Ultra-Shallow Junction Formation via SiC Layer Annealing
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Solution Overview
Problem
Existing methods for fabricating ultra-shallow junctions in Field Effect Transistor (FET) devices face challenges due to ion-channeling and transient enhanced diffusion phenomena, leading to deeper source/drain junctions and poor junction profiles, with carbon and fluorine co-implantation methods creating point defects.
Innovation Solution
A method involving the deposition of a silicon carbon layer on a substrate, followed by exposure to a dopant and heating to temperatures above 950°C for annealing, using a plasma immersion ion implantation process to form an abrupt p-n junction with a graded carbon concentration, resulting in a dopant profile of about 3 nm/decade.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If ion implantation is used to form source and drain regions, then the transistor junction dimensions can be reduced, but transient enhanced diffusion causes deeper junctions and poorer junction profiles
Solution Approach 1:
A silicon carbon layer is deposited on the substrate before dopant implantation. This preliminary layer serves as a diffusion barrier during subsequent annealing, preventing dopants from diffusing too deeply into the substrate while still allowing adequate dopant activation and junction formation.
Solution Approach 2:
The invention uses a composite silicon carbon layer (SiC) rather than pure silicon. The carbon atoms in the SiC layer create a diffusion barrier that suppresses transient enhanced diffusion, while the silicon provides the necessary crystalline structure for device formation. This composite material simultaneously achieves shallow junction depth and good junction profile.
2Length of stationary object
If carbon co-implantation is used to reduce transient enhanced diffusion, then junction depth is controlled, but point defects are created in the film
Solution Approach 1:
Instead of co-implanting carbon with the dopant, the invention extracts the carbon introduction step and performs it separately through epitaxial deposition of a silicon carbon layer. This separates the functions of depth control and dopant introduction, allowing carbon to suppress diffusion without creating the same level of point defects as co-implantation.
Solution Approach 2:
The silicon carbon layer acts as an intermediary between the dopant source and the substrate. It provides a controlled environment for dopant diffusion, using the carbon-silicon bonding structure to moderate dopant movement and reduce point defect formation compared to direct co-implantation methods.
3Length of stationary object
If fluorine co-implants are used to reduce transient enhanced diffusion, then junction depth is controlled, but point defects remain after annealing
Solution Approach 1:
The invention changes the approach from co-implantation to epitaxial deposition, and from fluorine to carbon as the diffusing element. The silicon carbon layer is deposited with controlled carbon concentration, and subsequent annealing at temperatures above 950°C transforms the carbon into substitutional sites, changing the physical state and distribution of carbon to achieve diffusion suppression without persistent point defects.
4Reliability
If high annealing temperature is used to activate dopants, then dopant activation is improved, but transient enhanced diffusion increases
Solution Approach 1:
The silicon carbon layer is deposited beforehand to provide a cushioning effect during high-temperature annealing. The carbon in the SiC layer suppresses dopant diffusion even at annealing temperatures above 950°C, allowing high dopant activation without the corresponding increase in junction depth that would normally occur at such temperatures.
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 effectively reduces transient enhanced diffusion, achieves an abrupt junction with minimal point defects, and maintains high crystallinity of the silicon carbon epitaxial film, facilitating the formation of ultra-shallow junctions with improved precision and reduced depth.
Implementation Method 1
The substrate is heated to a temperature greater than 950° C. so as to cause substantial annealing of the dopant within the silicon carbon layer
Implementation Method 2
the dopant is implanted into the silicon carbon layer using a plasma immersion ion implantation process
Implementation Method 3
An epitaxial silicon carbon layer is deposited on the substrate
Data Source
AI summary
A method for forming an ultra shallow junction on a substrate is provided. In certain embodiments a method of forming an ultra shallow junction on a substrate is provided. The substrate is placed into a process chamber. A silicon carbon layer is deposited on the substrate. The silicon carbon layer is exposed to a dopant. The substrate is heated to a temperature greater than 950° C. so as to cause substantial annealing of the dopant within the silicon carbon layer. In certain embodiments the substrate is heated to a temperature between about 1000° C. and about 1100°. In certain embodiments the substrate is heated to a temperature between about 1030° C. and 1050° C. In certain embodiments, a structure having an abrupt p-n junction is provided.