Joachim Bauer

Deep-UV Technology for the Fabrication of Bragg Gratings on SOI Rib Waveguides

In this letter, we present a wafer level technology based on deep-ultraviolet lithography to fabricate Bragg gratings on silicon-on-insulator rib waveguides. The principle of the used double-patterning technique is presented, as well the influence of the process variation on the device performances. The fabricated Bragg gratings were characterized and compared to analogue structures patterned with electron-beam lithography.

Novel Ring Resonator Combining Strong Field Confinement With High Optical Quality Factor

Slot waveguide ring resonators appear promising candidates for several applications in silicon photonics. Strong field confinement, high device tunability, and low power consumption are beneficial properties compared with strip waveguides. Slot waveguide ring resonators suffer, however, from rather low optical quality factors due to optical losses. This letter proposes and experimentally demonstrates a novel concept based on a partially slotted ring and a strip-to-slot mode converter. An exceptional high quality factor of ~105 has been measured.

ARC technology to minimize CD variations during emitter structuring: experiment and simulation

Coming out of our in-house SiGe-hetero-bipolar-technology we found that the variations of some of the important electrical parameter like the emitter current are depending on the variations of the critical dimension (CD) during the emitter structuring and this effect is mainly caused by the used i-line photolithography. To minimize the CD variations we used anti reflective coatings. For comparison reasons we applied three different resist technologies, without any ARC, with top ARC (TARC), and with bottom ARC (BARC). During our 0.4 micrometers emitter structuring the CD variations could be reduced down to +/- 40-30 nm for the resists and the resist/TARC combination. The smallest CD variation +/- nm was found by applying the BARC Resist Technology. As an optimization strategy calculations of the resist reflection and the resist absorption were very helpful.

E-beam and deep-UV exposure of PMMA-based resists: identical or different chemical behavior?

The chemical reactions and the dissolution properties of homopolymeric PMMA and a P(MMA-co-MAA) copolymer were investigated during DUV (KrF, 248 nm) and e-beam exposure. The chain scission reaction was analyzed using GPC. The polymer degradation reaction is very similar at both exposure procedures. In both cases a bimodal and, later, a multimodal character of the molecular weight distribution is observed.

Partially slotted silicon ring resonator covered with electro-optical polymer

In this work, we present for the first time a partially slotted silicon ring resonator (PSRR) covered with an electro-optical polymer (Poly[(methyl methacrylate)-co-(Disperse Red 1 acrylate)]). The PSRR takes advantage of both a highly efficient vertical slot waveguide based phase shifter and a low loss strip waveguide in a single ring. The device is realized on 200 mm silicon-on-insulator wafers using 248 nm DUV lithography and covered with the electro-optic polymer in a post process. This silicon-organic hybrid ring resonator has a small footprint, high optical quality factor, and high DC device tunability. A quality factor of up to 105 and a DC device tunability of about 700 pm/V is experimentally demonstrated in the wavelength range of 1540 nm to 1590 nm. Further, we compare our results with state-of-the-art silicon-organic hybrid devices by determining the poling efficiency. It is demonstrated that the active PSRR is a promising candidate for efficient optical switches and tunable filters.

Characterization of Structural Defects in Germanium Epitaxially Grown on Nano-Structured Silicon

Selective epitaxial growth of germanium (Ge) on nano-structured Si(001) wafers is studied to evaluate the applicability of the nano-heteroepitaxy (NHE) approach on Ge-Si system. Based on a gate spacer technology established in advanced silicon microelectronics periodic arrays of nano-scaled Si islands are prepared, where Ge is deposited on top by reduced pressure CVD. The spacing of these structures is 360 nm. The structural perfection of the deposited Ge is investigated by transmission electron microscopy and X-ray diffraction. It is found that SiO2 used as masking material is responsible for the suppression of the desired strain partitioning effect according to NHE. Even for 10 nm oxide thickness, the lattice of Ge layers deposited on Si nano-islands relaxes completely by generation of misfit dislocations at the interface. The occurrence of additional structural defects like stacking faults and micro twins can be controlled by suited growth conditions.

