Capping layers in metal gates of transistors
A method of forming a semiconductor device includes forming a gate electrode in a wafer. The formation of the gate electrode includes depositing a work-function layer, after the work-function layer is deposited, performing a treatment on the wafer, wherein the treatment is performed by soaking the wafer using a silicon-containing gas; after the treatment, forming a metal capping layer over the work-function layer; and depositing a filling metal over the metal capping layer.
1. A method comprising:
forming a gate electrode in a wafer comprising:
depositing a first metal capping layer over a semiconductor region;
performing a first treatment process on the first metal capping layer using a chlorine-containing precursor;
performing a second treatment process on the first metal capping layer that has been treated by the first treatment process to form a silicon-containing layer, wherein the second treatment process is performed using a silicon-containing gas, and wherein the first metal capping layer and the second treatment process are performed without vacuum break in between;
after the second treatment process for forming the silicon-containing layer, performing a vacuum break process to oxidize the silicon-containing layer and to convert the silicon-containing layer into a silicon oxide layer, wherein at a time the vacuum break process is performed, the silicon-containing layer is a topmost layer of the wafer;
after the vacuum break process, depositing a second metal capping layer over the silicon oxide layer; and
depositing a filling metal over the first metal capping layer.
2. The method of claim 1 further comprising depositing a work-function layer over the semiconductor region, wherein the first metal capping layer is deposited over the work-function layer to form an interface in between.
3. The method of claim 1 being free from an oxidation process between the first treatment process and the second treatment process.
4. The method of claim 1 , wherein the depositing the first metal capping layer is performed using TiCl 4 as a precursor.
5. The method of claim 1 , wherein the second treatment process comprises a thermal soaking process using a silicon-containing process gas.
6. The method of claim 1 further comprising:
performing a third treatment process on the second metal capping layer using an additional silicon-containing gas; and
after the third treatment process, performing a vacuum break to expose the second metal capping layer to air.
7. The method of claim 1 , wherein the second treatment process is performed using silane or disilane.
8. The method of claim 1 , wherein the first metal capping layer comprises TiN.
9. The method of claim 1 , wherein the first metal capping layer comprises TaN.
10. A method comprising:
forming a p-type source/drain region on a side of a dummy gate stack;
removing the dummy gate stack to leave a trench between two gate spacers;
forming a gate dielectric layer extending into the trench;
depositing a work-function layer over the gate dielectric layer;
depositing a first metal capping layer over the work-function layer;
performing a treatment process on the first metal capping layer using a silicon-containing gas, with a silicon-containing layer being formed on the first metal capping layer;
performing a vacuum break to introduce oxygen to the silicon-containing layer and to convert the silicon-containing layer into a silicon oxide layer, wherein at a time the vacuum break is performed, the silicon-containing layer is a topmost layer of a respective wafer that comprises the silicon-containing layer; and
after the vacuum break, depositing a second metal capping layer over the silicon oxide layer.
11. The method of claim 10 , wherein the first metal capping layer and the second metal capping layer are formed of a same material.
12. The method of claim 11 , wherein the depositing the first metal capping layer and the depositing the second metal capping layer comprise depositing titanium nitride.
13. A method comprising:
depositing a first metal capping layer on a work-function layer;
performing a silicon-containing gas soaking process on the first metal capping layer to form a silicon-containing layer, wherein the depositing the first metal capping layer and the silicon-containing gas soaking process are performed in a same vacuum environment;
after the silicon-containing layer is formed, introducing oxygen (O 2 ) to the silicon-containing layer through a vacuum break process to form a silicon-oxide-containing layer, wherein the silicon-containing layer is converted into an oxide layer, and wherein at a time the vacuum break process is performed, the silicon-containing layer is a topmost layer of a respective wafer that comprises the silicon-containing layer;
depositing a second metal capping layer over the oxide layer, wherein the first metal capping layer and the second metal capping layer are formed of a same material; and
forming a filling-metal region over the second metal capping layer.
14. The method of claim 13 , wherein the second metal capping layer is deposited over and contacting the silicon-oxide-containing layer.
15. The method of claim 13 , wherein the second metal capping layer is deposited over and contacting the silicon-containing layer, and wherein the first metal capping layer and the second metal capping layer are formed of a same material.
16. The method of claim 13 , wherein the introducing the oxygen is performed when the second metal capping layer is exposed.
17. The method of claim 13 , wherein the introducing the oxygen is performed through a vacuum break.
18. The method of claim 10 , wherein the first metal capping layer comprises TaN.
19. The method of claim 13 , wherein the first metal capping layer comprises TiN.
20. The method of claim 13 , wherein the first metal capping layer comprises TaN.