Yasushi Shimanuki

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.

Effects of Thermal History on Microdefect Formation in Czochralski Silicon Crystals

The mechanism of formation of microdefects in Czochralski silicon crystals is investigated, with particular attention to the effects of the thermal history in the growth process on the nucleation and growth of oxygen precipitates. The density and size of the nuclei of oxygen precipitates in the asgrown state of a crystal subjected to a special thermal history are analyzed in detail. The behaviors of the nuclei at various temperature ranges of the thermal history are then discussed on the basis of these analyses.

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.

Origins of metal impurities in single-crystal Czochralski silicon

Abstract We examine the origins of metal impurities in Czochralski (Cz) single-crystal silicon in order to develop improved crystal purification techniques. We calculate the mass of metal impurities incorporated into molten silicon from each origin during crystal growth and estimate the concentration of impurities in the molten silicon and single-crystal silicon. To confirm these results, we analyze a sample of the residual melt after crystal growth. By comparing the calculated and experimental results, it is shown that the main origins of Al and Ni are probably the quartz crucible and polysilicon, respectively, while Fe originates from both. The calculated concentration of Fe and Ni in single-crystal silicon is 10 8 – 10 9 cm −3 , and that of Al is 10 11 – 10 12 cm −3 . We confirm that the concentrations of Fe and Ni can be reduced by using high-purity silicon as a raw material.

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.

Anomalous depth distributions of bulk microdefects in heat‐treated Czochralski silicon wafers due to nonequilibrium self‐interstitials

Anomalous depth distributions of bulk microdefects (BMDs) are observed in Czochralski silicon wafers subjected to two‐step annealing [(550–700 °C)×t1+(850–950 °C)×t2, where t1 and t2=1–100 h]. The number density of BMDs near the surface is smaller than that in the bulk when t1 is short, and is larger when t1 is long. The anomalous distribution extends deeper than 100 μm from wafer surfaces and cannot be explained by the behavior of interstitial oxygen atoms. Distributions are examined under various annealing conditions, such as annealing temperature, rate of temperature ramping, ambient atmosphere, and initial oxygen concentration. The anomalous distributions are found to be formed in the early stage of second‐step annealing only when the annealing starts with a rapid temperature rise. A formation model of anomalous distributions is proposed based on the following assumptions: (1) self‐interstitials exist in the thermal equilibrium state, (2) wafer surfaces are a permanent source and sink of self‐intersti...

Computer simulation of point-defect fields and microdefect patterns in Czochralski-grown Si crystals

Computer simulation of the point-defect fields in Czochralski Si crystals is reported. Our model includes the following factors: for crystals, variable pull rate V(t), the lagging of crystallization rate \widetildeV behind V, crystal length increasing with time l(t), temperature field T(r,z) dependent on l or \widetildeV, and actual shape of the crystal–melt interface; for native point defects, transport with the moving crystal, Fickian diffusion and thermodiffusion, the vacancy–self-interstitial recombination, and annealing at the crystal surface. Temperature fields established during crystal growth are calculated using a global model of heat transfer in the system. Important cases of variable V and pulling halts are considered. Simulations successfully reproduce experimental data such as the shape and position of the interstitial and vacancy regions, including the R-OSF bands. The values of model constants, except for the critical point-defect concentrations, are the same as those obtained for pedestal Si crystals.

Radial Distribution of Oxygen Precipitates in Czochralski Silicon Single Crystals

The effect of annealing conditions on the radial distribution of oxygen precipitates in Czochralski (CZ) silicon crystals was examined through two-step annealing. When the preannealing temperature was lower than 800°C, the oxygen precipitation depended on the initial oxygen concentration, and precipitation near the periphery of the crystal was often suppressed. When the preannealing temperature was higher than 900°C, the oxygen precipitation was enhanced near the periphery. This result indicates that extremely stable nuclei, whose density is low compared with the total amount of nuclei, exist near the periphery of the CZ crystals.