DRY PROCESSED, THROUGH-WAFER VIA HOLES FOR GAAS POWER DEVICES

The fabrication of through-wafer via holes in GaAs substrates by plasma etching and laser drilling is reported. Using a low pressure (15-20 mTorr), low dc bias ( - 150 V) Cl2/BCl3 discharge with Cl2-to-BCl3 ratios <0.2, we are able to produce narrow (less-than-or-equal-to 30 mum) via holes. This enables the use of a higher density of vias in closer proximity to the active GaAs power devices than can be achieved with normal diameter (100-150 mum) holes. Microwave enhancement of the plasma density using an electron cyclotron resonance source increases the GaAs vertical and lateral etch rates and requires use of low Cl2-to-BCl3 ratios in order to retain the anisotropic nature of the vias. Multiple pass (approximately 100 per hole) drilling of vias with a Q-switched Nd-YAG frequency doubled (532 nm), 30 mW laser has also successfully produced through-wafer connections. This provides a maskless, versatile method for producting vias customized for a particular wafer, but is less developed than plasma etching.