Epitaxial Layer Formation on (111) Planes via Germanium Mediation
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Solution Overview
Problem
Conventional epitaxial layer formation techniques face challenges in achieving proper formation on (111) crystallographic planes due to atomic radius differences, leading to incomplete source/drain regions in NMOS transistors, which adversely affect transistor performance.
Innovation Solution
A method involving a first epitaxial growth process with silicon, carbon, phosphorous, and germanium, followed by a second epitaxial growth process with fewer elements, where germanium is doped into the phosphorous doped silicon-carbide layer to compensate lattice mismatches, ensuring a predetermined shape and improved transistor performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If phosphorous doped silicon-carbide layer is formed on (111) crystallographic planes, then the source/drain region should be properly formed, but the atomic radius difference between phosphorous and carbon with silicon prevents proper formation
Solution Approach 1:
Germanium is introduced as an intermediary element between phosphorous/carbon and silicon. The patent forms a phosphorous-doped silicon-carbide-germanium layer where germanium atoms (with atomic radius closer to silicon) mediate the lattice mismatch caused by the significant atomic radius difference between phosphorous/carbon and silicon, enabling proper epitaxial layer formation on (111) crystallographic planes
Solution Approach 2:
The patent changes the compositional parameters of the epitaxial layer by incorporating germanium into the phosphorous-doped silicon-carbide structure. This parameter change (adding Ge) modifies the lattice constant and atomic radius characteristics of the layer, making it compatible with the silicon substrate's (111) planes while maintaining the desired electrical properties
2Reliability
If multiple elements are doped into epitaxial layer, then carrier mobility is enhanced, but lattice mismatch due to atomic radius difference causes formation defects
Solution Approach 1:
Germanium serves as a mediator that reconciles the conflicting requirements of multi-element doping for carrier mobility enhancement and lattice matching for shape control. By positioning germanium between the dopants (phosphorous, carbon) and the silicon substrate, it enables multiple elements to coexist in the epitaxial layer without causing formation defects
Solution Approach 2:
The patent creates a composite material structure - a phosphorous-doped silicon-carbide-germanium epitaxial layer - that combines the beneficial properties of multiple elements: phosphorous for n-type doping and carrier mobility enhancement, carbon for structural stability, and germanium for lattice matching with silicon. This composite approach allows simultaneous achievement of enhanced transistor performance and proper layer formation
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 approach allows for the proper formation of an epitaxial layer with silicon, carbon, phosphorous, and germanium on silicon wafers, enhancing carrier mobility and stress distribution, thereby improving NMOS transistor performance.
Implementation Method 1
a first epitaxial growth process is performed to form a first epitaxial layer on a substrate
Implementation Method 2
a gas source of silicon, a gas source of carbon, a gas source of phosphorous and a gas source of germanium are introduced during the first epitaxial growth process
Implementation Method 3
a second epitaxial growth process is performed to form a second epitaxial layer
Data Source
AI summary
A method of forming an epitaxial layer includes the following steps. At first, a first epitaxial growth process is performed to form a first epitaxial layer on a substrate, and a gas source of silicon, a gas source of carbon, a gas source of phosphorous and a gas source of germanium are introduced during the first epitaxial growth process to form the first epitaxial layer including silicon, carbon, phosphorous and germanium. Subsequently, a second epitaxial growth process is performed to form a second epitaxial layer, and a number of elements in the second epitaxial layer is smaller than a number of elements in the first epitaxial layer.