Overlay metrology performances highly depend on the detailed design of the measured target. Hence performing simulations is an essential tool for optimizing target design. We demonstrate for scatterometry overlay (SCOL) three key factors which enable consistency in ranking between simulated and measured metrology performance for target design. The first factor, to enable high fidelity simulations for the purpose of target design, is stack and topography verification of model inputs. We report in detail the best known film metrology methods required to achieve model integrity. The second factor is the method of calculation of metrology performance metrics based on target cell reflectivities from electro-magnetic (EM) simulations. These metrics enable ranking of different designs, and subsequent choice of the best performing designs among all simulated design options, the ranking methodology being the third factor. We apply the above steps to a specific stack, where five different designs have been considered. Simulated versus measured values are compared. A good agreement between simulation and measurement is achieved.
Overlay metrology target design is an essential step prior to performing overlay measurements. This step is done through the optimization of target parameters for a given process stack. A simulation tool is therefore used to improve measurement performances. This work shows how our Metrology Target Design (MTD) simulator helps significantly in the target design process. We show the role of film and Optical CD measurements in improving significantly the fidelity of the simulations. We demonstrate that for various target design parameters we are capable of predicting measured performance metrics by simulations and correctly rank various designs performances.
Computational metrology target design requires both an accurate metrology simulation engine and an accurate geometric model. This paper deals with the later. Optical critical dimension metrology and cross-section SEM are demonstrated as two useful methods of geometric model verification with differing capabilities. Specifically, a methodology is proposed which allows the metrology engineer to quantify the level of accuracy required by the model as a function of the tolerable uncertainty in the prediction of metrology performance metrics. The methodology identifies a subset of model parameters which need to be verified enabling the metrology engineer to invest the minimum effort in stack and topography verification which will lead to performing target designs on the first design round.
To combine low-cost fabrication and high-speed data communication like 100 GBit/s, multi-section DBR lasers are
developed with nanoimprint compatible surface defined gratings. This laser design has the potential to enhance the
modulation bandwidth by exciting a higher order optical mode, the so-called photon-photon resonance (PPR). ICP-RIE
etching was used to transfer the e-beam exposed surface pattern in one step into the semiconductor. High aspect ratios of
> 1:15, vertical trenches with a width of about 140 nm and an etch depth of > 2 μm were obtained for the lateral gratings.
Three-section DBR lasers are fabricated on an MOVPE grown 1.5 μm InP laser material exhibiting CW threshold
currents of 94 mA for a 0.9 mm long device. A side mode suppression ratio of > 50 dB could be achieved demonstrating
a high enough coupling strength of the lateral gratings. The influence of different operation conditions (currents,
temperature) and dependence on the grating period on threshold current and emission wavelength are studied and will be
discussed in this paper. First high frequency measurements in operation conditions without PPR enhancement show a -
3dB bandwidth of about 15 GHz.
The conventional distributed feedback and distributed Bragg reflector edge-emitting lasers employ buried gratings,
which require two or more epitaxial growth steps. By using lateral corrugations of the ridge-waveguide as surface
gratings the epitaxial overgrowth is avoided, reducing the fabrication complexity, increasing the yield and reducing the
fabrication cost. The surface gratings are applicable to different materials, including Al-containing ones and can be easily
integrated in complex device structures and photonic circuits. Single-contact and multiple contact edge-emitting lasers
with laterally-corrugated ridge waveguide gratings have been developed both on GaAs and InP substrates with the aim to
exploit the photon-photon resonance in order to extend their direct modulation bandwidth. The paper reports on the
characteristics of such surface-grating-based lasers emitting both at 1.3 and 1.55 μm and presents the photon-photon
resonance extended small-signal modulation bandwidth (> 20 GHz) achieved with a 1.6 mm long single-contact device
under direct modulation. Similarly structured devices, with shorter lengths are expected to exceed 40 GHz small-signal
modulation bandwidth under direct modulation.