Method for fabricating stress enhanced MOS circuits
View Patent ↗A stress enhanced MOS circuit and methods for its fabrication are provided. The stress enhanced MOS circuit comprises a semiconductor substrate and a gate insulator overlying the semiconductor substrate. A gate electrode overlies the gate insulator; the gate electrode has side walls and comprising a layer of polycrystalline silicon having a first thickness in contact with the gate insulator and a layer of electrically conductive stressed material having a second thickness greater than the first thickness overlying the layer of polycrystalline silicon. A stress liner overlies the side walls of the gate electrode.
1. A method for fabricating a stress enhanced MOS circuit, the method comprising the steps of:
depositing a layer of polycrystalline silicon gate forming material onto a layer of gate insulator;
etching the layer of polycrystalline silicon gate forming material to form a polycrystalline silicon gate structure overlying the layer of gate insulator;
depositing a stress liner layer in contact with the polycrystalline silicon gate structure formed from the layer of polycrystalline silicon gate forming material;
planarizing the stress liner layer to expose a top portion of the polycrystalline silicon gate structure;
etching the polycrystalline silicon gate structure to remove a first portion of the polycrystalline silicon gate structure, leaving a second portion of the polycrystalline silicon gate structure in contact with the gate insulator, and leaving an etched void bounded in part by the stress liner layer;
filling the void with an electrically conductive stressed material, wherein the electrically conductive stressed material contacts the polycrystalline silicon gate structure; and
planarizing a surface of the electrically conductive stressed material.
2. The method of claim 1 wherein the step of filling the void comprises the step of filling the void with a compressive stressed titanium nitride.
3. The method of claim 2 wherein the step of depositing a stress liner layer comprises the step of depositing a layer of tensile stressed silicon nitride.
4. The method of claim 1 wherein the step of filling the void comprises the step of filling the void with a tensile stressed material.
5. The method of claim 4 wherein the step of depositing a stress liner layer comprises the step of depositing a layer of compressive stressed silicon nitride.
6. A method for fabricating a stress enhanced MOS circuit, the method comprising the steps of:
depositing and etching a layer of polycrystalline silicon gate material to form a dummy polycrystalline silicon gate electrode;
depositing a layer of insulating material in contact with the dummy polycrystalline silicon gate electrode formed from the layer of polycrystalline silicon gate forming material;
removing a portion of the layer of insulating material to expose a top portion of the dummy polycrystalline silicon gate electrode;
removing at least a portion of the dummy polycrystalline silicon gate electrode to leave a void; and
filling the void with a stressed material, wherein the stressed material contacts a remaining portion of the dummy polycrystalline silicon gate electrode.
7. The method of claim 6 wherein the stress enhanced MOS circuit is formed on a semiconductor substrate, the method further comprising the steps of:
forming side wall spacers on the dummy gate electrode;
implanting conductivity determining impurities into the semiconductor substrate to form source and drain regions self aligned to the dummy polycrystalline silicon gate electrode; and
wherein the step of depositing a layer of insulating material comprises the step of depositing a layer of stressed silicon nitride overlying the side wall spacers and the source and drain regions.
8. The method of claim 7 wherein the step of depositing a layer of stressed silicon nitride comprises the step of depositing a layer of tensile stressed silicon nitride.
9. The method of claim 7 wherein the step of depositing a layer of stressed silicon nitride comprises the step of depositing a layer of compressive stressed silicon nitride.
10. The method of claim 6 wherein the step of depositing and etching a layer of polycrystalline silicon gate material comprises the steps of:
depositing the layer of polycrystalline silicon gate material; and
impurity doping the dummy layer of polycrystalline silicon gate material to establish a desired device threshold voltage.
11. The method of claim 10 wherein the step of removing at least a portion of the dummy polycrystalline silicon gate electrode comprises the step of etching the dummy polycrystalline silicon gate material and leaving at least 10 nm of polycrystalline silicon to fix the desired device threshold.
12. The method of claim 11 wherein the step of filling the void comprises the step of filling the void with a stressed material having a thickness of at least 80 nm.
13. The method of claim 6 wherein the step of filling the void comprises the step of filling the void with a compressive stressed material.
14. The method of claim 6 wherein the step of filling the void comprises the step of filling the void with compressive stressed titanium nitride.
15. The method of claim 6 wherein the step of filling the void comprises the step of filling the void with a tensile stressed material.