Methodology for measuring and controlling film thickness profiles

DETAILED DESCRIPTION The invention improves the control of film thicknesses within semiconductor manufacturing processes by evaluating an entire profile of a film layer (as opposed to an individual point, or the average of many points, within the film layer).
Therefore, the invention does more than just evaluate whether the average thickness of a film layer is within an acceptable range.
To the contrary, the invention evaluates whether the entire "profile" (e.
g.
, cross-section) of the film layer is within an acceptable thickness profile range.
By evaluating the profiles of the films, the invention more accurately evaluates the quality of the film layer in question, as well as the true variability of the film processing equipment and or film measurement equipment.
This in turn allows the film formation processing to be refined more precisely, thereby reducing defects substantially and increasing yield.
An example of a sequence of semiconductor fabrication processing follows.
Step one of the process is the film deposition (polysilicon growth).
Step two of the process is lithographic patterning (gate conductor mask).
Finally, step three of the process is film etching (polysilicon etch).
The process equipment for each step has some "natural" behavior that results in a particular process pattern.
For instance, film deposition (depending on the exact equipment) may vary in thickness from center to edge.
In an LPCVD (low pressure chemical vapor deposition) polysilicon reactor the film thickness is a radial symmetric profile described by a simple polynomial (thin in the middle, thick on the edges).
This is shown in FIG.
1, where the local thicknesses at the edges are above the average thickness, while the local thickness at the center is below the average thickness.
However, design specifications are for a uniform film across the wafer with a target thickness and some allowed deviation.
When controlling the LPCVD process as long as the specified average thickness and allowed standard deviation are met, then the process is conventionally said to be in "control`