| 摘要 |
The present invention provides a method of forming a PMOS transistor or an NMOS transistor on a semiconductor wafer. The semiconductor wafer comprises a silicon substrate and a gate positioned on a predetermined area of the silicon substrate. First, a protection layer of uniform thickness made of silicon nitride is formed on the semiconductor wafer to cover the surface of the gate. Then, a first ion implantation process is performed to form a first ion implantation layer with a first predetermined thickness on the silicon substrate around the gate. Then, an RCA cleaning process is performed to remove impurities on the semiconductor wafer. Next, a spacer is formed around the gate. Finally, a second ion implantation process is performed to form a second ion implantation layer with a second predetermined thickness on the silicon substrate around the gate. The second ion implantation layer is used as a source or drain (S/D) of the MOS transistor. The portion of the first ion implantation layer that is not covered by the second ion implantation layer is used as a lightly doped drain (LDD). The protection layer is used to protect the surface of the silicon substrate from being etched during the RCA cleaning process so as to prevent an increase of the electrical resistance of the LDD.
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