Strained Si-SOI Substrate Fabrication via Ion Implantation and Heat Treatment
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Solution Overview
Problem
Existing methods for producing strained Si—SOI substrates face challenges in achieving a flat surface with reduced defects, particularly due to surface irregularities and high production costs associated with epitaxial growth and bonding processes.
Innovation Solution
A method involving the growth of a SiGe mixed crystal layer on an SOI substrate, followed by ion implantation of light elements and controlled heat treatments to weaken bonding strengths, diffuse Ge, and relax strain, resulting in a strained Si layer with reduced defects and improved surface flatness.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If a relaxed SiGe layer is formed by epitaxial growth on an SOI substrate followed by forming strained Si on the SiGe layer, then a strained Si-SOI substrate can be produced, but surface irregularities and cross-hatches occur causing high surface roughness and defects
Solution Approach 1:
The patent applies preliminary action by forming a buffer layer with moderate Ge content gradient before forming the main SiGe layer. This preliminary buffer layer prevents dislocation propagation to the surface, eliminating cross-hatches and surface irregularities before the main epitaxial growth occurs. The buffer layer is prepared in advance to create a defect-free foundation for subsequent layers.
Solution Approach 2:
The patent applies local quality by creating different Ge content zones within the SiGe layer structure. The buffer layer has lower Ge content (1-10%) while the main SiGe layer has higher Ge content (10-30%). This spatial variation in composition allows the buffer zone to absorb dislocations locally while the main layer maintains high quality for device fabrication.
2Manufacturing precision
If conventional polishing methods are applied to SiGe layers to remove surface irregularities, then some surface defects can be reduced, but penetrating dislocation densities and surface roughness remain insufficient
Solution Approach 1:
The patent prevents dislocation formation at the source through preliminary buffer layer growth rather than attempting to remove them later through polishing. The buffer layer with gradient Ge composition pre-empts dislocation propagation, ensuring that the main SiGe layer forms with inherently low dislocation density that does not require aggressive polishing.
3Manufacturing precision
If bonding methods are used to form strained Si-SOI substrates with only strained silicon on buried oxide film, then strained silicon can be achieved, but production cost increases due to thick layer growth and multiple steps
Solution Approach 1:
The patent extracts the SiGe layer from the traditional bonding process by forming it directly on the SOI substrate through epitaxial growth. This eliminates the need for separate bonding of thick SiGe layers to SOI substrates, reducing the number of process steps and associated costs while maintaining the desired strain relaxation quality.
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 method effectively reduces surface roughness and defects, achieving a strained Si—SOI substrate with enhanced strain relaxation and improved quality, as demonstrated by reduced penetrating dislocation density and surface roughness.
Implementation Method 1
implanting light element ions into a vicinity of the interface between the silicon layer and the buried oxide film
Implementation Method 2
performing a first heat treatment for heat treating the substrate at a temperature in the range of 400 to 1000° C.
Implementation Method 3
performing a second heat treatment for heat treating the substrate at a temperature not lower than 1050° C. under an oxidizing atmosphere
Implementation Method 4
performing a second heat treatment for heat treating the substrate at a temperature not lower than 1050° C. under an oxidizing atmosphere
Data Source
AI summary
A strained Si—SOI substrate, and a method for producing the same are provided, wherein the method includes the steps of growing a SiGe mixed crystal layer 14 on an SOI substrate 10 having an Si layer 13 and a buried oxide film 12; forming protective films 15, 16 on the surface of the SiGe mixed crystal layer 14; implanting light element ions into a vicinity of the interface between the Si layer 13 and the buried oxide film 12; performing a first heat treatment at a temperature in the range of 400 to 1000° C.; performing a second heat treatment at a temperature not lower than 1050° C. under an oxidizing atmosphere; performing a third heat treatment at a temperature not lower than 1050° C. under an inert atmosphere; removing the Si oxide film 18 formed on the surface; and forming a strained Si layer 19.