Oxide Defect Density, Failue Rate and Screen Yield

The concepts of "weakness factor", w, and defect density, D(w), are introduced for thin oxide study. The defect density is sensitive to silicon material qualities and process conditions and can be characterized by simple time-to-breakdown or ramp-breakdown field measurements (see Figure 1). We present an experimentally verified method of predicting the time-dependent dielectric breakdown (TDDB) behavior for different oxide area and field using D(w). We also demonstrate a method for determining the stress time and stress field required for screening to meet a given failure rate for any oxide area and operating field, and the yield loss due to screening. Based on this study, there appears to be a large window between adequate screen and over-screen.