Two-Sided Electron Beam Irradiation for Wafer Stack Uniformity
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Solution Overview
Problem
Existing semiconductor device manufacturing methods using electron beam irradiation face challenges in achieving uniform characteristics and high-speed switching while maintaining low costs, due to variations in irradiation dose and crystal defect concentration across multiple wafers, particularly in bipolar power semiconductor devices.
Innovation Solution
A method involving two-sided electron beam irradiation of a wafer stack with the same acceleration energy from both principal surfaces, allowing for precise dose adjustment and uniform crystal defect distribution, combined with heat treatment and surface electrode formation to achieve consistent semiconductor device characteristics.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If multiple wafers are irradiated simultaneously from one side, then productivity increases, but manufacturing precision deteriorates due to non-uniform irradiation dose distribution
Solution Approach 1:
The irradiation process is segmented into two separate operations: first irradiating one surface of the wafer stack, then flipping the stack and irradiating the opposite surface. This segmentation allows each irradiation operation to target a specific depth range, ensuring uniform dose distribution within each half of the stack while maintaining high throughput by processing multiple wafers simultaneously in each operation.
Solution Approach 2:
The wafer stack is inverted (flipped over) between two irradiation operations. By irradiating from both opposite surfaces, the method compensates for the non-uniform dose distribution that would occur with single-sided irradiation, achieving uniform crystal defect concentration throughout the entire wafer thickness while maintaining productivity.
2Speed
If irradiation dose is increased to achieve high-speed switching, then switching performance improves, but device characteristics become non-uniform due to dose variation
Solution Approach 1:
The total irradiation dose required for high-speed switching is segmented into two equal portions, each applied from opposite surfaces of the wafer stack. This ensures that the cumulative dose is uniform throughout the wafer thickness, achieving consistent switching characteristics across all devices while maintaining the high switching speed required for bipolar power semiconductor applications.
Solution Approach 2:
By irradiating from both surfaces with equal doses, the method achieves homogeneous distribution of crystal defects throughout the wafer stack. This homogeneity ensures uniform switching characteristics across all devices, eliminating the variability that would result from single-sided irradiation while maintaining the high switching performance needed for the application.
3Reliability
If number of irradiations is increased to achieve desired dose, then switching characteristics improve, but productivity decreases and cost increases
Solution Approach 1:
Two irradiation operations from opposite surfaces are merged into a single processing cycle by flipping the wafer stack between operations. This combining approach achieves the desired total dose with uniform distribution in just two steps, avoiding the need for multiple sequential irradiations from one side, thereby maintaining high productivity while ensuring consistent switching characteristics.
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 variability in semiconductor device characteristics, enhances high-speed switching performance, and lowers production costs by ensuring uniform crystal defect distribution and efficient defect management across multiple wafers.
Implementation Method 1
a first electron beam irradiation step of implementing electron beam irradiation from one principal surface of the wafer stack; and a second electron beam irradiation step of implementing electron beam irradiation with the same acceleration energy as in the previous irradiation from the other principal surface of the wafer stack
Implementation Method 2
Accelerated switching can then be achieved by annealing the wafer for a set period of time at 200° C. to 500° C. to form recombination centers
Data Source
AI summary
A semiconductor device manufacturing method is disclosed by which electron beam irradiation is accomplished at a low cost while exhibiting uniform characteristics. A wafer stack consisting of multiple stacked wafers is irradiated with an electron beam from both the front surface and reverse surface. As such, a semiconductor device manufacturing method is provided whereby the electrical characteristics are extremely uniform between wafers, and costs are reduced by reducing the number of electron beam irradiations.