Laser-assisted SEM for high-spatial resolution material metrology and inspection

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, such as breakdown voltage and damage, are of particular interest as they determine the characteristics as well as the reliability of the devices. 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 laser-assisted SEM; an SEM with laser irradiation capability to control the electrical state of the material under SEM observation. The laser can be used to inject carriers into insulators and neutralize insulator charging caused by the electron beam. By evaluating the energy of secondary electrons, we measured the charging voltage of insulators, defined as the difference in the surface potential between when the laser is irradiated and not irradiated. Similarly to breakdown voltage, we verified that the charging voltage increases with the insulator thickness. Furthermore, charging voltage was shown to be dependent on damage due to plasma in an etcher. Therefore, charging voltage measurements assisted by a laser is a unique way to evaluate the material property of insulators. We believe our laser assisted SEM will open the door to new types of electrical and material characterizations and go beyond the traditional role of SEMs in metrology and inspection.