Large scale graphene integration for silicon technologies

The main guarantor of success for silicon based semiconductor research and industry was the availability and continuous improve of wafer fabrication processes for large scale integration. New material integration in a stable and reliable silicon process platform has to face several challenges. Graphene as a 2D material is considered as a material with formidable properties. This can enable new functionalities and performance improvements in a large variety of applications. Using graphene devices in microelectronics requires beside appropriate performances certain techniques for large scale fabrication of graphene which are currently not yet in place. In this paper we present recent progress of process platform developments to enable wafer scale integration in a silicon cmos platform. Synthesis of graphene on silicon cmos compatible substrates are considered to fulfill a basic request for the integration of graphene related devices in a silicon environment with no risk of metallic cross contamination. We present recent results of graphene synthesis on Ge(100) and Ge (110). Therefore chemical vapor deposition (CVD) methods are used to realize Ge/Si substrates followed by a CVD graphene synthesis at ~890°C (1,2). Due to silicon diffusion inside germanium certain germanium thickness is required to allow the subsequent graphene process. We present high quality graphene on a 200mm silicon wafers with high uniformity, a 2D/G ratio of ~3 and low D mode over the entire 200mm wafer measured by Raman spectroscopy (Figure 1). To enable a selective graphene synthesis on a 200mm wafer we discuss first approaches of graphene growth on patterned germanium island. Please click Additional Files below to see the full abstract

High temperature reactive ion etching of iridium thin films with aluminum mask in CF4/O2/Ar plasma

Reactive ion etching (RIE) technology for iridium with CF4/O2/Ar gas mixtures and aluminum mask at high temperatures up to 350 °C was developed. The influence of various process parameters such as gas mixing ratio and substrate temperature on the etch rate was studied in order to find optimal process conditions. The surface of the samples after etching was found to be clean under SEM inspection. It was also shown that the etch rate of iridium could be enhanced at higher process temperature and, at the same time, very high etching selectivity between aluminum etching mask and iridium could be achieved

Investigation of oxide thin films deposited by atomic layer deposition as dopant source for ultra-shallow doping of silicon

Atomic layer deposition of solid dopant sources for silicon was carried out by using triethylantimony and ozone, and tris-(dimethylamido)borane and ozone as precursors for antimony or boron containing oxides, respectively. It was proved that homogenous antimony oxide deposition could be achieved on flat silicon wafers and in trench structures. Little growth was found below 100 °C deposition temperature and linear temperature dependence on the growth rate between 100 and 250 °C. The oxide films were not stable above 750 °C and therefore failed to act as dopant source for silicon so far. Boron containing films were only obtained at a deposition temperature of 50 °C. These films were highly instable after exposure to air but degradation could be delayed by thin films of antimony oxide or aluminium oxide that were in situ grown by ALD as well. Only little boron was found by ex-situ chemical analysis. However, rapid thermal annealing of such boron containing dopant source layers resulted in high concentrations of active boron close to the silicon surface. The dependence of the doping results on the thickness of the initial boron containing films could be shown

Application of atomic layer deposited dopant sources for ultra‐shallow doping of silicon

The advanced silicon semiconductor technology requires doping methods for production of ultra‐shallow junctions with sufficiently low sheet resistance. Furthermore, advanced 3‐dimensional topologies may require controlled local doping that cannot be achieved by ionimplantation. Here, the application of the atomic layer deposition (ALD) method for pre‐deposition of dopant sources is presented. Antimony oxide and boron oxide were investigated for such application. Ozone‐based ALD was carried out on silicon wafers by using triethylantimony or tris‐(dimethylamido)borane. Very homogeneous Sb2O5 deposition could be achieved on flat silicon wafers and in trench structures. The thermal stability of antimony oxide layers was investigated by rapid thermal annealing experiments. The layers were not stable above 750 °C. Therefore, this material failed to act as dopant source so far. In contrast, ultra‐shallow boron doping of silicon from ALD grown boron oxide films was successful. However, pure B2O3 films were highly unstable after exposure to ambient air. The boron oxide films could be protected by thin Sb2O5 or Al2O3 films that were in‐situ grown by ALD. Low temperature ALD of Al2O3 at 50 °C from trimethylaluminium (TMA) and ozone was investigated in detail with respect of its protective effect on boron oxide. Interestingly, it was observed that already one ALD cycle of TMA and O3 resulted in significant increase in stability of the boron oxide in air

