Evaluation of thin-film material properties using laser-assisted SEM

As semiconductor devices continue to introduce new materials and structures, not only the dimensions but the material properties are becoming important in determining the device properties. Properties of insulator films used in transistors and memory devices are of particular interest as they determine the characteristics as well as the reliability of the devices. The material properties can depend not only on their deposition conditions, but also on the processes they are later exposed to, such as annealing and etching. Therefore, the film properties can change over the course of device fabrication. To ensure efficient production of these devices, an inline tool for metrology and inspection of material properties is desirable. One way to evaluate the material properties is to measure the material’s response to application of voltage. For this purpose, we have developed a laser-assisted SEM, an SEM with laser irradiation capability to control the electrical state of the material under SEM observation. The laser is used to inject carriers into insulators to control or neutralize insulator charging caused by the electron beam. Therefore, the combination of an electron beam and laser irradiation can be used to control the sample voltage. The material response can be measured in either the amount or energy of the secondary electron signals. Therefore, how the signal changes depending on the electron beam or the laser condition can be used to indirectly evaluate the material properties of the sample. In this work, we have used the laser-assisted SEM to detect the change in material properties of insulator films under annealing and different etching plasma conditions. The laser-assisted SEM was found to be sensitive not only to bulk film properties, but also to buried interfaces. These new features can make the laser-assisted SEM useful as needs continue to grow for inline metrology and inspection of semiconductor devices.