The Next-Generation Wafer

Epitaxial wafers are expected to continue to be used at the 450mm diameter. These are high quality wafers consisting of a single crystal silicon vapor phase layer several microns thick (epitaxial layer) grown on the surface of a substrate wafer.
Substrate wafers whose conductive properties have been tailored by the addition of a highly concentrated dopant, such as boron (B) for p++ or phosphorus (P) for n++, are frequently used for epitaxial wafers. Adding such a highly concentrated dopant alters the lattice constant, which represents the atomic arrangement of the substrate. The resulting difference in the lattice constants between the epitaxial layer and the substrate causes the wafer to warp.

The graph shows a simulated example of wafer warp due to epitaxial growth. In order to achieve the projected standard warp of 30µm or less in a 45nm generation device using a p/p++ epitaxial wafer with a substrate wafer resistivity of 5mΩcm, a wafer thickness of at least 1,020µm would be required for a 2µm epitaxial layer. A wafer thickness of at least 1,430µm would be needed for a 4μm epitaxial layer.

* Epitaxial layers calculated on a non-doped basis.

As with epitaxial growth, warp occurs when growing various films on the surface of a wafer as part of the device process. As an example, a wafer with a 100nm nitride film grown or deposited on it would need to have a thickness of at least 1,180μm to restrict warp to roughly the same level as a 300mm wafer with a thickness of 775µm^*.

* Calculated based on an assumed film thickness of 100nm and film stress of 1GPa