Christian Rivero

Embedded Stress Sensors for Strained Technologies Process Control

Mechanical stress management becomes a major issue for state-of-the-art CMOS technologies. Mechanical stress induced by the process steps is often at the origin of yield losses but also opportunities for technologies performance enhancement. Usual methods for mechanical stress measurement generally require offline measurements and are not compatible with fast correction of process parameters. We propose here embedded stress piezoresistive sensors to allow fast monitoring of mechanical stress and enable real time correction of the process parameters. The test vehicle presented here is dedicated to the gate structure stress monitoring. It is especially very sensitive to the nitride contact etch stop layer stress level. It is shown, in particular, that the structure is able to monitor process-related stress change in the nitride layer. Its feasibility, sensitivity, and relevance in an advanced process control scheme are investigated.

Metallization Local Stress Monitoring In Industrial Semiconductor Processes

A new mechanical stress characterization method has been developed for Damascene copper interconnects. The micro strain gauge based on a rotating beam has been fabricated in situ on a standard industrial production line. An analytical model gives a direct value of the local stress in the copper line according to the pointers rotation. We show that this value is different from the one given by a curvature measurement method. The microstructure of the Damascene copper induces a higher stress level than full sheet deposition copper. The sensor was developed to be compatible within a CMOS process. It is suitable for in situ mechanical stress monitoring in Damascene lines and process optimization.

Mechanical–Electrical Measurements and Relevant Test Structures for Sensing Interconnect Stress Effects in CMOS Technology

For CMOS technology, the increase of interconnects metal density is responsible for heterogeneous mechanical stress fields in active regions of silicon. Coupled mechanical–electrical measurements are performed to evaluate the impact of stress at circuit and device levels. This mismatch originated by interconnects metal lines stress is measured through the use of piezoresistive test structures. Local mechanical stress can thus be monitored in a simple process control compatible approach.

Sensing mobility mismatch due to local interconnect mechanical stress in CMOS technology

For CMOS technology, the increase of interconnects metal density is responsible for heterogeneous mechanical stress fields in active region of silicon. This mismatch originated by interconnects metal lines stress is measured through the use of piezo-resistive test structures. Local mechanical stress can thus be monitored in a simple process control compatible approach.

Embedded Mechanical Stress Sensors for Advanced Process Control

For state of the art microelectronic technologies, reliability is a major challenge. Mechanical stress induced by the process steps is often at the origin of yield losses. Degradations of electronic devices are usually correlated to the presence of defects such as dislocations, cracks or delaminations. Usual methods for mechanical stress measurement generally require off-line measurements and are not compatible with fast correction of process parameters. We propose here embedded stress microsensors to allow fast monitoring of mechanical stress and enable real time correction of the process parameters. The test vehicle presented here is dedicated to polysilicon stress monitoring. Its feasibility, sensitivity and relevance in an advanced process control objective are particularly investigated.

Mechanical Stress Sensors for Copper Damascene Interconnects

We propose embedded microsensors to investigate the mechanical stress in copper damascene lines in a standard CMOS microelectronic technology. Those sensors are based on silicon piezoresistive effect where strain in the active silicon is induced by orientated copper lines. The challenge is to correlate the electrical sensors signal directly to stress variation in lines. We have performed electrical measurements of the structures as a function of temperature. A coupled analytical and Finite Element thermomechanical Model of the structure was developed and a good agreement with measurements was obtained.

Robust design of thermo-mechanical MEMS switch embedded in aluminium BEOL interconnect

Abstract A new concept of a thermo-mechanical lateral switch activation is proposed. Embedded in standard aluminium BEOL (Back End Of Line), it is fully integrated in CMOS technology. The simplicity of this low cost one-mask fabrication allows the straightforward scalability of design. Most functional problems have been solved through process, simulation and design: stiction, bending, displacement, and robustness. The present study of a thermo-mechanical MEMS switch focuses on three points. Firstly, the design is modified to increase the apparent area contact and the force applied. Secondly, in order to ensure the reversibility of the movement, a running-in step before operation is implemented. Finally, a new design is proposed, simulated and manufactured to avoid the undesirable activations by spurious homogeneous heating.

Determination of material properties and failure using in-situ thermo-mechanical probe

A metallic in-situ stress sensor is modified to address electrical polarization and thus to locally heat this sensor by Joule effect. By coupling SEM electrical nano-probing with analytical modeling and multiphysics Finite Element Method (FEM), the thermo-mechanical properties are identified. As a result, a tensile stress state of 190 MPa, coefficient of thermal expansion of 22.5×10-6 K-1 and thermal conductivity of 190 W/(K·m) are identified in the aluminum thin film in agreement with literature. Moreover, high current induces irreversible deformation and breaking. Using multiphysics FE model with identified thermo-mechanical properties, the failure of the sensor under electrical solicitation is investigated. The evolution of local temperature and mechanical deformation on different sensor designs allows the determination of the breaking location and condition.

In-situ study and modeling of the decreasing reaction rate at the end of CoSi 2 formation

In-situ X-Ray diffraction was used to determine CoSi2 kinetics growth from 100 nm CoSi. In this work, we discuss about an unexpectedly slow reaction that is observed at the end of CoSi2 formation. A 1D model has also been developed from these experiments in order to reproduce the sequential growth of cobalt silicides and the end of the reaction experimentally observed in this study.