| 摘要 |
At least three metal-oxide semiconductor transistors with different threshold voltages are formed in and above corresponding first, second and third parts of a semiconductor substrate. The second transistor has a lower threshold voltage than the second transistor, and the third transistor has a lower threshold voltage than the second transistor. The gate oxide layers for the three transistors are formed as follows: a first oxide layer having a first thickness is formed above the first, second and third parts. The first oxide layer above the second part is etched and a second oxide layer having a second thickness smaller than the first thickness is formed. The first oxide layer above the third part is etched and a third oxide layer having a third thickness smaller than the second thickness is formed. The second and the third oxide layers are then nitrided to form first and second oxy-nitride layers. |
