pad that can deliver rate, uniformity and scratch free polishing.
HP-8 Computer Simulation of Processes in Electron Beam Lithography Resists on High Temperatue Superconductor Thin Films
Y.M. Gueorguiev, K.G. Vutova, G.M. Mladenov (Bulgarian Academy of Sciences, Bulgaria)
In the present work a numerical modelling of the processes of exposure and development of the resist during electron beam litho- graphy (EBL) on structures incorporating YBa2Cu3O7 high temperature superconductor (HTS) thin films is performed. Monte Carlo method is used to simulate the exposure of the resist by the accelerated elec- trons and to obtain radial distributions of absorbed electron energy density (the so called “proximity function”) for the structures 125 nm polymethylmethacrylate (PMMA) resist layer / YBa2Cu3O7 film of thick- ness d=0, 100 or 300 nm / SrTiO3 or MgO substrate at beam energies EO = 25, 50 or 75 keV. These distributions stored as areas of numerical data are approximated by a proper analytical function. The parameters of the function are calculated by means of an original Monte Carlo technique and are used as input data in the subsequent modelling of the process of electron resist development.
Time Period WeP Sessions | Topic H Sessions | Time Periods | Topics | ICMCTF1998 Schedule