Nahomi Aoto

Device application and structure observation for hemispherical‐grained Si

A polycrystalline‐silicon surface with hemispherical grains (HSG) is deposited by low‐pressure chemical vapor deposition at 590 °C. At the temperature, 590 °C, the structure of the Si film just after deposition is amorphous, but crystallization of the amorphous Si occurs to produce HSG‐Si during annealing after deposition. The HSG‐Si is formed by the nuclei generation on the clean amorphous‐Si surface and by the crystalline growth during annealing. The surface area of the HSG‐Si film is about twice as large as Si films deposited at other temperatures. By applying the HSG‐Si film as the storage electrode for a 64‐M‐bit dynamic random access memories (DRAM) stacked‐capacitor with a SiO2/Si3N4 dielectric film, a capacitance of twice the value is obtained. The increase of the capacitance makes it possible to reduce the DRAM cell area, even by using a relatively thick dielectric film for higher reliability.

Low-energy electron energy loss spectroscopy of Cl adsorbed Si(111), Si(100) and Si(110) surfaces

Abstract The chlorine adsorption on Si(111)7×7, Si(100)2×1 and Si(110)16×2 surfaces is studied by low-energy electron energy loss spectroscopy (LEELS), Auger electron spectroscopy (AES) and reflection high energy electron diffraction (RHEED). Different primary electron energies are employed on the EELS measurement to vary the probing depth. The Cl/Si(111) surface shows one conspicuous LEELS peak which is related to the Cl(p z ) state, which forms a σ-like bonding state with the Si(p z ) state. The Cl/Si(100) surface shows two LEELS peaks presenting different depth profiles, which are thought to be related to the Cl(p z ) bonding state and to the Cl(p x , p y ) state, which forms a π-like bonding state. The difference of the LEELS spectra for different substrate orientations is attributable to different adsorption configurations; whereas Cl adatoms sit obliquely on Si atoms on the Si(100) and Si(110) surfaces, Cl adatoms sit on top of Si atoms on the Si(110) surface. The AES and RHEED results to the speculation that Cl adsorption does not function to resolve surface dimers but occurs, at dangling bonds on surface Si atoms and on steps.

An advanced technique for fabricating hemispherical-grained (HSG) silicon storage electrodes

In this new fabrication technology for high-density DRAMs, an electrode with even-surface amorphous-silicon is changed to one with uneven-surface hemispherical-grained Si (HSG-Si). This fabrication method consists of easily controllable processes: formation of smooth amorphous Si electrodes by low-pressure chemical vapor deposition followed by removal of native oxide and high-vacuum annealing. This annealing process can form HSG-Si covering the entire surface of all types of storage electrodes, including side-wall surfaces which had previously been dry-etched. The resulting storage electrode with HSG-Si can store 1.8 times as much charge as can be stored on an electrode without HSG-Si. Such an increase makes it possible to reduce the height of storage electrodes. This technique is applicable to the fabrication of high-density DRAMs. >

New stacked capacitor structure using hemispherical-grain polycrystalline-silicon electrodes

A new technology which makes storage electrode surfaces uneven has been developed for realizing 64 Mbit dynamic random access memories (DRAMs). This technology utilizes a Si film which is deposited by low‐pressure chemical vapor deposition at 550 °C and has hemispherical grains (HSG). The surface area of the HSG‐Si film is about twice as large as Si films deposited at other temperatures. The specific temperature, 550 °C, corresponds to the transition temperature of the film structure from amorphous to polycrystalline. By applying the HSG‐Si film as the storage electrode of a stacked capacitor, a capacitance of twice the value is obtained. The increase of the capacitance makes it possible to reduce the DRAM cell area, even by using a relatively thick dielectric film, thereby providing higher reliability.

Wafer Treatment Using Electrolysis-Ionized Water

Electrolysis-ionized water treatment is shown to be useful for removing polystyrene particles from contact holes, silicon surface cleaning and the removal of metal contamination such as copper. Electrolysis-ionized water has a controllable pH and a higher oxidation-reduction potential than chemicals. Moreover, this water does not contain acid or alkaline chemicals, and can easily be neutralized without adding chemicals. Electrolysis-ionized water treatment has great potential for ecologically safe and low cost semiconductor processing.

Native oxides on Si surfaces of deep‐submicron contact‐hole bottoms

The effects of cleaning and treatment on the characteristics of contact‐hole‐bottom Si surfaces are investigated in order to reveal the origin of the increased contact resistance and to find treatment processes that can be used to obtain low contact resistance. Contact‐hole‐bottom Si surfaces were analyzed by using thermal desorption spectroscopy, transmission electron microscope, and energy‐dispersive x‐ray spectroscopy. Nonpatterned Si surfaces, which roughly simulate the properties of the contact‐hole‐bottom Si surfaces, were also analyzed by using x‐ray photoelectron spectroscopy. It is revealed that suboxide‐rich native oxide layers are formed on dry‐etch‐damaged Si surfaces. The oxide layer persists after the samples are cleaned with a mixture of NH4OH, H2O2, and H2O, and with a mixture of HCl, H2O2, and H2O, and even after dipping in diluted HF. The roughly 1.3‐nm‐thick oxide layer remains at the plugging‐poly‐Si/Si–substrate interface, increasing the contact resistance. The carbon contamination in...

