Periphery Purge Shutter for CVD Reactor Vortex Elimination
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Solution Overview
Problem
Conventional chemical vapor deposition (CVD) systems experience unwanted buildup of pyrolyzed gases in the reactor chamber, leading to potential damage and non-uniform epitaxial layer growth due to vortex flow patterns and temperature gradients.
Innovation Solution
A two-part periphery purge system is implemented, using structural arrangements of shutters and controlled flow rates and gas compositions to eliminate or reduce vortex flow, allowing pyrolyzed gases to be rapidly removed from the reactor chamber, thereby preventing buildup and enhancing temperature gradient control for uniform epitaxial growth.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If conventional CVD systems use standard gas flow paths without periphery purge, then the system structure is simpler, but pyrolyzed gases build up in the reactor chamber causing non-uniform epitaxial layer growth and potential damage
Solution Approach 1:
The gas flow control system is segmented into multiple independent shutter components (upper shutter, lower shutter, periphery purge shutter) that can be individually controlled. Each shutter manages a specific region of the gas flow path, allowing precise control over precursor gas distribution and pyrolyzed gas removal to achieve uniform epitaxial layer growth.
Solution Approach 2:
Purge gas is introduced as an intermediary substance between the precursor gas flow and the reactor chamber walls. This purge gas creates a protective flow that prevents pyrolyzed gases from contacting and depositing on chamber surfaces, thereby preventing buildup and maintaining growth uniformity.
2Reliability
If the reactor chamber removes pyrolyzed gases slowly, then the flow control system is simpler, but buildup of undesirable materials occurs on reactor surfaces
Solution Approach 1:
The periphery purge system maintains continuous purge gas flow along the chamber walls throughout the deposition process. This continuous flow continuously sweeps pyrolyzed gases away from surfaces, preventing buildup without requiring interruption of the deposition process, thereby maintaining both reliability and productivity.
Solution Approach 2:
The system uses pneumatic flow control through strategically positioned shutters and purge gas injection to create controlled gas flow patterns. The periphery purge shutter specifically directs purge gas along the chamber periphery to rapidly remove pyrolyzed gases through pressure-driven flow rather than relying on slow diffusion.
3Productivity
If precursor gases are introduced at high temperature, then the deposition rate increases, but premature pyrolyzation occurs before gases reach the wafer
Solution Approach 1:
The reactor chamber creates different thermal zones: the injector block and gas flow paths are kept at lower temperatures to prevent premature pyrolyzation, while the wafer susceptor is maintained at high temperature for rapid deposition. This local temperature differentiation allows the system to achieve both controlled gas delivery and high productivity.
Solution Approach 2:
The system performs preliminary heating of the wafer susceptor before introducing precursor gases. This ensures the wafer is already at the optimal temperature for rapid deposition when the gases arrive, eliminating the need to heat the gases themselves and preventing premature pyrolyzation while maintaining high deposition rates.
4Quantity of substance
If vortex flow patterns are present in the reactor chamber, then gas circulation is enhanced, but unwanted buildup occurs on radially outer portions of the reactor housing
Solution Approach 1:
The periphery purge shutter is positioned asymmetrically at the radially outer portion of the chamber, specifically targeting the region where vortex-induced buildup occurs. This asymmetric placement creates a localized counter-flow that disrupts the symmetric vortex pattern and prevents deposit accumulation on the chamber housing.
Solution Approach 2:
The system changes the flow parameters (velocity, direction, composition) of the purge gas to create a flow pattern that opposes the vortex circulation. By adjusting the purge gas flow rate and direction through the periphery purge shutter, the system transforms the harmful vortex flow into a beneficial linear flow that sweeps pyrolyzed gases toward the center rather than allowing them to deposit on outer surfaces.
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 solution achieves reduced vorticity and recirculation of hot gases, preventing undesirable deposits and ensuring higher uniformity and quality of epitaxial layers grown on wafers by maintaining a controlled temperature gradient and flowpath.
Implementation Method 1
This is accomplished, in embodiments, by reducing or eliminating the vortex flow pattern common in conventional systems
Implementation Method 2
heat is transferred from the heating elements to the bottom surface of the wafer carrier and flows upwardly through the wafer carrier to the individual wafers
Implementation Method 3
pyrolyzation of the precursor gases can occur at an intermediate temperature between that of the input gases and the wafer. This pyrolyzation facilitates the interaction of the precursor gases and growth of the crystal structure
Implementation Method 4
semiconductor wafers on which layers of thin film are to be grown are placed on rapidly-rotating carousels, referred to as wafer carriers, to provide a uniform exposure of their surfaces to the atmosphere within the reactor chamber
Data Source
AI summary
An arrangement of two shutters radially outward from an injector block and a susceptor onto which a wafer carrier is removably mounted are configured to provide a flowpath through a reactor chamber that does not exhibit a vortex, thereby reducing or eliminating buildup on the inside of the reactor chamber and facilitating large temperature gradient between the injector block and the wafer carrier. This can be accomplished by introduction of a purge gas flow at a radially inner wall of an upper shutter, and in some embodiments the purge gas can have a different chemical composition than the precursor gas used to grow desired epitaxial structures on the wafer carrier.