Jiro Ryuta

Crystal-Originated Singularities on Si Wafer Surface after SC1 Cleaning

It is clarified that a new type of singularity is formed on Si wafer surface by the Standard Cleaning 1 (SC1) of the RCA cleaning process. Such singularities are perceived by laser particle counters as small particles on wafers. It is shown that the singularities correspond to small shallow pits caused by the etching effect of the SC1 cleaning solution. The origin of the pits is presumed to be some kind of defect in the melt-grown crystals.

Adsorption and Desorption of Metallic Impurities on Si Wafer Surface in SC1 Solution

Variation in the surface concentration of Fe, Ni, Cu and Zn on Si wafers due to treatment in NH4OH/H2O2/H2O solution is investigated. It is shown that adsorption and desorption of the metallic impurities occur simultaneously in the solution. The metal concentration on the wafer surface depends on the initial surface concentration, concentration in the solution, adsorption probability, desorption rate constant and the treatment time. The measured surface concentration is explained by taking into account the effects of these parameters. The variation in the desorption rate constant with the metal species, treatment temperature and the concentration in the solution is discussed.

Quantitative Analysis of Surface Contaminations on Si Wafers by Total Reflection X-Ray Fluorescence

A total reflection X-ray fluorescence (TRXRF) technique has been recently used to analyze metal contaminations on Si wafers. In this work, microdrop-contaminated Si wafers are used to make the calibration curves. Metal impurities in these wafers are shown to be condensed in a very small area near the center of the dropped area. To make the calibration curve, a relationship is derived between the intensity of the characteristic X-ray from metal impurities in the condensed area and that from the impurities uniformly distributed over the wafer surface. On the basis of this relationship, calibration curves for Fe, Ni, Cu and Zn are obtained.

Study of Si Etch Rate in Various Composition of SC1 Solution

Etching of Si wafer surface in an NH4OH:H2O2:H2O mixture (SC1 solution) is studied in regard to the effect of the composition of the solution. It is clarified that, when H2O2 concentration is constant, the etch rate increases linearly with OH- ion concentration and reaches a saturation etch rate. This saturation etch rate is inversely proportional to H2O2 concentration. Microroughness of Si surface after SC1 treatment is also investigated. It is also found that microroughness is independent of NH4OH concentration when the etch rate is kept constant.

Growth of Native Oxide and Accumulation of Organic Matter on Bare Si Wafer in Air

This letter reports the effect of organic matter on the growth of native oxide on a Si surface. Bare Si wafers and Si wafers with native oxide were stored under various conditions in a clean room and the thickness of native oxide was examined. In the case of the bare Si wafers, the native oxide hardly grew in a closed system but the native oxide grew to 6 A in an open system when the storage time was 24 h. On the other hand, in the case of Si wafers with native oxide, this suggests that accumulation of organic matter occurs on Si wafers in the open system in the clean room. It was suggested that the accumulation of organic matter on Si wafers facilitates the growth of native oxide.

Crystal Originated Singularities on Silicon Wafers After SC1 Cleaning

It is shown that a new type of singularity is formed on Si wafer surface by the Standard Cleaning 1 (SC1) of the RCA cleaning process″. Such singularities are perceived by laser particle counters as small particles on wafers. It is revealed that the singularities correspond to small shallow pits caused by the etching effect of the SCI cleaning solution. The origin of the pits seems to be some kind of defects in the melt–grown Si crystals. The authors named such “particles” as crystal originated “particles” (COPs). The size–distribution of COPs after single SC1 cleaning cycle is estimated on the basis of variation in the number of COPs with the repeated cleaning cycles. It is revealed that the crystal pulling rate affects the size distribution of COPs. As the pulling rate becomes faster, COP becomes larger in number. From the total number of COPs after the first cleaning cycle and the etching depth, the volume density of origin of COPs can be estimated. The results show that, as the pulling rate becomes faster, the volume density of origin of COPs increases.

Time-dependent variation of composition of SC1 solution

We investigated the time-dependent variation of composition of NH4OH/H2O2/H2O mixture, the standard cleaning 1 (SC1) solution in the RCA cleaning process. The NH4OH concentration decreased with time and that of H2O2 was almost constant. It was clarified that the decrease rate of NH4OH concentration depended on the temperature and H2O2 concentration in the SC1 solution. As the temperature was raised, the decrease rate accelerated. Conversely, as H2O2 concentration was raised, the rate decelerated. It is concluded that the hydrogen bond between NH3 and H2O2 prevents NH3 evaporation.

Effect of Native Oxide upon Formation of Amorphous SiOx Layer at the Interface of Directly Bonded Silicon Wafers

We have investigated the interface of directly bonded Czochralski silicon wafers with various thicknesses of initially grown native oxide film using high-resolution transmission electron microscopy (HR-TEM). It was found that the volume of the amorphous SiOx layer formed at the bonded interface decreased as the native oxide film thickness decreased. The estimated total number of oxygen atoms in the amorphous layer from HR-TEM observation was in fairly good agreement with the total number of oxygen atoms in the native oxide film. It is concluded, therefore, that the initial stage of the formation of the amorphous SiOx layer is mainly governed by the initially grown native oxide.

Measurement of Organic Matter on Si Wafer by Thermal Desorption Spectroscopy

Organic matter on a Si surface was investigated using thermal desorption spectroscopy (TDS). It was clarified that acetone, ethanol and toluene contaminants on a bare Si surface can be detected by the TDS system, ESCO EMD-WA1000K, and these organic contaminants have different desorption temperatures and fragment patterns. Therefore organic contaminants on Si wafers were thought to be separated by desorption temperature, and characterized from the fragment pattern at that desorption temperature. Here, the desorption temperature is thought to be proportional to the activation energy for desorption. Thus bonding strength between organic contaminants and the Si surface is qualitatively estimated from the desorption temperature.