Methods for assessing semiconductor structures
Methods for assessing the quality of a semiconductor structure having a charge trapping layer to, for example, determine if the structure is suitable for use as a radiofrequency device are disclosed. Embodiments of the assessing method may involve measuring an electrostatic parameter at an initial state and at an excited state in which charge carriers are generated.
1. A method for assessing a quality of a semiconductor structure, the semiconductor structure having a front surface and a back surface generally parallel to the front surface and comprising a charge trapping layer, the method comprising:
illuminating the semiconductor structure to generate charge carriers in the semiconductor structure;
measuring an initial electrostatic parameter of the semiconductor structure, the initial electrostatic parameter being selected from the group consisting of (1) a capacitance of the semiconductor structure and (2) a difference in voltage potential between the front surface of the semiconductor structure and an electrode;
measuring an excited electrostatic parameter of the semiconductor structure during illumination of the semiconductor structure to generate charge carriers in the semiconductor structure, the excited electrostatic parameter being a same parameter as the initial electrostatic parameter; and
assessing an efficiency of the charge trapping layer based on the measured electrostatic parameter of the semiconductor structure, the charge trapping layer being selected from the group consisting of polycrystalline silicon, amorphous silicon, silicon germanium, silicon doped with carbon, and germanium.
2. The method as set forth in claim 1 wherein the electrostatic parameter is the capacitance of the semiconductor structure.
3. The method as set forth in claim 1 comprising assessing the quality of a plurality of semiconductor structures, wherein each semiconductor structure is assessed by:
measuring an initial electrostatic parameter of the semiconductor structure, the initial electrostatic parameter being selected from the group consisting of (1) a capacitance of the semiconductor structure and (2) a difference in voltage potential between the front surface of the semiconductor structure and an electrode;
generating charge carriers in the semiconductor structure;
measuring an excited electrostatic parameter of the semiconductor structure during generation of charge carriers in the semiconductor structure, the excited electrostatic parameter being a same parameter as the initial electrostatic parameter;
determining the difference between the initial electrostatic parameter and the excited electrostatic parameter;
comparing the difference between the initial electrostatic parameter and the excited electrostatic parameter for each semiconductor structure to a baseline difference to assess the semiconductor structure; and
forming a radiofrequency device only on semiconductor structures which are determined to be suitable.
4. The method as set forth in claim 1 wherein the semiconductor structure comprises a handle wafer, a dielectric layer, a charge trapping layer disposed between the dielectric layer and the handle wafer, and a silicon device layer, the dielectric layer being disposed between the silicon device layer and the charge trapping layer.
5. The method as set forth in claim 1 comprising determining a difference between the initial electrostatic parameter and the excited electrostatic parameter.
6. The method as set forth in claim 5 wherein the difference is compared to a baseline difference to determine if the semiconductor structure is suitable for use in a radiofrequency device.