Haruko Akutsu

10-15 nm ultrashallow junction formation by flash-lamp annealing

Flash-lamp annealing (FLA) technology, a new method of activating implanted impurities, is proposed. FLA is able to reduce the time of the heating cycle to within the millisecond range. With this technology, an abrupt profile is realized, with a dopant concentration that can exceed the maximum carrier concentration obtained by conventional rapid thermal annealing (RTA) or furnace annealing. In contrast to a laser annealing method, FLA can activate dopants in an 8-inch-diameter substrate and, simultaneously, strictly control diffusion of dopants so as not to melt the substrate surface by radiation. FLA presents the possibility of fabricating sub-0.1-µm MOSFETs with good characteristics.

Flash Lamp Anneal Technology for Effectively Activating Ion Implanted Si

Device miniaturization requires reduction of the thermal budget in the annealing process for ultra-shallow junction and ultra-thin gate oxide. Recently, spike anneal technology has considerably reduced the time of the heating cycle. In heating the substrate above 1000°C, however, the total time of ramp-up and rampdown takes 10 sec or above. In order to minimize the heating cycle, we newly developed a flash lamp anneal (FLA) technology. FLA was able to reduce the heating cycle within the millisecond range and was successfully applied to activation process by combining appropriate assist heating. In this paper, we first report fundamental results on electrical activation of impurities by using FLA technology.

Advanced Ion Implantation Technology for High Performance Transistors

Cryo-implantation technology is proposed for reducing crystal defects in Si substrates. The substrate temperature was controlled to be below at -160°C during ion implantation. No dislocation was observed in the implanted layer after rapid thermal annealing. Pn junction leakage was successfully reduced by one order of magnitude as compared with room temperature implantation. Precise dose control is indispensable in channel region of high performance MOSFETs. In order to improve the precision of implanted dose, chip size implantation technology without photoresist mask was developed. In this technology, chip-by-chip implantation can be carried out by step-and-repeat wafer stage, and different implantation conditions are available in the same wafer independent of wafer size.

Mechanism of Contact Resistance Reduction in Nickel Silicide Films by Pt Incorporation

Platinum (Pt) incorporation into nickel silicide (NiSi) films improves silicide characteristics such as lower contact resistance RC at silicide/Si interface and higher thermal stability. The impact of Pt incorporation is widely accepted and recognized in research field; however, the role of Pt in NiSi films has not been fully clarified so far. In this paper, the spatial distributions of Pt and dopants (i.e., arsenic and boron) in silicide films are studied at an atomic level analysis using local electrode atom probe. In particular, Pt and dopant distributions were investigated in detail both at silicide/Si interface and at silicide-grain boundary. Silicide-grain size was also analyzed at various Pt concentrations in silicide films, and the relationship between the Pt concentration and physical properties of Ni1-xPtxSi films is pointed out. Finally, for further CMOS device scaling, the benefit of higher concentration of Pt incorporation into Ni1-xPtxSi films is described.

Contact resistance reduction of Pt-incorporated NiSi for continuous CMOS scaling ∼ Atomic level analysis of Pt/B/As distribution within silicide films ∼

Platinum (Pt)-incorporation into nickel silicide films is the promising approach to reduce the contact resistance (RC) at silicide/Si interface. Physical properties of Ni1-xPtxSi films were investigated by using local electrode atom probe (LEAP); The distributions of Pt and dopants (such as As and B) were analyzed both at silicide/Si interface and at silicide grain boundary. The silicide grain-size miniaturization was clearly observed by Pt-incorporation. The impacts of silicide grain size on electrical properties and thermal stability were clarified depending on the Pt concentration. Finally, RC reduction depending on the incorporated-Pt concentration was experimentally shown in both nMOSFETs and pMOSFETs.

Pt Segregation at the NiSi/Si Interface and a Relationship with the Microstructure of NiSi

Nickel monosilicide (NiSi) is used for lowering the parasitic resistances in source/drain. However, NiSi has a disadvantage of lower thermal instability such as NiSi2 nucleation and agglomeration. We first reported Pt segregation was found at a NiSi/Si interface by Atom Probe (AP) analysis.[6] In this study, we found that the scheme of Ni silicide grain growth and the resultant NiSi crystal shape is strongly affected by the existence of Pt by utilizing AP analysis, TEM and FE-SEM. AP observations were carried on a Ni-Pt as sputterd sample and on a Ni-Pt as annealed sample. The depth profile for the sample after silicidation indicates Pt atoms are segregated at a NiSi surface and NiSi/Si interface. For the analysis of the Pt distribution in the sample after silicidation in more details, we thoroughly analyzed the 3D image as follows: a cylindrical part is extracted from the 3D image; it is divided into 5nm thick slices; and 2D images depicting density-distribution of Pt and As. From these 2D images, we found Pt atoms exist around NiSi grains. The Atom Probe result indicates that Pt atoms segregate at the NiSi surface, grain boundaries and NiSi/Si interface. Plane view TEM and FE-SEM observations were carried out on Ni(Pt) silicide and on Ni silicide without Pt to find the influence of the segregated Pt atoms on the microstructure of NiSi. The spindle shape of NiSi(w/o Pt) grains were observed on the former. On the other hand, we observed on the latter that the Pt addition affected the shape of the NiSi grains and changed NiSi grains to round polygonal shape and the average grain size became smaller. It can be said that the Pt addition suppresses a crystal growth along in a longitudinal direction of a grain. We speculate that fine round shape NiSi grains are formed as a result of the suppression of the anisotropic crystal growth by Pt segregation, and provide the improvement of the thermal stability of the NiSi film.

