Masakatsu Tsuchiaki

Self-aligned nickel-mono-silicide technology for high-speed deep submicrometer logic CMOS ULSI

A nickel-monosilicide (NiSi) technology suitable for a deep sub-micron CMOS process has been developed. It has been confirmed that a nickel film sputtered onto n/sup +/- and p/sup +/-single-silicon and polysilicon substrates is uniformly converted into the mono-silicide (NiSi), without agglomeration, by low-temperature (400-600/spl deg/C) rapid thermal annealing. This method ensures that the silicided layers have low resistivity. Redistribution of dopant atoms at the NiSi-Si interface is minimal, and a high dopant concentration is achieved at the silicide-silicon interface, thus contributing to low contact resistance. This NiSi technology was used in the experimental fabrication of deep-sub-micrometer CMOS structures; the current drivability of both n- and p-MOSFETs was higher than with the conventional titanium salicide process, and ring oscillator constructed with the new MOSFETs also operated at higher speed. >

A new charge pumping method for determining the spatial distribution of hot-carrier-induced fixed charge in p-MOSFETs

A charge pumping method is proposed for the direct measurement of the hot-carrier-induced fixed charge near the drain junction of p-MOSFETs. By holding the rising and falling slopes of the gate pulse constant and then varying the highest and lowest levels, the local threshold and local flatband voltages are readily obtained. The spatial distribution of fixed charges is directly calculated from the changes that occur in these curves after the application of stress. This method is quite simple and, specifically, requires no information about impurity concentrations in the substrate. The validity and reliability of the method have been supported by computer simulations. >

A NiSi salicide technology for advanced logic devices

A nickel-silicide (NiSi) technology for deep submicron devices has been developed. It was confirmed that Ni films sputtered on n- and p-single and polysilicon can be changed to mono-silicide (NiSi) stably at low temperature (600 degrees C) over a short period without any agglomeration. The NiSi layer did not absorb boron or arsenic atoms during silicidation, and a high concentration of boron or arsenic was achieved at the silicide/silicon interface, contributing to a low contact resistance. NiSi technology was applied to a dual-gate CMOS structure. Excellent pn junction characteristics and high drivabilities of both the n- and p-MOSFETs were successfully obtained.<<ETX>>

Very lightly nitrided oxide gate MOSFETs for deep-sub-micron CMOS devices

The characteristics and reliability of the nitrided oxide gate n- and p-MOSFETs with less than 1 atom% nitrogen concentration gate films were investigated in detail. These very light nitridations were accomplished using NH/sub 3/ gas at low temperatures from 800 degrees C to 900 degrees C. The low nitrogen concentrations, such as 0.13 atom% were obtained by SIMS and AES (Auger electron spectroscopy) measurements. The optimum nitrogen concentration region for the deep-sub-micron device is discussed. It was shown that, with the 0.5 atom% nitrogen concentration, good drivability and good hot carrier reliability were attained at the same time, and they were equivalent to those of the oxynitride gate MOSFETs using N/sub 2/O gas. The suppression of boron penetration is also discussed.<<ETX>>

Suppression of Thermally Induced Leakage of NiSi-Silicided Shallow Junctions by Pre-Silicide Fluorine Implantation

Thermally unstable NiSi films on shallow junctions induce a large leakage current upon heat treatment. To improve their thermal stability, using damage-free junctions formed by solid-phase diffusion, a sensitive and comparative investigation is conducted on the efficacy of pre-silicide ion implantation (PSII) of fluorine and nitrogen. After annealing NiSi silicided junctions, the basic and systematic monitoring of thermally induced leakage revealed that leakage suppression strongly depends on the element being implanted, i.e., F-PSII is found to be markedly superior to N-PSII. Even at a low F dosage, F-PSII attains a uniform and efficient leakage suppression of up to 6 orders of magnitude. Furthermore, unlike N-PSII, the suppression is achieved without any major disturbances to the critical characteristics of complementary metal-oxide-semiconductor transistors (CMOS) for ULSI application. The distinctive F presence around the NiSi/Si interface confers a substantial thermal stability to the NiSi film. The resulting effective blockage of Ni infiltration into a Si substrate, as well as the complete immobilization of Ni migration inside the Si substrate, leads to a drastic leakage suppression by F-PSII.

