SIMOX Wafers Research Articles

窒素ドープ結晶利用によるSIMOXウェーハの高品質化( バルク成長分科会特集-最先端デバイスと科学技術-)

窒素ドープ結晶利用によるSIMOXウェーハの高品質化( バルク成長分科会特集-最先端デバイスと科学技術-)

Electrical Characterization of Silicon-on-Insulator Wafers Using Photo-Conductance Decay (PCD) Method

In this work the photo-conductance decay (PCD) technique is used to measure the effective carrier lifetime in 160 nm–180 nm thick active layers of silicon-on-insulator (SOI) substrates both SIMOX and bonded. Study was carried out using 405 nm excitation wavelength featuring 200 nm absorption depth in silicon which was selected to coincide with the thickness of the active layers in the SOI wafers studied. The results obtained indicate the effectiveness of PCD methodology adopted for this study in the measurements of the minority carrier lifetime in Si active layers in SOI substrates. They demonstrate differences between PCD characterization of bulk and SOI wafers which are related to the confinement of the depletion region within the Si active layer in the latter case making its electrical properties less sensitive to the variation of the surface chemical condition. On the other hand, the process related physical changes in the SOI surface morphology were readily detectable by PCD measurements. Furthermore, the specific outcome of this investigation is the result indicating higher minority carrier lifetime in the Si active layer of bonded SOI wafers as compared to SIMOX wafers used in this study.

Fabrication of large area silicon nanothickness membranes for channeling experiments

Membranes of micrometer lateral sizes and nanometer thickness are nowadays routinely fabricated through silicon micromachining processes, while more difficult is the fabrication of large areas membranes. In this paper we describe a method for fabrication of large area nanothickness silicon crystalline membranes starting from a SIMOX wafer. The realized structures have been characterized by means of high resolution X-ray diffraction and planar channeling of a 2MeV proton beam. This last analyses demonstrates a very interesting phenomenon: As the beam direction is inclined by less than the planar channelling critical angle with respect to the crystal planes, channeled particles undergo half a “channeling oscillation” and exit the crystal with reversed transverse momenta, i.e., the protons trajectories are ‘‘mirrored’’ by the crystal planes. Over-barrier particles are deflected of a minor extent in the opposite direction with respect to the “mirroring” direction. Observation of such effects not only proves the high crystalline quality of the Si membrane, but open new ways to manipulate high energy charged particle beams through crystals.

Crystallinity estimation of thin silicon-on-insulator layers by means of diffractometry using a highly parallel X-ray microbeam

An X-ray microbeam with a small angular divergence and a narrow energy bandwidth has been produced at BL24XU at SPring-8. The beam size was measured to be 3.1 microm and 1.6 microm in the horizontal and vertical directions, respectively, and the horizontal angular divergence was 4.0 arcsec. Using this microbeam the crystallinity estimation of thin layers on silicon-on-insulator (SOI) wafers is demonstrated. In reciprocal-space maps the lattice tilt variations were 80 arcsec and more than 220 arcsec in the SOI layers on bonded and SIMOX wafers, respectively. In equi-tilt maps, the typical equi-tilt areas of the SOI layers were 7 microm and 4 microm in size on the bonded and SIMOX wafers, respectively.

Interface electric charge modelling and characterization with δ – distribution generator strings in thin SOI films

Today's SOI technologies are able to produce buried oxides with a thickness spectrum from 400nm in the standard HTA SIMOX, down to tens of nm in Unibond technique. In the SOI structures, two oxide-semiconductor interfaces exist, with specific associated charges. Conventional models ignore the charges situated at the buried oxide-substrate interface, being focused just on the front and back channels conduction in the silicon film. All these fixed charges, classically expressed in ecm−2, are physically spread into a small volume that becomes significant in very thin films (nanofilms). This paper presents a new model of the flat-band voltage using δ–distribution generator strings. The model accuracy increases in the SOI nanofilms domain, accordingly with our theory and numerical simulations. On the other hand, an experimental setup is presented for the spreading parameters extraction, in the case of a HTA SIMOX wafer.

Research on nitrogen implantation energy dependence of the properties of SIMON materials

With different implantation energies, nitrogen ions were implanted into SIMOX wafers in our work. And then the wafers were subsequently annealed to form separated by implantation of oxygen and nitrogen (SIMON) wafers. Secondary ion mass spectroscopy (SIMS) was used to observe the distribution of nitrogen and oxygen in the wafers. The result of electron paramagnetic resonance (EPR) was suggested by the dandling bonds densities in the wafers changed with N ions implantation energies. SIMON-based SIS capacitors were made. The results of the C–V test confirmed that the energy of nitrogen implantation affects the properties of the wafers, and the optimum implantation energy was determined.

Design and fabrication of a micro PZT cantilever array actuator for applications in fluidic systems

In this article, a micro cantilever array actuated byPZT films is designed and fabricated for micro fluidic systems. The design features for maximizing tip deflections and minimizing fluid leakage are described. The governing equation of the composite PZT cantilever is derived and the actuating behavior predicted. The calculated value of the tip deflection was 15 µm at 5 V. The fabrication process from SIMOX (Separation by oxygen ion implantation) wafer is presented in detail with the PZT film deposition process. The PZT films are characterized by investigating the ferroelectric properties, dielectric constant, and dielectric loss. Tip deflections of 12 µm at 5 V are measured, which agreed well with the predicted value. The 18 µ1/s leakage rate of air was observed at a pressure difference of 1000 Pa. Micro cooler is introduced, and its possible application to micro compressor is discussed.

