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Application Case Study

Recently a LAUDA-Noah Model 3500 Point-Of-Use™ chiller was installed on a Lam 2300 Versys™ chamber for a temperature and CD repeatability evaluation. A LAUDA-Noah point-of-use chiller is located very close to the etch chamber and it operates with a small volume of dielectric fluid. Combined with its dynamic control architecture it responds immediately to changes in heat load, providing temperature control that can maintain set-point within a much tighter tolerance. We evaluated the temperature repeatability of our Poly Gate etch chamber with the point-of-use chiller vs. an identical chamber with a traditional compressor-based reservoir type chiller. We measured temperature repeatability with the OnWAFER device and CD repeatability with Known Good Wafers (KGW) from the Poly Gate etch.

Results Achieved

The evaluation was begun by running an OnWafer four times in a row. The data is given below along with the reservoir chiller data for comparison.

Lam 2300 with POU Chiller
Run 1Temp. = 78.7 °C
Run 2Temp. = 78.9 °C
Run 3Temp. = 78.9 °C
Run 4Temp. = 78.9 °C
Delta = 0.2 °C
Lam 2300 with Reservoir (static) Chiller
Run 1Temp. = 80.9 °C
Run 2Temp. = 81.0 °C
Run 3Temp. = 79.8 °C
Run 4Temp. = 78.8 °C
Delta = 2.2°C

We can see from this test the POU chiller has much better temperature repeatability than the reservoir chiller. It is interesting how both chillers end up in the same place over time. The POU chiller is stable from the start, while the reservoir chiller ramps up then down. Next, CD variation was measured across a lot for both cases. The Known Good Wafers from the Poly Gate etch were used for these tests. The results are shown below.

Lam 2300 with POU Chiller
Wafer SlotCDs
10.1371
30.1372
50.1366
70.1386
150.1393
200.1396
250.1396
Variation: 0.0030
Lam 2300 with Reservoir (static) Chiller
Wafer SlotCD's
10.1468
50.1417
100.1481
150.1463
200.1452
250.1450
Variation: 0.0064

We can see that the variation in the POU chiller case is much less, with only 3nm variation vs. a 6nm variation with the conventional chiller. Graphs of this data are shown below.

CD Variation Across a lot with a POU Chiller - Run 2
CD Variation Across a lot with a POU Chiller - Run 2
CD Variation Across a lot with a Standard Reservoir Chiller
CD Variation Across a lot with a Standard Reservoir Chiller

Again, these graphs show the POU chiller to be much more stable than the reservoir chiller. To check the stability of the POU chiller over time another across wafer CD tests was run a week after the first one. That data is shown below.

CD Variation Across a lot with a POU Chiller - Run 1
CD Variation Across a lot with a POU Chiller - Run 1
Second POU chiller across wafer CD test
Wafer SlotCD's
10.1386
50.1380
100.1380
150.1382
200.1374
250.1391
Variation: 0.0017

Again much lower variation in the POU case, But what is really striking is the CD repeatability lot to lot. The average for the first lot was .13822µm, the average for the second lot is .13823µm. Nice repeatability.

Conclusion

The LAUDA-Noah Point-of-Use™ thermoelectric chiller has demonstrated a significant improvement in CD Bias control. There is considerable benefit to be realized by implementation in the production environment for processes that are temperature sensitive, similar to the Poly gate etch tested in this evaluation.