Sidewall spacer formation

Sidewall spacers are formed alongside the polygates to prevent the high-dose dopants used in the S/D implant step from penetrating too close to the channel where S/D punch-through could occur. The sidewall spacer formation process comprises two major process steps. These include the deposition of a CVD oxide layer across the surface of the wafer, followed by etching back of this 

Following the spacer formation, medium-dose implants are made to penetrate the silicon slightly beyond the LDD junction depth, but not as deep as the original twin-well implants (see Section 16.2.1). The spacer oxide from the previous step serves to protect the channel from the dopant atoms during the implant process. TTiere are two S/D implant processes, namely, n S/D implant and S/D implant. 

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Figure 16.13 Process sequence for the sidewall spacer formation (a) spacer oxide deposition and (b) spacer oxide etch back.

Figure 17.19 Process sequence for self-aligned double-patterning technique by means of sidewall spacer formation.

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