In-situ nitride mask open [STI technology]

As feature sizes approach 0.25 μm and below, shallow trench isolation (STI) has become the most favorable isolation scheme. One challenge in the development of a production-worthy STI process is to combine the hard mask open and STI step into a single etch chamber. An STI process with an in situ hard mask open provides lower cost of ownership as well as higher throughput. Chamber cleanliness is another critical issue for STI processes using conventional etchants such as HBr, Cl₂, and O₂. HBr related etch by-products usually result in severe deposition inside the chamber, thus causing particle problems. This paper describes a nitride mask open process using a clean fluorine-based chemistry which has been successfully integrated into an STI process. However, the aggressive nature of the fluorine-based chemistry also attacks the photoresist and tends to etch the nitride isotropically. Therefore, it is essential to choose process parameters that maximize the selectivity to photoresist and yield the most vertical nitride etch. Source power, bias power, gas flow, and pressure were all studied in order to maximize process performance. A typical sample consisted of an 8" silicon wafer with 25 nm of thermally grown oxide, 200 nm of nitride, and a 700 nm DUV photoresist mask. SEM micrographs were used to monitor the effects on profile angle, corner rounding, selectivity, and microloading. Quartz crystal monitor data and a 1000 wafer burn in both indicate that there is no deposition on the dome or chamber walls