Objective There are a large number of high-aspect-ratio structures in silicon-based MEMS devices, and non-destructive testing of linewidth and depth of these structures is a hot issue at present. Generally, the depth-to-width ratio of MEMS high-aspect-ratio structures is generally between 10∶1 and 100∶1, and the trench width is a few microns to tens of microns. At present, in the silicon-based MEMS process line, anatomical testing is the main means of high-aspect-ratio structure testing, but there are the following defects: it is necessary to use scanning electron microscopy (SEM) for auxiliary measurement, which is inefficient and cumbersome; It is a destructive measurement that causes irreversible damage to MEMS products; It can only be sampled and cannot fully reflect the characteristics of the process. Based on this, a non-destructive measurement system with high-aspect-ratio structure near-infrared broad-spectrum microscopy measurement system was developed, and its measurement accuracy will directly affect the overall performance of the device under test, so it is necessary and urgent to calibrate the measurement system.
Methods In order to achieve the accurate calibration of the non-destructive measurement system of high-aspect-ratio structure, a series of standard samples of high-aspect-ratio trenches are designed and developed by semiconductor process, with a width range of 2-30 μm, a depth range of 10-100 μm, and a maximum high-aspect-ratio of 30∶1 (Tab.1). The samples were characterized and fixed, and finally the developed standard samples were applied to the calibration of the near-infrared broad-spectrum microscopy measurement system (Fig.13).
Results and Discussions In order to meet the calibration function of the standard samples, a variety of characteristic structures are designed (Fig.1), including auxiliary fixed value structure, measurement positioning structure and positioning angle structure, etc., and the characterization and assessment method of the sample value are designed (Fig.5-6). Measurement values include line width size, trench depth size, and uniformity. Finally, the developed standard template is applied to the near-infrared broad-spectrum microscopy measurement system to further verify the accuracy of the developed system, that is, the applicability of the template (Tab.2).
Conclusions In order to solve the calibration problem of the near-infrared broad-spectrum interferometric microscopy system, a series of standard samples of high-aspect-ratio grooves were developed, with a width range of 2-30 μm and a depth range of 10-300 μm, and its high-aspect-ratio reached a maximum of 30∶1. In order to meet the calibration function of the template, a variety of characteristic structures are designed, including auxiliary fixed value structure, measurement positioning structure and positioning angle structure, etc., and the characterization and assessment method of the sample measurement value is designed. Since there is no suitable measuring instrument to directly characterize the value of the standard template of the composite high-aspect-ratio trench, an auxiliary fixed value structure is designed for the standard template, and the cross-section of the high-aspect-ratio trench structure is displayed by sectioning, and then it is measured by scanning electron microscope or atomic force microscope, and the uniformity of the template is characterized to ensure the consistency of the measurement results of the template. Finally, the developed standard template was measured by the near-infrared broad-spectrum interferometric micrometry system, and the measurement results showed that the magnitude was basically consistent with the characterization results.
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