Cyclic thermal anneal for dislocation reduction

A method for reducing dislocation density in an epitaxial layer comprising germanium provided on a silicon substrate, the method comprising:

• heating the epitaxial layer and the substrate at a heating temperature that is less than about a characteristic temperature of melting of the epitaxial layer but greater than about a temperature above which the epitaxial layer is characterized by plasticity, for a first time duration;
• cooling the epitaxial layer and the substrate at a cooling temperature that is lower than about the heating temperature and that is between about 700° C. and about 900° C., for a second time duration;
• and
• carrying out the heating and cooling a selected number of cycles to reduce the dislocation density of the epitaxial.

A method for reducing dislocation density in an epitaxial layer comprising germanium, provided on a silicon substrate, the epitaxial layer comprising at least one germanium epitaxial mesa adjacent to which is provided a dislocation sink material comprising silicon dioxide, the method comprising:

• heating the epitaxial layer and the substrate at a heating temperature that is less than about a characteristic temperature of melting of the epitaxial layer but greater than about a temperature above which the epitaxial layer is characterized by plasticity, for a first time duration;
• cooling the epitaxial layer and the substrate at a cooling temperature that is lower than about the heating temperature, for a second time duration;
• and
• carrying out the heating and cooling a selected number of cycles to reduce the dislocation density of the epitaxial layer.

A method for reducing dislocation density in an epitaxial layer comprising germanium provided on a silicon substrate, the method comprising:

• forming a lower portion of the epitaxial layer by chemical vapor deposition at a first deposition temperature with a deposition gas comprising germanium bonded to hydrogen, for a first deposition duration selected to form at least a mono-epitaxial layer, and then forming an upper portion of the epitaxial layer by chemical vapor deposition at a second deposition temperature, higher than the first deposition temperature, with the deposition gas, for a second deposition duration;
• heating the epitaxial layer and the substrate at a heating temperature that is less than about a characteristic temperature of melting of the epitaxial layer but greater than about a temperature above which the epitaxial layer is characterized by plasticity, for a first duration;
• cooling the epitaxial layer and the substrate at a cooling temperature that is lower than about the heating temperature, for a second duration;
• and
• carrying out the heating and cooling a selected number of cycles to reduce the dislocation density of the epitaxial layer.

A method for reducing dislocation density in a semiconductor material formed as an epitaxial layer upon a dissimilar substrate material, the method comprising:

• heating the epitaxial layer and the substrate at a heating temperature that is less than about a characteristic temperature of melting of the epitaxial layer but greater than about a temperature above which the epitaxial layer is characterized by plasticity, for a first time duration;
• cooling the epitaxial layer and the substrate for a second time duration, at a cooling temperature that is lower than about the heating temperature, wherein the cooling temperature, TL, is selected to maximize glide velocity, Vdislocation, of epitaxial layer dislocations, where V dislocation ∝ ( α Sub - α Epi ) · ( T H - T L ) · exp ⁢ ⁢ ( - E v kT L ) ,
• for a given heating temperature, TH, where αSub and αEpi are coefficients of thermal expansion characteristic of the substrate and the epitaxial layer, respectively, EU, is an energy barrier to dislocation glide, and k is Boltzmann's constant;
• and
• carrying out the heating and cooling a selected number of cycles to reduce the dislocation density of the epitaxial layer.