High voltage device structure and methods of forming the same

A method, comprising:

• forming a first opening in a substrate;
• forming an oxide layer in the first opening;
• depositing a dielectric layer on the oxide layer in the first opening;
• depositing a conductive material on the dielectric layer to fill the first opening;
• removing a side portion of the conductive material to form a second opening, wherein the dielectric layer and a remaining portion of the conductive material are exposed in the second opening;
• and
• depositing a dielectric material in the second opening, wherein the oxide layer, the dielectric layer, the remaining portion of the conductive material, and the dielectric material form an isolation structure.

A method, comprising:

• forming a guard structure on opposite sides of a high-voltage metal-oxide-semiconductor (HVMOS) transistor, comprising:
• forming a deep well region in a substrate, wherein the deep well region is a first conductivity type;
• forming a first well region on a first side of the deep well region, wherein a bottom of the first well region and a bottom of the deep well region are at a same level;
• forming a first pick up region on the first well region;
• forming a second well region on a second side of the deep well region opposite the first side;
• and
• forming a second pick up region on the second well region;
• and
• forming a doped region on the deep well region, wherein the doped region is a second conductivity type opposite the first conductivity type.