Ag films grown by remote plasma enhanced atomic layer deposition on different substrates

Plasma-assisted atomic layer deposition (PALD) was carried for growing thin boron oxide films onto silicon aiming at the formation of dopant sources for shallow boron doping of silicon by rapid thermal annealing (RTA). A remote capacitively coupled plasma source powered by GaN microwave oscillators was used for generating oxygen plasma in the PALD process with tris(dimethylamido)borane as boron containing precursor. ALD type growth was obtained; growth per cycle was highest with 0.13 nm at room temperature and decreased with higher temperature. The as-deposited films were highly unstable in ambient air and could be protected by capping with in-situ PALD grown antimony oxide films. After 16 weeks of storage in air, degradation of the film stack was observed in an electron microscope. The instability of the boron oxide, caused by moisture uptake, suggests the application of this film for testing moisture barrier properties of capping materials particularly for those grown by ALD. Boron doping of silicon was demonstrated using the uncapped PALD B2O3 films for RTA processes without exposing them to air. The boron concentration in the silicon could be varied depending on the source layer thickness for very thin films, which favors the application of ALD for semiconductor doping processesInvestment Bank Berlin and EFR

Modulating the Filamentary-Based Resistive Switching Properties of HfO2 Memristive Devices by Adding Al2O3 Layers

The resistive switching properties of HfO2 based 1T-1R memristive devices are electrically modified by adding ultra-thin layers of Al2 O3 into the memristive device. Three different types of memristive stacks are fabricated in the 130 nm CMOS technology of IHP. The switching properties of the memristive devices are discussed with respect to forming voltages, low resistance state and high resistance state characteristics and their variabilities. The experimental I–V characteristics of set and reset operations are evaluated by using the quantum point contact model. The properties of the conduction filament in the on and off states of the memristive devices are discussed with respect to the model parameters obtained from the QPC fit

Use of B2O3 films grown by plasma-assisted atomic layer deposition for shallow boron doping in silicon

Plasma-assisted atomic layer deposition (PALD) was carried for growing thin boron oxide films onto silicon aiming at the formation of dopant sources for shallow boron doping of silicon by rapid thermal annealing (RTA). A remote capacitively coupled plasma source powered by GaN microwave oscillators was used for generating oxygen plasma in the PALD process with tris(dimethylamido)borane as boron containing precursor. ALD type growth was obtained; growth per cycle was highest with 0.13 nm at room temperature and decreased with higher temperature. The as-deposited films were highly unstable in ambient air and could be protected by capping with in-situ PALD grown antimony oxide films. After 16 weeks of storage in air, degradation of the film stack was observed in an electron microscope. The instability of the boron oxide, caused by moisture uptake, suggests the application of this film for testing moisture barrier properties of capping materials particularly for those grown by ALD. Boron doping of silicon was demonstrated using the uncapped PALD B2O3 films for RTA processes without exposing them to air. The boron concentration in the silicon could be varied depending on the source layer thickness for very thin films, which favors the application of ALD for semiconductor doping processes.Investment Bank Berlin and EFR

The bulk of the black hole growth since z ~ 1 occurs in a secular universe: no major merger-AGN connection

