RF Silicon Support Substrate Structure for Slip Line and Warp Control
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Solution Overview
Problem
Existing silicon-on-insulation (SOI) structures for radiofrequency (RF) applications face challenges in achieving optimal mechanical and electrical stability while maintaining reasonable manufacturing costs and avoiding defects such as 'Slip Lines' and significant curvature.
Innovation Solution
A support substrate for RF applications is developed, comprising a basic monocrystalline silicon substrate with specific resistivity and oxygen content, an epitaxied monocrystalline silicon layer with controlled resistivity and thickness, and a poly-crystalline silicon trapping layer. The substrate is designed to have a rough interface and optimized thickness and resistivity profiles to minimize distortion and enhance mechanical stability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a base substrate with low interstitial oxygen content (13-19 ppma) and high resistivity (>3 kOhm.cm) is used, then electrical stability is improved, but mechanical strength deteriorates leading to slip line defects during high temperature heat treatments
Solution Approach 1:
The substrate is divided into two distinct parts: a base substrate with low interstitial oxygen content (13-19 ppma) and high resistivity (>3 kOhm.cm) for electrical stability, and an epitaxial layer with standard oxygen content (13-19 ppma) and controlled resistivity (10-20 ohm.cm) for mechanical strength. This segmentation allows each layer to fulfill its specific function without compromise.
Solution Approach 2:
The invention creates a composite structure combining two silicon layers with different oxygen contents and electrical properties. The base substrate provides electrical stability while the epitaxial layer provides mechanical robustness, achieving a synergistic effect that neither layer could provide alone.
2Strength
If a base substrate with standard resistivity (10-20 ohm.cm) and average interstitial oxygen content (13-19 ppma) is used, then mechanical strength is improved, but electrical stability deteriorates causing higher insertion losses and signal distortion
Solution Approach 1:
The substrate structure is segmented into a base substrate with low oxygen content for electrical stability and an epitaxial layer with standard oxygen content for mechanical strength, allowing each layer to optimize its specific function.
Solution Approach 2:
Different regions of the substrate structure are assigned different oxygen contents and electrical properties: the base substrate has low interstitial oxygen (13-19 ppma) and high resistivity (>3 kOhm.cm) for electrical stability, while the epitaxial layer has standard oxygen content and lower resistivity (10-20 ohm.cm) for mechanical strength.
3Reliability
If a thick polycrystalline silicon trapping layer (>20 microns) is used to ensure high substrate resistivity, then electrical stability is improved, but manufacturing complexity increases due to significant curvature (bow/warp) and longer polishing time
Solution Approach 1:
The function of ensuring high substrate resistivity is extracted from the trapping layer and transferred to the base substrate, which has inherently low interstitial oxygen content (13-19 ppma) and high resistivity (>3 kOhm.cm). This allows the trapping layer to be thin (1-10 microns) and eliminates the need for thick deposition and long polishing.
Solution Approach 2:
The invention changes the key parameter of interstitial oxygen content in the base substrate to very low levels (13-19 ppma), which inherently provides high resistivity (>3 kOhm.cm). This parameter change eliminates the need for thick trapping layers to achieve the same electrical stability, thereby reducing manufacturing complexity.
4Reliability
If an epitaxial layer with thickness >30 microns is used to ensure high resistivity, then electrical stability is improved, but manufacturing time increases due to longer deposition and polishing processes
Solution Approach 1:
The function of providing high resistivity is extracted from the epitaxial layer and assigned to the base substrate with low interstitial oxygen content (13-19 ppma) and high resistivity (>3 kOhm.cm). This allows the epitaxial layer to be thin (2-30 microns) and reduces deposition and polishing time.
Solution Approach 2:
By changing the interstitial oxygen content parameter of the base substrate to very low levels (13-19 ppma), the invention achieves high resistivity (>3 kOhm.cm) inherently, eliminating the need for thick epitaxial layers and reducing manufacturing time.
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 proposed substrate achieves improved electrical and mechanical stability, reduces the risk of defects like 'Slip Lines', and maintains cost-effectiveness by optimizing the thickness and resistivity of the epitaxied layer and the trapping layer, thereby enhancing the performance and reliability of RF devices.
Implementation Method 1
an epitaxial layer made of monocrystalline silicon comprising P-type dopants, arranged on the base substrate and having a thickness of between 2 microns and 30 microns
Data Source
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AI summary
The invention relates to a support substrate (10) for a radiofrequency application comprising: - a base substrate (1) made of monocrystalline silicon comprising p-type dopants and having a resistivity that is greater than or equal to 250 ohm.cm and strictly less than 500 ohm.cm, and a content of interstitial oxygen between 13 ppma and 19 ppma, - an epitaxied layer (2) made of monocrystalline silicon comprising p-type dopants disposed on the base substrate (1) and having a thickness between 2 microns and 30 microns, a portion greater than at least the epitaxied layer having a resistivity greater than 3000 ohm.cm, - a charge-trapping layer (3) made of polycrystalline silicon having a resistivity greater than or equal to 1000 ohm.cm and a thickness between 1 micron and 10 microns. The invention also relates to a method for manufacturing such a support substrate (10).