Semiconductor devices and methods of manufacture thereof

A semiconductor device, comprising:

• a workpiece;
• a trench formed within the workpiece, the trench comprising an upper portion and a lower portion, the upper portion comprising a first width, the lower portion comprising a second width, the second width being greater than the first width, the trench comprising sidewalls and a bottom surface;
• a liner disposed over the sidewalls and the bottom surface of the upper portion and the lower portion of the trench, the liner comprising a first insulating material;
• a second insulating material disposed in the lower portion of the trench over the liner, wherein the second insulating material is disposed at least partially in regions where the second width of the lower portion is greater than the first width of the upper portion;
• and
• a third insulating material disposed in the upper portion of the trench and at least in the lower portion of the trench beneath the upper portion.

A method of fabricating a semiconductor device, the method comprising:

• providing a workpiece;
• forming at least one trench in the workpiece, the at least one trench comprising an upper portion and a lower portion, the upper portion comprising a first width, the lower portion comprising a second width, the second width being greater than the first width, the lower portion comprising a first region that extends beyond the first width of the upper portion, the lower portion comprising a second region comprising a third width, the second region being disposed beneath the first width of the upper portion;
• filling at least a portion of the first region of the lower portion of the at least one trench with a first material;
• and
• filling the upper portion and the second region of the lower portion of the at least one trench with a second material.

A method of forming an isolation structure for a semiconductor device, the method comprising:

• providing a workpiece;
• forming at least one trench in the workpiece, the at least one trench comprising an upper portion, a lower portion, a bottom surface, and sidewalls, the upper portion comprising a first width, the lower portion comprising a second width, the second width being greater than the first width in a cross-section of the at least one trench;
• forming a first material over the sidewalls and the bottom surface of the at least one trench, partially filling the at least one trench with the first material;
• removing the first material from at least the sidewalls of the upper portion of the at least one trench;
• and
• forming a second material over at least the first material and the sidewalls of the upper portion of the at least one trench, completely filling the at least one trench.

A method of filling a trench of a semiconductor device, the trench comprising an upper portion and a lower portion, wherein the trench comprises a retrograde shape wherein the upper portion comprises a first width, the lower portion comprises a second width, the second width being greater than the first width, wherein the method comprises:

• forming a liner over the trench, the liner comprising a first insulating material;
• forming a spacer material over the liner, the spacer material comprising a second insulating material, the second insulating material of the spacer comprising a material that is etchable selective to the first insulating material of the liner;
• anisotropically etching the spacer material, removing the spacer material from at least sidewalls of the trench in the upper portion and leaving the spacer material in regions of the bottom portion of the trench that are wider than the upper portion of the trench;
• and
• filling the trench with a third insulating material.