Proton Irradiation Field Stop Layer Disorder Compensation
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Solution Overview
Problem
The existing methods for forming a field stop layer in semiconductor devices using proton irradiation introduce disorder in the substrate, leading to reduced carrier mobility and increased leakage current, as the hydrogen-related donor concentration is often removed during annealing to correct disorder, resulting in a trade-off between desired donor concentration and disorder removal.
Innovation Solution
A method involving repeated proton irradiation steps with adjusted acceleration energy and dose to compensate for disorder, forming an n-type field stop layer with multiple impurity concentration peaks, where the second or subsequent proton irradiation is performed at a shallower depth than the previous, and the acceleration energy and dose are adjusted to compensate for reduced mobility, ensuring high hydrogen-related donor concentration without significant disorder.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If proton irradiation is used to form the field stop layer, then the hydrogen-related donor concentration is increased, but disorder is introduced into the substrate reducing carrier mobility
Solution Approach 1:
The field stop layer formation process is divided into multiple proton irradiation steps with different acceleration energies and doses. The first step uses higher energy to create donors at deeper positions, while subsequent steps use lower energy to create donors at shallower positions and compensate for disorder. This segmentation allows independent optimization of donor concentration and disorder control at different depths.
Solution Approach 2:
The patent employs periodic proton irradiation treatments with alternating acceleration energies (e.g., 2.0 MeV followed by 1.0 MeV, or 1.5 MeV followed by 0.5 MeV). This periodic action creates a layered donor concentration profile where each irradiation cycle adds donors while the subsequent lower-energy cycle compensates for disorder in the previously irradiated region.
2Length of stationary object
If high acceleration energy is used for proton irradiation, then deeper penetration depth is achieved, but more disorder is generated in the substrate
Solution Approach 1:
The deep irradiation task is segmented into multiple steps: a first high-energy step (2.0 MeV or 1.5 MeV) penetrates deeply to create donors at the desired depth, followed by one or more low-energy steps (1.0 MeV or 0.5 MeV) that create donors at shallower positions and compensate for disorder. This segmentation allows deep penetration without excessive disorder accumulation.
Solution Approach 2:
The patent performs preliminary high-energy irradiation to establish the deep donor profile, then follows with lower-energy irradiation to compensate for disorder in the shallower regions. This preliminary action followed by corrective action ensures that deep penetration is achieved while minimizing overall disorder through subsequent compensation steps.
3Manufacturing precision
If multiple proton irradiation steps are performed, then the field stop layer profile is improved, but the manufacturing process becomes more complex
Solution Approach 1:
The complex task of forming an optimized field stop layer profile is segmented into multiple irradiation steps with specific acceleration energies and doses. This segmentation enables precise control of the donor concentration profile at different depths, achieving manufacturing precision that would be impossible with a single step.
Solution Approach 2:
The patent systematically changes irradiation parameters (acceleration energy and dose) across multiple steps to achieve the desired field stop layer profile. By varying these parameters in a controlled manner, the complex manufacturing process becomes manageable and reproducible, with each step contributing a specific function to the overall profile formation.
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 approach reduces disorder in the semiconductor substrate, prevents deterioration in characteristics such as leakage current, and maintains high hydrogen-related donor concentration, improving the overall performance of the semiconductor device.
Implementation Method 1
a method involving repeated proton irradiation steps with adjusted acceleration energy and dose to compensate for disorder, forming an n-type field stop layer
Implementation Method 2
a heat treatment is performed to recover the crystal defects which are generated in an FZ bulk wafer by irradiation with proton ions
Data Source
Figure 1(a)~1(c)
Figure 2(a)~2(b)
Figure 3(a)~3(f)
AI summary
Proton irradiation is performed a plurality of times from the rear surface of an n-type semiconductor substrate, which is an n- drift layer, to form an n-type FS layer which has a lower resistance than the n-type semiconductor substrate in the rear surface of the n- drift layer. When the proton irradiation is performed a plurality of times in order to form the n-type FS layer, the next proton irradiation is performed to as to compensate for a reduction in mobility due to disorder (7) which remains in the previous proton irradiation. In this case, the second or subsequent proton irradiation is performed at the position of the disorder (7) which is formed by the previous proton irradiation. In this way, even after proton irradiation and a heat treatment, the disorder (7) is reduced and it is possible to prevent deterioration of characteristics, such as an increase in leakage current. In addition, it is possible to form an n-type FS layer including a high-concentration hydrogen-related donor layer.