Yoshinori Hayamizu

Enhanced nucleation of oxide precipitates during Czochralski silicon crystal growth with nitrogen doping

Thermal stability of oxide precipitate nuclei has been investigated for Czochralski silicon crystals with nitrogen doping. The experimental result indicates that generation of the grown-in oxide precipitate nuclei stable over 800 °C is enhanced by nitrogen doping. On the other hand, even though we confirmed this existence, doped nitrogen shows no influence on further oxide precipitate nucleation during the isothermal annealing at 600 °C after an epitaxial silicon growth process. Thus, it is found that the nitrogen doping only enhances the oxide precipitate nucleation at higher temperature during crystal cooling. The enhanced precipitate nucleation during the cooling is considered to be through excess vacancies which are suppressed to agglomerate by nitrogen.

Diffusivity of oxygen in Czochralski silicon at 400–750 °C

Diffusivity of oxygen in Czochralski silicon crystal in the temperature range of 400–750 °C has been determined from macroscopic oxygen precipitation behavior. The oxygen diffusivities at several nucleation temperatures from 400 to 750 °C were deduced from precipitated oxygen concentrations after a series of precipitate growth heat treatments, 800 °C/4 h and 1000 °C/16 h, using an extended nucleation theory. The measured oxygen diffusivity at 450–650 °C is 2–4×10−14 cm2/s, independent of the temperature, and considerably larger than the generally accepted normal diffusivity of Di=0.13 exp(−2.53 eV/kT). Moreover, the diffusivity at 450 °C is found to be roughly proportional to the interstitial oxygen concentration. It is suggested that this dependence of oxygen diffusivity on interstitial oxygen concentration can be explained by a model involving fast diffusing oxygen molecules.

Temperature dependence of minority‐carrier lifetime in iron‐diffused p‐type silicon wafers

Minority‐carrier recombination lifetime was measured with a noncontact laser/microwave method for nondiffused and iron‐diffused p‐type silicon wafers in the temperature range from 28 °C to 230 °C. The lifetime increased monotonically with temperature in nondiffused silicon, while the lifetime in iron‐diffused silicon showed a broad peak around 110 °C and a depression around 170 °C. The temperature dependence of the lifetime in iron‐diffused silicon was analyzed based on Shockley–Read–Hall statistics. The origin of the lifetime temperature dependence was attributed to the dissociation of iron‐boron pairs. Our experimental data supported that an electron trap for an iron‐boron pair at Ec−0.29 eV was more effective as a recombination center than a hole trap at Ev + 0.1 eV. It was also shown that the effect of iron in concentrations as low as 1×1011 cm−3 on the lifetime can be detected with the noncontact laser/microwave method.

Novel evaluation method of silicon epitaxial layer lifetimes by photoluminescence technique

A novel method, the short wavelength laser excited photoluminescence (PL) technique at room temperature, is applied to evaluate carrier lifetime characteristics of silicon epitaxial (epi) layers, which are grown on heavily doped p+ substrates with approximately 1019 cm-3 of boron. The band-edge PL intensity of the epi-layer is closely related to the carrier recombination lfietime at room temperature. The carrier excitation at 488 nm wavelength and the existence of the p/p+ structure, which acts as a stopper for the excess carrier diffusion, enable one to evaluate the epi-layer lifetime characteristics of the epi-layer thicker than 3 micrometers . Applying the method to epi-quality evaluation of the p/p+ epi-wafers, trace metallic contamination in epi-layers introduced by the epi- growth processes has been evaluated successfully. It has been found that a dilute HF cleaning is enough for the sample preparation instead of surface passivation heat treatment, which is usually required for other lifetime measurements. This is a great advantage of the method which enables one to do an in-line epi-quality monitoring. We also found that molybdenum contamination degraded the epi-lifetime and the time dependent dielectric breakdown of thin oxide films grown on p/p+ epi-wafers in this study.

EQUILIBRIUM CONSTANT OF SEGREGATION-INDUCED FE GETTERED BY HEAVY BORON DOPING IN SI

The equilibrium constant of segregation-induced Fe gettering by heavy boron (B) doping in Si is obtained by experimental determination of the activation energy and the site density parameter of the gettering reaction. The activation energy is determined to be 0.68±0.03 eV by analyzing the temperature dependence of the equilibrium constant of the reaction. This result indicates that the Fe gettering is strongly related to formation of the Fe–B complex whose binding energy is very close to the value determined for the activation energy. Furthermore, the gettering site density is found to be proportional to the doped B concentration in the substrate crystal. It is understood from the activation energy value that the Fe gettering ability of each reaction site for heavy B doping is less than that for thin polycrystalline Si film on the back surface of a substrate. The well known high overall gettering capability of the heavily B-doped substrate is not simply due to the activation energy effect it is predominan...

Creation of Bonded SOI Substrates with CZ Silicon Higher than 1000 Ωcm in Resistivity

1,. Introduction RF devices to create wireless communication systems require semiconductor material higher than 1.000 Qcm in resistivity in order to minimize energy loss due to eddy current in signal propagation. Since the concept of system LSIs has been widely spread, RF devices are designed as a part of LSI so that highly functional devices are proposed(l). Thus, ideal material for them is bonded SOI with base silicon (Si) wafers higher than 1000 Qcm in resistivity, as shown in Fig. L. Strong dernands of larger diarneter Si wafers have made us develop CZ wafers with such high resistivity instead of FZwaf.ers whose high resistivity is easily obtained. Usually CZ wafers are available in resistivity range lower than 100 Qcm. It is true when tight tolerance in resistivity is required. However, since wafers are used for base wafers in bonded SOI structure, the target to develop is just resistivity higher than 1000 Qcrn By controlling impurities effective to conductivity in source material such as poly-Si, CZ wafers with several thousand Qcm in resistivity were actually obtained. However, the other issue for high resistivity is oxygen donors. Oxygen donors are generated by the change of interstitial oxygen (Oi) in silicon when annealed at 450C(2). 450C annealing is common for aluminum sintering at the very end of device processes. The rate of resistivity drop by these donors depends on the arnount of Oi as well as annealing time at 450C. We have studied the effect of Oi donors on resistivity by using CZ wafers with several thousand Qcm in resistivity. This paper reports these results and will propose silicon wafers available for base wafers in bonded SOI.