Test structures for measuring silicon thickness in fully depleted silicon-on-insulator technologies

1. An apparatus for determining a thickness of a fully depleted silicon-on-insulator layer disposed in a CMOS integrated circuit, the apparatus being disposed on a FDSOI substrate that also includes the CMOS integrated circuit, the apparatus comprising:

a test structure that includes at least one test circuit, the at least one test circuit including an isolated fully depleted silicon-on-insulator layer disposed above an isolated buried oxide layer and a gate dielectric disposed above the isolated fully depleted silicon-on-insulator layer and which further includes a first Epi region surrounding the isolated fully depleted silicon-on-insulator layer to bias the isolated fully depleted silicon-on-insulator layer, the test structure further including:

a total capacitance measurement circuit configured to output a total capacitance measurement, the total capacitance measurement circuit including a first terminal connected to the gate dielectric disposed above the isolated fully depleted silicon-on-insulator layer and a second terminal connected to one of an n-well and a p-well, for obtaining the total capacitance measurement;

a gate dielectric capacitance measurement circuit configured to output a gate dielectric capacitance measurement, the gate dielectric capacitance measurement circuit including the first terminal connected to the gate dielectric and a third terminal connected to source/drain regions disposed adjacent the isolated fully depleted silicon-on-insulator layer and the second terminal connected to one of an n-well and p-well, for obtaining the gate dielectric capacitance measurement; and

a buried oxide capacitance measurement circuit configured to output a buried oxide capacitance measurement, the buried oxide capacitance measurement circuit including the first terminal connected to the gate dielectric and the second terminal connected to one of an n-well and p-well, for obtaining the buried oxide capacitance measurement.

2. The apparatus according to claim 1 , wherein the at least one test circuit includes a plurality of test circuits, wherein each of the plurality of test circuits include the isolated fully depleted silicon-on-insulator layer disposed above the isolated buried oxide layer, wherein a desired thickness of the isolated fully depleted silicon-on-insulator layer and a desired thickness of the isolated buried oxide layer on the plurality of test circuits is representative of, respectively, a thickness of the isolated fully depleted silicon-on-insulator layer and a thickness of the isolated buried oxide layer on the CMOS integrated circuit, the test structure further including:

the total capacitance measurement circuit as one of the plurality of test circuits;

the gate dielectric capacitance measurement circuit as another of the plurality of test circuits; and

the buried oxide capacitance measurement circuit as a further one of the plurality of test circuits.

3. The apparatus according to claim 2 wherein the plurality of test circuits each further include a ground plane disposed between the buried oxide and one of an n-well and a p-well.

4. The apparatus according to claim 2 wherein at least some of the plurality of test circuits are a same size.

5. The apparatus according to claim 2 , wherein at least some of the plurality of test circuits are a different size.

6. The apparatus according to claim 2 , wherein the plurality of test circuits are each disposed in close proximity to each other on a scribe lane of the FDSOI substrate.

7. The apparatus according to claim 2 , wherein the plurality of test circuits includes at least two sets of the plurality of test circuits disposed in disparate locations of the FDSOI substrate.

8. The apparatus according to claim 7 , wherein the plurality of test circuits within each set of the plurality of test circuits are each disposed in close proximity to each other and within a single scribe lane of the FDSOI substrate.