Ion Beam Induced Charge Imaging Research Articles

Testing of radiation detectors by IBIC imaging

The nuclear microprobe technique IBIC (Ion Beam Induced Charge) was used for tests of different radiation detectors. By using a 2–6 MeV proton microbeam with a current of less than 1000 protons per second, images and profiles of charge collection efficiency in radiation detectors can be produced. This application of the IBIC technique provides results that can be used to study mobility of charge carriers or inhomogeneities of the electric field inside the depletion region. Presented are examples of IBIC tests performed on CVD diamond, CdTe and Si detectors.

Unconnected junction contrast in ion beam induced charge microscopy

A new contrast mechanism in ion beam induced charge imaging in semiconductors is reported. Junctions not directly connected to the charge collection preamplifier were found to give rise to significant charge collection signals. Imaging with these signals is carried out, thus enabling the mapping of junctions not directly connected to the charge collection amplifier.

High signal to noise level ion beam induced charge images

The use of MeV α particles to generate ion beam induced charge images with a signal to noise level approximately ten times larger than previously obtained using protons is described. The effect of α particle induced damage on the resultant image contrast is shown and a method of image formation in which the effects of ion induced damage are compensated for is described which enables the use of a higher ion dose.

A comparison between MeV protons and α particles for IBIC analysis

There are two major problems with the IBIC (ion beam induced charge) technique which hampers its wider use for the analysis of semiconductor materials. The small measured charge pulses give a low signal to noise ratio, and ion induced damage limits the maximum ion dose which can be used to form an IBIC image. This paper investigates the different charge pulse heights obtained using MeV protons and α particles, and the rate at which the ion induced damage decreases the measured charge pulse height.

The effect of ion induced damage on IBIC images

Ion induced damage limits the number of charge pulses which can be measured in an IBIC (ion beam induced charge) image because the average measured charge pulse size decreases with cumulative beam dose. The cause and effects of MeV light ion induced damage in Si is reviewed here, and the merits of using MeV protons or MeV α-particles for IBIC is discussed. Results are presented showing how ion induced damage is detectable in a 4 Mbit DRAM (dynamic random access memory) device after a dose of ∼ 100 3 MeV protons/μm 2. A method of compensating for the effects of ion induced damage which enables more ions/μm 2 to be used to generate an IBIC image is described, and results of compensating IBIC images of the DRAM are shown.

The generation and applications of ion beam induced charge images

It is important to be able to study the distribution and position of the active areas of microelectronic devices in order to study whether the device layers have been correctly fabricated and aligned. Ionising radiation can generate electron-hole pairs in semiconducting material, and photons and keV electrons are used to image device active regions using this effect, but their use is limited by low penetration of thick metallisations and passivation layers present. In addition keV electrons suffer from large scattering in the sample which severely degrades the spatial resolution. However, the high penetrating power of MeV light ions allows them to generate electron-hole pairs from deeply buried active areas within intact devices with very little loss of spatial resolution of the beam size on the sample surface. This paper describes the generation, limitations and capabilities of the technique ion beam induced charge (IBIC) for imaging the active regions of devices through the passivation and metallisation layers.

Study of nuclear microprobe beam halo using IBIC

There are many factors which can give rise to a halo around a focused MeV ion beam, and a method of detecting the distribution and determining the amount of beam current in the halo will help to assess its effect on spatial resolution. This paper describes how the technique IBIC (ion beam induced charge) can be used as an extremely sensitive method of imaging and quantifying the beam halo around focused 3 MeV proton beam current of 200 pA and 0.3 fA. It is also shown how the momentum of the beam fraction in the halo can be calculated from its spatial extent in the IBIC images.

Advances of nuclear microscopy in microelectronics analysis

This paper shows how the nuclear microprobe can be used to image microelectronic device active junction regions and also the layer structure. The high penetrating power of megaelectronvolt light ions allows them to generate electron-hole pairs from deeply buried active areas within intact microelectronic devices. The capability of a nuclear microprobe to form ion beam induced charge images of the device active regions through the passivation and metallization layers using this effect is described here. The use of the nuclear microprobe in conjunction with proton induced X-ray emission (PIXE), scanning transmission ion microscopy (STIM) and Rutherford backscattering spectrometry (RBS) represents a powerful combination of techniques for imaging the spatial and depth distribution of device metallization layers. Results are presented here which show how the nuclear microprobe gives information on the device layer structure and distribution without the need to etch the surface layers.

Microcircuit imaging using an ion-beam-induced charge

Ionizing radiation such as photons, keV electrons, or MeV ions can generate electron-hole pairs in semiconducting material. The high penetrating power of MeV light ions allows them to generate electron-hole pairs from deep within intact microelectronic devices, so images can be formed of the device active areas with very little degradation of the spatial resolution of the focused MeV ion beam. Furthermore, the ion-beam-induced charge (IBIC) image contrast is not strongly affected by the energy loss through the overlying device layers. This article is the first to demonstrate the capability of a nuclear microprobe to generate IBIC images of the active regions of devices through the passivation and metallization layers. The effect of the carrier generation volume on IBIC resolution is assessed. The ability of IBIC to align the major crystal axes of semiconductor samples is shown, and the effect of ion-induced damage on IBIC image contrast is considered.