Formation of multi-height MUGFET

A method comprising:

• forming trench isolation regions in a silicon layer of a substrate to define a first silicon region and a second silicon region bounded by said trench isolation regions;
• patterning a first hardmask layer to form a first hardmask island on said first silicon region and a second hardmask island on said second silicon region;
• patterning a second hardmask layer on said first silicon region and said first hardmask island and on said second silicon region and said second hardmask island;
• removing said second hardmask layer from said second silicon region and said second hardmask island to provide second exposed areas of said second silicon region;
• patterning first and second mandrels over said first silicon region and said second silicon region;
• forming a third hardmask layer over said substrate;
• removing said first and second mandrels to form openings in said third hardmask layer;
• etching said second exposed areas of said second silicon region to form second trenches to a second depth in said second silicon region;
• removing said second hardmask layer from said first silicon region and said first hardmask island to provide first exposed areas of said first silicon region;
• simultaneously etching said first exposed areas of said first silicon region to form first trenches to a first depth in said first silicon region and further etching said second trenches to a third depth, said third depth being greater than said first depth;
• removing said third hardmask layer to leave said first silicon region and said second silicon region exposed as silicon fins;
• patterning a source and drain protective layer over said silicon fins, said source and drain protective layer protecting source and drain regions of said silicon fins and leaving channel regions of said silicon fins exposed;
• forming a gate insulator on said channel regions;
• patterning at least one gate conductor on said gate insulator;
• removing said source and drain protective layer;
• and
• implanting an impurity into said source and drain regions.