Oxide Semiconductor Device Silicon Interface Control
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Solution Overview
Problem
Conventional designs for oxide semiconductor transistors, assuming insensitivity to impurities, result in increased source and drain region resistances and decreased on-state current due to impurity incorporation, particularly silicon, at the interface with the gate insulating film.
Innovation Solution
A semiconductor device structure is implemented where the oxide semiconductor film has a region near the gate insulating film interface with a silicon concentration of 1.1% or less, and a carbon concentration of 1.0×10^20 atoms/cm^3 or less, to minimize impurity incorporation and maintain optimal electric characteristics.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a gate insulating film containing silicon is formed by sputtering over the oxide semiconductor film, then the gate insulating film can be formed with good insulating properties, but silicon impurities are incorporated into the oxide semiconductor film interface region causing increased resistance and decreased on-state current
Solution Approach 1:
The oxide semiconductor film is divided into two distinct regions: a first region adjacent to the gate insulating film interface with controlled silicon concentration (≤1.1 at %), and a second region farther from the interface with different composition. This segmentation allows the interface region to maintain low impurity concentration while the bulk region can have optimized composition for electrical performance.
Solution Approach 2:
Different regions of the oxide semiconductor film are given different local compositions: the first region near the interface has restricted silicon content to prevent impurity accumulation, while the second region can have higher silicon content or different stoichiometry to optimize carrier concentration and electrical conductivity. This local quality variation resolves the contradiction between interface purity and bulk electrical properties.
2Length of moving object
If the oxide semiconductor film is made thinner to miniaturize the transistor, then the device size is reduced and short-channel effect is suppressed, but the film becomes more sensitive to impurity incorporation at the interface
Solution Approach 1:
By segmenting the thin oxide semiconductor film into distinct composition regions, the invention allows the overall film thickness to be reduced for miniaturization while ensuring that the critical interface region (first region) maintains extremely low silicon concentration. This prevents the thin film from being overwhelmed by impurity effects that would otherwise dominate in scaled-down devices.
Solution Approach 2:
The invention changes the compositional parameters locally within the oxide semiconductor film. The first region has silicon concentration ≤1.1 at % to minimize impurity effects in the thin film regime, while the second region can have adjusted composition to maintain adequate carrier concentration and on-state current even when the overall film thickness is reduced for device miniaturization.
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 effectively suppresses the decrease in on-state current and improves the operational characteristics of the transistor by reducing impurity-induced resistance increases and maintaining high on-state current performance.
Implementation Method 1
A sputtering method is used as one of methods for forming the gate insulating film. When the gate insulating film is formed by a sputtering method over the oxide semiconductor film, an element ejected from a sputtering target might be taken into the oxide semiconductor film.
Data Source
AI summary
To suppress a decrease in on-state current in a semiconductor device including an oxide semiconductor. Provided is a semiconductor device including the following: an oxide semiconductor film which serves as a semiconductor layer; a gate insulating film including an oxide containing silicon, over the oxide semiconductor film; a gate electrode which overlaps with at least the oxide semiconductor film, over the gate insulating film; and a source electrode and a drain electrode which are electrically connected to the oxide semiconductor film. In the semiconductor device, the oxide semiconductor film overlapping with at least the gate electrode includes a region in which a concentration of silicon distributed from the interface with the gate insulating film toward the inside of the oxide semiconductor film is lower than or equal to 1.1 at. %.