Hiroshi Takenoshita

Nondestructive Internal Observation and Distribution of Potential with Bias Application of npn Si Darlington Transistor Chip Using Electron-Acoustic Microscopy

Study of an npn Si Darlington transistor chip under bias application was carried out using electron-acoustic microscopy (EAM). The results were as follows. (1) The distribution of potential in the chip with applied bias voltage could be determined. (2) The acceleration voltage (HV) of the irradiating electron beam was the major factor which determined the observable depth (tx) by EAM. (3) tx corresponded to approximately 60% of the range of excited electrons as a function of HV. Thus, EAM could nondestructively provide information on the internal structure of the device in the operating condition of the chip. The above results could not be obtained from the scanning electron microscopy (SEM) mode images.

p-CuGa1-xInxS2/n-ZnSe Heterojunction by LPE Method from In Solution

p-CuGa1-xInxS2/n-ZnSe heterojunction was made by the LPE method from the In solution of solute CuGaS2 and solvent In, though a p-CuGaS2/n-ZnSe heterojunction was not obtained. The reflection electron diffraction pattern from the interface indicates an epitaxial growth. The measurements of EPMA have shown that Zn and Se decrease monotonically, and Cu, Ga and S increase monotonically, from the substrate to the over-growth layer. Indium from the solvent showed a monotonic increase from the substrate to the over-growth layer. The maximum temperature Tm of 650°C and cooling rate of 0.5°C/min were taken. The epitaxial layer is represented by the formula CuGa1-xInxS2, where x was 0.16 for Tm of 650°C. It is suggested that a complete series of solid solutions (CuGa1-xInxS2)1-y-(2ZnSe)y alloys is formed. The thickness of the mixedcrystal layer was 4.9 µm.

Nondestructive Internal Observation of Metal-Oxide-Semiconductor LSI Designed by 0.8 µm Rule

A metal-oxide-semiconductor (MOS)-LSI chip was designed by the 0.8 µm rule, and a passivated film on the chip was etched off while keeping the chip mounted on a ceramic package. The acoustic signal generated by irradiation of a chopped electron beam was picked up by a piezoelectric detector (PZT element) attached to the back of the package. The results of observation by electron-acoustic microscopy (EAM) are as follows: (a) the observable depth (tx) was proportional to the electron range (Re); (b) tx shifted to a shallower side (about 50% of Re) compared to the case of bipolar transistors; (c) contact holes (0.8 µm2) were distinctly observed at HV=19 kV; and (d) the resolution of our EAM was estimated to be about 0.4 µm at a chopping frequency of the electron beam of 1 MHz and an acceleration voltage of 18–19 kV.

LPE Growth of CuGa1-xInxS2 on ZnSe Substrate Using a Mixture of CuGaS2 and CuInS2 as a Solute

Liquid Phase Epitaxial (LPE) growth using (CuGaS2)1-Y–(CuInS2)Y as a solute, ZnSe as a substrate and In as a solvent has been studied by varying Y under the growth conditions of a maximum temperature Tm of 700 and 650°C, and constant cooling rate CR of 0.5°C/min. The over-growth layer is confirmed to be epitaxial CuGa1-xInxS2 by means of EPMA and electron diffraction under the growth conditions of Tm=700°C for all Y and Tm=650°C for Y0.7 for Tm=700°C, x is not proportional to Y and is almost constant for low Y. For Tm=650°C, the x-Y relation is similar to that for Tm=700°C, but the In content is higher than that for Tm=700°C. When Y>0.8, the growth rate and Cu content in the overgrowth layer rapidly decrease, where the ternary compound and/or ternary-ternary alloy growth layer could no longer be obtained. Thus, the range of epitaxial growth was Y0.7 for Tm=650°C. The above results are discussed and compared with those of our previous reports.

