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Step Coverage Calculator
Enter film thicknesses measured at the top surface, sidewall, and feature bottom. This calculator returns step coverage ratios, aspect ratio, and a pass/fail check against your minimum thickness requirement.
Use one length unit for every value.
Calculated in your browser. Nothing is sent to a server.
How it is calculated
Measure film thickness at three points on a cross-section: the top (field) surface, the sidewall, and the feature bottom. Enter all three values in the same length unit.
The calculator divides each interior thickness by the top-surface thickness to give bottom step coverage (bottom ÷ top × 100 %) and sidewall step coverage (sidewall ÷ top × 100 %). It also reports the thinnest-point ratio.
Optionally, enter the feature opening width and depth. The calculator displays the aspect ratio as depth ÷ width, shown as N : 1.
If you set a minimum required thickness — for example, the thinnest a barrier or liner can be and still remain continuous — the calculator checks whether the thinnest measured point meets that threshold and shows the margin.
Limits to keep in mind
- Three single-point thicknesses do not capture the full sidewall profile.
- Overhang near the opening, bowing, or a thin spot mid-wall will be missed.
- Results depend on exactly where each thickness was measured — for instance, the position chosen in a cross-section TEM image.
FAQ
- What is step coverage?
- Step coverage is the thickness of a deposited film at a point inside a feature divided by the thickness on the top surface, expressed as a percentage. Most groups report the bottom-to-top ratio; others report sidewall-to-top. The two are not interchangeable, so always state which ratio you mean and at what aspect ratio.
- Why does the film thin at the bottom of a high-aspect-ratio feature?
- In ALD, each half-cycle must deliver enough precursor or reactant to saturate all the way to the feature bottom. The half-cycle that runs short sets the bottom coverage. Insufficient purge can also cause CVD-like overhang at the opening, further starving the bottom.
- Is conformality the same as step coverage?
- Conformality is often used as a synonym. Some authors reserve it for how uniform the film is along the entire sidewall — something a single ratio at one point does not capture.
- Is my data sent to a server?
- No. All calculations run in your browser. Nothing is transmitted.
Read the full article
Semi Process Lab predicts step coverage by aspect ratio for ALD, CVD and PVD, with a 3D thickness profile and a pinch-off warning.
Predict step coverage by aspect ratio