Porous Silicon Insulator Layer Formation for Floating-Body Effect Mitigation
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Solution Overview
Problem
The integration of logic circuits and DRAM on a single semiconductor chip using SOI-MOSFETs is hindered by the floating-body effect, which causes fluctuations in leak current and threshold values, leading to increased cell area and reduced high integration capabilities in DRAMs.
Innovation Solution
A method for manufacturing a bonded substrate with a partially varying insulator layer using porous silicon technology, involving porous layer formation, heat treatment to convert the porous layer into an insulator layer, selective etching, and bonding, allowing for the formation of an optimum insulator layer thickness at specific positions on the substrate.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a non-SOI region is formed on an SOI substrate by conventional methods (etching, selective epitaxial growth), then the floating-body effect is overcome and circuit performance is improved, but the manufacturing process becomes complex and the number of fabrication steps increases
Solution Approach 1:
The patent uses porous silicon as an intermediate material to form the non-SOI region. Porous silicon is formed by anodization of the SOI substrate, creating a porous layer that can be selectively removed or transformed. This porous structure serves as a precursor that simplifies subsequent processing steps compared to conventional etching and epitaxial growth methods, while achieving the same functional result of creating a non-SOI region to eliminate the floating-body effect
Solution Approach 2:
The patent changes the physical and chemical parameters of the silicon substrate by controlling the anodization process parameters (electrical current density, electrolyte composition, temperature) to create porous silicon with specific properties. By adjusting these parameters, the porous layer's thickness, porosity, and oxidation behavior can be controlled, enabling selective formation of non-SOI regions without complex fabrication steps
2Ease of manufacture
If the insulator layer thickness is uniformly reduced across the entire substrate, then manufacturing is simplified, but the ability to control floating-body effect in specific regions is lost
Solution Approach 1:
The patent applies local quality by forming porous silicon only in specific regions of the substrate where non-SOI characteristics are needed. By using photolithography masks and controlled anodization, the porous layer is created only in areas requiring floating-body effect mitigation, while other areas maintain their original SOI structure. This localized approach allows selective thickness reduction of the insulator layer only where necessary
3Ease of manufacture
If porous silicon is formed across the entire substrate surface, then insulator layer formation is simplified, but selective region control is lost and manufacturing precision decreases
Solution Approach 1:
The patent applies preliminary action by forming a photolithography mask pattern before the anodization process. This pre-formed pattern defines exactly which regions will undergo porous silicon formation. The mask is applied to the substrate, and then anodization is performed, ensuring that porous silicon is created only in the exposed regions. This preliminary patterning step ensures high manufacturing precision while maintaining the simplicity of subsequent insulator 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
This approach enables the easy and cost-effective manufacturing of a bonded substrate with a partial SOI substrate, reducing the number of fabrication steps and enhancing the performance of multi-functionalized devices by controlling the insulator layer thickness, thus mitigating the floating-body effect and maintaining high integration capabilities.
Implementation Method 1
an insulator layer forming step of performing a heat treatment to the base substrate having the porous layer formed thereon to change the porous layer into the insulator layer
Implementation Method 2
an insulator layer removing step of removing the insulator layer whose thickness varies by an amount corresponding to a thickness of a small-thickness portion by etching
Implementation Method 3
a bonding step of bonding the bonding surface of the base substrate on which the unetched remaining insulator layer is exposed to the bond substrate
Data Source
Figure 1(a)~1(l)
Figure 2(a)~2(j)
Figure 3
AI summary
According to the present invention, there is provided a method for manufacturing a bonded substrate that has an insulator layer in part of the bonded substrate, the method comprising: a porous layer forming step of partially forming a porous layer or forming a porous layer whose thickness partially varies on a bonding surface of the base substrate; an insulator layer forming step of performing a heat treatment to the base substrate having the porous layer formed thereon to change the porous layer into the insulator layer, and thereby forming the insulator layer whose thickness partially varies on the bonding surface of the base substrate; an insulator layer removing step of removing the insulator layer whose thickness varies by an amount corresponding to a thickness of a small-thickness portion by etching; a bonding step of bonding the bonding surface of the base substrate on which an unetched remaining insulator layer is exposed to a bond substrate; and a thin film forming step of reducing a thickness of the bonded bond substrate and thereby forming a thin film layer. As a result, the method for easily manufacturing a bonded substrate having an insulator layer in part of the substrate with use of the porous silicon technology can be provided.