Range evaluation in SIMS depth profiles of Er-implantations in silicon

In the last decade ion implantation of common dopants in silicon has been almost full characterised. However, data of inner transition elements are based on few measurements or even extrapolations. Our investigations focus on erbium, an upcoming dopant in photonic applications. Some of us have previously found errors of 20% in the projected range of Er in Si and SiO 2 when comparing the range profiles measured with SIMS and simulations using SRIM, T2D, and our own binary collision simulator IMSIL. Because of the far-reaching consequences, we have performed additional, more precise experiments to confirm our previous results. Equal doses of Er has been implanted into SIMOX wafers with energies of 100, 200, 300, 400, 500, and 600 keV. Profiles have been measured with secondary ion mass spectrometry (SIMS). Relative sensitivity factors (RSF) were gathered from low-energy implantations, remaining within the Si top layer. We used the Si/SiO 2 interface at exactly 217.7 nm to calibrate the depth scale of all profiles. In addition dynamical Monte-Carlo simulations of the sputter process were taken to correct the depth scale and the interface position.

Silicon nanowires fabricated by means of an underetching technique

Silicon wires with nanometric dimensions have been fabricated on SIMOX wafers by means of e-beam lithography and wet chemical etchings, exploiting the underetching properties of the KOH etchant. The cross section of the resistors has a trapezoidal shape; a minimum top width of 40 nm has been obtained. The whole process required only two writing steps. I– V characteristics were measured at room temperature as a function of the backgate voltage.

Spectroscopic ellipsometry chraracterization of the interfacial roughness in simox wafers

The performance of thin film microelectronic devices on SIMOX SOI substrates is highly dependent on the nature and perfection of the top-Si/BOX interfaces. In this research, we demonstrate a non-destructive and in-situ characterization method of spectroscopic ellisometry that is sensitive to these interfacial regions. The dielectric functions of the composite materials in the transition regions were calculated using the effective medium approximation (EMA). In addition, the interfacial roughness was also studied by TEM and AFM.

Higher harmonic thermal wave detection in thermoreflectance microscopy with combined electrical and optical heating

Insulating lines and channels prepared by focused ion beam implantation on SIMOX wafers have been investigated by thermally modulated optical reflectance microscopy using optical and electrical excitation. Continuous hot lines and hot spots can be visualized by modulated electrical heating, whereas insulating lines forming channels can be imaged only with simultaneous optical and electrical excitation. Three different schemes have been investigated for the combined excitation: (i) optical modulation with additional DC voltage, (ii) optical and electrical pumps modulated at the same frequency with the detection effected at higher harmonics and (iii) two different modulation frequencies used for optical and electrical excitation with the detection effected at sum and difference frequencies. When detecting at higher frequencies, best contrast for the observation of the insulating lines adjacent to a channel is achieved by recording the modulated reflectance signal at the fourth harmonic 4 f where f is the modulation frequency of the optical and electrical pump. The observed contrast enhancement of the double excited thermoreflectance signal is found to be mainly of a thermal origin.

Electrical Investigation of Si/SiGe Layers Grown on a Nanometer-Thick SOI by CVD

The performance of devices formed by chemical vapor deposition (CVD) on the nanometer silicon-on-insulator (SOI) of a SIMOX wafer may possibly be influenced by the crystalline quality of the SOI surface layer, because there are many defects in the interface region of the SOI on the buried oxide. We grew Si/SiGe/Si layers on SOI, 7, 21, and 283 nm thick, and fabricated p-type metal-oxide-semiconductor field-effect transistors (MOSFETs) on the layers. The crystalline quality evaluation for the layers was done through I-V characteristics. The drain current decreased as the SOI thickness decreased. The effective hole mobility for the device with the thinnest SOI was nearly 15% lower than those for the other devices. We showed that the thinnest SOI was affected by the defects in the SOI and SOls thicker than 21 nm were not influenced by the defects because the crystalline quality of the surface layers grown on SOI was promoted.

Technological innovation in low-dose SIMOX wafers fabricated by an internal thermal oxidation (ITOX) process

A high-quality SIMOX wafer was produced by a combination of low-dose implantation and annealing using the ITOX process, which enables precise control of the superficial silicon thickness and improvement of the BOX characteristics, together with an increase in BOX thickness. Recently, a further quality improvement was achieved using nitrogen-doped Czochralski silicon as the SIMOX starting material, which is effective in eliminating shallow surface pits. 300 mm SIMOX samples were manufactured successfully in the late 2000s, showing that the advantage of SIMOX technology will be maintained through the next generation.

