Gas Dopant Vaporization Control in Silicon Crystal Growth
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Solution Overview
Problem
Conventional methods for growing single crystal silicon using the Czochralski process face challenges with volatile dopants, including uncontrolled vaporization, oxide particle formation, and non-uniform dopant distribution, leading to crystal failure and increased contaminant particles, as well as the need for higher dopant concentrations due to low segregation coefficients.
Innovation Solution
A method and apparatus for controlling the vaporization rate of volatile dopants by adjusting the height and speed of a feed tube within the ingot pulling apparatus, using radiant heat to vaporize dopants and introducing them into the silicon melt as a gas, ensuring uniform dopant distribution and maintaining targeted resistivity during crystal growth.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If dopant is fed into the melt from a feed hopper located a few feet above the silicon melt level, then the dopant can be introduced into the melt, but the volatile dopant vaporizes uncontrolled into the surrounding environment, resulting in the generation of oxide particles that may fall into the melt and become incorporated into the growing crystal
Solution Approach 1:
The patent introduces an intermediary gas flow system that carries dopant granules from the feed hopper to the melt surface in a controlled manner. The gas flow acts as a mediator between the dopant source and the melt, preventing uncontrolled vaporization and oxide particle formation while ensuring uniform dopant distribution.
Solution Approach 2:
The patent changes the physical state of dopant delivery from solid granules falling into the melt to gaseous dopant carried by gas flow. This parameter change allows for controlled vaporization and transport of dopant, preventing the formation of harmful oxide particles while maintaining effective doping.
2Quantity of substance
If the sublimation of dopant granules at the melt surface occurs, then dopant can be introduced into the melt, but it causes a local temperature reduction of the surrounding silicon melt, which results in the formation of silicon boats adjacent the dopant granules, preventing dopant granules from sinking into the melt
Solution Approach 1:
The patent uses gas flow as an intermediary to transport dopant to the melt surface, replacing direct contact between dopant granules and melt surface. This eliminates the local temperature reduction effect that causes silicon boat formation, allowing dopant to be introduced without creating thermal barriers to sinking.
3Speed
If inert gas is used to feed volatile dopants into a growth chamber and carry gas dopants from the feed hopper to the surface of the silicon melt, then dopant can be transported to the melt, but the use of inert gas dilutes the gaseous dopant, thereby decreasing the dopant concentration and purging the evaporated dopant from the growth chamber too quickly
Solution Approach 1:
The patent optimizes the gas flow rate and composition parameters to balance dopant transport efficiency with concentration maintenance. By adjusting these parameters, the system achieves effective dopant delivery to the melt surface while preventing excessive dilution and premature purging of evaporated dopant.
4Quantity of substance
If gas dopants are formed by vaporizing the volatile dopants in the feed hopper, then dopant can be introduced into the melt as gas, but the systems tend to supply dopant non-uniformly during a growth process, thereby increasing the variation in dopant concentration in the radial and/or axial direction of the grown ingot
Solution Approach 1:
The patent implements feedback control mechanisms that monitor dopant concentration and adjust the vaporization rate and gas flow accordingly. This ensures uniform dopant distribution throughout the ingot by continuously adapting the doping process to maintain consistent concentration levels in both radial and axial directions.
Solution Approach 2:
The patent employs periodic adjustment of dopant introduction rates and gas flow patterns to achieve uniform distribution. By varying the doping process parameters in a controlled periodic manner, the system compensates for radial and axial variations in dopant concentration, ensuring homogeneous doping throughout the ingot.
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 allows for precise control of dopant introduction, reducing contaminant particles and achieving consistent resistivity profiles along the ingot, enhancing the crystal growth process by maintaining targeted dopant concentrations and preventing dopant loss to the atmosphere.
Implementation Method 1
heating, by the heat source and radiant heat from the surface of the melt, the capsule containing the volatile dopant to form a gaseous dopant
Implementation Method 2
heating, by the heat source and radiant heat from the surface of the melt, the capsule containing the volatile dopant
Implementation Method 3
The dopant species in the melt are then transported, by diffusion and convection, from the surface of the melt toward the solid-liquid interface
Implementation Method 4
The dopant species in the melt are then transported, by diffusion and convection, from the surface of the melt toward the solid-liquid interface
Implementation Method 5
positioning the feed tube within the inner chamber such that the open end of the feed tube has a first height relative to a surface of the melt
Data Source
AI summary
A method of growing a single crystal ingot includes growing a single crystal silicon ingot from a silicon melt in a crucible within an inner chamber, adding a volatile dopant into a feed tube, positioning the feed tube within an inner chamber at a first height relative to a surface of the melt, adjusting the feed tube within the inner chamber to a second height at a speed rate, and heating the volatile dopant to form a gaseous dopant as the feed tube is moved from the first height to the second height at the speed rate. Each of the second height and the speed rate are selected to control a vaporization rate of the volatile dopant. The method also includes introducing dopant species into the melt while growing the ingot by contacting the surface of the melt with the gaseous dopant.