Etsuro Morita

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.

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.

Effect of SC1 Process on Silicon Surface Microroughness and Oxide Breakdown Characteristics

Surface microroughness and its effects on dielectric breakdown characteristics have been investigated for silicon wafers treated in SC1-based solutions. Surface microroughness was quantified using atomic force microscopy (AFM) and phase shift interferometry (PSI). In contrast to previous reports that SC1 treatment caused undulation of the surface, our observation showed a nominal amount of deterioration. Even prolonged dipping in a solution with high etching rate did not roughen the surface, and the dielectric breakdown characteristics were not affected.

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.

Characterization of thin bonded silicon-on-insulator structures by the microwave photoconductivity decay method

Thin silicon-on-insulator (SOI) layers of 0.5–2 µ m thickness are characterized by the microwave photoconductivity decay (µ-PCD) method with an N2 laser as the excitation source. The penetration depth of the N2 laser light is less than 0.1 µ m, and thus the excess carriers are excited only in the SOI layers. The measured recombination lifetime is sensitive to SOI thickness and interface properties, and thus the µ-PCD method can be used for characterization of the interface and observation of thickness variation. The surface (interface) recombination is considered as the dominant recombination mechanism.

Contactless Estimation of the Surface Recombination Velocity at High-Low Junction Surfaces Fabricated by the Ion-Implantation Technique

Surface properties of ion-implanted silicon are investigated by the microwave photoconductivity decay method. The effective surface recombination velocity (S) is estimated by fitting of the experimental decay curve of excess carrier concentration with a theoretical decay curve. The results show that S is almost inversely proportional to the carrier concentration of the heavily doped layer formed by the ion-implantation for both types of high-low junction ( n+n, p+p). Thus the present method is a powerful tool for surface characterization.

Wet Cleaning (Part 4): Micro-Roughness and COPs Created by SC-1

Although over thirty years have passed since Kern first introduced RCA cleaning, at present it is still the fundamental method of cleaning wafers [1]. Ammonia water and hydrogen peroxide solution (SC-1) provide the optimum cleaning method for removing particles. In order to remove particles, it is necessary to have etching action in SC-1 cleaning, and etching depth and particle removal capability are related.

Contactless Evaluation of the Surface Recombination Property of Silicon with an Ion-Implanted Layer

The surface properties of silicon are investigated by the noncontact laser (λ=774nm)/microwave method. The effective surface recombination velocity (S eff ) at an n + n high-low junction interface is estimated by fitting the experimental decay curve for excess carriers with the theoretical decay curve. The results show that Seg decreases as the dopant concentration increases and that Seff at the n+n high-low junction formed with a dose of 1×l0 15 ions/cm 2 has values lower than 1 cm/s. And it is shown that Scff is inversely proportional to the potential barrier height of the n + n high-low junction. Similar results are obtained using an N 2 laser (λ=337.1nm) instead of a laser diode (λ=774nm, 904nm) as a carrier excitation pulse source.