Planar Gate IGTO Device Resolving Trench Depth Variations
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Solution Overview
Problem
Existing insulated gate turn-off (IGTO) devices with trenched gates are costly to manufacture, have variations in turn-on voltage due to trench depth inconsistencies, and are difficult to reproduce, limiting their reliability and integration with other devices.
Innovation Solution
A vertical IGTO device design utilizing planar gates instead of trenched gates, with a structure that includes a p+ substrate, lightly doped n-type and p-type layers, shallow n+ regions, and distributed p+ regions, allowing for precise control of gate voltage and current flow to turn the device on and off.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If trenched gates are used in IGTO devices, then the device can achieve high current density and on-off switching capability, but the manufacturing process becomes time-consuming and expensive, and there is significant variation in turn-on voltage due to trench depth inconsistencies
Solution Approach 1:
The invention extracts the gate structure from the trench configuration and places it at the surface level. The gate electrode is positioned at the top surface of the semiconductor device, eliminating the need for deep trench formation while maintaining the essential gate control function. This extraction resolves the manufacturing complexity issue by removing the time-consuming trench etching process while preserving the device's switching capability.
Solution Approach 2:
The gate structure transitions from a vertical trench configuration to a horizontal surface-mounted configuration. Instead of embedding the gate vertically within trenches, the invention positions the gate electrode horizontally at the surface, changing the spatial dimension of the gate structure. This dimensional change eliminates trench depth variation problems while maintaining effective gate control over the current flow.
2Manufacturing precision
If trenched gates are used to control current flow, then the device achieves controlled latch-up and turn-on capability, but the gate trench depth variation causes difficulty in reproducing consistent turn-on voltage across different manufacturing lots
Solution Approach 1:
The gate structure is extracted from the trench and repositioned at the surface, eliminating the critical parameter of trench depth from the device architecture. By removing the trench structure entirely, the invention eliminates the source of manufacturing variation, allowing consistent turn-on voltage reproduction across different manufacturing lots without requiring precise trench depth control.
Solution Approach 2:
The invention changes the critical geometric parameter from trench depth to surface-level gate dimensions. Instead of controlling turn-on voltage through precise trench depth (which varies during manufacturing), the gate electrode dimensions and positioning at the surface become the controlling parameters, which are much easier to control with high precision during fabrication.
3Productivity
If planar gates are used instead of trenched gates, then manufacturing efficiency improves and integration with other devices becomes easier, but the device structure must be redesigned to maintain vertical NPN and PNP bipolar transistor operation
Solution Approach 1:
The gate structure is extracted from the trench and repositioned at the surface, simplifying the overall device structure. This extraction eliminates the need for complex trench formation processes and allows for easier integration with other surface-mounted devices, improving manufacturing efficiency while reducing structural complexity.
Solution Approach 2:
The surface-mounted gate structure serves multiple functions: it provides gate control for the vertical bipolar transistors, enables easier integration with other devices, and simplifies the manufacturing process. This universal gate configuration can be applied to various device types and integration schemes, enhancing the overall versatility and productivity of the semiconductor fabrication process.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The planar gate IGTO device offers improved manufacturing efficiency, precise turn-on voltage control, and enhanced integration with other devices, while avoiding latch-up issues and providing reliable on-off switching capabilities.
Implementation Method 1
When there is a sufficient positive voltage (e.g., 2 volts) applied to the gate... electrons from the n+ layer 18 become the majority carriers along the sidewalls and below the bottom of the trenches 24 in an inversion layer, causing the effective width of the NPN base (the portion of the p-well 16 below the trenches 24) to be reduced.
Implementation Method 2
The resistance between a surface p+ region and the p-type layer increases with distance, allowing a voltage differential of at least 0.6 volts to exist between the n+ regions and the p-type layer at sufficiently high currents.
Data Source
AI summary
An insulated gate turn-off (IGTO) device has a layered structure including a p+ layer (e.g., a substrate), an n-type layer, a p-type layer (which may be a p-well), n+ regions formed in the surface of the p-type layer, and insulated planar gates over the p-type layer between the n+ regions. The layered structure forms vertical NPN and PNP transistors. The p-type layer forms the base of the NPN transistor. When the gates are sufficiently positively biased, the underlying p-type layer inverts to reduce the width of the base to increase the beta of the NPN transistor. This causes the product of the betas of the NPN and PNP transistors to exceed one, and the device becomes fully conductive. When the gate voltage is removed, the base width increases such that the product of the betas is less than one, and the device shuts off. No latch-up occurs in normal operation.