Investigation on the Optimization of GaN Etching for FinFET Applications

Abstract: In the framework of this thesis, the optimization of the etching process of GaN for FinFET applications has been investigated. FinFETs are transistors with a vertical architecture in the shape of fins. These fins are fabricated by etching a pattern into a GaN substrate. The etching is carried out in two steps, a dry etch and a wet etch. In this thesis, these etching steps have been carried out while different parameters have been varied. The resulting fins have been examined in a SEM. The dry etch is carried out with ICP-RIE where the RF power, ICP power, and BCl3/Cl2 gas ratios have been varied. Increasing the RF power results in an increase of both physical and chemical etching components, resulting in increased etch rate and smoother fin walls. Increasing the ICP power however only increases the chemical etching component, resulting in increased etch rate but unchanged fin shape. Increasing the BCl3 gas ratio on the other hand reduces the chemical etching component, resulting in a reduced etch rate. By pre-heating the chemical and carrying out the process in a single time interval, instead of multiple short intervals, the most complete wet etch process can be achieved. A complete wet etch results in a fin with smooth sidewalls and no rough surfaces. The increased BCl3 gas ratio actively worsens the etching process and the ICP power increase only affects the rate, making it a not worthwhile change to the etching process. Only the RF power increase is a worthwhile change to the etching process. A proposed optimized recipe would be ICP-RIE etching with an RF power of 120 W, an ICP power of 300 W, and a BCl3/Cl2 ratio of 10% BCl3. This should be followed by wet etching in TMAH, heated to 40◦C for 50 minutes.