Angled Ion Implantation for MOSFET Trench Bottom Oxide Control
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Solution Overview
Problem
Conventional thermal oxidation processes in trench-based MOSFETs result in non-uniform oxide formation, leading to trench-bottom oxide thinning and degraded breakdown voltage, which hinders scalability and increases on-resistance, especially in power MOSFETs used in high-frequency applications.
Innovation Solution
A method involving the formation of a high-density plasma oxide layer within trenches and an angled ion implantation process to selectively increase the etch rate of the oxide layer, allowing for precise control of the oxide thickness, particularly at the trench bottom, while maintaining a thicker oxide layer to reduce gate charge and improve breakdown voltage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If conventional thermal oxidation processes are used to form oxide in trenches, then oxide layer is formed, but the oxide thickness becomes non-uniform with thinning at the trench bottom
Solution Approach 1:
The patent applies local quality by making different portions of the oxide layer have different etch rates through selective ion implantation. The trench bottom oxide is implanted with ions at a first angle to increase its etch rate, while the top surface oxide is implanted at a second angle to maintain or reduce its etch rate. This creates spatially varying etch rates that enable precise local control of oxide thickness during subsequent etching, resolving the uniformity issue while maintaining breakdown voltage.
Solution Approach 2:
The patent changes physical parameters of the oxide layer by controlling ion implantation angles and energies. By varying the ion implantation angle (first angle for trench bottom, second angle for top surface) and energy levels, the etch rate parameters of different oxide regions are modified. This allows differential etching to achieve uniform final oxide thickness across the trench structure, eliminating the thinning problem at the trench bottom.
2Productivity
If trench width is reduced to improve device scaling, then device density increases, but trench-bottom oxide thins due to oxygen diffusion and crystal orientation
Solution Approach 1:
The patent applies preliminary action by performing ion implantation on the oxide layer before the final etching step. The oxide layer is first formed with uniform thickness, then ion implantation is used to pre-condition different regions with different etch rates. This preliminary modification of etch rate properties allows the subsequent etching step to automatically compensate for the natural thinning at the trench bottom, achieving uniform final thickness even in scaled-down trenches.
Solution Approach 2:
The patent applies local quality by creating spatially varying etch rate properties in the oxide layer through targeted ion implantation. The trench bottom region receives ion implantation at a first angle that increases its etch rate, compensating for the natural thinning effect. This local differentiation of etch rate properties enables precise control of final oxide thickness at the trench bottom, maintaining manufacturing precision during device scaling.
3Quantity of substance
If thicker bottom oxide is used to reduce gate charge, then gate charge decreases, but breakdown voltage may be affected
Solution Approach 1:
The patent applies local quality by enabling different oxide thicknesses at different locations through selective ion implantation and differential etching. The trench bottom oxide can be made thicker to reduce gate charge, while the top surface oxide thickness is controlled separately. This spatial differentiation allows optimization of gate charge without compromising breakdown voltage, as each region's oxide thickness can be independently tuned to its optimal value.
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 precise trench bottom oxide formation, enhancing scalability and reducing on-resistance and gate charge, thereby improving the electrical performance and reliability of MOSFETs.
Implementation Method 1
implanting a first portion of the oxide layer using an ion implant delivered to the device structure at a non-zero angle of inclination relative to a perpendicular extending from a top surface of the device structure
Data Source
AI summary
Disclosed herein are methods for forming MOSFETs. In some embodiments, a method may include providing a device structure including a plurality of trenches, forming an oxide layer over the device structure including within each of the plurality of trenches and over a top surface of the device structure, and implanting a first portion of the oxide layer using an ion implant delivered to the device structure at a non-zero angle of inclination relative to a perpendicular extending from a top surface of the device structure. The method may further include removing the oxide layer from the top surface of the device structure and from a sidewall of each of the plurality of trenches, wherein a second portion of the oxide layer remains along a bottom of each of the plurality of trenches.