In situ electron spectroscopy study of Si surfaces after Ar‐ion‐assisted Cl2 etching

Si surfaces after Ar‐ion‐assisted Cl2 etching are studied with in situ observation methods. Low‐energy electron energy loss spectroscopy (LEELS), x‐ray photoelectron spectroscopy (XPS), Auger electron spectroscopy, and reflection high‐energy electron diffraction are employed for the analysis. Different primary electron energies are used on LEELS measurements to vary the probing depth from approximately 2 to 7 A. Etched surfaces show two conspicuous LEELS peaks that present different depth profiles. One of these peaks is related to SiCl3‐type surface reaction products detected with XPS, while the other peak is related to SiCl‐type surface reaction products. The SiCl3‐type reaction products exist at more superficial regions than those of the SiCl type. An amorphous reaction‐product layer is formed through ion mixing on Cl‐adsorbed Si surfaces by simultaneous supply of Cl2 molecules and an Ar‐ion beam. The results of this study provide new information for the understanding of the Si dry‐etching mechanism.

Cleaning Technologies using Electrolytic Ionized Water and Analysis Technology of Fine Structures for Next Generation Device Manufacturing

To reduce the consumption of chemicals and ultra pure water (UPW) in cleaning processes used in device manufacturing, we have developed wet processes that use electrolytic ionized water (EIW), which is generated by the electrolysis of a diluted electrolyte solution or UPW. EIW can be controlled for wide ranges of pH and oxidation-reduction potential. Anode EIW with diluted electrolyte, which has high oxidation potential, can remove metallic contamination such as Cu and Fe on Si surfaces. EIW contains less than 1/100 of the amount of chemicals contained in conventional cleaning solutions, thus drastically reduces chemical consumption in wet processes. Moreover, electrolyzed UPW can be used as a substitute for conventional UPW to achieve better rinsing characteristics. Electrolyzed UPW reduces the level of residual SO 4 2− ions after SPM cleaning more efficiently than conventional UPW. Thus the amount of rinse water needed is reduce to 1/6 that of the conventional UPW rinse. We also developed a method for analyzing remaining metallic contamination and residual ions in deep-submicron-diameter holes with high aspect ratios. The method is based on conventional atomic absorption spectrometry (AAS), and uses device patterns with high density contact holes. With this method, metallic (Fe) contamination on the order of 10 10 atoms/cm 2 can be easily analyzed inside 0.1 μm-diameter holes with an aspect ratio of 10. The residual ions in the fine holes can also be detected by thermal desorption spectroscopy (TDS).

INFLUENCE OF O2 AND OXIDE ON CL/SI SURFACE REACTIONS

Abstract Variation of Si(111) and Si(100) surface conditions under sequential Cl 2 exposure, O 2 exposure, and other O-related treatments are examined by Auger electron spectroscopy (AES) and low-energy electron energy loss spectroscopy (LEELS). Cl-adsorbed Si surfaces, particularly Cl-adsorbed Si(111) surfaces, have a passivation effect under dry O 2 atmosphere, where O adsorption and oxidation are suppressed. On the other hand, Cl desorption and oxidation take place immediately on Cl-adsorbed surfaces when exposed to wet environments: humid clean-room air or de-ionized water. When O 2 -treated Si surfaces are exposed to Cl 2 atmospheres, Cl adsorption occurs on SiO x but not on SiO 2 .

Multilayer resist dry etching technology for deep submicron lithography

Using an O2+HBr mixed gas plasma, multilayer resist dry etching under low substrate temperature is applied to the 0.25 μm design‐rule 256Mb dynamic random access memory fabrication. Anisotropic etching profiles with a critical dimension (CD) loss less than 0.02 μm are obtained by optimizing the amount of HBr in the plasma. With exceeding amounts of HBr, the pattern width varies with the spacing of the patterned lines due to variations of the thickness of deposited on the resist sidewall, causing a large CD loss. This phenomenon is named ‘‘the pattern‐dependent deposition.’’ An increase in the HBr flow rate enhances the pattern‐dependent deposition. It is also found that the resist overetching can cause the pattern‐dependent deposition. An electron dispersive x‐ray spectroscopy analysis reveals that under etching conditions of the pattern‐dependent deposition, the characteristics of deposited film are similar to that of an oxidized silicon film. In comparison, the deposited film is close to the silicon‐ric...