Abstract
A design of experiment for nonselective etching InGaAs/GaAs/InGaP in inductively coupled plasma (ICP) BCl3/HBr discharges has been investigated. The influences of variations in pressure, RF1 power (chuck power-13.56MHz), RF2 power (ICP power-2MHz), and gas flow (BCl3/HBr) ratio on the etching performance were examined. The combination of BCl3/HBr plasmas made it possible to have a new process window for nonselective etching of InGaAs/GaAs/InGaP in an ICP reactor with high etch rate (> 2700 A/min), steep epitaxial sidewall (>80o), and over 5 of selectivity of epitaxial layer to silicon nitride.The design of experiment utilized is the L9 (34) table in Taguchi Method. Prior to Taguchi Method, some pre-experiments were done to realize the proper ranges of the process parameters and to choose either photo-resist or silicon nitride as the mask in L9 (34) experiment. After analyzing the results in L9 Method, experiments using the optimized recipe from L9 Method were run to verify the reliability.As the pressure increases, the mean free path of gas shortens. It results in reducing physical ion bombardment. Therefore, the more pressure decreases, the steeper the epitaxial profile and the higher the etch rate are.Ion energy increases as RF1 power. It results in sharper epitaxial sidewall and higher etching rate, but it may cause damage to the device. Moreover, higher RF2 power leads to higher ion density, so the etching profile becomes steeper and the etch rate of epitaxial layer is higher.BCl3-based mixtures have been found to be attractive plasma chemistries for patterning GaAs and related compounds because of its ability to getter water vapor and readily remove the native oxides on these materials. Nevertheless, as the Indium-based compound semiconductors are etched in the BCl3 discharges, the InClx products are much less volatile than their GaClx counterparts. Bromine-based chemistry, such as HBr, is a good etching chemistry for dry etching indium and phosphorous containing materials because of the relatively low reaction product vapor pressures, InBrx and PBrx, compared to the respective chlorides. The more gas flow ratio of HBr, the higher the etch rate and the more abrupt the epitaxial profile are. However, the HBr gas has high ionization potential so that it is hard to be ignited. We can’t use too high gas flow ratio of HBr; otherwise, the plasma will be unstable.