Investigation of the factors determining the SIMS depth resolution in silicon-isotope multiple layers

In order to identify their controlling factors, the depth resolution parameters for secondary ion mass spectrometry, which include the decay length and the standard deviation of the Gaussian function (also referred to as the depth resolution function), for silicon atoms in a silicon matrix with silicon-isotope multiple layers were investigated under oxygen (O2+) and cesium (Cs+) ion bombardments with a wide ion energy range (from 200 eV to 10 keV) and with several incident angles. The use of silicon-isotope multiple layers in this investigation eliminated the chemical segregation effect caused by the sample composition. Measures were also taken to prevent ripple formation on the sputtered sample surface. The obtained depth resolution parameters were proportional to E1/2cos θ, where E is the primary ion energy per atom and θ is the incident angle relative to the surface normal. The relationships for decay length and standard deviation were different for the Cs+ ion, the O2+ ion with full oxidization, and t...

Novel model of haze generation on photomask

ArF lithography sometimes generates the haze defects on the photomask substrate, resulting in serious yield deterioration in ULSI production. In order to solve this problem, experimental and theoretical studies have been carried out on the generated haze defects. In characterizing the haze defects, the composition and chemical structure of the haze defects were analyzed by focusing on 1.0 x 0.3μm sizes defects using Raman, ToF-SIMS and AES spectroscopy with their highest spatial and mass resolution level. To confirm the experimental analyses, theoretical ab initio molecular orbital calculations were carried out on the model compounds of the generated haze defects. These experimental and theoretical studies indicate that the haze defects on quartz surface consist of (NH4)2SO4 and that those on half-tone (HT) film surface, on the other hand, consist of (MoO3)x(SO4)y(NH4)z complex including Mo from HT film material. In the latter case, NH4 ion was observed only in surface region of the haze defects. Based on these results, we have proposed a novel model of haze generation mechanism on quartz and HT film surfaces of photomask substrate.

Depth profile analysis of helium in silicon with high-resolution elastic recoil detection analysis

Helium depth profiling in silicon was investigated by high-resolution elastic recoil detection analysis (HERDA) using a high-resolution Rutherford backscattering spectrometry system. A 0.7 μm Mylar film was installed in front of the detector of this system to eliminate the background signals originating from incident nitrogen ions scattered at the sample surface. This film successfully eliminated the background signals without the loss of helium signals or serious degradation of the depth resolution. The HERDA has several attractive features for helium depth profiling in silicon, including high sensitivity (detection limit of 1 at. % or less), excellent depth resolution (less than 1 nm), and good quantitative accuracy, giving it significant advantages over other surface analysis methods such as secondary ion mass spectrometry.

Matrix and element dependences of useful yield in Si and SiO2 matrices using laser-ionization sputtered neutral mass spectrometry

The element and/or material dependence of the useful yield in laser-ionization sputtered neutral mass spectrometry (SNMS) using a high-photon-flux laser was investigated. Useful yields obtained from Si, B, As, and O in Si and SiO2 matrices using both secondary ion mass spectrometry (SIMS) and SNMS were compared, and the possibility of the accurate analysis of impurities in multilayers was investigated in terms of tunnel ionization. The behavior of atoms released from the surface by ion bombardment was calculated, and it was considered that the flying speed of sputtered atoms depends on the mass and that this causes the elemental difference in the fractions of laser-irradiated atoms. In the case of SNMS, excluding O, whose ionization probability is considered to be much lower than for the other elements, the useful yields of Si, B, and As are within 1 order of magnitude in both the Si and SiO2 matrices, and the difference between the matrices for each element is within a factor of two. These differences are much smaller than in the result of SIMS. It was confirmed that the distribution of B in a SiO2/Si stacked layer can be analyzed more accurately by SNMS than by SIMS. SNMS with a high-photon-density laser is considered to be effective for the analysis of more than one element in multilayers.The element and/or material dependence of the useful yield in laser-ionization sputtered neutral mass spectrometry (SNMS) using a high-photon-flux laser was investigated. Useful yields obtained from Si, B, As, and O in Si and SiO2 matrices using both secondary ion mass spectrometry (SIMS) and SNMS were compared, and the possibility of the accurate analysis of impurities in multilayers was investigated in terms of tunnel ionization. The behavior of atoms released from the surface by ion bombardment was calculated, and it was considered that the flying speed of sputtered atoms depends on the mass and that this causes the elemental difference in the fractions of laser-irradiated atoms. In the case of SNMS, excluding O, whose ionization probability is considered to be much lower than for the other elements, the useful yields of Si, B, and As are within 1 order of magnitude in both the Si and SiO2 matrices, and the difference between the matrices for each element is within a factor of two. These differences ar...