Oxide Semiconductor Transistor with Embedded Cap Layer for Flat Surface
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Solution Overview
Problem
Miniaturization of transistors for high-speed operation and low power consumption is hindered by the need for flat film surfaces and the challenge of reducing steps in oxide semiconductor films, which affects yield and electrical characteristics.
Innovation Solution
A semiconductor device structure is developed with an oxide film embedded in a base insulating film, planarization treatment is performed to create a flat surface, and a multilayer oxide film structure is used to improve the channel length and reduce defects, allowing for high-performance transistors with improved on-state current and reliability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If the oxide semiconductor film is miniaturized to achieve high-speed operation and low power consumption, then the transistor performance is improved, but the film surface flatness deteriorates and steps are generated
Solution Approach 1:
The oxide semiconductor film is divided into multiple layers (first oxide semiconductor layer and second oxide semiconductor layer) with different functions. The first layer provides the channel formation region with controlled thickness for proper electrical characteristics, while the second layer serves as a cap layer to maintain surface flatness and prevent step generation, thus resolving the contradiction between miniaturization and surface flatness
Solution Approach 2:
Different regions of the oxide semiconductor structure are assigned different thicknesses and properties. The channel formation region has a specific thickness range (3 nm to 20 nm) for optimal electrical performance, while the cap layer has different thickness and composition to provide surface protection and flatness, allowing each region to optimize its local function
2Volume of moving object
If the oxide semiconductor film is miniaturized, then the transistor size is reduced, but the yield of manufacturing process decreases
Solution Approach 1:
A cap layer is formed beforehand to protect the underlying oxide semiconductor structure during subsequent manufacturing processes. This cap layer prevents damage and step generation that would otherwise occur during miniaturization processing, thereby maintaining high manufacturing yield while enabling transistor size reduction
Solution Approach 2:
The cap layer acts as an intermediary protective layer between the oxide semiconductor channel and the external environment or subsequent processing steps. This intermediary structure prevents direct exposure of the miniaturized channel region to damaging processes, thus preserving yield during miniaturization
3Length of moving object
If the oxide semiconductor film is miniaturized, then the transistor dimensions are reduced, but the electrical characteristics deteriorate
Solution Approach 1:
The thickness of the oxide semiconductor layer in the channel formation region is precisely controlled within the range of 3 nm to 20 nm to achieve proper electrical characteristics. This parameter optimization ensures that even in miniaturized transistors, the electrical properties such as mobility and threshold voltage remain within acceptable ranges, maintaining reliability despite reduced dimensions
Data Source
AI summary
A miniaturized transistor having high electrical characteristics is provided with high yield. In a semiconductor device including the transistor, high performance, high reliability, and high productivity can be achieved. The semiconductor device includes a base insulating film, an oxide semiconductor film with a bottom surface and side surfaces in the base insulating film and a top surface exposed from the base insulating film, a source electrode and a drain electrode over the base insulating film and the oxide semiconductor film, a gate insulating film over the oxide semiconductor film, the source electrode, and the drain electrode, and a gate electrode over the gate insulating film and overlapping the oxide semiconductor film.