Applying optimal experiment design in reversed self-aligned contact etch of nor flash for profile performance improvement

The reversed self-aligned contact (R-SAC) scheme has been introduced into NOR flash memory technology. A key process challenge is the notorious trade-off among bowing profile control, shoulder nitride loss and process window margin. In this course, we investigated the potential of bowing profile optimization by applying an optimal experiment design (OED) to the SAC step. OED is an appropriate method for the screening experiments of non-linear parameters in dynamic process models, especially for cost intensive industry. In our case, the experiments were carried out with a four factors/two levels response surface method (RSM). Three center points are considered in the design table. Four factors are screened from SAC step's parameters, including pressure, power, fluorocarbon gas ratio and Ar flow rate. The specific factor levels were tailored based on previous learning. The optimal SAC condition was finally identified among the designed 18 OED pi-runs by means of statistically scientific analysis and delivered much less bowing profile than the baseline condition.