Cindy Colinge

Room Temperature Wafer Bonding Using Oxygen Plasma Treatment in Reactive Ion Etchers With and Without Inductively Coupled Plasma

The effects of oxygen plasma treatment on silicon surface topography and the properties of bonded interfaces formed using the oxygen plasma pretreatment were investigated. Bonded samples of silicon or oxidized silicon wafers using oxygen plasma pretreatment in reactive ion etchers with and without inductively coupled plasma were characterized in terms of surface energies obtained at room temperature. Annealing experiments at 1000°C were made to study the origin of thermally generated voids. Atomic force microscopy was used to study how the surface roughness of plasma-treated silicon wafers evolved over time. Furthermore, the influence of water dipping on the roughness of plasma-treated silicon surfaces was investigated. The results showed that plasma treatment of one wafer results in a surface energy of approximately I J m 2 at room temperature. The role of water in the increase of surface energy was found to be crucial. From annealing experiments it is concluded that water present at the wafer surfaces before bonding has a pronounced influence on void generation upon annealing. A dramatic change in the topography of silicon surfaces treated in oxygen plasma was observed during storage at room temperature, while water dipping the wafers after plasma treatment appeared to stabilize the surface topography.

Low temperature germanium to silicon direct wafer bonding using free radical exposure

A low temperature germanium (Ge) to silicon (Si) wafer bonding method was demonstrated by in situ radical activation bonding in vacuum. In order to gain further insight into the bonding mechanism, the Ge surface chemistry after either oxygen or nitrogen radical activation was analyzed by means of angle-resolved x-ray photoelectron spectroscopy. After low temperature direct bonding of Ge to Si followed by annealing at 200 and 300 °C, advanced imaging techniques were used to characterize the bonded interface.

Low temperature exfoliation process in hydrogen-implanted germanium layers

The feasibility of transferring hydrogen-implanted germanium to silicon with a reduced thermal budget is demonstrated. Germanium samples were implanted with a splitting dose of 5×1016 H2+ cm−2 at 180 keV and a two-step anneal was performed. Surface roughness and x-ray diffraction pattern measurements, combined with cross-sectional TEM analysis of hydrogen-implanted germanium samples were carried out in order to understand the exfoliation mechanism as a function of the thermal budget. It is shown that the first anneal performed at low temperature (≤150 °C for 22 h) enhances the nucleation of hydrogen platelets significantly. The second anneal is performed at 300 °C for 5 min and is shown to complete the exfoliation process by triggering the formation of extended platelets. Two key results are highlighted: (i) in a reduced thermal budget approach, the transfer of hydrogen-implanted germanium is found to follow a mechanism similar to the transfer of hydrogen-implanted InP and GaAs, (ii) such a low thermal bu...

UV Activation Treatment for Hydrophobic Wafer Bonding

Enhanced hydrophobic bond strength can be achieved by exposing prime grade silicon wafers to ultraviolet (UV) light and heat prior to bonding. The following independent variables were explored: platen temperature, UV exposure time, oxygen-containing vs non-oxygen-containing (nitrogen only) bonding atmosphere, and annealing temperature. The results suggest exposure to UV can be used as an activation process which removes the passivation of the silicon surface rendering the silicon highly reactive. Exposure of silicon wafers to UV appears to be a promising low-temperature surface activation method.

Characterization of germanium/silicon p-n junction fabricated by low temperature direct wafer bonding and layer exfoliation

The current transport across a p-Ge/n-Si diode structure obtained by direct wafer bonding and layer exfoliation is analysed. A low temperature anneal at 400 °C for 30 min was used to improve the forward characteristics of the diode with the on/off ratio at −1 V being >8000. Post anneal, the transport mechanism has a strong tunnelling component. This fabrication technique using a low thermal budget (T ≤ 400 °C) is an attractive option for heterogeneous integration.

A Simulation Comparison between Junctionless and Inversion-Mode MuGFETs

The devices were simulated using the Atlas 3D software. Both JNTs and pi-gate MuGFETs have a gate length of 25nm and an EOT of 1nm. In all devices the gate material workfunction is chosen such that the off drain current at VD=1V and VG=0V is equal to 100 nA/um. A pitch equal to 2×WSi is considered for all devices. Thus if WSi=10nm, the off current in an individual nanowire is equal to 100nA/um×20nm=2nA. The current drive of JNTs is similar to that of the IM MuGFET. It is quite dependent on the underlap with highdoping (10cm) S&D regions (Fig 1). In lightly-doped JNTs (10cm) an accumulation layer may be formed at VD=1V. In JNTs with higher doping concentrations, the current is purely a bulk current (Fig. 2).

Comprehensive investigation of Ge–Si bonded interfaces using oxygen radical activation

In this work, we investigate the directly bonded germanium-silicon interfaces to facilitate the development of high quality germanium silicon hetero integration at the wafer scale. X-ray photoelectron spectroscopy data is presented which provides the chemical composition of the germanium surfaces as a function of the hydrophilic bonding reaction at the interface. The bonding process induced long range deformation is detected by synchrotron x-ray topography. The hetero-interface is characterized by measuring forward and reverse current, and by high resolution transmission electron microscopy.

Fabrication of Germanium-on-Insulator by low temperature direct wafer bonding

A Germanium-on-Insulator (GeOI) wafer was fabricated using low temperature direct wafer bonding method. A hydrogen implanted Ge donor wafer was bonded to a thermally oxided Si handle wafer with in-situ oxygen radical activation before bonding in a vacuum chamber. Ex-situ anneals were use to enhance the bond strength or exfoliate the implanted Ge wafer. The insight into the exfoliation mechanism of the hydrogen implanted Ge wafer was observed by the surface roughness and x-ray diffraction pattern (XRD) measurements, combined with the high resolution transmission electron microscopy (HRTEM). The Ge surface after radical activation was analyzed by angle-resolved x-ray photoelectron spectroscopy (ARXPS). Scanning electron microscopy (SEM) was used to characterize the exfoliated Ge surface on handle SiO2 film.

Ge/Si heterojunction photodiodes fabricated by low temperature wafer bonding.

We report on the photoresponse of an asymmetrically doped p(-)-Ge/n(+)-Si heterojunction photodiode fabricated by wafer bonding. Responsivities in excess of 1 A/W at 1.55 μm are measured with a 5.4 μm thick Ge layer under surface-normal illumination. Capacitance-voltage measurements show that the interfacial band structure is dependent on both temperature and light level, moving from depletion of holes at -50 °C to accumulation at 20 °C. Interface traps filled by photo-generated and thermally-generated carriers are shown to play a crucial role. Their filling alters the potential barrier height at the interface leading to increased flow of dark current and the above unity responsivity.

Realization of an active book for multichannel intrathecal root stimulation in spinal cord injury — Preliminary results

After spinal cord injury, electrical stimulation of the roots inside the spinal column at the level of the cauda equina is a safe and effective way to regain some degree of control over lower body function, e.g. bladder and bowel management and leg movement. The success of current systems used for so-called intrathecal stimulation is limited by the low number of stimulation channels, which are in consequence of the maximum acceptable number of transdural cables. In order to overcome this limitation, we developed an active electrode with integrated electronics, providing four individual stimulation channels that requires one cable only. This paper outlines the different elements of the so-called active book with the emphasis on its preliminary construction and assembly.