The Shepherd: A Graphical Example

The Shepherd’s goal is to monitor and manage inactive lots to control variability in the fab. Inactive lots are lots that have been at their current operation, without moving, for some period of time that the fab defines as “inactive.” The general methodology for what the Shepherd does is:

Set a goal for maximum inactive time per lot (e.g. 12 hours).

Monitor the number of inactive lots (both the total in the factory, and the numbers by area and/or key tool groups).

Identify and address the root causes for lot inactivity, to prevent situations from recurring.

Regular Monitoring

On a daily basis, the Shepherd monitors fab performance through a series of summary charts (or dashboard charts). These typically include things like: inactive trend, inactive trend for just engineering lots, inactives by module, and inactives by tool group charts. Click here to see a series of sample Shepherd dashboard charts. We have observed that maintaining a set of dashboard charts such as this one helps people using the Shepherd style to be successful. The reason for this is that the Shepherd encourages other people in the fab to watch the same dashboard, and thus ensures that problems are noticed immediately, rather than after the fact.

In-Depth Analysis

When specific problems come up, the Shepherd performs more in-depth analysis, to understand root causes. This type of analysis is illustrated with a five-part example, broken into the following sections:

1. Early Warning Indicators
2. Lot History Analysis
3. Analyzing the Problem Operation
4. Root Cause Analysis
5. Consequences and Corrections

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