Etch Rate Uniformity Log Worksheet
Etch rate and within-wafer uniformity are tracked for every chamber qualification and after every maintenance event. This worksheet keeps the log in one table and calculates non-uniformity and depth for you.
| Wafer ID | Chamber | Mean etch rate (nm/min) | Max site rate (nm/min) | Min site rate (nm/min) | Etch time (min) | Non-uniformity (max-min)/(2 x mean) | Mean etch depth (nm) | Run date | |
|---|---|---|---|---|---|---|---|---|---|
3% | 468 | ||||||||
3.4% | 463.5 | ||||||||
5.2% | 447 | ||||||||
2% | 477 | ||||||||
6% | 436.5 |
Many fabs define non-uniformity as half-range over mean, as used here, while others use standard deviation over mean. State your definition on the report and keep it consistent. Enter site data from your metrology tool. Control limits and spec values come from your own qualification procedure.
Qualification data by chamber without exports
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How to use the worksheet
Add one row per monitor wafer. Enter the wafer ID, chamber, mean etch rate, maximum and minimum site rates, and the etch time. The sheet calculates the non-uniformity percentage and mean etch depth in each row, and gives the average and worst non-uniformity for the batch. Replace the sample rows with your own, then export to Excel or PDF to attach to the qualification record or to hand to the equipment engineer after a preventive maintenance.
- Use the same site map on every monitor wafer.
- Keep the measurement tool and recipe consistent between runs.
- Record chamber and maintenance events in the wafer ID or notes.
The formulas and definitions
Non-uniformity is calculated as (max minus min) divided by (2 times mean), as a percent. Another widely used definition is one standard deviation divided by the mean. The two give different numbers for the same wafer, so always state which is in use. Etch depth equals the mean rate times time. The worksheet also reports the spread of mean etch rate across runs, which is a quick check of chamber-to-chamber matching.
Reading the example
In the example, PM1 shows about 3% non-uniformity at 310 nm per minute, while PM2 shows about 5% and a falling mean rate over two days. That pattern, a decreasing rate with worsening uniformity in one chamber, often points to consumable wear, a coating change in the chamber, or a gas flow or pressure drift. Use the spread value to see when matching is outside what your process can tolerate, and escalate with an out-of-control action plan.
Common mistakes
Mixing definitions of non-uniformity is the main error, followed by mixing wafer types or films in the same log. Excluding edge sites on some wafers and including them on others also distorts the number. Finally, do not use a single wafer to approve a chamber: look at the trend over several runs and across the maintenance cycle before releasing production.
Frequently Asked Questions
Which uniformity definition should I use?
Use the one in your qualification procedure or customer agreement. Half-range over mean, as in this sheet, is very common for etch qualification, while standard deviation over mean is used in many process-control charts. Never compare values that use different definitions.
How many sites should I measure?
That is set by your metrology recipe, commonly five to forty-nine points depending on wafer size and the sensitivity needed. More points give a better view of radial and edge patterns, and cost more metrology time.
What if my etch rate drifts down over time?
A steady decline often indicates consumable wear, chamber wall conditioning changes or flow and pressure drift. Check the maintenance log, gas flows and endpoint behavior before adjusting recipe time to compensate.
Can I add columns?
The worksheet is fixed to these columns, but you can export to Excel and add your own fields, such as film type, recipe name or measurement tool, before filing it with the qualification record.
If etch qualification data is in a metrology system and your ERP or MES holds the lots, Netray can help connect them so the trend is visible by chamber without exporting files.
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