A comparative reliability study of copper-plated glass vias, drilled with CO2 and ArF excimer lasers

Interposer technologies for 2.5D and 3D integration schemes require formation of high density and reliable Through-Package-Vias (TPVs) at high throughput and low cost. Glass is proposed to be an ideal candidate material for interposer applications. Among various methods to form TPVs in glass, a variety of laser processing methods have been proposed as feasible methods. The via hole formation mechanisms of different lasers differ from each other which leads to variations in via quality. To study the effects of via quality on reliability, accelerated lifetime tests were conducted on copper-plated TPVs formed with different lasers in glass interposers. Two different lasers for the TPV formation were investigated in this study - a high power CO₂ laser and an ArF-based excimer laser. Separate test vehicles containing vias drilled with each of these two methods were fabricated for thermal cycle tests (TCT). The test vehicles contained daisy chains. No failures were detected in the TCT based on a failure criterion of 10 % increase in resistance per daisy chain. TPVs were characterized with optical and electron microscopy after drilling, after fabrication, and after the tests.