DUV and e-beam chemistry of high-sensitivity positive PMMA-based resist

We present an investigation to study the degradation of PMMA, poly(methyl methacrylate), and ARP-610, poly(methyl methacrylate-co-methacrylic acid), during e-beam and DUV exposure. The change in the chemical structure of the polymer materials were analyzed using UV, IR, NMR spectroscopy, gel permeation chromatography and GC-MS. The formation of anhydrides within the isotactic parts of the co-polymer causes a bimodel and multimodal distribution of the fragments and, therefore, a more efficient dissolution process.

Hybrid-Waveguide Ring Resonator for Biochemical Sensing

This paper proposes a hybrid-waveguide ring resonator for on-chip biochemical sensing. Consisting of a low-loss strip-waveguide and a highly sensitive slot-waveguide integrated in a silicon photonic platform, it combines advantages of both waveguide types. In this way, it provides the unique feature to increase the sensitivity while maintaining low optical losses. Thus, this resonator structure may represent a promising alternative approach for future integrated biochemical sensing applications. This is suggested by a theoretical analysis, involving numerical simulation of the hybrid-waveguide ring resonator and an optimization of the slot-waveguide structure with regard to light-analyte-interaction. It is demonstrated that the hybrid-waveguide concept may overcome limitations in terms of overall resonator sensitivity, which is described by a figure of merit, connecting the optical losses with the resonator sensitivity.

Very high aspect ratio through silicon via reflectometry

Through Silicon Via (TSV) technology is a key feature of new 3D integration of circuits by creation of interconnections using vias, which go through the silicon wafer. Typically, the highly-selective Bosch Si etch process, characterized by a high etch rate and high aspect ratio and forming of scallops on the sidewalls is used. As presented in this paper, we have developed an experimental setup and a respective evaluation algorithm for the control and monitoring of very high aspect ratio TSV profiles by spectroscopic reflectometry. For this purpose square via arrays with lateral dimension from 3 to 10 μm were fabricated by a Bosch etch process and analyzed by our setup. By exploiting interference and diffraction effects of waves reflected from the top and bottom surfaces as well as from the side walls of the TSV patterns, the measurements provided etch depths, CD values and scallop periods. The results were compared with data obtained by a commercial wafer metrology tool. Aspect ratios of up to 35:1 were safely evaluable by our setup.

Development of graphene process control by industrial optical spectroscopy setup

The successful integration of graphene into microelectronic devices depends strongly on the availability of fast and nondestructive characterization methods of graphene grown by CVD on large diameter production wafers [1-3] which are in the interest of the semiconductor industry. Here, a high-throughput optical metrology method for measuring the thickness and uniformity of large-area graphene sheets is demonstrated. The method is based on the combination of spectroscopic ellipsometry and normal incidence reflectometry in UV-Vis wavelength range (200-800 nm) with small light spots (~ 30 μm2) realized in wafer optical metrology tool. In the first step graphene layers were transferred on a SiO2/Si substrate in order to determine the optical constants of graphene by the combination of multi-angle ellipsometry and reflectometry. Then these data were used for the development of a process control recipe of CVD graphene on 200 mm Ge(100)/Si(100) wafers. The graphene layer quality was additionally monitored by Raman spectroscopy. Atomic force microscopy measurements were performed for micro topography evaluation. In consequence, a robust recipe for unambiguous thickness monitoring of all components of a multilayer film stack, including graphene, surface residuals or interface layer underneath graphene and surface roughness is developed. Optical monitoring of graphene thickness uniformity over a wafer has shown an excellent long term stability (s=0.004 nm) regardless of the growth of interfacial GeO2 and surface roughness. The sensitivity of the optical identification of graphene during microelectronic processing was evaluated. This optical metrology technique with combined data collection exhibit a fast and highly precise method allowing one an unambiguous detection of graphene after transferring as well as after the CVD deposition process on a Ge(100)/Si(100) wafer. This approach is well suited for industrial applications due to its repeatability and flexibility.