Method for making a semiconductor device including threshold voltage measurement circuitry
A method for making a semiconductor device may include forming active circuitry on a substrate including differential transistor pairs, and forming threshold voltage test circuitry on the substrate. The threshold voltage test circuitry may include a pair of differential test transistors replicating the differential transistor pairs within the active circuitry, with each test transistor having a respective input and output, and at least one gain stage configured to amplify a difference between the outputs of the differential test transistors for measuring a threshold voltage thereof. The differential transistor pairs and the pair of differential test transistors each includes spaced apart source and drain regions, a channel region extending between the source and drain regions, and a gate overlying the channel region. Moreover, each of the channel regions may include a superlattice.
1. A method for making a semiconductor device comprising:
forming active circuitry on a substrate and comprising a plurality of differential transistor pairs; and
forming threshold voltage test circuitry on the substrate and comprising
a pair of differential test transistors replicating the differential transistor pairs within the active circuitry, each test transistor having a respective input and output, and
at least one gain stage configured to amplify a difference between the outputs of the differential test transistors for measuring a threshold voltage thereof;
wherein the plurality of differential transistor pairs and the pair of differential test transistors each comprises spaced apart source and drain regions, a channel region extending between the source and drain regions, and a gate overlying the channel region;
wherein each of the channel regions comprises a superlattice, the superlattice comprising a plurality of stacked groups of layers with each group of layers comprising a plurality of stacked base semiconductor monolayers defining a base semiconductor portion and at least one non-semiconductor monolayer thereon constrained within a crystal lattice of adjacent base semiconductor portions.
2. The method of claim 1 wherein the at least one gain stage comprises a plurality of gain stages configured to successively amplify the difference between the outputs of the differential test transistors over an input voltage range.
3. The method of claim 1 wherein the semiconductor substrate comprises a semiconductor wafer; wherein the active circuitry comprises a plurality of spaced apart active circuitry areas separated by scribe lines; and wherein the threshold voltage test circuitry is positioned within at least one of the scribe lines.
4. The method of claim 1 wherein the active circuitry comprises at least one memory cell array.
5. The method of claim 1 wherein the at least one gain stage comprises a sense amplifier coupled to first conduction terminals of the pair of differential test transistors, and a current source coupled to second conduction terminals of the pair of differential test transistors.
6. The method of claim 1 wherein the pair of differential test transistors comprises a pair of NMOS differential test transistors.
7. The method of claim 1 wherein the pair of differential test transistors comprises a pair of PMOS differential test transistors.
8. The method of claim 1 wherein each base semiconductor portion comprises silicon.
9. The method of claim 1 wherein each base semiconductor portion comprises germanium.
10. The method of claim 1 wherein the at least one non-semiconductor monolayer comprises a non-semiconductor selected from the group consisting of oxygen, nitrogen, fluorine, and carbon-oxygen.
11. The method of claim 1 wherein at least some semiconductor atoms from opposing base semiconductor portions of each superlattice layer are chemically bound together through the non-semiconductor layer therebetween.
12. A method for making a semiconductor device comprising:
forming a plurality of active circuitry areas spaced apart on a semiconductor wafer by scribe lines therebetween, each active circuitry area comprising a plurality of differential transistor pairs; and
forming threshold voltage test circuitry on the substrate within at least one of the scribe lines and comprising
a pair of differential test transistors replicating the differential transistor pairs within the active circuitry, each test transistor having a respective input and output, and
a plurality of gain stages configured to successively amplify the difference between the outputs of the differential test transistors over an input voltage range for measuring a threshold voltage thereof;
wherein the plurality of differential transistor pairs and the pair of differential test transistors each comprises spaced apart source and drain regions, a channel region extending between the source and drain regions, and a gate overlying the channel region;
wherein each of the channel regions comprises a superlattice, the superlattice comprising a plurality of stacked groups of layers with each group of layers comprising a plurality of stacked base semiconductor monolayers defining a base semiconductor portion and at least one non-semiconductor monolayer thereon constrained within a crystal lattice of adjacent base semiconductor portions.
13. The method of claim 12 wherein each active circuitry area comprises a memory cell array.
14. The method of claim 12 wherein a first one of the plurality of gain stages comprises a sense amplifier coupled to first conduction terminals of the pair of differential test transistors, and a current source coupled to second conduction terminals of the pair of differential test transistors.
15. The method of claim 12 wherein the pair of differential test transistors comprises a pair of NMOS differential test transistors.
16. The method of claim 12 wherein the pair of differential test transistors comprises a pair of PMOS differential test transistors.
17. A test method for a semiconductor device comprising active circuitry on a substrate and comprising a plurality of differential transistor pairs, the method comprising:
operating threshold voltage test circuitry on the substrate comprising a pair of differential test transistors replicating the differential transistor pairs within the active circuitry, with each test transistor having a respective input and output, and at least one gain stage configured to amplify a difference between the outputs of the differential test transistors; and
determining a threshold voltage of the differential test transistors based upon the amplified difference in the outputs of the differential test transistors;
wherein the plurality of differential transistor pairs and the pair of differential test transistors each comprises spaced apart source and drain regions, a channel region extending between the source and drain regions, and a gate overlying the channel region;
wherein each of the channel regions comprises a superlattice, the superlattice comprising a plurality of stacked groups of layers with each group of layers comprising a plurality of stacked base semiconductor monolayers defining a base semiconductor portion and at least one non-semiconductor monolayer thereon constrained within a crystal lattice of adjacent base semiconductor portions.
18. The method of claim 17 wherein the at least one gain stage comprises a plurality of gain stages configured to successively amplify the difference between the outputs of the differential test transistors over an input voltage range.
19. The method of claim 17 wherein the semiconductor substrate comprises a semiconductor wafer; wherein the active circuitry comprises a plurality of spaced apart active circuitry areas separated by scribe lines; and wherein the threshold voltage test circuitry is positioned within at least one of the scribe lines.
20. The method of claim 17 wherein the active circuitry comprises at least one memory cell array.