Semiconductor devices and methods of manufacturing thereof

A semiconductor device, comprising:

• a fin, extending along a first direction of a lateral surface of the semiconductor device;
• a gate structure extending along a second direction of a lateral surface, perpendicular to the first direction, the gate structure straddling the fin, the gate structure comprising:
• a metal gate;
• a pair of first spacers laterally bounding the metal gate along the first direction, having a proportion of oxygen lowest along a first sidewall proximal to the metal gate and highest along a second sidewall distal from the metal gate and proximal to a first sidewall of a pair of second spacers laterally bounding the first spacers;
• and
• a proportion of carbon of the second spacers is less than the proportion of carbon of the first spacers.

A semiconductor device, comprising:

• a first spacer disposed between a metal gate and a second spacer, the first spacer comprising:
• a plurality of cross-linked first silicon-oxygen-silicon backbones;
• or
• a plurality of cross-linked first silicon-carbon-silicon backbones;
• and
• wherein the second spacer extends along the first spacer and comprises at least one of:
• a plurality of cross-linked second silicon-oxygen-silicon backbones;
• or
• a plurality of cross-linked second silicon-carbon-silicon backbones.