Specific Process Knowledge/Thermal Process/Oxidation/Dry oxidation C1 furnace

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The C1 furnace can be used for dry oxidation of 4" and 6" wafers.

There is space for up to 30 wafers in the furnace at a time (including test and dummy wafers).

The maximum possible oxidation temperature is 1000^oC, and the maximum allowed oxidation time is 23 hours.

Dry Oxidation uniformity for 4" wafers

A dry oxidation has been done with 30 4" wafers in the quartz boat in the furnace to get an idea of how uniform the oxide layer is from wafer to wafer over the boat.

The following parameters were used for the oxidation:

• Recipe: "DRY1100"
• Oxidation time: 500 minutes
• Annealing time: 20 minutes

After the oxidation, the oxide thickness was measured on all the wafers.

The graph below shows the measured oxide thickness as function of the wafer slot. Slot 1 is furthest inside the furnace, towards the service area. For each wafer the oxide thickness has been measured in 49 points, and the average oxide thickness has been calculated.

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The oxidation and measurements were done by Martin Ommen (former DTU Nanotech).

As can be seen from the graph, the oxide layer is not the same for all the wafers, and for the outer wafers the oxide layer is quite thin compared to the thickness on the center wafers.

The reason for this is that the flat zone, i.e. the area where the temperature in furnace is uniform, is not much longer than the quartz boat, and the diameter of the furnace tube is larger than in the other C-stack furnaces and the A-stack furnace (the C1 furnace was upgraded at some point to increase the tube diameter).

Furthermore, the wafers in the boat will heat each other, so the outer wafers will always be coldest and thus get the thinnest oxide layer. We therefore recommend to place two dummy wafers in each end of the boat, right next to the wafers that have to be oxidized. You can find some dummy wafers in a box on the furnace shelf.

If you have 4” wafers, you can also use the A1 or A3 furnace for the oxidation, but then you will have to RCA clean the wafers first. We make QC (quality control) for these furnaces, and you can find the results in LabManager to see what uniformity you can expect. Alternatively, you can of course just oxidize less wafers at a time in the C1 furnace.

If you have 6” wafers, I suggest that you use the new E1 oxidation furnace, because this will give a very uniform oxide thickness. Here the flat zone is quite long, and there are more boats with a fixed number of dummy wafers.

Regarding the cantilevers, I have opened the furnace to check them today, and I think they look fine. The cantilevers are perhaps tilting a bit downwards, but it has been like that for a while, and since the furnace is closing as it should and without any quartz parts touching each other, it is not a problem.