Seigo Kishino

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.

A new intrinsic gettering technique using microdefects in Czochralski silicon crystal: A new double preannealing technique

A new intrinsic gettering technique using microdefects in Czochralski‐grown silicon wafers is proposed where a new double preannealing technique is applied to the wafer before the conventional silicon process. In the first step, high temperature (∼1000 °C), nonoxygen ambient annealing is carried out in order to diffuse dissolved oxygen from near the wafer surface. In the second step, extremely low‐temperature (∼650 °C) annealing is added to introduce a high density of microdefects in the inner part of the wafer. This produces a wafer having both a nearly perfect denuded zone near the surface and a gettering site region in its bulk, regardless of the original quality of the wafer. This technique has proved to be effective in eliminating ion‐implanation oxidation‐induced stacking faults.

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.

Lifetime improvement in Czochralski‐grown silicon wafers by the use of a two‐step annealing

Minority‐carrier lifetime improvement by a two‐step annealing has been demonstrated using MOS capacitors fabricated on Czochralski‐grown (CZ) silicon wafers. It is shown that an intrinsic gettering effect does not always follow a single annealing in an oxygen‐free ambient, even in the wafers containing high oxygen content (∼1018 cm−3). This is probably because nuclei of precipitate‐dislocation complexes (PDC) are two small in size to grow into PDC during a single annealing of recent high‐grade CZ wafers. In the present study, an additional low‐temperature annealing at 800 °C is performed in order to improve the situation. A few critical conditions to the effectiveness of the intrinsic gettering are discussed in connection with the crystalline quality of the wafer.

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.

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...

Photoliminescence Analysis of `New Donors' in Silicon

An anneal around 650°C for a long duration introduces a new type of donors (new donors)in CZ–Si crystals. We have investigated the properties of the new donors by the photoluminescence method for the first time. The introduction of the characteristic broad bands (C-type pattern) in the PL spectra shows one to one correspondence with the generation of the new donors defined by the resistivity measurements. The appearance of the C-type spectra is enhanced by the presence of a high concentration of carbon (\gtrsim5×1016 cm-3) and/or the preanneal at 470°C.

X-ray channeling technique using anomalous transmission and its application to si micro-defects induced by heat treatment

X-ray channeling (XRC) technique using anomalous transmission is newly developed as a method of evaluating micro-defects in bulk single crystals. It is ascertained that there is a definite correlation between the decrease of the (hkl) anomalously transmitted intensity and the characteristic of the lattice defect. The present XRC technique has been tentatively applied to micro-defects (M.D.’s) induced in Si during heat treatment. As a result, it is conjectured that dislocation loops and stacking faults are preferentially induced during N2 atmosphere annealing at 1040‡C and wet O2 atmosphere annealing at 1100‡C, respectively, though precipitates are also generated during both annealings.