The Zeta-Series optical profilers provide accurate measurement and automated analysis of high aspect ratio structures such as HEMT vias using non-destructive and high throughput metrology techniques.
The Zeta-Series optical profilers provide accurate measurement and automated analysis of high aspect ratio structures such as HEMT vias using non-destructive and high throughput metrology techniques.
Introduction
Wide bandgap semiconductor materials are extremely attractive for use in power electronics, due to their performance capability at high temperature, power and frequency. Among wide bandgap semiconductors, Gallium Nitride (GaN) is used in power device manufacturing (a) to exceed the performance of silicon high-voltage devices and (b) to be more cost effective than silicon carbide (SiC) power devices. The properties of GaN high-electron mobility transistor (HEMT) devices using a SiC substrate are optimized for high temperature electronics, radio frequency (RF) power amplifiers and power microwave applications.
The GaN/SiC HEMT manufacturing flow typically consists of the following steps: SiC substrate formation; GaN epitaxy; etch; front side device development; wafer bonding to carrier; wafer thinning; hard mask fabricating; via-hole etching; Au electroplating; wafer debonding/cleaning, packaging, via-hole etching process and Au electroplating. Figure 1 shows the backside via structure before (top) and after (bottom) the Au electroplating step. Monitoring the via etch process is critical because the quality of the etch directly impacts HEMT device performance. The key metrology parameters at this step include the opening diameter and average depth of the via holes. Although scanning electron microscopes (SEMs) can be used to measure hole depth of high aspect ratio (~ 1:3) structures, SEM techniques are either destructive or have low throughput. In contrast, 3D optical profiling offers a non-destructive, high-thruput means of measuring the critical dimensions vias.
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