Toshihiko Itoga

Advantages of Fluorine Introduction in Boron Implanted Shallow p+/n-Junction Formation

The advantages of fluorine introduction on fabrication of shallow p+/n-junctions have been demonstrated. This was done by implanting fluorine onto the boron implanted p+/n-junction area prior to annealing. By introducing optimized amounts of fluorine, (1) the boron redistribution after annealing is suppressed, (2) the concentration of activated boron becomes higher, and (3) the leakage current level of the p+/n-junction decreases. These behaviors may be due to interactions between fluorine and defects in the silicon substrate or at the SiO2/Si interface.

Improvement of SiO2/Si Interface Properties Utilising Fluorine Ion Implantation and Drive-in Diffusion

Thermal drive-in diffusion of ion-implanted F atoms has been employed to fluorinate SiO2/Si interfaces and thereby improve their electrical properties. The interface state density can be lowered with little fixed charge generation. Correspondingly, pn-junction surface leakage current decreases. Furthermore, the interfaces can be hardened against hot-electrons due to Fowler-Nordheim current injection and avalanche current at the junction surface. As a result, a fluorinated MOSFET shows higher hot-carrier immunity. It is pointed out that there is an optimal F dose for these improvements to be achieved.

X‐ray photoelectron spectroscopy study of submonolayer native oxides on HF‐treated Si surfaces

This article investigates, by a novel spectral analysis technique, the possibility of applying conventional x‐ray photoelectron spectroscopy to characterize the initial oxidation process. Quantitative analysis of submonolayer native oxides is made possible by spectral decomposition of Si 2p into Si4+, Six+, and Si0+ based on the O 1s binding energy, and by calculation of the SiO2 and SiOx thicknesses using the decomposition results. Here, the sensitivity for oxide‐thickness change is about 1/10 monolayer. Using this technique, the initial oxidation processes of HF‐treated Si(111) and Si(100) are precisely characterized. The influence of the dissolved‐oxygen concentration in the HF solution is also investigated.

Development of Ammonia Adsorption Filter and Its Application to LSI Manufacturing Environment.

Activated carbon treated with a hydrogen salt is found to be effective in suppressing ammonia concentration in LSI cleanrooms. The hydrogen salt which contains neither phosphor nor metals is utilized. Its adsorption capacity is about 1000 mol/m3-carbon. This corresponds to a lifetime of about two years in an ordinary cleanroom. Compared to this, untreated activated carbon adsorbs less than 10 mol/m3, so it cannot be used for more than 10 days. A chemically amplified resist, known to be susceptible to degradation from alkaline gaseous substances in cleanrooms, is shown to maintain its 0.25-µm line and space patterns under hydrogen salt treated carbon filtered air, even when the developing is delayed for 60 min after excimer laser exposure.

Process and properties of Pt/Pb(Zr, Ti)O3/Pt integrated ferroelectric capacitors

Abstract A one-mask-patterned ferroelectric capacitor memory cell structures designed with a 0.5-μm feature size were fabricated. Oxygen plasma treatment after dry etching decreased the leakage current to as low as as-deposited film. The one-mask-patterned ferroelectric capacitors with switching charge almost equal to as-deposited film were achieved. Ferroelectric memories as dense as dynamic random access memories will become possible with this technology.

Intrinsic Gettering of Copper in Silicon Wafers

We have investigated the intrinsic gettering (IG) of Cu in silicon wafers Oxygen precipitates for IG were formed in wafers subjected to two-step annealing consisting of thermal treatment for 16 h at 800°C. then for 0-16 h at 1000°C. Cu was deposited on the back surface by dipping the wafers into a contaminant solution, and introduced into the wafer bulk from the back surface by heating for 5 min at 1000°C. The surface concentration of Cu was measured by total-reflection X-ray fluorescence. We found that the gettering efficiency, which was determined from the difference between the surface concentration on reference wafers and the corresponding concentration on the IG-treated wafers, depends on the Cu contamination concentration. Moreover, we used a simulation based on the Fokker-Planck equation to analyze the data with regard to the dependence of gettering efficiency on oxygen precipitate density. As a result, we have shown that the total number of oxygen precipitates, rather than their size determines the gettering efficiency. These experimental and calculated results can provide useful information for achieving effective IG of Cu.

The Effect of Isopropyl Alcohol Adsorption on the Electrical Characteristics of Thin Oxide.

The effect of isopropyl alcohol (IPA) adsorption on the electrical characteristics of thin oxide has been investigated. Metal-oxide-semiconductor (MOS) capacitors were fabricated on Si substrates after IPA was intentionally adsorbed on the substrate surfaces. The leakage current was raised in the low electric field region for the 5-nm-thick thin oxide due to increased IPA adsorption, but the leakage current was not affected in the 8- and 10-nm-thick oxides. Using X-ray photoelectron spectroscopy, we found that the heat treatment creates C-Si bonds in the oxide due to organic adsorbates including IPA. These bonds appear likely to cause weak points or prevent uniform oxidation. A pre-annealing treatment was found to be effective in suppressing the formation of the C-Si bonds.

A 7.03-/spl mu/m/sup 2/ Vcc/2-plate nonvolatile DRAM cell with a Pt/PZT/Pt/TiN capacitor patterned by one-mask dry etching

A ferroelectric memory cell with an area of only 7.03 /spl mu/m/sup 2/ designed with a 0.5-/spl mu/m rule has been fabricated. It performs Vcc/2-plate nonvolatile DRAM operation: ordinary DRAM operation and automatic nonvolatile writing when Vcc is shut down. A non-separated plate electrode and a capacitor patterned by one-mask dry etching reduce cell area. Planarization of the poly-Si plugs and the use of H-less metallization/passivation processes retain the PZT capacitor characteristics (Pr=50 fC/bit) and achieves ferroelectric write/read under /spl plusmn/2.5-V operation in 4-K bit memory cell arrays.

Radiation effects on fluorinated field oxides and associated devices

Fluorine has been introduced into the LOCOS field oxide by high-energy (2-MeV) F implantation and subsequent annealing at 950 degrees C for 60 min. Improved radiation hardness of the field oxide and its associated device parameters was observed. N-channel MOSFETs isolated by the fluorinated oxide exhibit a lower radiation-induced source-drain leakage current. This is attributed to the smaller density of radiation-induced positive oxide charge in the fluorinated field oxide compared to its control. This is consistent with experimental results showing that threshold voltage shifts of the field-oxide FETs are smaller than their control. In addition, the radiation-induced leakage currents of reverse biased n/sup +/p-junction diodes fabricated with the F implantation process are suppressed, suggesting that the generation of interface traps at the gate SiO/sub 2/-Si and the field SiO/sub 2/-Si interfaces is also reduced in the fluorinated devices. >

Influence of ion-implantation on native oxidation of Si in a clean-room atmosphere

Abstract We investigated the native oxidation of ion-implanted Si(100) surfaces in anticipation of a future necessity for controlling native oxidation during semiconductor device fabrication. Quantitative analysis of XPS spectra was used to estimate SiO2 and SiOx thicknesses. Native oxidation of Si(100) wafers in which were implanted with As, P, B or Si was examined. The results show that oxidation of As or P-implanted Si is much faster than that of Si without implantation, however, no conclusive difference was found between the oxidation rates of B or Si-implanted Si and that of Si without implantation. These results indicate that native oxidation is influenced mainly by the species of implanted ions. Neither ion-implantation induced defects nor surface roughness was found to have major effect on the native oxidation rate.