Semiconductor Wafer Doping for Diode Voltage Control
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Solution Overview
Problem
Conventional epitaxial (EPI) wafers are costly and methods to reduce their cost often result in EPI layers with thicknesses less than 1 micrometer, limiting the performance of semiconductor devices due to large junction capacitances.
Innovation Solution
A method involving a non-EPI semiconductor substrate with specific doping processes through the back and front surfaces to form diffusion layers with controlled dopant concentrations, allowing for tailored forward and reverse breakdown voltages without the need for expensive EPI wafers.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional EPI wafers are used, then the forward voltage drop is low and reverse breakdown voltage can be controlled, but the cost is very high (up to $50.00 or more per wafer)
Solution Approach 1:
The patent replaces expensive EPI wafers with cheaper non-EPI silicon wafers that have higher initial resistivity (greater than 20 ohm-sq). By using multiple doping steps (ion implantation and/or diffusion) through front and back surfaces, the invention achieves the desired electrical characteristics at a fraction of the cost of conventional EPI wafers.
Solution Approach 2:
The invention changes the electrical parameters of the substrate by controlling dopant concentration profiles through multiple doping steps. By adjusting implantation doses, diffusion temperatures, and times, the patent tailors the resistivity distribution to achieve target forward voltage drop and reverse breakdown voltage, transforming a high-resistivity substrate into a device with EPI-like performance.
2Ease of manufacture
If less expensive methods are used to reduce EPI wafer cost, then the cost decreases but the EPI layer thickness becomes less than 1 micrometer, causing large junction capacitances and limited device performance
Solution Approach 1:
Instead of relying on thin EPI layer growth in the vertical dimension, the patent uses doping diffusion from both front and back surfaces to create complex three-dimensional dopant concentration profiles. This approach allows control of electrical characteristics without being constrained by the thickness of an epitaxial layer, effectively adding the dimension of bidirectional doping to solve the problem.
Solution Approach 2:
The patent performs preliminary doping through the back surface to create a base dopant concentration profile before performing front surface doping. This preliminary action establishes the foundation for achieving the desired resistivity distribution and electrical characteristics, allowing subsequent doping steps to fine-tune the profiles for optimal device performance.
3Ease of manufacture
If non-EPI wafers are used, then the cost is lower but the forward voltage drop is generally greater due to difficulty in providing low overall series resistance
Solution Approach 1:
The patent segments the doping process into multiple distinct steps: back surface doping to create a low-resistance substrate region, and front surface doping to form the junction region. This segmentation allows independent optimization of each region's electrical characteristics, achieving low overall series resistance while maintaining cost advantages of non-EPI wafers.
Solution Approach 2:
The invention applies local quality by creating different dopant concentration profiles in different regions of the wafer. The back surface region is doped to provide low series resistance, while the front surface junction region is doped to provide the desired reverse breakdown voltage. This local differentiation of electrical properties enables non-EPI wafers to achieve EPI-like device performance.
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 method enables the production of semiconductor junction diode devices with reduced forward voltage drop and tailored reverse breakdown voltage, achieving performance comparable to EPI wafers at a lower cost.
Implementation Method 1
at least one of the doping steps includes implanting and diffusing the first dopant
Implementation Method 2
at least one of the doping steps includes implanting and diffusing the first dopant
Data Source
Figure 1~2
Figure 3~5
AI summary
A method is provided of making a semiconductor wafer for a semiconductor junction diode device having a target forward voltage drop and a target reverse breakdown voltage. The method begins by doping a semiconductor substrate of a first conductivity type through the back surface with a first dopant of the first conductivity type in an amount sufficient to form a semiconductor junction diode device having a target forward voltage drop. Next, the substrate is doped through the front surface with a second dopant of the first conductivity type in an amount sufficient to form the semiconductor junction diode device such that it has a target reverse breakdown voltage.