SOI Device Second Buried Oxide Layer Punch-Through Prevention
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Solution Overview
Problem
Conventional Silicon On Insulator (SOI) devices fail to achieve a floating body effect and are prone to punch-through due to inadequate junction region isolation by the buried oxide layer, leading to reduced effective channel length and increased power consumption.
Innovation Solution
The formation of a second buried oxide layer at the lower portion of the silicon layer, in contact with the first buried oxide layer, along with a junction region that extends to and is in contact with the second buried oxide layer, is achieved through ion implantation and heat treatment, ensuring full isolation and preventing punch-through.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If ion implantation is performed at high dose to make the junction region extend vertically to contact the buried oxide layer, then the floating body effect is obtained, but the distance between adjacent junction regions is reduced causing punch-through
Solution Approach 1:
The patent applies dimensionality change by forming a second buried oxide layer at a different vertical position (lower portion of the silicon layer) to provide isolation. This additional dimensional approach allows the junction region to achieve full isolation contact without requiring excessive vertical extension that would cause horizontal encroachment on adjacent channels, thereby preventing punch-through while maintaining the floating body effect.
Solution Approach 2:
The second buried oxide layer acts as an intermediary isolation structure between the junction region and the first buried oxide layer. This intermediate layer provides the necessary isolation function, enabling the junction region to be fully isolated without extending too far vertically, thus avoiding the punch-through problem while still achieving the floating body effect.
2Object-affected harmful factors
If the junction region is formed without full contact to the buried oxide layer, then punch-through is prevented, but the floating body effect cannot be obtained
Solution Approach 1:
The isolation structure is segmented into two distinct buried oxide layers: the first buried oxide layer providing baseline isolation, and the second buried oxide layer providing additional isolation at a lower position. This segmentation allows the junction region to achieve full isolation contact for the floating body effect while the second layer ensures adequate spacing is maintained to prevent punch-through.
Solution Approach 2:
By introducing the second buried oxide layer at a different vertical dimension (lower portion of the silicon layer), the patent achieves full isolation contact necessary for the floating body effect without requiring the junction region to extend excessively upward, thereby maintaining adequate horizontal spacing to prevent punch-through.
3Speed
If the effective channel length is increased to prevent punch-through, then device speed is reduced, but if the channel length is decreased for higher speed, punch-through occurs
Solution Approach 1:
The second buried oxide layer serves as an intermediary isolation structure that enables the use of shorter channel lengths for higher device speed. By providing enhanced isolation through this intermediate layer, the patent allows reduced channel length without suffering from punch-through, thus achieving both high speed and reliability.
Solution Approach 2:
The addition of the second buried oxide layer at a lower vertical position provides an extra dimensional isolation mechanism. This allows the effective channel length to be shortened for higher device speed while the dual-layer oxide structure prevents punch-through through improved vertical isolation, resolving the speed-reliability tradeoff.
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 SOI device to obtain a floating body effect, maintain effective channel length, and prevent punch-through, thereby enhancing performance and reducing power consumption.
Implementation Method 1
The step of forming the second buried oxide layer comprises ion implanting impurities for promoting oxidation into the portion of the silicon layer at both sides of the gate
Implementation Method 2
heat treating the portion of the silicon layer into which the impurities are ion implanted so as to oxidate the portion
Data Source
AI summary
An SOI device includes an SOI substrate having a structure in which a first buried oxide layer and a silicon layer are stacked in turn over a semiconductor substrate. A gate is formed over the silicon layer of the SOI substrate. A second buried oxide layer is formed at both sides of the gate in a lower portion of the silicon layer so that a lower end portion of the second buried oxide layer is in contact with the first buried oxide layer. A junction region is then formed in the portion of the silicon layer above the second buried oxide layer so that the lower end portion of the junction region is in contact with the second buried oxide layer.