The performance of radio frequency (RF) electronic switching devices, such as RF CMOS devices, can depend upon the electrical resistivity of the substrate from which they are fabricated. Recently, advanced semiconductor-on-insulator (SeOI) substrates such as, for example, high resistivity silicon-on-insulator (HR-SOI) have been utilized to fabricate RF CMOS devices with enhanced performance. For example, RF devices fabricated from HR-SOI have been demonstrated with reduced RF losses.
Double (or dual) layer transfer (DLT) of an active layer of devices can allow for the replacement of an initial substrate with a final substrate that is better suited for providing improved RF performance of devices formed thereon.
Briefly, a device layer, for example, comprising a plurality of RF CMOS devices, may be fabricated in or on an initial substrate. The device layer may subsequently be attached to a temporary substrate. With the device layer attached to the temporary substrate, a portion of the initial substrate may be removed and replaced with a final substrate better suited to enhanced RF performance. Once the device layer is attached to the final substrate, the temporary substrate may be removed completing the DLT processing of the device layer. For example, DLT for RF CMOS has been demonstrated utilizing an initial SOI-type substrate.
When utilizing an initial SOI-type substrate, the bulk silicon carrier portion of the SOI-type substrate is completely removed during the DLT process, removing an unwanted low resistivity path, which may compromise RF performance. However, in the case of RF CMOS devices fabricated from a standard bulk substrate a residual thickness of the initial substrate may remain adjacent to the RF CMOS devices as a result of the fabrication process. The remaining residual thickness of the initial substrate may act as a low resistivity path resulting in RF losses and a reduction in the RF performance of the device layer.