Guenther Ruhl

Residual Metallic Contamination of Transferred Chemical Vapor Deposited Graphene

Integration of graphene with Si microelectronics is very appealing by offering a potentially broad range of new functionalities. New materials to be integrated with the Si platform must conform to stringent purity standards. Here, we investigate graphene layers grown on copper foils by chemical vapor deposition and transferred to silicon wafers by wet etching and electrochemical delamination methods with respect to residual submonolayer metallic contaminations. Regardless of the transfer method and associated cleaning scheme, time-of-flight secondary ion mass spectrometry and total reflection X-ray fluorescence measurements indicate that the graphene sheets are contaminated with residual metals (copper, iron) with a concentration exceeding 10(13) atoms/cm(2). These metal impurities appear to be partially mobile upon thermal treatment, as shown by depth profiling and reduction of the minority charge carrier diffusion length in the silicon substrate. As residual metallic impurities can significantly alter electronic and electrochemical properties of graphene and can severely impede the process of integration with silicon microelectronics, these results reveal that further progress in synthesis, handling, and cleaning of graphene is required to advance electronic and optoelectronic applications.

Influence of the electrode material on HfO2 metal-insulator-metal capacitors

TaN and TiN are investigated as bottom electrode materials for metal-insulator-metal (MIM) capacitor applications. Atomic vapor deposited HfO2 films are used as high-k dielectric. The influence of the interfacial layer between HfO2 and the bottom electrode on the electrical performance of MIM capacitors is evaluated. The capacitance density as well as the capacitance voltage linearity of high-k MIM capacitors is affected by the electrode material. There is also an impact by TaN and TiN on leakage current density and breakdown strength of the devices.

Going ballistic: Graphene hot electron transistors

This paper reviews the experimental and theoretical state of the art in ballistic hot electron transistors that utilize two-dimensional base contacts made from graphene, i.e. graphene base transist ...

Optimizing edge topography of alternating phase-shift masks using rigorous mask modeling

This paper describes mask topography effects of alternating phase shift masks for DUV lithography. First two options to achieve intensity balancing are discussed. Global phase errors of +/- 10 degrees cause a CD change of 3 nm and 8 nm CD placement errors. The CD placement appears to be the parameter affected most by phase errors. A sloped quartz edge with an angle of 3 degrees causes a CD change of 10 nm. The CD sensitivity on local phase errors, i.e. quartz bumps or holes was also studied. The critical defect size of a quartz bump was seen to be 150 nm for 150 nm technology. For the investigation the recently developed topography simulator T-mask was used. The simulator was first checked against analytical tests and experimental results.

Plasma enhanced atomic layer batch processing of aluminum doped titanium dioxide

Among many promising high-k dielectrics, TiO2 is an interesting candidate because of its relatively high k value of over 40 and its easy integration into existing semiconductor manufacturing schemes. The most critical issues of TiO2 are its low electrical stability and its high leakage current density. However, doping TiO2 with Al has shown to yield significant improvement of layer quality on Ru electrodes [S. K. Kim et al., Adv. Mater. 20, 1429 (2008)]. In this work we investigated if atomic layer deposition (ALD) of Al doped TiO2 is feasible in a batch system. Electrical characterizations were done using common electrode materials like TiN, TaN, or W. Additionally, the effect of plasma enhanced processing in this reactor was studied. For this investigation a production batch ALD furnace has been retrofitted with a plasma source which can be used for post deposition anneals with oxygen radicals as well as for directly plasma enhanced ALD. After evaluation of several Ti precursors a deposition process for...

Chrome dry etch process characterization using surface nanoprofiling

In this paper we describe the development of a chrome dry etch process on a new type of mask etch tool. One crucial goal was to minimize the CD etch bias. To meet this goal, a procedure for the direct characterization of CD etch bias was developed. The common methods for measuring the CD etch bias as resist-to-chrome CD difference, such as confocal optical microscope or SEM measurement, only give correct results, if the sidewalls are identical to the calibration standard. This is normally not the case as, due to the differing step height of resist and chrome, and the fact that during process development, in particular, the sidewall shapes and angles can vary significantly. Thus, it is very important to use a CD measurement method which takes the sidewall shapes (slope, foot) into account. One novel method is the use of a Scanning Nano Profiler (SNP) which was derived from the AFM principle. In contrast to AFM the use of a special high aspect ratio tip with 90° sidewall angle, in combination with pixelwise scanning of the substrate surface, provides information about the true sidewall shape and CD.

