Takashi Imaoka

Dependence of thin-oxide films quality on surface microroughness

The effects of silicon surface microroughness on electrical properties of thin-oxide films, such as breakdown electric field intensity (E/sub BD/) and time-dependent dielectric breakdown (Q/sub BD/), have been studied, where the microroughnesses of silicon and silicon dioxide surfaces are evaluated by the scanning tunneling microscope (STM) and the atomic force microscope (AFM), respectively. An increase of surface microroughness has been confirmed to severely degrade the E/sub BD/ and Q/sub BD/ characteristics of thin-oxide films with thicknesses of 8-10 nm and to simultaneously decrease channel electron mobility. An increase of surface microroughness has been demonstrated to originate mainly from wet chemical cleaning processing based on the RCA cleaning concept, particularly the ammonium-hydrogen-peroxide cleaning step. In order to keep the surface microroughness at an initial level, the content ratio of NH/sub 4/OH/H/sub 2/O/sub 2//H/sub 2/O solution has been set at 0.05:1:5 and the room-temperature DI water rinsing has been introduced right after the NH/sub 4/OH/H/sub 2/O/sub 2//H/sub 2/O cleaning step in conventional RCA cleaning procedure. >

Metallic Impurities Segregation at the Interface Between Si Wafer and Liquid during Wet Cleaning

It is crucial to make Si wafer surfaces ultraclean in order to realize low-temperature processing and high-selectivity in ultralarge scale integrated production. The ultraclean wafer surface must be perfectly free from particles, organic materials, metallic impurities, native oxides, surface microroughness, and adsorbed molecular impurities. Metallic contamination, the major type of contaminants to be overcome, has a fatal effect on device characteristics and must be suppressed to at least below 10 10 atom/cm 2 . The current dry processes, such as reactive ion etching or ion implantation, cause metallic contamination as high as 10 12 -10 13 atom/cm

Native Oxide Growth and Organic Impurity Removal on Si Surface with Ozone‐Injected Ultrapure Water

To manufacture ULSI devices with high performance and reliability in large volume, further integration and miniaturization are being promoted. The key issue in realizing what we call «Noise-Free Manufacturing» is to keep the wafer surface ultraclean all the time. To realize the ultraclean wafer, organic impurities adsorbed on the wafer surface must be removed first before other wafer cleaning procedures. This is because native oxide and metallic impurities on the wafer cannot be removed completely in the presence of residual organic impurities on the surface. The conventional wet cleaning process is designed to have the H 2 SO 4 /H 2 O 2 /H 2 O cleaning performed at the first stage to remove organic impurities on the wafer

Segregation and Removal of Metallic Impurity at Interface of Silicon and Fluorine Etchant

Realization of an ultraclean Si wafer surface is essential for achieving the advanced process in the ultralarge scale integrated production such as low-temperature process and high selectivity. An ultraclean wafer surface is defined as a surface completely free from particles, organic impurities, metallic impurities, native oxide, surface microroughness, and adsorbed impurities. Since metallic impurities, one of the above contaminants, cause fatal damage to device characteristics, metallic impurities on the wafer surface need to be suppressed at least below 10 10 atom/cm 2 which is the level of the detection limit of total reflection x-ray fluorescence

Advanced ultrapure water systems with low dissolved oxygen for native oxide free wafer processing

In the manufacture of submicron or deep submicron ULSIs, it is important to completely suppress native oxide growth on the silicon wafer surfaces. In a wet process, dissolved oxygen must be removed from the ultrapure water used for the final rinsing of the wafer. Two independent systems for the supply of ultrapure water, augmented with new techniques to remove dissolved oxygen, have been installed in the mini-super-clean room at Tohoku University. Both systems use two-stage dissolved oxygen removing methods. System one uses vacuum degassing through membrane and catalytic resin-based reduction, while system two uses vacuum degassing through membrane and nitrogen gas bubbling. Both systems can supply ultrapure water of 10 ppb or less in dissolved oxygen concentration. The concentrations of other impurities such as TOC, silica and total residue are also 1 ppb or less. >

Ozone Decomposition in Ultrapure Water and Continuous Ozone Sterilization for a Semiconductor Ultrapure Water System

Ultrapure water production technology is basic to ultralarge scale integrated (ULSI) manufacturing. To improve cleanliness on the Si surface, impurities in ultrapure water must be reduced. In a study of ozone behavior in ultrapure water the reaction order of ozone decomposition was 1.5 in ultrapure water inside oxidation-passivated stainless steel tubing. However, inside plastic tubing the reaction order of ozone decomposition was not 1.5 even when impurities including organic materials in ultrapure water were suppressed to an extremely low level. Oxidation-passivated SUS3 16L stainless steel resisted elution and ozone attack excellently

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).