Replacement Fin Epitaxy for Germanium Film Defect Reduction
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Solution Overview
Problem
The semiconductor industry faces challenges in forming high-concentration germanium and III-V compound semiconductor films with low defect densities and sufficient thickness for MOS transistors, particularly FinFETs, due to the critical thickness limitations and lattice structure breakdown when grown on silicon wafers.
Innovation Solution
The method involves forming Fin Field-Effect Transistors (FinFETs) using replacement fins grown epitaxially with varying germanium concentrations or III-V compound semiconductor materials, which replace the original fins and are integrated into an integrated circuit structure, allowing for the growth of thicker films with reduced defect densities by using a process that includes etching, oxidation, and epitaxial growth.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If germanium films are grown on silicon wafers to achieve high germanium concentration, then electron mobility and hole mobility are improved, but the critical thickness is exceeded causing lattice structure breakdown and high defect densities
Solution Approach 1:
The fin structure is divided into two distinct parts: a silicon base fin grown on the silicon wafer, and a separate germanium or III-V compound semiconductor layer grown epitaxially on the silicon fin. This segmentation allows each part to be optimized independently - the silicon base provides a lattice-matched foundation, while the germanium layer provides high carrier mobility without exceeding critical thickness constraints
Solution Approach 2:
The silicon base fin is grown first to establish a stable, lattice-matched foundation before the germanium layer is deposited. This preliminary action creates a prepared substrate that prevents lattice mismatch issues and enables subsequent growth of high-quality germanium films with controlled thickness
2Reliability
If the germanium percentage in silicon germanium film is increased to improve mobility, then electron mobility and hole mobility increase, but the critical thickness reduces significantly causing relaxation and lattice structure breakdown
Solution Approach 1:
Different regions of the fin structure have different material compositions optimized for their specific functions: the silicon base fin provides mechanical support and lattice matching, while the germanium layer provides high carrier mobility. This local quality differentiation allows high germanium concentration (up to 100%) in the mobility-critical region without compromising structural integrity
Solution Approach 2:
The fin structure uses a composite of silicon and germanium materials, where the silicon base and germanium layer work together to provide both structural stability and high carrier mobility. The composite structure allows optimization of each material's properties in its appropriate region
3Productivity
If thick germanium films are formed to improve MOS transistor performance, then drive currents increase, but defect densities increase significantly when exceeding critical thickness
Solution Approach 1:
The fin is segmented into a thick silicon base portion and a thinner germanium layer, allowing the overall fin structure to be thick enough for good device performance while the germanium layer itself remains below critical thickness to avoid relaxation and defects
Solution Approach 2:
The silicon base fin is grown first to provide a thick, defect-free foundation, then the germanium layer is grown epitaxially on top with controlled thickness to maximize mobility without exceeding critical thickness limits
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 enables the formation of high-quality germanium and III-V compound semiconductor films with improved thickness and reduced defects, enhancing the performance and manufacturability of MOS transistors, particularly FinFETs, by overcoming the limitations of silicon germanium film critical thickness and lattice structure issues.
Implementation Method 1
semiconductor fins and replacement fins grown epitaxially
Implementation Method 2
oxidizing surface portions of the first semiconductor fin to form a first oxide layer
Data Source
AI summary
A method includes forming a first semiconductor fin, and oxidizing surface portions of the first semiconductor fin to form a first oxide layer. The first oxide layer includes a top portion overlapping the first semiconductor fin and sidewall portions on sidewalls of the first semiconductor fin. The top portion of the first oxide layer is then removed, wherein the sidewall portions of the first oxide layer remains after the removing. The top portion of the first semiconductor fin is removed to form a recess between the sidewall portions of the first oxide layer. An epitaxy is performed to grow a semiconductor region in the recess.