In-situ shallow trench isolation etch with clean chemistry

An in-situ hard-mask open and self-clean shallow trench isolation (STI) etch process with a bromine and fluorine based chemistry was developed using an Applied Materials DPS chamber. SEM micrograghs from an etched photoresist-patterned wafer show a desired trench profile with rounded bottom corners and smooth side walls. Quartz crystal micro-balance (QCM) measurements, coupon tests, and a 1000 wafer extended run demonstrate a dean STI process. No dry clean are necessary. The STT step used a chemistry which balanced oxygen passivation with fluorine based etching. More tapered profiles can be achieved by increasing the O2 flow rate. Furthermore, the side wall passivation and oxidation improve the bottom corner rounding, which is desired to minimize stress and current leakage. Fluorine radicals chemically etch the silicon. With increasing fluorine content, the formation of side wall passivation becomes less pronounced, and therefore the trench profile becomes more vertical. This strategy of balancing chemical etchants, passivators, and energetic ions enables tuning of the profile within a wide range. In addition to chemistry, the source power and bias power were all varied. The effect of these parameters on the trench profile angles, corner rounding and microloading are discussed. The simplicity, cleanliness, and excellent profile performance of the process make it a most promising candidate for sub-micron STI manufacturing.