Ventilated Substrate Gap for Epitaxial Auto-Doping Control
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Solution Overview
Problem
The epitaxial deposition of low-doped semiconductor layers on highly doped substrates often results in auto-doping issues due to dopant diffusion from the backside, leading to resistivity limitations and backside defects, with existing solutions either being costly or reducing epitaxial growth rates.
Innovation Solution
An apparatus and method utilizing a substrate support ring and spacer ring to create a ventilated gap region between the substrate and susceptor, using inert gases to ventilate auto-dopants and isolate reactant gases, preventing dopant migration and deposition on the backside.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the substrate is processed at high temperature during epitaxial deposition, then the epitaxial growth rate is improved, but dopant diffusion from the backside increases causing auto-doping
Solution Approach 1:
The processing system is segmented into distinct zones: a first processing zone for the front surface and a second processing zone for the backside. This spatial segmentation allows independent control of processing conditions in each zone, enabling high temperature epitaxial growth on the front while preventing dopant diffusion from the backside through the ventilated gap and selective gas flow.
Solution Approach 2:
Different local conditions are applied to different surfaces of the substrate. The front surface receives reactant gases at high temperature for rapid epitaxial growth, while the backside is exposed to a ventilated gap with inert gas flow that prevents dopant diffusion. This local differentiation of processing conditions resolves the contradiction between growth rate and auto-doping prevention.
2Object-generated harmful factors
If oxidizing the backside of the substrate is performed to seal it, then dopant out-diffusion is reduced, but processing cost increases due to additional deposition and removal steps
Solution Approach 1:
The harmful dopant atoms are extracted from the backside region through the ventilated gap using inert gas flow. Instead of adding complex sealing layers through oxidation, the system extracts dopants as they diffuse out, preventing their migration to the front surface. This extraction approach eliminates the need for additional deposition and removal steps.
Solution Approach 2:
An inert gas flow is introduced as an intermediary medium in the ventilated gap between the substrate backside and the processing chamber. This intermediary inert gas carries away diffusing dopant atoms, preventing them from reaching the front surface. This approach provides dopant control without requiring chemical modification of the substrate backside.
3Object-generated harmful factors
If lowering the processing temperature is used to reduce dopant out-diffusion, then auto-doping is reduced, but the epitaxial growth rate is substantially reduced
Solution Approach 1:
The processing system is divided into separate thermal zones, allowing the front surface to be maintained at high temperature for rapid epitaxial growth while the backside experiences different conditions through the ventilated gap. This segmentation enables independent optimization of temperature for growth rate without compromising dopant control.
4Manufacturing precision
If adding more dopant to the middle of the wafer is performed to provide uniform resistivity, then resistivity uniformity is improved, but the process is limited to low resistivity epitaxial layers only
Solution Approach 1:
The dopant diffusion that was previously a harmful cause of auto-doping is converted into a beneficial process. By allowing controlled dopant diffusion to the edges through the ventilated gap and inert gas flow, the system achieves uniform resistivity across the wafer while simultaneously preventing dopant contamination of the epitaxial layer. This approach extends applicability to high resistivity layers.
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 epitaxial layers while maintaining high growth rates, thus improving semiconductor processing efficiency.
Implementation Method 1
a spacer ring for positioning the substrate support ring above a susceptor plate to define a substrate gap region between the susceptor plate and the backside of the substrate, the spacer ring comprising a plurality of openings formed therethrough that facilitate passage of a gas into and out of the substrate gap region
Implementation Method 2
a substrate support ring having a substrate holder structure configured to support the substrate in a position for processing along an edge defined by the backside of the substrate and a sidewall of the substrate or along a plurality of discrete points on or proximate to the edge
Data Source
AI summary
Methods and apparatus for reducing autodoping and backside defects on a substrate during epitaxial deposition processes are provided herein. In some embodiments, an apparatus for reducing autodoping and backside defects on a substrate includes a substrate support ring having a substrate holder structure configured to support the substrate in a position for processing along an edge defined by the backside of the substrate and a sidewall of the substrate or along a plurality of discrete points on or proximate to the edge; and a spacer ring for positioning the substrate support ring above a susceptor plate to define a substrate gap region between the susceptor plate and the backside of the substrate, the spacer ring comprising a plurality of openings formed therethrough that facilitate passage of a gas into and out of the substrate gap region.