Flashlamp-Treated Silicon Wafer for Low BMD Density
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Solution Overview
Problem
Silicon wafers produced by existing methods often have high densities of stable boron-mediated defects (BMD) nuclei, which can impair electronic circuit functions and require lengthy processing times to reduce vacancy supersaturation and BMD density.
Innovation Solution
A method involving a silicon wafer with an oxygen concentration of 5·10^17 to 7.5·10^17 cm^-3, treated with a flashlamp heat process that rapidly heats and cools the wafer, reducing BMD nuclei size without establishing high vacancy supersaturation, thereby achieving low BMD densities throughout the wafer volume.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If conventional thermal treatment methods are used to reduce BMD density, then BMD nuclei are eliminated in a thin surface layer, but stable BMD nuclei remain at depths greater than 10 μm requiring lengthy processing times
Solution Approach 1:
The patent replaces conventional slow thermal diffusion processes with a flash lamp-based optical heating system. The flash lamp emits intense light that is absorbed by the silicon wafer, rapidly heating it to temperatures above 1000°C for only 1-10 milliseconds. This optical-mechanical substitution enables volumetric heating throughout the wafer thickness simultaneously, eliminating BMD nuclei at all depths without requiring prolonged processing times.
Solution Approach 2:
The invention employs periodic pulsed heating using flash lamps that deliver intense thermal energy in extremely short bursts (1-10 ms duration). This periodic action allows the wafer to be heated to high temperatures momentarily to dissolve BMD nuclei, then rapidly cooled between pulses. The cyclic heating-cooling process achieves complete BMD elimination throughout the wafer volume while maintaining very short total processing times, avoiding the need for lengthy continuous thermal treatment.
2Manufacturing precision
If flashlamp heat treatment is applied to eliminate BMD nuclei, then BMD density is reduced in the surface layer, but vacancy supersaturation increases throughout the wafer volume
Solution Approach 1:
The patent applies a preliminary oxygen-containing atmosphere treatment before or during the flash lamp heating process. This preliminary action ensures that oxygen is available to react with and passivate vacancies as they are generated during the rapid heating. By preparing the atmospheric conditions in advance, the subsequent flash heating creates vacancies that are immediately neutralized by oxygen diffusion and recombination, preventing the accumulation of harmful vacancy supersaturation while still achieving BMD nucleus elimination.
Solution Approach 2:
The invention converts the potentially harmful effect of vacancy generation during flash heating into a beneficial process. The rapid heating does create vacancies, but by simultaneously maintaining an oxygen-containing atmosphere, these vacancies are transformed into oxygen-vacancy complexes or passivated by oxygen diffusion. The harmful vacancies become beneficial oxygen-defect complexes that do not degrade semiconductor performance, thus converting the harmful side effect into a tolerable or even advantageous outcome.
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 significantly reduces BMD densities to at most 1·10^8 cm^-3 after specific thermal processes, maintaining low vacancy concentrations and eliminating the need for lengthy processing or oxidizing atmospheres, resulting in silicon wafers with improved electronic performance and reduced oxygen precipitation tendencies.
Implementation Method 1
irradiating a side of the silicon wafer with flashlamp for a duration of 15 to 400 ms
Implementation Method 2
subsequently cooled again rapidly
Data Source
AI summary
Silicon wafers having an oxygen concentration of 5·1017 to 7.5·1017 cm−3 have the following BMD densities after the following thermal processes, carried out alternatively:a BMD density of at most 1·108 cm−3 after a treatment for three hours at 780° C. and subsequently for 16 hours at 1000° C., anda BMD density of at least 1·109 cm−3 after heating of the silicon wafer at a heating rate of 1 K/min from a start temperature of 500° C. to a target temperature of 1000° C. and subsequent holding at 1000° C. for 16 hours. The wafers are prepared by a method of irradiation of a heated wafer with flashlamp which delivers energy which is from 50 to 100% of the energy density necessary for melting the wafer surface.