Through silicon via profile metrology of Bosch etching process based on spectroscopic reflectometry

• 3D metrology of deeply-etched structures with an aspect ratio of more than 10.
• Estimation position and size (amplitude and period) of scallops on the side wall.
• Monitoring realized by spectroscopic reflectometry using wafer metrology tool.

Through silicon via (TSV) technology is a key feature of new 3D integration of circuits by creation of interconnections using vias, which go through the silicon wafer. Typically, the highly-selective Bosch Si etch process is used which is characterized by a high etch rate and high aspect ratio forming a series of scallops on the sidewall. The large scallops may reduce the reliability of the devices, appearing as leakage currents, thermo-mechanical stress or slow device response. The etch profile which is defined by top and bottom dimensions, depth, scallop size (period and amplitude) need to be both monitored and well controlled. Usually using secondary electron microscopy (SEM) cross-section image analysis is destructive, time consuming and depends on the cutting technique. In this work, the nondestructive 3D metrology of deeply-etched structures with an aspect ratio of more than 10 and patterns with lateral dimensions from 3 to 7 μm was performed by spectroscopic reflectometry. The TSV depths were determined using the interference effect between waves reflected from TSV’s top and bottom surfaces. The scallop size was estimated from the back diffraction effect of light from the side wall. The rigorous coupled wave analysis (RCWA) has been applied for scallop amplitude and top and bottom dimensions evaluation. By the characterization of the scallop size variation, the etch process (etch depth, rate, and reproducibility) can be controlled.

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