Cathodoluminescence Study on Diffusion Coefficients of Al, Ga and In in ZnSe

The temperature dependence on the diffusion coefficients of Al, Ga and In in ZnSe was studied. The cleavage cross-sectional surface of a diffused ZnSe wafer was observed by the cathodoluminescence mode of SEM. The following relations were obtained: DAl=1.18×10-1 exp (-1.92 eV/kT), DGa=6.76×10-2 exp (-1.80 eV/kT) and DIn=4.45×10-1 exp (-1.84 eV/kT).

Observation of Dislocation Lines in a Transistor by Electron-Acoustic Microscopy

Electron acoustic images, EAIs, by electron-acoustic microscopy were studied by in situ observation at the same area of a Si transistor-chip Tr-chip under several bias conditions applied between the collector and the emitter. The results confirmed that the EAI contrast varies depending not only on the difference in the materials and the flatness of the surface but also on the bias conditions. Dislocation lines were clearly observed at the base region of the Tr-chip and were induced by the thermal diffusion process of the base layer production. However, dislocation lines were not observed from the structually same emitter region.

Electrical and Optical Properties of p ? ZnSnAs2/n?ZnSe Heterodiode

A pZnSnAs2/nZnSe heterodiode was prepared by LPE from Sn solution on a low-resistivity nZnSe substrate. The I-V characteristics of the diode were measured, and it was found to have a good rectification ratio of 104 at 1 V. The diode showed a photoresponse extending over a wide wavelength region between 0.4 and 1.9 µm. The measurements of the C-V characteristics showed that the diode had an abrupt junction with a diffusion potential of 0.60 V. The dielectric constant for ZnSnAs2 was first estimated from the analysis of the C-V characteristics: eA=12.0e0. The values of the minority carrier lifetime were obtained from the decay curves of EBIC as 70 ns and 0.4 ns for nZnSe and pZnSnAs2, respectively.

Comparative study of scanning electron microscopy and electron-acoustic microscopy images

Many reports have been published which compare between scanning electron microscopy (SEM) images and electron acoustic microscopy (EAM) images (EAIs). Thus far, these images have been independently obtained for all areas under the microscopic field, and any corelational factors immanent in their formation have been neglected. We subject quasi-color-coded SEM and EAM images of a test element group of metal-oxide-semiconductor LSI chips to a detailed comparative analysis. It was found, for the same sampling of sites on a specimen, that each technique offers a different set of signal intensities. Results show (1) that back scattered electron image and electron beam induced current image of obtained in the SEM mode, and EAIs obtained in the EAM mode, corresponding to the same geometrical siteson a specimen, reveal information concerning their proper and interrelated differences, and (2) that collective observations of the three types of images yield more useful information concerning the internal properties of a specimen than that obtained heretofore by nondestructive observation.

Generation of Electron-Acoustic Signals and Distribution of Potential in Transistor Chip under Applied of Bias

An observation area was first selected using scanning electron microscopy (SEM)-mode images. Switching to an electron-acoustic microscopy (EAM)-mode, the area selected from SEM images was then studied with EAM images using electron-acoustic signals. We carried out nondestructive internal observation at the fixed area of an Si transistor chip put into operation by application of bias voltage (V b) in situ by EAM. The results showed that (a) the distribution of potential caused by V b application in the chip could be determined nondestructively from the change in the contrast of EAM images and (b) the internal structure of devices in operation could be observed nondestructively by EAM.

The Range of Observable Depth in a pnp Si Darlington Tr-Chip by Electron-Acoustic Microscopy

Using a pnp Si Darlington Tr-chip as a specimen, images of electron-acoustic microscopy (EAM) and several modes of SEM images were observed in situ within the same area. The EAM was operated at a blanking frequency of 1 MHz and a duty ratio of 50%. In the EAM mode, the p-n junction, which was short-circuited to an Al electrode (~3 µm) on the surface, was identified at HV 25 kV. In the SEM mode, however, it was observed only as surface irregularity. The results were as follows: (1) the contrast of the EAM image varied with the bias condition, (2) the observable depth in EAM was related to the electron range, and (3) the depth corresponded to approximately 60% of the electron range. The results agreed with those previously reported using npn-type Tr-chips. A mechanism of acoustic signal generation is also discussed in this paper.