What is the relevance of major mergers and interactions as triggering mechanisms for active galactic nuclei (AGNs) activity? To answer this long-standing question, we analyze 140 XMM-Newton-selected AGN host galaxies and a matched control sample of 1264 inactive galaxies over z ~ 0.3–1.0 and M_∗ < 10^(11.7) M_⊙ with high-resolution Hubble Space Telescope/Advanced Camera for Surveys imaging from the COSMOS field. The visual analysis of their morphologies by 10 independent human classifiers yields a measure of the fraction of distorted morphologies in the AGN and control samples, i.e., quantifying the signature of recent mergers which might potentially be responsible for fueling/triggering the AGN. We find that (1) the vast majority (>85%) of the AGN host galaxies do not show strong distortions and (2) there is no significant difference in the distortion fractions between active and inactive galaxies. Our findings provide the best direct evidence that, since z ~ 1, the bulk of black hole (BH) accretion has not been triggered by major galaxy mergers, therefore arguing that the alternative mechanisms, i.e., internal secular processes and minor interactions, are the leading triggers for the episodes of major BH growth.We also exclude an alternative interpretation of our results: a substantial time lag between merging and the observability of the AGN phase could wash out the most significant merging signatures, explaining the lack of enhancement of strong distortions on the AGN hosts. We show that this alternative scenario is unlikely due to (1) recent major mergers being ruled out for the majority of sources due to the high fraction of disk-hosted AGNs, (2) the lack of a significant X-ray signal in merging inactive galaxies as a signature of a potential buried AGN, and (3) the low levels of soft X-ray obscuration for AGNs hosted by interacting galaxies, in contrast to model predictions

Less than 10 percent of star formation in z=0.6 massive galaxies is triggered by major interactions

Both observations and simulations show that major tidal interactions or mergers between gas-rich galaxies can lead to intense bursts of starformation. Yet, the average enhancement in star formation rate (SFR) in major mergers and the contribution of such events to the cosmic SFR are not well estimated. Here we use photometric redshifts, stellar masses and UV SFRs from COMBO-17, 24 micron SFRs from Spitzer and morphologies from two deep HST cosmological survey fields (ECDFS/GEMS and A901/STAGES) to study the enhancement in SFR as a function of projected galaxy separation. We apply two-point projected correlation function techniques, which we augment with morphologically-selected very close pairs (separation <2 arcsec) and merger remnants from the HST imaging. Our analysis confirms that the most intensely star-forming systems are indeed interacting or merging. Yet, for massive (M* > 10^10 Msun) star-forming galaxies at 0.4<z<0.8, we find that the SFRs of galaxies undergoing a major interaction (mass ratios <1:4 and separations < 40 kpc) are only 1.80 +/- 0.30 times higher than the SFRs of non-interacting galaxies when averaged over all interactions and all stages of the interaction, in good agreement with other observational works. We demonstrate that these results imply that <10% of star formation at 0.4 < z < 0.8 is triggered directly by major mergers and interactions; these events are not important factors in the build-up of stellar mass since z=1.Comment: Submitted to ApJ. 41 pages, 11 figure

A sub-atmospheric chemical vapor deposition process for deposition of oxide liner in high aspect ratio through silicon vias

The formation of a Through Silicon Via (TSV) includes a deep Si trench etching and the formation of an insulating layer along the high-aspect-ratio trench and the filling of a conductive material into the via hole. The isolation of the filling conductor from the silicon substrate becomes more important for higher frequencies due to the high coupling of the signal to the silicon. The importance of the oxide thickness on the via wall isolation can be verified using electromagnetic field simulators. To satisfy the needs on the Silicon dioxide deposition, a sub-atmospheric chemical vapor deposition (SA-CVD) process has been developed to deposit an isolation oxide to the walls of deep silicon trenches. The technique provides excellent step coverage of the 100 mu m depth silicon trenches with the high aspect ratio of 20 and more. The developed technique allows covering the deep silicon trenches by oxide and makes the high isolation of TSVs from silicon substrate feasible which is the key factor for the performance of TSVs for mm-wave 3D packaging