Abstract: There is provided a method for calculating a more accurate metal impurity concentration contained in a silicon wafer by correcting measured values with a calibration based on a dependent relationship of the minority carrier diffusion length with a period of time elapsing from the activation to the actual measurement, an electric resistivity, and a temperature if there is such a relationship, in the measurement of the metal impurity concentration by utilizing the surface photovoltage. In the calibration step, such dependent relationship may be obtained by utilizing the metal impurity concentration measured by methods of different principles and actually measured values are corrected in light of the dependent relationship in the measuring step such that the metal impurity concentration is measured more accurately.

Abstract: There is provided a method for calculating a more accurate metal impurity concentration contained in a silicon wafer by correcting measured values with a calibration based on a dependent relationship of the minority carrier diffusion length with a period of time elapsing from the activation to the actual measurement, an electric resistivity, and a temperature if there is such a relationship, in the measurement of the metal impurity concentration by utilizing the surface photovoltage. In the calibration step, such dependent relationship may be obtained by utilizing the metal impurity concentration measured by a chemical method and actually measured values are corrected in light of the dependent relationship in the measuring step such that the metal impurity concentration is measured more accurately.

Abstract: In the wafer-bonding method of fabricating an SOI (silicon-on-insulator) substrate, even if there exists thickness variation in the silicon layer, devices fabricated onto the silicon layer, in accordance with the present invention, have a decreased threshold voltage variation. According to the present invention, after bonding two wafers, the thickness of the thinned silicon layer atop the SOI substrate is measured to precisely determine the local thickness distribution. However, the fabricated devices' threshold voltage depends upon the doping concentration as well as the thickness of the silicon layer. Shielding masks of photoresist are thereafter formed selectively on a portion of the silicon that are thicker. Then, through the masks as shielding, impurities are implanted into the silicon layer to adjust the doping concentration therein. Accordingly, the doping concentration is varied corresponding to the thickness, with the result that the threshold voltage variation nearly approaches zero.

Abstract: A surface processing method for evaluating semiconductor substrate is intended to clean a semiconductor substrate, which has the surface of a silicon layer exposed by removing the epitaxial layer by an acid mixture, by buffered HF and then to perform SC-1 cleaning. Placing the substrate for about 2 hours after the processing, then the varying rate of the SPV value is quite stable at about 5%, so that the minor carrier diffusion length can be measured with high precision. Furthermore, the lead time of evaluating a semiconductor substrate can be significantly reduced over the prior-art method.

Abstract: The present invention, a silicon-on-insulator (SOI) substrate and its fabrication method, is suited to the wafer-bonding method. A pre-oxidation treatment accompanying the oxidation treatment and the adhesive thermal treatment to prevent metal impurities from polluting semiconductor wafers. Before an oxide layer is thermally grown on one wafer or after two bonded wafers are subjected to a adhesive thermal treatment at a temperature T1, the pre-oxidation treatment is performed at a temperature of T2, which satisfies the relation equation of T1-300.ltoreq.T2.ltoreq.T1-100 (.degree.C.). Water steam, pure oxygen, or diluted oxygen, is conducted into the furnace, in which the pre-oxidation treatment is performed in an oxidation ambient. Accordingly, an oxide film having a predetermined thickness is formed on the surface of the SOI substrate serving as a barrier for preventing metal impurities, such as Fe, Cr, or the like, from invading the substrate and degrading the electrical characteristics thereof.

Abstract: An evaluation method to efficiently and precisely measure high-density oxygen-precipitation defects in the bulk of a silicon wafer is disclosed. A number of silicon wafers containing oxygen-precipitation defects are provided. The SPV method is utilized to measure the diffusion length of the minority carriers in the silicon wafers. The density of oxygen-precipitation defects is measured by the infrared tomography method. The diffusion length and the defect density are plotted and are found to be correlated. That is, the SPV measured diffusion length of the minority carriers and the defect density obtained by the infrared tomography method have specific relationships. A constant A can then be obtained from the plot. The diffusion length L of minority carriers in silicon wafers provided for evaluation is measured by the SPV method. Finally, the bulk oxygen-precipitation defects density can be calculated from the formula A.times.L.sup.-2.

Abstract: An evaluation method of a silicon wafer by correctly calculating the Fe--B concentration is disclosed. Even when the SPV method is utilized, the over-estimated Fe--B concentration in silicon wafers containing oxygen-precipitation defects can be avoided. Diffusion lengths Lb and La of minority carriers in a P-type silicon wafer before and after an activation step are measured by the SPV method. A value of (Lb--La)/Lb calculated from La and Lb is compared with a constant C which is read from the plot of Lb vs. (Lb--La). If (Lb--La)/Lb is smaller than constant C, the concentration calculation is terminated since there are oxygen-precipitation defects in the silicon wafer. The calculation is carried out for silicon wafers containing no oxygen-precipitation defects, and is based on the formula of Fe--B concentration (cm.sup.-3).apprxeq.1.times.10.sup.16 (La.sup.-2 --Lb.sup.-2).