FinFET Doping via Oblique Ion Implantation
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Solution Overview
Problem
Current doping methods for Fin type FETs do not effectively utilize the upper portion of the silicon Fin part, leading to degraded drive current due to the lack of impurity implantation in the upper flat portion, which results in reduced transistor performance.
Innovation Solution
A method involving the formation of a thin film with a thicker deposition on the upper flat portion compared to the side walls, followed by diagonal ion implantation from opposite directions to achieve equal impurity concentration in both areas using a recoil effect, allowing for uniform impurity distribution across the cubic concavity and convexity parts.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional doping methods are used for Fin type FETs, then the side wall portions are doped with impurity atoms, but the upper flat portion is not effectively doped, resulting in degraded drive current
Solution Approach 1:
The patent applies local quality by depositing the impurity-containing film with different thicknesses at different locations: a first thickness on the upper flat portion and a second thickness on the side wall portions. This non-uniform initial deposition compensates for the geometric differences, ensuring that after oblique ion implantation, both regions receive equal impurity concentrations. The local variation in film thickness is precisely controlled to achieve uniform doping results across different surfaces.
Solution Approach 2:
The patent utilizes asymmetry in the ion implantation process by employing oblique irradiation at a specific angle (α) relative to the normal of the upper flat portion. This asymmetric implantation angle, combined with the asymmetric film thickness distribution, ensures that the impurity atoms are implanted into both the upper flat portion and side wall portions with equal concentrations. The asymmetric approach transforms the geometric asymmetry of the Fin structure into a controlled doping uniformity.
2Productivity
If the upper portion of the silicon Fin part is not utilized as a channel region, then the existing doping method is sufficient, but the Fin height cannot be reduced and Fin width increased, limiting transistor performance improvement
Solution Approach 1:
The patent applies preliminary action by pre-depositing the impurity-containing film with carefully controlled non-uniform thickness before the ion implantation step. This preliminary film deposition prepares the structure in advance so that when oblique ion implantation is performed, the impurity atoms are released from the film into the silicon substrate with equal concentrations in both the upper flat portion and side wall portions. This preliminary preparation enables the upper portion to be effectively utilized as a channel region, allowing Fin height reduction and Fin width increase for improved transistor performance.
Solution Approach 2:
The patent employs parameter changes by controlling the deposition thickness of the impurity-containing film as a key parameter. Specifically, the film thickness is set to a first value on the upper flat portion and a second value on the side wall portions, with the ratio between these thicknesses being carefully controlled. This parameter control, combined with the ion implantation angle, ensures equal impurity concentrations are achieved, enabling effective utilization of the upper portion for enhanced transistor characteristics.
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 effective utilization of the upper flat portion of the silicon Fin part, improving the drive current and characteristics of the Fin type FET by ensuring equal impurity concentration in both side walls and the upper flat portion.
Implementation Method 1
by obliquely irradiating an ion beam 5 from an upper left direction (diagonal upper direction) of the silicon Fin part 11, a heavy ion such as Ge, Xe or the like is implanted
Implementation Method 2
by a knock on effect (or action) which will be described later, electro-active impurity in silicon, which are present in the deposited film 2 is implanted into a left side wall of the silicon Fin part 11
Data Source
AI summary
After formation of a silicon Fin part on a silicon substrate, a thin film including an impurity atom which becomes a donor or an acceptor is formed so that a thickness of the thin film formed on the surface of an upper flat portion of the silicon Fin part becomes large relative to a thickness of the thin film formed to the surface of side wall portions of the silicon Fin part. A first diagonal ion implantation from a diagonal upper direction to the thin film is performed and subsequently a second diagonal ion implantation is performed from an opposite diagonal upper direction to the thin film. Recoiling of the impurity atom from the inside of the thin film to the inside of the side wall portions and to the inside of the upper flat portion is realized by performing the first and second diagonal ion implantations.