Dual damascene is an established patterning process for back-end-of-line to generate copper interconnects and lines. One of the critical output parameters is the electrical resistance of the metal lines. In our 200 mm line, this is currently being controlled by a feed-forward control from the etch process to the final step in the CMP process. In this paper, we investigate the impact of alternative feed-forward control using a calibrated physical model that estimates the impact on electrical resistance of the metal lines* . This is done by simulation on a large set of wafers. Three different approaches are evaluated, one of which uses different feed-forward settings for different radial zones in the CMP process.
In a 200 mm high volume environment, we studied data from a dual damascene process. Dual damascene is a combination of lithography, etch and CMP that is used to create copper lines and contacts in one single step. During these process steps, different metal CD are measured by different measurement methods. In this study, we analyze the key numbers of the different measurements after different process steps and develop simple models to predict the electrical behavior* . In addition, radial profiles have been analyzed of both inline measurement parameters and electrical parameters. A matching method was developed based on inline and electrical data. Finally, correlation analysis for radial signatures is presented that can be used to predict excursions in electrical signatures.
KEYWORDS: Distortion, Overlay metrology, Process control, Virtual reality, Metrology, Environmental sensing, Front end of line, Back end of line, Reliability, Statistical analysis, Semiconducting wafers, Model-based design, Metals, Data modeling, Optical alignment
Overlay measurements are done for verification of the exposure and creation of process corrections for the next lots. As throughput of the overlay measurement tools is limited, it is desirable to avoid unnecessary measurements. Another concern can be that in-transparent stacks do not allow measuring a critical overlay relation directly. We developed methods for calculation of the overlay relation between two different layers between which there is no direct overlay measurement. We qualify the impact of sampling plans and the number of dependent layers. The indirect overlay calculation is applied on a significant high volume data set.
We have been utilizing rigorous simulation software in order to predict the alignment mark signal quality and mark contrast variation induced by processes changes reliably. We have run simulations in order to understand which parameters influence alignment mark quality most and to determine the important parameters that can be manipulated in order to improve it. Simulation of alignment signals (also referred to as waveforms) has been done for resist marks and etched marks, coated and uncoated, as well as in presence of increasing topography complexity. To validate simulation analysis, mark signal collection for different processes (and/or variations of those) and products has been carried out; cross sections have also been generated.
AIM grating targets were optimized and implemented on the metal 2 Aluminum layer in high volume production of 110-nm DRAM devices. Grating target structures are intrinsically more compatible with Aluminum process design rules, allowing overlay target optimization to better fit the process and better cope with the large grain structure of the Aluminum layer. With the implementation of AIM overlay targets we were able to achieve tighter control of the Aluminum patterning, we also achieved smaller overlay residuals, better matching between post litho and post etch measurements, better modeling and less rework. Above all, AIM targets improve the overlay metrology tool capability and provide a better tool-to-tool matching performance.
The paper describes a sensor head for long-term high-precision measurements of very small deflections of a diaphragm used for pressure gauges. High precision deformation measurement is assured by using a fiber Fabry-Perot interferometer sensor; identification of zero-point changes, and thus, long-term stable measurement is achieved by a specially designed absolute interferometer sensor. Several fiber optic solutions based on fiber Fabry-Perot technique have been investigated to find out a reliable sensor design. The presented sensor design has reached prototype status and allows to measure unambiguously static deformations with high precision. In order to evaluate repeatability and possible changes of zero-point reference if the head has been disconnected, validation of the described pressure gauge has been started. This validation work includes calibration and enables to evaluate possible drift effects, and to identify mechanical or thermal hysteresis.
Contact layers of the DRAM manufacturing process can be printed well using alternating phase-shifting masks. State-of-the-art mask making tools have sufficient performance to manufacture defect free contact masks. The enlarged process window compared to conventional masks allows to shrink the contacts size or to substitute advanced scanners by older generation steppers for contact layer patterning. Using older generation exposure systems may cause problems originating in worse lens aberration performance. A method will be described how to overcome overlay problems by applying a specifically designed OL measurement target.
