Epitaxial Deposition Wafer Gap Venting for Auto-Doping Control
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
The epitaxial deposition of low-doped semiconductor layers on highly doped substrates often results in auto-doping, where dopants from the backside diffuse into the wafer-susceptor gap and contaminate the epitaxial layer, limiting the maximum resistivity and causing defects, especially when boron is the dopant, and existing solutions like backsealing or lowering processing temperature are either costly or reduce throughput.
Innovation Solution
Creating a wafer gap region between the substrate and susceptor plate with adjustable thickness, ventilating this region with inert gas to remove auto-dopants while preventing inert gas flow over the front side and reactant gases from reaching the backside, using a spacer and wafer processing structure to isolate gas flows and reduce contamination during epitaxial deposition.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the substrate is heated to high temperature for epitaxial deposition, then the rate of epitaxial growth increases, but dopant out-diffusion from the backside increases causing auto-doping
Solution Approach 1:
The patent divides the processing space into two separate zones: a first zone above the substrate front surface where reactant gases flow for epitaxial growth, and a second zone at the backside where inert gas flows to remove dopants. This spatial segmentation prevents dopant migration to the epitaxial layer while maintaining high growth rates.
Solution Approach 2:
The patent extracts and removes dopants from the backside zone using inert gas flow before they can migrate to the front surface. By continuously pumping out dopants from the second zone, the system prevents auto-doping while maintaining high processing temperatures for rapid epitaxial growth.
2Object-generated harmful factors
If inert gas is flowed over the front side to remove dopants, then auto-doping is reduced, but reactant gases are displaced reducing epitaxial growth
Solution Approach 1:
The patent creates separate gas flow zones: reactant gases flow only over the front surface in the first zone for epitaxial growth, while inert gas flows only at the backside in the second zone for dopant removal. This segmentation allows both functions to occur simultaneously without interfering with each other.
Solution Approach 2:
The patent uses a physical barrier (such as a susceptor or chamber structure) to separate the reactant gas flow from the inert gas flow. This intermediary structure prevents the two gas streams from mixing, allowing reactant gases to reach the front surface for growth while inert gas removes dopants from the backside.
3Object-generated harmful factors
If processing temperature is lowered to reduce dopant diffusion, then auto-doping is reduced, but epitaxial growth rate decreases
Solution Approach 1:
The patent actively extracts dopants from the backside using inert gas flow and pumping, rather than relying on low temperature to suppress diffusion. This allows the system to maintain high processing temperatures for rapid epitaxial growth while continuously removing dopants before they can migrate to the front surface.
Solution Approach 2:
The patent uses gas flow dynamics to control dopant removal: inert gas is flowed through the backside zone to sweep dopants away from the substrate, and vacuum pumping creates pressure gradients that enhance dopant extraction. This pneumatic control enables high-temperature processing without auto-doping.
4Object-generated harmful factors
If backside oxidation is performed to seal dopants, then auto-doping is reduced, but process complexity and cost increase
Solution Approach 1:
The patent removes dopants from the backside using inert gas flow during the epitaxial deposition process itself, eliminating the need for separate backside oxidation and removal steps. This continuous extraction approach simplifies the overall process while effectively preventing auto-doping.
Solution Approach 2:
The patent performs dopant removal continuously during the epitaxial growth process by maintaining inert gas flow through the backside zone throughout deposition. This continuous action eliminates the need for discrete preprocessing steps like backside oxidation, reducing process complexity while maintaining effectiveness.
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
Substantially reduces auto-doping and backside defects, allowing for higher resistivity and uniformity of the epitaxial layer without compromising throughput, enabling the formation of epitaxial layers with improved resistivity and reduced risk of contamination.
Implementation Method 1
a means for ventilating auto-dopants out of the wafer gap region with a flow of inert gas
Implementation Method 2
dopant from the backside of the substrate 102 may diffuse out of the substrate 102 and into the wafer-susceptor gap 112
Data Source
AI summary
According to one aspect of the invention, an apparatus for reducing auto-doping of the front side of a substrate and reducing defects on the backside of the substrate during an epitaxial deposition process for forming an epitaxial layer on the front side of the substrate comprising: a means for forming a wafer gap region between the backside of the substrate and a susceptor plate, having an adjustable thickness; a means for ventilating auto-dopants out of the wafer gap region with a flow of inert gas, while inhibiting or prohibiting the flow of inert gas over the front side of the substrate; and a means for flowing reactant gases over the surface of the front side of the substrate, while inhibiting or prohibiting the flow of reactant gases near the surface of the backside of the substrate.