Jae Gab Lee

Highly Conformal Deposition of Pure Co Films by MOCVD Using Co2 ( CO ) 8 as a Precursor

Highly conformal Co thin films were deposited on SiO 2 trenches with an aspect ratio of 13 by metallorganic chemical vapor deposition (MOCVD) using Co 2 (CO) 8 as a precursor in a low-temperature regime of 50-70°C where the growth rate was 3.5-7.0 nm/min. Lowering the pressure of the process reduces the number of collisions in the gas phase and, thus, widens the temperature regime in which the surface reaction controls the growth rate. A processing pressure of 26.7 Pa (0.2 Torr) allows for conformal deposition only at 50°C, whereas deposition at a reduced pressure of 4.0 Pa (0.03 Torr) widens the temperature regime (50-70°C) in which excellent conformality can be obtained. The confonnal Co thin film, produced at 50°C and 4.0 Pa, showed a resistivity of 10-12 μΩ cm and contained 1.0 atom % oxygen and less than 1.0 atom % carbon. After annealing this film at 600°C, its resistivity was reduced to 6 μΩ cm, which is close to the bulk resistivity (5.7 μΩ cm) of Co. Therefore, this low-temperature process, which allows for the excellent conformal deposition of pure Co films, can be utilized to produce silicided contacts for advanced devices which require a low contact resistance and good electrical performance.

A novel methodology on tuning work function of metal gate using stacking bi-metal layers

We demonstrate that the work function of a metal gate can be varied by inserting a very thin metal layer (metal A) between a thick metal (metal B) and the gate dielectric. The flat band voltage (VFB) of the MOS (metal-oxide-semiconductor) capacitor structure can be controlled within the range bounded by metal A and metal B individually, as demonstrated with various stacked bi-metal layers. For continuous thin layers, we speculate that the work function tunability may be due to the drastic change of the electron density in the thin continuous metal layer in direct contact with a bulk metal. This drastic change of electron density results in a larger junction depth than that expected for a bulk metal. Non-uniform thin layers also appear effective for work function tuning as well, and the observed VFB shift is attributed to the metal island formation at the dielectric/metal A interface.

Factors Affecting Passivation and Resistivity of Cu(Mg) Alloy Film

We have investigated the variables affecting passivation and resistivities of Cu alloy, which was sputter prepared from a Cu(6 at.%Mg) target. The results show that oxidation of Cu(Mg) alloy includes the surface segregation of Mg and its preferential oxidation. Sufficient surface segregation of Mg is necessary to form the high quality, protective MgO layer on the surface. The interfacial oxide layer produced from the reaction of Mg and SiO 2 does not serve as a barrier against Mg diffusion, thereby the generation of free Si seems to continue until Mg is exhausted in copper. Therefore, lowering the contents of Mg in copper is required to reduce the resistivity of Cu(Mg) alloy. In-situ heating of substrate is very effective to reduce the Mg contents in copper alloy and to enhance the surface segregation of Mg, thereby facilitating the passivation of Cu(Mg) alloy with the low resistivity, especially during the low temperature oxidation.

Ferroelectric properties of crystalline oriented Pb(Zr, Ti)O3 thin films prepared by sol-gel technique

Abstract Ferroelectric properties and reliability characteristics of (111) and (100) preferred tetragonal Pb(Zr 0.2 Ti 0.8 )O 3 (PZT) thin film capacitors have been investigated as a function of top electrode thickness. The (111) preferred films exhibit better squareness of the hysteresis loop with larger remanant polarization and coercive field than the (100) preferred films. Top electrode thickness dependence of switching polarization can be explained by the compressive stress induced by the top electrode annealing. The film with thinner top electrode shows less initial switching polarization, however, better endurance characteristics due to enhancing partial switching region.

Influence of annealing on the ferroelectric properties of Pt/Pb(Zr,Ti)O3/Pt thin film capacitors

The deformation in the hysteresis loop of Pt/Pb(Zr,Ti)O3/Pt capacitors has been investigated by varying the annealing temperature after patterning the top sputter-deposited electrode using reactive ion etching (RIE) with Ar gas. It was observed that as-patterned capacitors were positively poled by the dc plasma potential during RIE of Pt. Voltage shift and slant in the hysteresis loop are found to be due to space charges trapped at domain boundaries during both sputtering and RIE rather than a nonferroelectric second phase. As Zr:Ti ratio decreases, internal bias field increases, and annealing temperature, at which maximum in polarization occurs, also increases due to lower permittivity and higher Curie temperature.

