Kazuhide Ino

ION ENERGY, ION FLUX, AND ION SPECIES EFFECTS ON CRYSTALLOGRAPHIC AND ELECTRICAL PROPERTIES OF SPUTTER-DEPOSITED TA THIN FILMS

The effects of ion bombardment conditions on the crystallographic and electrical properties of tantalum thin films grown on SiO2 and Si have been systematically investigated in Ta thin film formation process employing low-energy (<100 eV) inert-gas ion bombardment on a growing film surface. It is demonstrated that the properties of Ta films are strongly dependent upon ion energy and ion flux as well as substrate materials. The bcc-Ta can be formed on SiO2 by controlling impinging ion energy and normalized ion flux defined as the ratio of ion flux to Ta flux ranging lower than 20 eV and higher than 13, respectively, for Ar plasma. Based on these results, low-resistivity bcc-Ta thin films (14.8 μΩ cm at 300 K) have been successfully formed. It is also experimentally shown that the irradiation by ions with different mass numbers has different effects on growing film properties, even if the energy or momentum of the ions is the same. When normalized ion flux is 26, bcc-Ta films can be grown on Si at ion energ...

Tantalum-gate thin-film SOI nMOS and pMOS for low-power applications

The threshold voltages of thin-film fully-depleted silicon-on-insulator (FDSOI) nMOS and pMOS have been controlled by employing tantalum (Ta) as the gate materials. Ta-gate FDSOI MOSFETs have excellent threshold voltage control for 1.0 V application on low impurity concentration SOI layers in both nMOS and pMOS. The low-temperature processing after the gate oxidation step leads to good on/off characteristics in Ta-gate SOI MOSFETs because of no reaction between Ta gate electrode and SiO/sub 2/ gate insulator. This technology makes it possible to drastically decrease the number of the process steps for CMOS fabrication, because the same gate material is available for both nMOS and pMOS.

Plasma enhanced in situ chamber cleaning evaluated by extracted-plasma-parameter analysis

We have demonstrated that high-efficiency in situ chamber cleaning with short gas residence time is possible for SiO/sub 2/ etching chambers by use of NF/sub 3/ plasma, and that the endpoint determination of the cleaning is possible by monitoring the optical emission intensities of CO or H. Nitrogen trifluoride (NF/sub 3/), which has a low N-F bond energy, can generate a plasma with a high density of ions and radicals featuring low kinetic energy. The cleaning efficiency of several halogenated-gas plasmas has been evaluated based on extracted-plasma-parameter analysis. In this analysis important plasma parameters, such as ion energy and ion flux density, can be extracted through a simple rf waveform measurement at the plasma excitation electrode. The accuracy of this technique has been confirmed with a newly developed rf plasma direct probing method and by ion current measurements.

Gate oxide reliability concerns in gate-metal sputtering deposition process: an effect of low-energy large-mass ion bombardment

Abstract The effects of ion species/ion bombardment energy in sputtering deposition process on gate oxide reliability have been experimentally investigated. The use of xenon (Xe) plasma instead of argon (Ar) plasma in tantalum (Ta) film sputtering deposition for gate electrode formation makes it possible to minimize the plasma-induced gate oxide damage. The Xe plasma process exhibits 1.5 times higher breakdown field and five times higher 50%-charge-to-breakdown ( Q BD ). In the gate-metal sputtering deposition process, the physical bombardment of energetic ion causes to generate hole traps in gate oxide, resulting in the lower gate oxide reliability. The simplified model providing a better understanding of the empirical relation between the gate oxide damage and the ion-bombardment energy to gate oxide in gate-metal sputtering deposition process is also presented.

Improvement of gate oxide reliability for tantalum-gate MOS devices using xenon plasma sputtering technology

The effects of ion species in the sputtering deposition process on gate oxide reliability have been experimentally investigated. The use of xenon (Xe) plasma instead of argon (Ar) plasma in tantalum (Ta) film sputtering deposition for gate electrode formation makes it possible to improve the gate oxide reliability. The Xe plasma process exhibits 1.5 times higher breakdown field and five times higher 50%-charge-to-breakdown (Q/sub BD/). In the Ta sputtering deposition process on gate oxide, the physical bombardment of energetic inert-gas ion causes the generation of hole trap sites in gate oxide, resulting in the lower gate oxide reliability. A simplified model providing a better understanding of the empirical relation between the gate oxide damage and the inert-gas ion bombardment energy in the gate-Ta sputtering deposition process is also presented.