Substrate Orientation Dependent Suppression of NiSi Induced Junction Leakage by Fluorine and Nitrogen Incorporation

Using n+/p junctions formed by solid-phase diffusion, the efficacy of pre-silicide ion implantation (PSII) of fluorine and nitrogen on Si(110) for suppressing thermally induced leakage through NiSi-silicided shallow diodes is thoroughly examined in full contrast with Si(100). Unlike Si(100), N-PSIIs efficiency improves on Si(110) over F-PSII. Furthermore, whereas in-film F has no ability to reduce leakage, in-film N suppresses leakage. Thus, N-PSIIs leakage suppression is speculated to be mainly due to stabilization by N of abundant grain boundaries of highly oriented and finely structured NiSi films on Si(110), whereas leakage reduction by F-PSII is attained primarily by passivating the incoherent and unstable NiSi/Si(100) interface. From a practical point of view, in-film N incorporation offers a useful and complementary means of leakage suppression on Si(110) besides F-PSII, without any disturbance in contact resistance. Considering the vulnerability of Si(110) to light ion channeling, the best way to suppress leakage on a hybrid orientation substrate is a low-dose or selective F-PSII just prior to silicidation for Si(100), complemented by damage-free N doping or high-dose N-PSII together with source/drain implantation for Si(110).

Substrate Orientation Dependence of NiSi Silicided Junction Leakage Induced by Anisotropic Ni Migration in Crystal Si

Using n+/p junctions formed by solid-phase diffusion, the intrinsic leakage current induced by the NiSi thermal instability is thoroughly monitored for both Si(100) and Si(110) substrates to elucidate the crystallographic influence of Si. Although thermal instability caused by Ni clusters migrating away from the NiSi layers is confirmed for both substrates, the ways of leakage generation and associated Ni migration are notably different. The virtual immobility at the bottom of NiSi on Si(110) of otherwise mobile Ni clusters indicates effective in-plane diffusion along the horizontal (110) plane. The downward mobility at the Si(110) perimeter of otherwise impermeable Ni clusters at the bottom demonstrates the possible alignment of the migration plane on some {110} planes other than the horizontal (110) plane. The discrepancy observed in the deeper ingression of perimeter leakage along the [100] and [110] directions reveals a directional preference of Ni cluster migration even within the {110} planes. The crystal orientation dependence of the thermally induced leakage of NiSi junctions can be explained in terms of anisotropic Ni migration, whose diffusion ellipsoid is practically degenerated within one of the {110} planes and is elongated by a factor of 1.7 toward the direction.

Leakage Reduction by Thermal Annealing of NiPtSi Silicided Junctions and Anomalous Grain-Incompatible Pt Network

Using highly reliable damage-free junctions, the effectiveness and limitation of Pt addition for the stabilization of thin NiSi films are accurately specified and practically formulated in terms of the thermally induced leakage. In addition to the thermal leakage, the unexpected emergence of initial leakage is also witnessed and attributed to the emission of Si interstitials during silicidation and the subsequent formation of boron interstitial clusters. Rapid evanescence of the initial leakage by post-annealing is also successfully demonstrated owing to the Pt-induced thermal stabilization. Moreover, unlike other Pt distributions considered so far, Pt atoms are revealed to concentrate in a distinctive manner, forming an anomalous in-layer web-like structure which even extends within single NiSi grains. This grain-incompatible Pt network is thought to be a remnant of Pt-aggregation around grain boundaries of an earlier metal-rich silicide phase (e.g., Ni2Si), incorporated and left intact in the final phase (i.e., NiSi). Such intermediate-phase Pt-rearrangement may have interfered with the phase transition sequence and reoriented the final NiSi grains to constitute a crystallographically stable and thermally robust interface structure, resulting in the effective stabilization by Pt addition.

Drastic suppression of thermally induced leakage of NiSi silicided shallow junctions by pre-SALICIDE fluorine implantation

Thermally unstable NiSi films on shallow junctions are known to induce large leakage current on heat stimulus. Thus, a sensitive and comparative investigation is conducted on efficiency of leakage suppression by pre-SALICIDE ion implantation (PSII) for NiSi formation. F-PSII is found to be greatly superior to N-PSII. Unlike N-PSII, F-PSII drastically reduces the leakage without causing any major disturbances to critical CMOS characteristics. Leakage suppression up to 6 orders of magnitude is successfully attained.