Chemical Vapor Deposition Of Tin Films From Tetrakis(methylethylamido)titanium And Ammonia

TiN films were prepared using a new Ti precursor, tetrakis(ethylmethylamido)titanium (TEMAT) and ammonia. The premixing of NH3 and TEMAT provided the control over the gas phase reaction of the two reactants to generate the intermediates required for the deposition of high-quality TiN films. Film resistivities of 800–1200 µ Ω-cm and low levels of impurities were obtained in TiN films deposited under the condition of low NH3/TEMAT ratios, wafer temperature of 350°C and total reactor pressure of 1 Torr. In addition, the introduction of a small amount of ammonia improved the diffusion barrier property for Cu metallization up to 600°C. Slight degradation in the conformality of TiN films was observed at the low ratio of NH3/TEMAT. Furthermore, the addition of NH3 tended to improve the surface morphology of TiN films and did not cause any particle generation due to the low process pressure of 1 Torr. X-ray photoelectron spectroscopy (XPS) analysis revealed the role of ammonia in the homogeneous reaction.

Characteristics of ZrO 2 Thin Films by Atomic Layer Deposition for Alternative Gate Dielectric Applications

We investigated material and electrical properties of ZrO 2 films deposited by atomic layer deposition (ALD) using Zr t-butoxide and water (H 2 O). As-deposited ZrO 2 films show 2.4nm of CET measured at 100kHz with frequency dispersion and high leakage current (3A/cm2) at 1V. These undesirable properties may results from metallic Zr and carbon contamination in the films. The post-deposition annealing was performed in an O 2 ambient at 500 ¯ to improve the capacitance and reduce the leakage current. ZrO 2 films deposited by ALD and annealed at 500°C exhibit CET(Capacitance Equivalent Thickness) of 2nm without dispersion issues and leakage current less than 10 m 3 A/cm 2 at 1V.

A comparison of the mechanical properties of RF-and DC-sputter-deposited Cr thin films

Chromium (Cr) films were deposited on plain carbon steel sheets by DC and RF magnetron sputtering as well as by electroplating. Effects of DC or RF sputtering power on the deposition rate and properties such as hardness and surface roughness of the Cr films were investigated. X-ray diffraction (XRD), atomic force microscopy (AFM), scanning electron microcopy (SEM) analyses were performed to investigate the crystal structure, surface roughness, thickness of the Cr films. The deposition rate, hardness and surface roughness of the Cr film deposited by either DC or RF sputtering increase with the increase of sputtering power. The deposition rate and hardness of the Cr film deposited by DC sputtering are higher than those of the Cr film deposited by RF sputtering, but RF sputtering offers smoother surface. The sputter-deposited Cr film is harder and has a smoother surface than the electroplated one.

A comparison of transmittance properties between ZnO: Al films for transparent conductors for solar cells deposited by sputtering of AZO and cosputtering of AZO/ZnO

Aluminum-doped zinc oxide (AZO) thin films were deposited on sapphire (002) and glass substrates by two different sputtering techniques radio frequency magnetron cosputtering of AZO and ZnO targets and sputtering of an AZO target. The dependence of the photoluminescence (PL) and transmittance properties of the AZO films deposited by cosputtering and sputtering on the AZO/ZnO target power ratio, R and the O2/Ar flow ratio, r were investigated, respectively. Only a deep level emission peak appears in the PL spectra of cosputtered AZO films whereas both UV emission and deep level emission peaks are observed in the PL spectra of sputtered AZO films. The absorption edges in the transmittance spectra of the AZO films shift to the lower wavelength region as R and r increase. Effects of crystallinity, surface roughness, PL on the transmittance of the AZO films were also explained using the X-ray diffraction (XRD), atomic force microscopy (AFM), and PL analysis results.

Influences of hydrogen damages in ferroelectric thin film capacitors

Abstract During the CMOS process, ferroelectric capacitors show degraded ferroelectric properties due to a hydrogen involving process. When hydrogen diffused in PZT thin films through noble metal electrodes (such as Pt, Ir), XRD data indicate a change of lattice parameters and XPS spectra exhibit a change of Pb-O bond in crystalline perovskite phase. Especially, the variation of lattice parameter of PZT (Zr/Ti=20/80) depends on the thickness of top electrodes (Pt).