Properties of stacked SrTiO3/Al2O3 metal–insulator–metal capacitors

The possibilities to grow thin films of SrTiO3 and Al2O3 by atomic layer deposition for stacked metal–insulator–metal capacitors have been investigated in this work. In order to tune the functional properties of the capacitors, different processing steps have been employed to realize different combinations of the dielectric stacks. Electrical properties, extracted after the postdeposition annealing and sputter deposition of the Au top electrodes, indicated that the metal–insulator–metal (MIM) structures with additional Al2O3 layer provided better leakage currents densities, compared to the ones with single SrTiO3 based MIM capacitors, but the dielectric constant values have also decreased if additional Al2O3 film was inserted. Attempts to optimize the properties of the MIM stacks have been done by manufacturing heterostructures of Al2O3/SrTiO3/Al2O3 as well as SrTiO3/Al2O3/SrTiO3. In the first case, Al2O3 prevented the crystallization of SrTiO3 in the multilayer dielectric structure and therefore reduced ...

Endpoint solution for photomask chrome loads down to 0.25

Endpoint measurement sensitivity requirements in photomask can make or break an etch. The exposed chrome on todays photomask can vary between 0.25 percent and approximately 50 percent. Although excessive overetch does not deleteriously impact the underlying quartz, accurate endpoint detection is essential for preserving the critical dimension (CD) and CD uniformity across the mask. In order to provide a strong endpoint solution for photomask etch, a systematic investigation of etches with varying chrome loads was conducted. Passive monitoring of the optical emission spectra does not impact or interfere with the etch process. Also this method does not need specified endpoint sites on the mask as interferometric methods and provides an integrated endpoint signal over the whole mask area independent of the chrome clearing pattern. Two strong candidate wavelengths for calling endpoint in chrome etch were identified. However, optical emission spectroscopy endpoint detection has two drawbacks, which have historically limited its applicability. Firstly, the exposed area may be too low and/or secondly, the etch rate may be too slow for detection. Both of these concerns have been addressed in this paper by varying the exposed area on the photomasks from 0.25 percent to 99 percent. Endpoint was easily detected even for the slowest possible etch rate and for low exposed area.

Metal-Insulator-Metal capacitors with ALD grown SrTiO3: Influence of Pt electrodes

Metal-Insulator-metal (MIM) capacitors with atomic layer deposited (ALD) single SrTiO3 dielectric have been investigated in this work. Structural and electrical properties were studied after the formation of the MIM stack consisting of the platinum (Pt) bottom electrode, 50 nm SrTiO3 layer and the top Pt electrode. The as deposited films were amorphous and had a dielectric constant of ~ 10, whereas the annealing of the samples in the nitrogen (N2) or oxygen (O2) atmosphere at 550-600 °C led to the crystallization of the SrTiO3 and therefore to the increased dielectric constant of ~ 85. In addition, the electrical results revealed that the combination of SrTiO3 with the high work function electrode like Pt, provided better leakage current performance in comparison with TiN/ SrTiO3 stacks. The values as low as ~ 10−7 A/cm2 at 2 V were observed for both in N2 or O2 annealed SrTiO3 layers. On the other hand, the samples annealed in O2 atmosphere at 600 °C possessed lower capacitance-voltage nonlinearity coefficients (−645 ppm/V2) than the ones for N2 annealed samples (-2700 ppm/V2).

Numerical and experimental study of oxide growth on EUV mask capping layers

The interface roughness of EUV mask multilayers was taken into account for the numerical calculation of blank reflectance, and models for the growth of oxide on Si capping layers were proposed and evaluated. The simulations were then checked and validated with reflectometry measurements at different steps of the mask blank processing as well as for various angles of incidence, and ellipsometry data on layer thickness. The benchmarked models made it possible to characterize EUV mask blank Mo/Si multilayers (period, thickness ratio, number of bilayers), as well as Si capping layers and native oxide layers from reflectivity measurements. This enabled the study, via a combination of experiments and simulations, of the growth of SiO2 layers, bringing deeper understanding into this phenomenon. Finally, the simulations were used to more properly optimize multilayers and quantify the influence of the exposure tool illumination numerical aperture. Having successfully matched reflectivity data around the actinic wavelength, it was also possible to extend the models to inspection wavelengths in order to predict inspection contrast values.