Cutline and Circular Profiles of Parameter Distributions

Introduction

It is well known that due to the physical nature of certain process steps, the SPICE model parameters as well as defect density distributions follow some spatial distribution. To detect process deviation from specification limits and improve the process operation it is very critical to have a tool to detect such spatial distribution within the specification limits of parameters. Cutline and circular profiles of parameter distributions, a new feature of SPAYN, are designed to give users an effective and intuitive way to fulfill this goal. With the emerging 8 inch fab lines, the spatial distribution of parameters across an 8 inch wafer will be a critical parameter to monitor.

 


Figure 1. Histogram distribution for a parameter found through a vertical stack of the same die location.

Features Definition

This new feature of SPAYN provides three options for displaying the distributions of parameter values:

1. At any one die location, the vertical distribution of any SPICE model parameters can be displayed by using the histogram window.

2. Any cutline distribution of SPICE model parameters, for one wafer and/or a set of wafers.

  1. Any circular distribution of SPICE model parameters, for one wafer and/or a set of wafers.


Figure 2. An arbitrary cutline can be drawn on the wafer map with a mouse.


Figure 3. Histogram distribution for a parameter found along the cutline.


Figure 4. Histogram distribution for a parameter found along the circle.

Application Example

The data set used here as an example is a complete SPICE level3 NMOS and PMOS parameter set extracted from selected wafer lots. The parameter sets include extracted SPICE model parameters. The parameter selected for this analysis is the threshold voltage VTO.


Figure 5. An arbitrary circle can be drawn on the wafer map with a mouse.