SIMS study of oxygen in- and out-diffusion in SIMOX wafers during thermal annealing using [formula omitted] implantation

Most recently low-dose (4E17 ions/cm 2) SIMOX technology has been developed in order to restrain the dislocation density and the production cost. However, in- and out-diffusion of oxygen and internal oxidation (ITOX) phenomena have never been understood during high-temperature annealing process as yet. In this study, we use the sample, which was implanted 18 O + with the dose of 4E17 ions/cm 2 into silicon substrate and then non-oxidizing anneal was done at around 1300 °C. As the results, it was proven that the diffusion of oxygen into thermal oxide layer above 1300 °C was not in agreement with the Deal–Grove theory. The mechanism of oxygen in- and out-diffusion in SIMOX wafer is discussed.

Atomic structure of the buried oxide layer in SIMOX wafers

Atomic structure of the buried oxide layer in SIMOX wafers

A thorough investigation of hot-carrier-induced gate oxide breakdown in partially depleted N- and P-channel SIMOX MOSFETs

In this paper, the hot-carrier-injected oxide region in the front interfaces is systematically investigated for partially depleted silicon-on-insulator (PDSOI) metal-oxide-semiconductor field-effect transistors (MOSFETs) devices fabricated on a SIMOX wafer. The gate oxide properties associated with channel hot-carrier effects are investigated and the hot-carrier-induced device degradations are analyzed using stress experiments with three main types of hot-carrier injections-maximum gate current, maximum substrate current and parasitic bipolar transistor action. Based on experimental results, the influence of these injected carriers on the gate oxide properties is clarified. As a matter of fact, NMOSFETs degradation mechanism is shown to be caused by hot holes injected into the drain side of the gate oxide, and electrons trapped in the gate oxide can accelerate the gate oxide breakdown. PMOSFETs degradation mechanism depends on the biasing conditions. For the first time, we conclude that the electrical characteristics of NMOSFETs are significantly different from that of PMOSFETs after the gate oxide breakdown. An extensive discussion of the experimental results is provided.

Tensile testing system for sub-micrometer thick films

A new type of tensile tester for sub-micrometer thick films has been developed. The tester has a grip that allows chucking one end of a thin-film specimen by electrostatic force while the other end is fixed to a silicon substrate. It uses a servo-controlled balance for small-force measurement. Sub-micrometer thick single-crystal-silicon specimens were fabricated using bulk micromachining starting with a SIMOX wafer. The specimens were 0 to 500 μm long, 20 or 50 μm wide and 0.14 μm thick. Young’s modulus is 158 GPa, which is measured using the differential stiffness method. The tensile strength ranged from 1.4 to 4.9 GPa for 12 samples; the large distribution of the tensile strength is observed.

Microstructural Evolution and Defects in Ultra-thin SIMOX Materials during Annealing

AbstractThe microstructure of ultra-thin SIMOX depends strongly on implantation dose, energy and annealing conditions. We used TEM combined with AES and RBS to determine the microstructural evolution of SIMOX wafers subjected to various temperatures during annealing. We found that an optimum dose window to produce a continuous buried oxide layer without Si islands is 3.0-3.5×1017 O+/cm2 for 100 keV. The thickness of the silicon overlayer and BOX layer produced in this dose window was about 170 nm and 75 nm respectively. RBS analysis showed that a high quality crystalline Si layer was produced after annealing at 1350 °C for 4 hrs. The defect density was very low (< 300/cm2) for all samples implanted at 100 keV.

Evolution of microstructure during annealing of low-dose SIMOX wafers implanted at 65 keV

The microstructural changes that occur during annealing of ultra-thin oxygen-implanted silicon-on-insulator have been studied using transmission electron microscopy (TEM), Rutherford backscattering spectrometry (RBS), and Auger electron spectroscopy (AES). Silicon substrates were implanted at 65 keV with a dose of 4.5×1017 O+ cm−2, followed by annealing at various temperatures. TEM results show that the defects observed in the as-implanted material (stacking faults and {1 1 3} defects) were reduced after annealing at 900 °C for 2 h and were eliminated after annealing at 1100 °C for 2 h. A continuous buried oxide (BOX) layer was formed after annealing at 1300 °C for 6 h. Numerous silicon islands were present in the BOX layer. The silicon islands can be traced to a precursor structure that developed at the implantation step. RBS results indicate that the crystallinity of the top Si layer is significantly restored after annealing at 1100 °C for 2 h and is completely restored after annealing at 1300 °C for 6 h. It was also found through AES analysis that the redistribution of oxygen during annealing is initiated at 1100 °C.

Gated-diode characterization of the back-channel interface on irradiated SOI wafers

A silicon-on-insulator (SOI) MOSFET-based technique has been applied to study the Si-film/buried-oxide interface of devices that were fabricated on a SIMOX wafer. Since the gated-diode technique is sensitive to recombination current caused by the presence of interface states, the samples were exposed to 10 keV X-ray irradiation to enhance the development of SOI back-channel interface states. The measured peak in the gated-diode current curve was observed to increase in magnitude and move in voltage as a function of exposure to radiation in a manner consistent with increasing interface states and increasing trapped oxide charge. Using a two-dimensional numerical simulator, with a single acceptor interface trap at 0.7 eV, the gated-diode current was modeled as a function of 10 keV X-ray exposure.