Yoji Mashiko

Formation Mechanisms of the Deformed Oxide Layer in a Tungsten Polycide Structure

Destructive oxidation mechanisms in a tungsten polycide structure were investigated. In the experiments, the dependencies of the variation in the process flow, structural variations and annealing temperature application on the formation of destructive oxidation were examined. Surface and structural analyses were performed using a variety of analytical techniques such as transmission electron microscopy. The deformed oxide layer, having a pathological morphology of the oxide surface, was formed on the silicide layer during the oxide process after the removal of the surface layer of silicon oxide that initially covered the crystallized silicide film. It was revealed that destructive oxidation resulted from the formation of volatile metal-oxides, which originated during the process of low temperature annealing in ambient O2.

Effects of N distribution on charge trapping and TDDB characteristics of N/sub 2/O annealed wet oxide

Wet pyrogenic oxide of different thicknesses was annealed in N/sub 2/O ambient and the N concentration in the films was studied by using SIMS (secondary ion mass spectroscopy). It was found that for a certain annealing time and temperature, the N concentration (at %) increases with decreasing wet oxide thickness and the location of the peak of N is observed near the interface of nitrided oxide and Si substrate. On the contrary, after nitridation the concentration of H is higher in the thicker wet oxide of thickness 100 /spl Aring/ and also does not change much from the surface to the interface. For the thinner wet oxide of thickness 40 /spl Aring/, the concentration of H is less and decreases toward the interface. Gate dielectrics were characterized using high-frequency and quasi-static measurements. After a constant current stress, a large distortion was observed for the N/sub 2/O annealed wet oxide of 98 /spl Aring/ whereas for the N/sub 2/O annealed wet oxide of 51 /spl Aring/ the distortion was small. With increasing stressing time, hole trap is followed by electron trapping for the wet oxide of 98 /spl Aring/ whereas for the N/sub 2/O annealed wet oxide of 51 /spl Aring/, hole trapping increases a little at the beginning and then saturates. From the TDDB characteristics, a longer t/sub BD/ was observed for N/sub 2/O annealed wet oxide of 51 /spl Aring/ compared to 98 /spl Aring/. From the experimental results, it can be suggested that the improved reliability of thin gate oxide is due to the large amount of N concentration near the interface only. Hence for the device fabrication process, if the wet oxide is nitrided in N/sub 2/O ambient, the reliability of gate oxide will be improved in the ultrathin region.

A New VLSI Diagnosis Technique: Focused Ion Beam Assisted Multi-level Circuit Probing

This paper describes a new VLSI diagnosis technique using the focused ion beam(FIB) technique combined with FIB assisted chemical vapor depostion of W films. It was found that this technique was very useful for failure analysis of VLSI by allowing for the capability of probing a specific internal circuit node on VLSI multi-level circuits. FIB induced damages on MOS transistors and methods to remove the dmages are also described.

Detection of defects in metal interconnects by the nonbias-optical beam induced current technique

The mechanism for detecting defects by the nonbias-optical beam induced current technique is clarified by examining images and conducting simulations. This technique, using an electromotive current as a result of optical laser irradiation with no application of voltage, is very useful for analysis of metal interconnect failure in ultra large scale integrated devices. The characteristic images obtained by this technique, consisting of pairs of bright and dark regions, reveal point defects, such as voids in metal stripes and vias. It is found, by examining the characteristic images of defects, that the electromotive current generated near the defects originates as a result of the thermoelectromotive effect. Furthermore, it is confirmed by thermal simulations and transient current simulations, that the asymmetric temperature profiles near the defects generate the electromotive current and show the characteristic images.

Generation kinetics of pyramidal hillock and crystallographic defect on Si(111) vicinal surfaces grown with SiH2Cl2

Abstract The generation kinetics and surface morphology of crystallographic defects were investigated on Si(111) vicinal surfaces grown with SiH 2 Cl 2 . By chemical etching observation, it was found that on the Si(111) 0° off surface with a small misorientation angle the crystallographic defect always develops as a pyramidal hillock with different apex morphology depending on the type of defect. Dislocations, stacking faults and polycrystalline Si are associated with hillocks with sharp and flat apexes and bright particles, respectively. On the other hand, no hillocks were observed on the Si(111) 4° off surface with a large step density irrespective of the existence of such defects. This drastic change of the surface morphology of the crystallographic defect indicates that the crystallographic defect can play the role of growth nucleus of the hillock with a large growth rate on the Si(111) 0° off surface, leading to the growth of a triangular hillock independent of the type of defect. Therefore, without chemical etching of the as-grown surface, the pyramidal hillock can be employed as a finger print of a crystallographic defect, whose type is distinguished by giving attention to its apex morphology. Furthermore, the crystallographic defect generation was observed to be hardly affected by increasing step density in spite of the drastic disappearance of the corresponding hillock.

