In semiconductor manufacturing process, identification of device defects in early phase of the process flow is critical for accelerate process ramp-up times. On the other hand, the number of invisible electrical and material defects which cannot be detected by conventional dimensional metrology is increasing as semiconductor devices become more complex. To overcome this difficulty, we have developed an SEM equipped with two features: an electron beam modulator to generate pulsed electron beam and a laser irradiation feature. The laser enables control of the electrical state while the electron beam modulation enables charge dynamics measurement of device elements. In this report, we present (1) a technique to improve the detection sensitivity of contact defects by utilizing wavelength tunability and (2) evaluation results of contact resistance from voltage contrast using RC estimation systems.
In addition to the conventional process control method like dimensional metrology, there is a growing need to measure the electrical characteristics of device structures. Detection of defective electrical characteristics during device fabrication is important to improve device yield and shorten the ramp-up time of the manufacturing process. Voltage contrast of traditional scanning electron microscopes can be used to measure some of the electrical characteristics but is limited in its sensitivity and, hence, its applicable processes. We have developed a Laser-assisted SEM (LA-SEM) with (1) laser irradiation function and (2) electron beam modulation function to control and enhance the voltage contrast (VC) for in-line electrical inspection and measurement. In this report, for samples with high-impedance components obstructing the view of defect of interest, we confirmed that ultraviolet laser irradiation provides defect contrast that cannot be obtained with electron-beam-only VC. For Not-Open defects on a PN junction, the VC was improved by a factor of 1.19 by using a laser in the near-infrared region. Furthermore, to extract electrical properties of defects and monitor their changes during the manufacturing flow, a VC circuit simulation function was developed to quantitatively estimate VC transients obtained by modulated electron beam irradiation. As an example, a quantitative estimation of RC by transient voltage contrast analysis was performed on floating plugs with varying resistance using metal film deposition on its side walls. A decent correlation between the estimated electrical properties and the sheet resistance of the metallic film was demonstrated.
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.
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