Study On The Solutions To Sti Oxide Aa Damage Defects

The semiconductor integrated circuit takes great changes with the development of semiconductor technology in the recent years. During these changes, the technology of semiconductor's isolation also changes greatly. In the past time, when semiconductor critical dimension is more than 0.25μm, Local Oxidation of Silicon (LOCOS) is used for isolation of semiconductor. LOCOS is the mature technology, which is used widely for the isolation in semiconductor micron times. But when semiconductor critical dimension is less than 0.25μm, especially the nanometer times is coming, STI (Shallow Trench Isolation) technology replaces LOCOS technology entirely in semiconductor isolation field because there are several insurmountable technical problems for LOCOS. After that, STI technology wakes up to historical arena and takes great contributions to semiconductor technology development.After semiconductor enters into nanometer times, STI thermal oxide thickness will be thinner and thinner because of the smaller and smaller critical dimension. For example, 90nm technology STI thermal oxide thickness is only 100 Angstrom. So the problem is coming that SiO gaseous unstable matter is made in the interface of silicon and silicon dioxide due to silicon and oxygen incomplete reaction when making thermal oxide layer. The SiO gaseous unstable matter will be exploded in condition of high temperature due to too thin oxide layer thickness, which results in thermal oxide damage in STI area. The defects will induce product wafer unstable electricity characteristic and reduce product yield and reliability. We call the STI thermal oxide defects as the STI oxide AA damage (AA, active area) defects. The article introduces the AA damage defects in 90nm logic and flash process. The STI oxide thickness is defined in different shallow trench positions through Transmission Electron Microscope. Then with different thickness oxide wafer experiments, we define the thickness borderline of SiO gaseous unstable matter exploding.Finally, we optimize STI thermal oxide and STI high temperature anneal recipes to combine two separate recipes as one recipe. In the recipe, not only STI oxide step exists oxygen gas, but also high temperature anneal step exists a little oxygen gas. With the method, SiO gaseous unstable matter can be reacted as SiO2 solid even in condition of high temperature thermal anneal, so the gas will not be exploded and the AA damage defects are solved, which can improve product wafer yield from 87.7% to 95.9%, reduce product cost for several million dollars and achieve huge economic benefits.