Highly-reliable, low-resistivity bcc-Ta gate MOS technology using low-damage Xe-plasma sputtering and Si-encapsulated silicidation process

We present for the first time highly reliable metal-gate MOS technology with low-resistivity bcc-Ta. Low sheet resistance of 1.7 /spl Omega//sq. has been obtained by precisely controlling the ion bombardment conditions during Ta sputtering process, and by employing Si-encapsulation technique to suppress oxidation or hydrogen-accumulation in Ta thin film. By comparing Ta-gate and poly-Si gate MOS devices, it is confirmed that Ta-gate structure does not induce significant degradation in the gate-oxide reliability by using low-damage Xe-plasma sputtering and the Si encapsulation technique. It is also demonstrated that carrier mobility/velocity in the inversion layer of Ta gate SOI MOSFET is slightly higher than that of poly-Si gate SOI MOSFET because of higher thermal-conductivity of the metal gate.

In situ chamber cleaning using halogenated-gas plasmas evaluated by plasma-parameter extraction

We have demonstrated that high-efficiency in situ chamber cleaning with high gas flow rate is possible for SiO2 reactive-ion-etching chambers by use of NF3 plasma. The plasma of NF3 gas, which has a low bond energy, can generate a high density of ions and radicals with low kinetic energy. The cleaning efficiency of several halogenated-gas plasmas has been evaluated based on extracted-plasma-parameter analysis. In this analysis important plasma parameters, such as ion energy and ion flux density, could be extracted from a simple rf waveform analysis at the excitation electrode. The accuracy of this technique has been confirmed with a newly developed rf-plasma direct probing method. Furthermore, the waveform of the rf-excited plasma potential has been directly measured by the rf-plasma probing method, which has clarified the relationship between the plasma potential and the rf electrode voltage.

Formation of Ultra-Shallow and Low-Reverse-Bias-Current Tantalum-Silicided Junctions Using a Si-Encapsulated Silicidation Technique and Low-Temperature Furnace Annealing below 550°C

Low-temperature processing, below 550°C, has been developed to form ultra-shallow, low-leakage, and low-contact-resistance junctions with tantalum silicide. We have experimentally demonstrated that the amount of residual defects after ion implantation and subsequent low-temperature annealing is strongly dependent on the substrate dopant concentration for both n+p and p+n junctions. It is also confirmed that ion implantation through Ta is not the main factor inducing larger leakage due to metal-knock-on. As a result, ultra-low leakage current (7.8×10-10 A/cm2 and 6.6×10-10 A/cm2 for n+p and p+n junctions at reverse-bias of 5 V) and ultra-shallow junction depth (70 nm and 40 nm for n+p and p+n junctions) have been achieved in Ta-silicided junctions at an annealing temperature of as low as ~550°C, by employing an ultraclean ion implanter, Si-encapsulated silicidation, and low-dopant-concentration substrate.

IMPROVEMENT OF TURBOMOLECULAR PUMPS FOR ULTRACLEAN, LOW-PRESSURE, AND HIGH-GAS-FLOW PROCESSING

Turbomolecular pumps (TMP) have been widely used in low-pressure processing, because TMP can pump a large flow of gas as well as can exhaust the system to a suitable base pressure. A TMP, however, has the problem that its pumping speed is severely degraded at inlet pressures higher than ∼10 mTorr, where most of the low-pressure processing of semiconductor manufacturing is performed. In this study, it is confirmed that the occurrence of such a degradation in TMP performance is primarily determined by the inlet pressure of TMP and not by the outlet pressure. As the inlet pressure is increased to ∼10 mTorr, the gas flow in the front blades as well as the rear blades of the TMP goes into the transition flow, and TMP pumping speed consequently begins to decrease. Once the degradation occurs, however, the pumping speed is strongly dependent upon the pumping speed of the backing pumps, namely the foreline pressure. In order to improve the TMP performance under high gas flow, a characteristic dimension in the pum...

Enhancement of Silicon Epitaxy by Increased Phosphorus Concentration in a Low-Energy Ion Bombardment Process

For a low-energy (<30 eV) ion bombardment process, the effect of phosphorus concentration on low-temperature (350–400°C) silicon epitaxial growth is reported. The conditions of ion energy and ion flux required for realizing low-temperature epitaxial growth were precisely investigated. We found that phosphorus doping significantly enhanced silicon epitaxial growth. It is difficult to realize high-quality film growth with lightly phosphorus-doped silicon. However, large-mass, large-radius ion (xenon) bombardment is quite effective for improving the quality of silicon film with lightly phosphorus-doped silicon.