Etching method and structure in a silicon recess for subsequent epitaxial growth for strained silicon mos transistors

A method for forming a semiconductor integrated circuit comprising:

• providing a semiconductor substrate;
• forming a dielectric layer overlying the semiconductor substrate;
• forming a gate layer overlying the dielectric layer;
• patterning the gate layer to form a gate structure including edges, the gate structure being formed overlying a channel region;
• implanting lightly doped source/drain regions into the semiconductor substrate;
• heat treating the lightly doped source/drain regions to form diffused pocket regions underlying portions of the gate structure;
• forming a dielectric layer overlying the gate structure to protect the gate structure including the edges;
• patterning the dielectric layer to form sidewall spacers on the gate structure;
• anisotropic etching a source region and a drain region adjacent to the gate structure using the dielectric layer as a protective layer to form a first source region and a first drain region, each of the first source region and the first drain region being characterized by a recessed region having substantially vertical walls, a bottom region, and sharp corners connecting the vertical walls to the bottom region;
• isotropic etching the source region and the drain region to cause a change of the sharp corner regions to rounded corner regions connected to the bottom region of each of the source and drain regions and to cause an undercut region within a vicinity of the channel region, the rounded corner regions having a radius of curvature of more than a few nanometers.
• maintaining the etched surfaces during the isotropic etching free from any damage associated with an anisotropic etching process;
• depositing silicon germanium material into the source region and the drain region to fill the etched source region and the etched drain region;
• and
• causing the channel region between the source region and the drain region to be strained in compressive mode from at least the silicon germanium material formed in the source region and the drain region.

A semiconductor integrated circuit device comprising:

• a semiconductor substrate;
• a dielectric layer overlying the semiconductor substrate;
• a gate structure overlying the dielectric layer;
• a channel region within a portion of the semiconductor substrate within a vicinity of the gate structure;
• a lightly doped source/drain regions in the semiconductor substrate to from diffused pocket regions underlying portions of the gate structure;
• sidewall spacers on edges of the gate structure;
• an etched source region and an etched drain region, each of the first source region and the first drain region being characterized by a recessed region having substantially vertical walls, a bottom region, and rounded corner regions connecting the vertical walls to the bottom region;
• an undercut region underlying a portion of the gate structure and within a vicinity of the channel region, the undercut region being within each of the recessed regions;
• a radius of curvature of more than a few nanometers characterizing the rounded corner regions;
• one or more exposed surfaces of the recessed region being free from any damage associated with an anisotropic etching process;
• a silicon germanium material formed into the source region and the drain region to fill the etched source region and the etched drain region;
• and
• a strained region characterizing the channel region between the source region and the drain region, the strained region being in a compressive mode from at least the silicon germanium material formed in the source region and the drain region.