Taisuke Furukawa

Drivability improvement on deep-submicron MOSFETs by elevation of source/drain regions

Deep submicron MOSFETs with elevated source/drain (S/D) structures, where S/D extension regions were partially elevated besides deep S/D regions, were fabricated by use of Si selective epitaxial growth technique. As fairly compared with a well-developed conventional MOSFET, we clarify an advantage of the elevated S/D structures, i.e., improvement upon driving performance with keeping excellent short-channel characteristics, which is enhanced for decrease in gate sidewall spacer width. The experimental results are explained in terms of the reduction in S/D parasitic resistance by addition of the Si epitaxial layer where the impurity profile is suitable.

Parasitic Resistance Reduction in Deep Submicron Dual-Gate Transistors with Partially Elevated Source/Drain Extension Regions Fabricated by Complementary Metal-Oxide-Semiconductor Technologies

Deep submicron dual-gate metal-oxide-semiconductor field-effect transistors (MOSFETs) with partially elevated source/drain (S/D) structures were fabricated using complementary MOS (CMOS) technologies. In comparison with well-defined conventional MOSFETs, it is revealed that the drivability is appreciably enhanced by the S/D elevation and, further, that a p-channel MOSFET gains more from the S/D elevation than an n-channel MOSFET. Investigation of the parasitic resistance is consistent with the results of the transistor characteristics.

Low thermal budget surface cleaning after dry etching for selective silicon epitaxial growth

We studied the influence of plasma etching damage on epitaxial Si growth using ultrahigh vacuum chemical vapor deposition. The damaged layer induced on substrate surface had an amorphous structure that had some carbon, oxygen, and fluorine in its composition. The damaged layer was removed by in situ preheating above 850°C, before the growth, or by chemical dry etching (CDE). We found that CDE has the effect of decreasing the preheating temperature by 200°C as compared to the case without CDE. Furthermore, the dependence of the surface roughness of grown films on post-etching treatments is also discussed.

Selective Epitaxial Growth by Ultrahigh-Vacuum Chemical Vapor Deposition with Alternating Gas Supply of Si2H6 and Cl2

Selective epitaxial growth of Si using a Si3N4 mask has been carried out by ultrahigh-vacuum chemical vapor deposition with an alternating supply of disilane (Si2H6) and chlorine (Cl2) gases. In the present gas supply method, selectivity of Si to Si3N4 is attained mainly by etching of poly-Si deposited on Si3N4 with Cl2, while grown film structures depend on the substrate temperature and the total supply of Si2H6 and Cl2 gases. The passivation effect of chlorine on growing film surfaces dominates at a low growth temperature (600°C). On the other hand, the passivation effect weakens with increasing temperature and thus the epitaxial film thickness is determined by both the growth rate with Si2H6 and the etching rate with Cl2 on Si.

Recovery of time-dependent dielectric breakdown lifetime of thin oxide films by thermal annealing

Electrical properties of thin silicon dioxide films have been investigated for samples that suffered from the Fowler–Nordheim (F–N) stress and subsequent annealing. The time-dependent dielectric breakdown (TDDB) lifetime for samples after annealing >400 °C was found to be longer than that without anneal; about 60% of the amount of damage responsible for the lifetime was annealed out at a temperature of typically 800 °C for 30 min. On the other hand, capacitance–voltage (C–V) measurements indicated that trapped charges were almost annealed out even at a temperature of 300 °C for 30 min. Moreover, the reinjection of F–N current showed that the trapping sites of holes and electrons which are electrically neutral remained after the annealing of trapped charges at temperatures >300 °C. It follows that the recovery of TDDB lifetime presently observed through annealing at temperatures >400 °C was caused by the anneal of neutral trapping sites created by F–N stresses.

Significant Effects of As Ion Implantation on Si-selective Epitaxy by Ultrahigh Vacuum Chemical Vapor Deposition

The relation between As ion implantation and Si-selective epitaxy is investigated, taking account of the application of ultrahigh vacuum chemical vapor deposition to LSI devices. For a non-implanted wafer, undesirable island-like growth occurred because oxygen was introduced into the Si substrate by previous etching processes. The implantation of a sufficient dosage of As ions restored layer-by-layer growth with excellent surface morphology, which is explained in terms of the removal of the disturbed layer by the additional sputtering effect of ion implantation.

Si Deposition into Fine Contact Holes by Ultrahigh-Vacuum Chemical Vapor Deposition

An ultrahigh-vacuum chemical vapor deposition technique with disilane (Si2H6) molecular flux is applied to fine contact hole filling. Structural observations reveal that a completely buried Si contact has a stacked structure, in which the lower portion consists of pyramidal epitaxial Si, whose height depends not only on the growth temperature and the Si2H6 flow rate but also on the hole diameter, and polycrystalline Si is deposited on the epitaxial Si. The mechanism of selective epitaxy is interpreted in terms of incubation time and facet growth rate depending on growth temperature and Si2H6 flow rate.

Magnetic tunnel junctions for magnetic field sensor by using CoFeB sensing layer capped with MgO film

We evaluated MgO-based magnetic tunnel junctions (MTJs) for magnetic field sensors with spin-valve-type structures in the CoFeB sensing layer capped by an MgO film in order to obtain both top and bottom interfaces of MgO/CoFeB exhibiting interfacial perpendicular magnetic anisotropy (PMA). Hysteresis of the CoFeB sensing layer in these MTJs annealed at 275 °C was suppressed at a thickness of the sensing layer below 1.2 nm by interfacial PMA. We confirmed that the CoFeB sensing layers capped with MgO suppress the thickness dependences of both the magnetoresistance ratio and the magnetic behaviors of the CoFeB sensing layer more than that of the MTJ with a Ta capping layer. MgO-based MTJs with MgO capping layers can improve the controllability of the characteristics for magnetic field sensors.

Fatigueless Ferroelectric Capacitors with Ruthenium Bottom and Top Electrodes Formed by Metalorganic Chemical Vapor Deposition

Ferroelectric Ru/Bi4-xLaxTi3O12/Ru capacitors were fabricated by combining metalorganic chemical vapor deposition (MOCVD) of top and bottom Ru electrodes and spin-coating of the ferroelectric film. After optimization of the deposition conditions, good ferroelectric properties (2Pr=18 µC/cm2, Pr: remanent polarization) and low leakage current density (2×10-6 A/cm2) were achieved. No significant fatigue phenomenon (decrease of Pr) was observed even after 1010 switching cycles.

Initial stage of oxidation of Si(100) surfaces in dry oxygen

The initial stage of oxidation of hydrogen-terminated Si(100) surfaces in dry oxygen gas has been studied using Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, and atomic force microscopy. Heating the wafer up to 300°C in vacuum caused the desorption of hydrogen primarily from defects such as steps on the surface, and the following preoxidation in dry oxygen at 300°C progressed therein. The preoxides thus formed on surfaces were stable during thermal oxidation at 900°C, preventing an increase of the surface microroughness caused during heating the wafer at high temperatures. Such preoxides prior to thermal oxidation were also found to cause structural modification of very thin oxide films.