Power semiconductor devices and methods of manufacture
Various embodiments for improved power devices as well as their methods of manufacture, packaging and circuitry incorporating the same for use in a wide variety of power electronic applications are disclosed. One aspect of the invention combines a number of charge balancing techniques and other techniques for reducing parasitic capacitance to arrive at different embodiments for power devices with improved voltage performance, higher switching speed, and lower on-resistance. Another aspect of the invention provides improved termination structures for low, medium and high voltage devices. Improved methods of fabrication for power devices are provided according to other aspects of the invention. Improvements to specific processing steps, such as formation of trenches, formation of dielectric layers inside trenches, formation of mesa structures and processes for reducing substrate thickness, among others, are presented. According to another aspect of the invention, charge balanced power devices incorporate temperature and current sensing elements such as diodes on the same die. Other aspects of the invention improve equivalent series resistance (ESR) for power devices, incorporate additional circuitry on the same chip as the power device and provide improvements to the packaging of charge balanced power devices.
1. A semiconductor device comprising:
a drift region of a first conductivity type;
a well region extending above the drift region and having a second conductivity type opposite the first conductivity type;
an active trench extending through the well region and into the drift region, the active trench having its sidewalls and bottom lined with dielectric material, and the active trench being substantially filled with a first conductive layer, a second conductive layer and a first gate conductive layer, the first conductive layer being disposed below the first gate conductive layer and separated from the gate electrode by an inter-electrode dielectric material, the second conductive layer being disposed below the first conductive layer and separated from the first conductive layer by the inter-electrode dielectric material;
source regions having the first conductivity type formed in the well region adjacent the active trench; and
a first Schottky structure formed on a first mesa between two adjacent trenches;
wherein the two adjacent trenches, between which the first Schottky structure is formed, are substantially filled with the first conductive layer, the second conductive layer and the first gate conductive layer.
2. The semiconductor device of claim 1 wherein the first conductive layer is configured to be a shield electrode.
3. The semiconductor device of claim 1 wherein the first conductive layer is configured to be a second gate electrode.
4. The semiconductor device of claim 1 wherein the second conductive layer is configured to be a shield electrode.
5. The semiconductor device of claim 1 wherein the first conductive layer is configured to be electrically biased to a potential and the second conductive layer is configured to be electrically biased to a potential.
6. The semiconductor device of claim 1 further comprising a second Schottky structure formed on a second mesa adjacent the first mesa.
7. The semiconductor device of claim 1 wherein the first Schottky structure is formed in a manner that is perpendicular to a longitudinal axis of the two adjacent trenches.
8. A semiconductor device comprising:
a drift region of a first conductivity type;
a well region extending above the drift region and having a second conductivity type opposite the first conductivity type;
a plurality of trenches extending through the well region and into the drift region, each of the plurality of trenches having its sidewalls and bottom lined with dielectric material, and each of the plurality of trenches being substantially filled with a first conductive layer, a second conductive layer, and a third conductive layer, the second conductive layer being disposed below the first conductive layer and separated from the first conductive layer by an inter-electrode dielectric material, the third conductive layer being disposed below the second conductive layer and separated from the second conductive layer by the inter-electrode dielectric material;
source regions having the first conductivity type formed in the well region adjacent a trench; and
a first Schottky structure formed on a first mesa between two adjacent trenches of the plurality of trenches;
wherein the two adjacent trenches, between which the first Schottky structure is formed, are substantially filled with the first conductive layer, the second conductive layer and the third conductive layer.
9. The semiconductor device of claim 8 wherein in active trenches the first conductive layer is configured to be a gate electrode and the second conductive layer is configured to be a shield electrode.
10. The semiconductor device of claim 8 wherein the first Schottky structure comprises a layer of Schottky barrier metal extending over the first mesa and the two adjacent trenches.
11. The semiconductor device of claim 10 wherein the layer of Schottky barrier metal is configured to electrically couple to the first conductive layer in the two adjacent trenches.
12. The semiconductor device of claim 11 wherein the layer of Schottky barrier metal is configured to electrically couple to the source regions.
13. The semiconductor device of claim 8 wherein the second conductive layer in each of the two adjacent trenches are configured to electrically couple together.
14. The semiconductor device of claim 8 further comprising a second Schottky structure formed on a second mesa adjacent the first mesa.
15. The semiconductor device of claim 14 wherein the first mesa and the second mesa are formed by three adjacent trenches, and wherein the first conductive layer in each of the three adjacent trenches are configured to electrically couple to the source regions and the second conductive layer in each of the three adjacent trenches are configured to electrically couple together.
16. The semiconductor device of claim 13 wherein the second electrodes in the active trenches are configured to electrically couple to the source regions at a periphery of the device, while the second electrodes in the two adjacent trenches are configured to electrically couple to the source regions in the middle of the device.
17. The semiconductor device of claim 8 further comprising a plurality of Schottky structures interspersed between the plurality of trenches, wherein each Schottky structure is formed on a mesa between two adjacent trenches.