Semiconductor device having silicon-germanium layer on fin and method for manufacturing the same

A method for manufacturing a semiconductor device, comprising:

• providing a substrate with an isolation layer formed thereon, wherein the substrate has a fin protruding up through the isolation layer to form a top surface and a pair of lateral sidewalls of the fin above the isolation layer;
• epitaxially growing a silicon-germanium (SiGe) layer on the top surface and the pair of lateral sidewalls of the fin, wherein the SiGe layer formed on the top surface has a first thickness, the SiGe layer formed on said lateral sidewall has a second thickness, and a ratio of the first thickness to the second thickness is in a range of 1:10 to 1:30;
• and
• forming a gate stack on the isolation layer and across the top surface and the pair of lateral sidewalls of the fin, wherein the fin extends along a first direction, and the gate stack extends along a second direction different from the first direction.