Accurate Thickness Determination of Both Thin SiO2 on Si and Thin Si on SiO2 by Angle-Resolved X-Ray Photoelectron Spectroscopy

Thicknesses of both ultrathin silicon oxide on silicon substrate and ultrathin silicon on silicon oxide are accurately determined by angle-resolved X-ray photoelectron spectroscopy (AR-XPS). The effective attenuation lengths of Si 2p photoelectrons in silicon oxide, λO, and silicon substrate, λS, are accurately determined by considering the photoelectron yields in both materials, which were obtained experimentally from the damping of intensities of the plasmon-loss peaks therein. Photoelectron yields for silicon oxide and silicon substrate are YO = 0.91 and YS = 0.74, respectively, and consequently the relationship between λO and λS is λO=1.4 λS. The value of λS is accurately determined from the silicon-on-insulator (SOI) sample with a thickness of 5 nm to be λS = 2.3 nm and the value of λO is subsequently determined to be 3.2 nm. Finally, the value of λO is confirmed by comparing the oxide thicknesses of SiO2 on Si(100) systems determined by AR-XPS with those determined by ellipsometry.

Variation of Size and Density of Pyramidal Hillock during Epitaxial Growth of Silicon Using Dichlorosilane Gas

For Si epitaxial growth on Si(111) with dichlorosilane (SiH 2 Cl 2 ), the kinetics of nucleation and growth of pyramidal hillock (PH) has been investigated by measuring the variations of size and density of PH as a function of growth temperature, SiH 2 Cl 2 volume concentration, and gas pressure. The nucleation of PH can be considerably suppressed by reducing SiH 2 Cl 2 volume concentration or gas pressure under a constant SiH 2 Cl 2 mole concentration. The reason for the reduction in PH density is discussed in terms of the previous findings that the nucleation of PH is always associated with the existence of growth defects such as stacking faults, dislocations, or polycrystalline Si. Furthermore, the PH size increases in proportion to the layer thickness and decreases drastically as the PH density increases or the growth temperature is raised. This indicates that the growth of PH is dominated by three factors : layer thickness, distribution of Si adatoms into the individual PH, and surface migration of Si adatoms. Thus it is likely that PH plays a role of growth site as kink and step edge, whereas Si adatoms are more preferentially incorporated into step and kink sites during Si growth.

Evaluation of surface defects on SIMOX and their influences on device characteristics

Abstract Surface defects on two types HD SIMOX wafers that made of CZ wafers and epitaxial wafers as starting materials were examined for their shape and density. It was found that surface defects on HD SIMOX wafers were mainly classified into two categories. One was “pit-type” and another was “undulation-type”. It is considered that the former defects are originated from grown-in defects, such as COPs, and the latter defects are caused by SIMOX process, such as oxygen ion implantation and/or SIMOX anneal. Furthermore, deformations of surface defects by sacrificed oxidization for SOI thinning and the influences on GOI and BOX quality were investigated. It was found that some undulation-type defects that lost the SOI layers during SOI thinning degraded GOI and that some other undulation-type defects that lost aboriginally the SOI layers degraded both the GOI and BOX quality.

Kikuchi-Band Analysis of X-Ray Photoelectron Diffraction Fine Structure of Si(100) by Precise Angle-Resolved X-Ray Photoelectron Spectroscopy

X-ray photoelectron diffraction fine structure of Si(100) is studied with precise angle-resolved X-ray photoelectron spectroscopy. Polar-angle intensity distributions of the Si 2p photoelectron emission excited by Al Kα X-rays are measured from H-terminated Si(100) along some azimuthal angles, and are qualitatively interpreted using both forward-focusing peaks along zone axes and Kikuchi bands associated with planes of low indices ({220}, {400}, {111} and {311}). To confirm the interpretation experimentally, we prepare ultrathin Si(100) layers on SiO2 from silicon-on-insulator (SOI) wafers. The thicknesses of the ultrathin Si(100) layers are adjusted so that the SOI layer is thick enough to exhibit the forward-focusing peak along [100] but slightly thinner than the thickness in which the contribution of the Kikuchi pattern weakens. It is observed experimentally, for the first time, that the intensities of X-ray photoelectron diffraction fine structure due to Kikuchi lines decreases for such ultrathin Si(100), while the forward-focusing peak remains unchanged, as expected from our interpretation.

Direct observation of local strain field for ULSI devices

Abstract The in-depth profile of strain distribution from the silicon surface is one of the most important pieces of information for optimizing the device performance. The convergent-beam electron diffraction(CBED) method has been applied to analyze the local strain filed of the active regions for both test structure with the shallow trench isolation(STI) and the conventional LOCOS on a cross-sectional surface. As a result, strain distribution was observed successfully. It was found that the compressive stress exist all over the survey regions. The active region close to the bottom corner of the STI shows a larger stress than that of the conventional LOCOS. It is demonstrated that the CBED technique is very effective for the determination oflocal strain field in a small area of semiconductors and the optimizing of the STI structure andfabrication process.