KEYWORDS: Fiber Bragg gratings, Sensors, Aluminum, Optical fibers, Temperature metrology, Signal attenuation, Digital signal processing, Silica, Calibration, Structured optical fibers
For the last decade sensor architectures with embedded fibers found their application in large structure monitoring and proved their capability to replace existing techniques for monitoring of linear strain, temporary or permanent none-uniform strain and load, temperature, vibrations, bending, or complex strain-temperature, vibrations-temperature influences, etc. Such sensor architectures, called smart structures, use different sensing mechanisms, in one of which - fiber Bragg grating (FBG) - is applied as a sensitive element. Because of high sensitivity, absolute measurement ability, possibility to work reliable in adverse environment, such as electromagnetic fields, radiation, extreme temperature, and quick response time, FBGs are object of numerous research of leading laboratories worldwide. Some problems are still remaining in this field, although there have been some ways found to solve part of them. This paper discusses some aspects of different fixing mechanisms of FBG and provides evaluation and comparison of methods of FBG integration in sensor housing or in sensor architecture.
The bond behavior of textiles embedded in concrete and consisting of multi filament yarns (rovings) differs from that of homogenous materials such as steel. Test results published in the literature as well as own investigations revealed that, for textile reinforced concrete, it has to be distinguished between external and internal bond of the fibers (filaments). The outer filaments which have direct contact to the cement matrix show a good bonding performance. In contrast to this, the inner filaments (core filaments) of a roving transfer forces only by friction, resulting in a less bonding to the surrounding matrix. In order to confirm such a bonding model, strain and slip measurements at single filaments are necessary in pull-out-samples. However, such measurements are not possible with strain gauges usually used in structural engineering. Therefore, strains in outer and inner filaments as well as in the cement matrix of selected samples are measured by using flexible Fabry-Perot fiber interferometer sensors.
In a German slab track system (Feste Fahrbahn FF, system Boegl) for speeds up to 300 km/h and more different fiber optic sensors have been embedded in several levels and locations of the track system. The track system consists of prestressed precast panels of steel fiber concrete which are supported by a cat-in-situ concrete or asphalt base course. The sensors are to measure the bond behavior or the stress transfer in the track system. For that, tiny fiber-optic sensors - fiber Fabry-Perot and Bragg grating sensors - have been embedded very near to the interface of the layers. Measurements were taken on a full scale test sample (slab track panel of 6.45 m length) as well as on a real high speed track. The paper describes the measurement task and discusses aspects with regard to sensor design and prefabrication of the sensor frames as well as the embedding procedure into the concrete track. Results from static and dynamic full scale tests carried out in the testing laboratory of BAM and from measurements on a track are given.
A new central railway station - Lehrter Bahnhof - is being built in Berlin. Because of construction activities in immediate vicinity and because of difficult soil conditions, different vertical displacements have to be expected. In order to avoid damage to the bridges and to a widely spanned glass roof which will be supported by two concrete bridges these two bridges have to be monitored with regard to their deformation performance right from the beginning of construction until commissioning as well as later on for several years. For this purpose, a monitoring concept has been developed and sensors with excellent long-term stability have been chosen. This paper describes the system for monitoring settlements and heaves by means of laser-based optics and hydrostatic leveling. Additionally, strain and inclination of the prestressed concrete bridges are redundantly monitored by embedded long-gage length fiber-optic strain sensors as well as resistive strain gages, and inclinometers. Measurements on-site are referenced by measurements on two test beams well-defined loaded under laboratory and field conditions. The paper also describes the measuring concept and the sensor techniques as well as installation of the sensor system and first results.
In a reinforced concrete wall the deformation during concrete hardening was measured by means of embedded extrinsic fibre-Fabry-Perot-interferometers. The sensors were specifically modified in order to provide a self-calibration cycle and to ensure the functional efficiency under adverse conditions at the building site. The installation was done in the wall's cage of reinforcement before its concreting. The measurement was carried out automatically over a period of 35 days. The measuring results are very satisfactory and give a resolution of 0.1 micrometers /m.
Fiber optical sensors were applied on a cracked prestressed concrete bridge in Berlin to get the static and dynamic structure response under load. Interferometric sensors (extrinsic Fibre-Fabry-Perot) were adhered on prestressing steels of a tendon opened inside the box girder; Intensity- modulated fiber sensors were tightened over the cracked concrete region. The very high resolution of interferometric sensors ((epsilon) equals +/- 0.024 micrometers /m) simultaneously allowed to measure strain of tendon and dynamic (natural frequency) response. This bridge is the first prestressed concrete structure in Germany to have fiber optic interferometric sensors installed. The optimization of the adhesive bonding and embedment technique are problems that need to be addressed as part of the further development.
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