Methods of making power semiconductor devices with thick bottom oxide layer

A method of of manufacturing a semiconductor device having a charge control trench and an active control trench with a thick oxide bottom comprising:

• forming a drift region of a first conductivity type;
• forming a well region extending above the drift region and having a second conductivity type opposite the first conductivity type;
• forming an active trench extending through the well region and into the drift region;
• forming a charge control trench extending deeper into the drift region than the active trench;
• forming a layer of pad oxide on the substrate;
• depositing a thin layer of silicon nitride on the pad oxide;
• performing an anisotropic etch to remove silicon nitride from horizontal surfaces leaving silicon nitride on active trench sidewalls;
• depositing oxide on horizontal surfaces including the bottom of the active trench using a sub-atmospheric chemical vapor deposition process;
• removing a sandwich layer of oxide-nitride-oxide from active trench sidewalls by an etch process;
• forming an electrode in the active trench;
• and
• forming source regions having the first conductivity type in the well region adjacent the active trench.

A method of manufacturing a semiconductor device having a charge control trench and an active control trench with a thick oxide bottom comprising:

• forming a drift region of a first conductivity type;
• forming a well region extending above the drift region and having a second conductivity type opposite the first conductivity type;
• forming an active trench extending through the well region and into the drift region;
• forming a charge control trench extending deeper into the drift region than the active trench;
• forming a substantially flat layer of oxide having a target thickness at the bottom of the active trench;
• lining the sidewalls of the active trench with an oxide material;
• depositing a first conductive layer over the thick oxide layer on the bottom of the active trench;
• depositing an inter-electrode dielectric material over the first conductive layer;
• depositing a second conductive layer over the inter-electrode dielectric material;
• and
• forming source regions having the first conductivity type in the well region adjacent the active trench.

A method of manufacturing a semiconductor device having a charge control trench and an active control trench with a thick oxide bottom comprising:

• forming a drift region of a first conductivity type;
• forming a well region extending above the drift region and having a second conductivity type opposite the first conductivity type;
• forming an active trench extending through the well region and into the drift region;
• forming a charge control trench extending deeper into the drift region than the active trench;
• forming a substantially flat layer of oxide having a target thickness at the bottom of the active trench;
• forming an electrode in the active trench;
• and
• forming source regions having the first conductivity type in the well region adjacent the active trench;
• depositing in the charge control trench a plurality of conductive layers stacked vertically and separated from each other and from the trench sidewalls by dielectric material;
• wherein the thickness of the plurality of conductive layers inside the charge control trench vary.

A method of manufacturing a semiconductor device having a charge control trench and an active control trench with a thick oxide bottom comprising:

• forming a drift region of a first conductivity type;
• forming a well region extending above the drift region and having a second conductivity type opposite the first conductivity type;
• forming an active trench extending through the well region and into the drift region;
• forming a charge control trench extending deeper into the drift region than the active trench;
• forming a substantially flat layer of oxide having a target thickness at the bottom of the active trench;
• forming an electrode in the active trench;
• and
• forming source regions having the first conductivity type in the well region adjacent the active trench;
• depositing in the charge control trench a plurality of conductive layers stacked vertically and separated from each other and from the trench sidewalls by dielectric material;
• wherein the thickness of a first conductive layer that is deeper inside the charge control trench is smaller than the thickness of a second conductive layer that is disposed above the first conductive layer.