Germanium Channel Strain via Ion Implantation
Solution Overview
Problem
Conventional ultra large scale integrated circuit fabrication technologies face challenges in increasing the mobility of charge carriers due to issues like increased longitudinal electric field, interface roughness, and impurity scattering, which deteriorate the mobility of charge carriers and reduce driving current in MOSFET devices.
Innovation Solution
A method for fabricating a semiconductor device using a germanium-based substrate with ion implantation processes to introduce uniaxial tensile stress parallel to the channel and compressive stress perpendicular to the channel plane by implanting silicon or carbon impurities into the source and drain extension regions, followed by annealing, to enhance carrier mobility.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If the geometric dimension of the device is scaled down to improve speed and reduce production cost, then the device size is reduced, but the mobility of charge carriers deteriorates due to increased longitudinal electric field, interface roughness, and impurity scattering
Solution Approach 1:
The patent changes the material parameter from silicon to germanium, exploiting the inherent superior mobility characteristics of germanium material to overcome the mobility degradation caused by device scaling. Germanium provides higher and more symmetrical mobility for both electrons and holes, directly addressing the charge carrier mobility issue while maintaining scaled device dimensions.
Solution Approach 2:
The patent employs composite material structures including germanium-silicon alloy layers and strain-induced composite regions. By introducing silicon or carbon impurities into germanium source and drain extension regions, the patent creates a composite material system that generates strain in the channel to enhance charge carrier mobility beyond what pure germanium can provide.
2Manufacturing precision
If germanium material is used as channel material to increase charge carrier mobility, then the mobility increases, but the process complexity increases due to additional ion implantation and annealing steps
Solution Approach 1:
The patent merges the formation of source and drain extension regions with the strain induction process by implanting silicon or carbon impurities during the same ion implantation steps used for doping. This combination allows simultaneous achievement of electrical doping and mechanical strain in the channel, reducing the number of separate process steps compared to implementing strain through separate thin film deposition and patterning processes.
Solution Approach 2:
The implanted silicon or carbon impurities serve multiple functions: they act as dopants to establish the electrical characteristics of source and drain regions, and simultaneously serve as strain-inducing elements that modify the band structure of the germanium channel. This multi-functionality reduces process complexity by eliminating the need for separate strain introduction steps.
3Manufacturing precision
If ion implantation process is used to introduce strain in the channel to increase charge carrier mobility, then the mobility increases, but the process steps and manufacturing complexity increase
Solution Approach 1:
The patent combines the strain induction function with the standard doping process by using the same ion implantation equipment and process flow to introduce both dopant atoms and strain-inducing impurities. This merging of functions allows the strain effect to be achieved using existing manufacturing infrastructure without adding dedicated strain introduction equipment or process steps.
Solution Approach 2:
The silicon or carbon impurities automatically generate the desired tensile strain in the germanium channel through their presence and lattice mismatch, without requiring external mechanical stress application or complex process control. The strain is self-generated by the material composition itself, simplifying the manufacturing process compared to methods requiring precise control of thin film deposition conditions or external stressors.
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 increases the mobility of charge carriers, improving the driving current and performance of NMOS transistors without increasing process complexity, by directly applying stress to the germanium channel and preventing impurity diffusion, thus forming a shallow junction and enhancing solid solubility of N-type impurities.
Implementation Method 1
performing a first ion implantation process with respect to the source and drain extension regions, wherein the ions implanted in the first ion implantation process include silicon or carbon
Implementation Method 2
performing an annealing process with respect to the germanium-based semiconductor substrate which has been subjected to the third ion implantation process
Implementation Method 3
introducing a uniaxial tensile stress in the direction parallel to the channel plane and also may simultaneously introduce a compressive stress in the direction perpendicular to the channel plane, so as to increase the mobility of the electrons in the channel
Data Source
AI summary
The present invention provides a semiconductor device and a method for fabricating the same, wherein the method comprises: providing a germanium-based semiconductor substrate having a plurality of active regions and device isolation regions between the plurality of the active regions, wherein a gate dielectric layer and a gate over the gate dielectric layer are provided on the active regions, and the active regions include source and drain extension regions and deep source and drain regions; performing a first ion implantation process with respect to the source and drain extension regions, wherein the ions implanted in the first ion implantation process include silicon or carbon; performing a second ion implantation process with respect to the source and drain extension regions; performing a third ion implantation process with respect to the deep source and drain regions; performing an annealing process with respect to the germanium-based semiconductor substrate which has been subjected to the third ion implantation process. According to the method for fabricating a semiconductor device, through the implantation of silicon impurities, appropriate stress may be introduced into the germanium channel effectively by the mismatch of lattices in the source and drain regions, so that the mobility of electrons in the channel is enhanced and the performance of the device is improved.