Schottky Rectifier Cathode Trench Structure for Forward Voltage Margin
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Solution Overview
Problem
Conventional Schottky rectifiers face challenges with high epi-resistivity and cathode contact resistance, leading to low yield and forward voltage margin issues, particularly in Chip-Scale Package (CSP) applications, due to high substrate thickness and process fluctuations.
Innovation Solution
The development of a semiconductor Schottky rectifier with a trench structure cathode and anode configuration, where the cathode trench has vertical sidewalls and a horizontal extension, covered with a gate oxide film, and polysilicon elements, along with a multi-step etching process to form dielectric and metal silicide layers, reducing parasitic resistance and improving yield.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional planar Schottky CSP device structure is used, then manufacturing is simpler, but forward voltage margin is poor due to high epi-resistivity and high cathode contact resistance
Solution Approach 1:
The device structure is segmented into distinct functional regions: a first trench structure for the cathode contact, a second trench structure for the anode contact, and intermediate regions. This segmentation allows optimization of each region's electrical characteristics independently, reducing overall parasitic resistance and improving forward voltage margin.
Solution Approach 2:
The invention transitions from a conventional planar two-dimensional layout to a three-dimensional trench-based structure. The trench structures extend vertically into the substrate, creating additional dimensional space for optimizing contact geometry and reducing resistance without increasing the device's planar footprint.
2Reliability
If substrate thickness is reduced to 50 um, then forward voltage is improved, but costly wafer bonding and grinding processes are required
Solution Approach 1:
Instead of uniformly thinning the entire substrate, the invention applies localized trench structures only where contact is needed. The substrate maintains its original thickness in most areas, avoiding the need for costly wafer bonding and grinding processes while still achieving improved forward voltage through localized geometric optimization.
Solution Approach 2:
The invention changes the geometric parameters of the contact structures (trench depth, width, and shape) rather than changing the substrate thickness parameter. This allows optimization of electrical characteristics through geometric parameter adjustment without requiring expensive substrate thinning processes.
3Reliability
If POCl3 doped area density is increased, then cathode contact resistance is reduced, but process fluctuation causes yield problems with Vf spreading
Solution Approach 1:
The invention extracts the dopant dependency from the contact resistance optimization process by using trench geometry rather than dopant density to reduce resistance. This removes the source of process fluctuation and Vf spreading associated with POCl3 doping while still achieving low contact resistance through optimized trench dimensions.
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
This configuration enables Schottky rectifiers to operate at higher currents with improved forward voltage and leakage current characteristics, suitable for small dimensions and broader applications in CSP, while reducing the need for costly wafer bonding and grinding processes.
Implementation Method 1
The surfaces of the sidewall and the bottom extension are covered with a gate oxide film. The gate oxide film separates the epi-layer from a polysilicon element.
Implementation Method 2
depositing a first metal layer and performing a thermal treatment to form metal silicide in the Schottky diode region and the cathode region
Data Source
AI summary
A semiconductor Schottky rectifier built in an epitaxial semiconductor layer over a substrate has an anode structure and a cathode structure extending from the surface of the epitaxial layer. The cathode contact structure has a trench structure near the epi-layer and a vertical sidewall surface covered with a gate oxide layer. The cathode structure further comprises a polysilicon element adjacent to the gate oxide layer.