Masaru Kanamori

Comparison of two kinds of oxygen donors in silicon by resistivity measurements

Donor formation during heat treatment of silicon in the 550–800 °C temperature range has been investigated by resistivity measurements. The maximum donor concentration obtained here is about 1×1016/cm3 in p‐type Czochralski‐grown silicon. The donor is confirmed to be correlated with oxygen impurity as is the ’’thermal donor’’ formed in 300–500 °C annealing. The new donor, however, differs greatly in annealing behavior from the thermal donor. Preannealing at 470–550 °C and/or high carbon concentration promote the new donor generation at 650 °C annealing. A two‐step reaction is proposed to interpret the donor‐formation mechanism.

Method of making fault-free surface zone in semiconductor devices by step-wise heat treating

In a gettering method for processing semiconductor wafers a semiconductor wafer such as a silicon wafer is first annealed in a non-oxidizing atmosphere, for example, in a nitrogen atmosphere, at a temperature in the range of 950° to 1,300° C., preferably at 1,050° C., for more than 10 minutes, for example for four (4) hours, to diffuse out oxygen near the surfaces of the semiconductor wafer. Then the semiconductor wafer is annealed at a temperature in the range of 600° to 800° C., for example at 650° C., for more than one hour, preferably for 16 hours, to create in the interior of the semiconductor wafer microdefects of high density.

Thermally Induced Microdefects in Czochralski-Grown Silicon: Nucleation and Growth Behavior

The current understanding of thermally induced microdefects in Czochralski-grown silicon crystals is briefly reviewed and our investigations of the defects are described. The microdefects originate in oxygen precipitation occurring during thermal treatments after crystal growth. Both homogeneous and heterogeneous nucleation models have been proposed for the oxygen precipitation. The homogeneous nucleation model is contradicted because a low density of microdefects are induced in recent high-quality crystals even at high oxygen concentrations. A heterogeneous nucleation model is proposed, based on detailed investigations of the thermal behaviors of microdefects. It is demonstrated that the oxygen precipitation is governed by nucleation sites (carbon atoms) and the thermal history of wafers after crystal growth besides the oxygen concentration of the wafer.

Carbon and oxygen role for thermally induced microdefect formation in silicon crystals

Thermally induced microdefect formation phenomena are investigated in connection with oxygen and carbon in silicon crystals by using x‐ray diffraction, infrared absorption, and etching/optical microscope observation techniques. In order to investigate the carbon and oxygen role for microdefect formation, oxygen‐diffused floating‐zone‐grown silicon crystals, containing various carbon contents, are thermally treated. As a result, it is ascertained that the coexistence of both carbon and oxygen is necessary for the microdefect formation. It is also determined that the critical oxygen concentration for microdefect introduction by the heat treatment is about (5–6) ×1017 cm−3.

Heat‐treatment behavior of microdefects and residual impurities in CZ silicon crystals

Thermal behavior of both microdefects and residual impurities in pulled silicon wafers has been studied, using x‐ray diffraction and infrared absorption techniques. Several tens of wafers from different suppliers have been investigated after heat treatments at temperatures between 450 and 1250 °C. The results separate the wafers into two categories. In some wafers (category I), interstitial oxygen content is significantly decreased by heat treatments at temperatures between 650 and 800 °C. A high microdefect density is induced by heat treatment at a high temperature around 1050 °C. On the other hand, only slight oxygen reduction and defect introduction by heat treatments occur in other wafers (category II). Conversion from the category I to the category II wafers and vice versa are successfully performed by adding an appropriate preannealing. It is proposed that the wafer category depends on both the carbon content and thermal history of the crystal in addition to the oxygen content.

A study on thermally induced microdefects in czochralski-grown silicon crystals: Dependence on annealing temperature and starting materials.

Thermally induced microdefects in Czochralski-grown (CZ) silicon crystals have been investigated by both TEM and IR absorption techniques. Dependence of the defect behavior on both the annealing temperature and the starting materials was studied. It was found that the defect nature varies with the temperature, and that the defect density increases exponentially with the decrease of the annealing temperature. The increase in density also has a strong correlation with the initial carbon concentration in the wafer. It is concluded that the oxygen precipitates are heterogeneously formed at sites which have certain correlation with carbon atoms.

Behaviours of Thermally Induced Microdefects in Heavily Doped Silicon Wafers

Thermally induced microdefects in heavily doped silicon wafers are investigated. It has been shown that the generation of thermally induced microdefects is strongly affected by the type and concentration of dopants, and that microdefects necessary for intrinsic gettering are not easily generated in heavily doped n-type wafers. To generate the microdefects in heavily doped n-type wafers, an improved heat treatment procedure is developed. The observed results are discussed in terms of the difference of point defect density between p- and n-type wafers.

Photoluminescence analysis of annealed silicon crystals

The photoluminescence (PL) technique has been used in the analysis of heat‐treated silicon crystals to investigate the origin and the behavior of thermally induced defects. The PL measurements were made at liquid helium and liquid nitrogen temperatures on various groups of commercial wafers which were subjected to an isochronal annealing at a temperature between 450 and 1250 °C for 64 h. The PL results were compared with the results obtained by other characterization techniques, in particular, the infrared (IR) spectroscopy. After heat treatment at 450 °C, a new PL pattern appeared at 4.2 K, if the crystal contained a high concentration of oxygen. The new pattern is proved to be associated with the thermally induced donors. The PL and IR results classified Czochralski‐grown wafers into two categories. Various heat treatments made a great change in the PL spectra for some wafer groups (category I), but a little change for the other wafer groups (category II). Correspondingly, the decrease in the interstiti...

Microdefects Formed in Carbon-Doped CZ Silicon Crystals by Oxygen Precipitation Heat Treatment

In order to clarify the role of carbon regarding interstitial oxygen precipitation and secondary defect formation in a CZ silicon crystal, we performed various nucleating preanneals for carbon-doped (intentional) crystals and examined microdefect formation and the perfectness of the denuded zone by selective etching, TEM observation and spreading-resustance measurements following donor formation and angle lapping near the surface. In a high carbon content crystal many anomalies such as etch-pit density reduction, thermal-donor formation at 1000°C and large defect formation below the surface were observed. Carbon atoms acted as oxygen-precipitation nuclei, resulting the generation of a very small precipitate, which induced a low-density secondary defect and partly acted as a high-temperature donor. At an appropriate [Oi]/[C] ratio near the surface, large oxides were formed with secondary defects. The favorable carbon content for gettering site formation during a short time was estimated from these experiments.

Junction Leakage Current in BF 2 + -Implanted, Rapid-Thermal-Annealed Diodes

Junction leakage current was studied in shallow p+-n diodes formed by using BF+2-implantation and rapid thermal annealing (RTA). It is s hown that the bulk leakage component is 3 to 4 times larger in BF+2-implanted diodes than in B+-implanted diodes. Dislocations created in the BF+2-implanted layer during the RTA are not the direct cause of this leakage increase. It was also found that the surface leakage component is increased by the RTA. Rapid heat treatment may increase interface states and/or g-r centers in the Si/SiO2 interface layer.