CAAC-OS Film Stability Against Light Irradiation
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Solution Overview
Problem
Oxide semiconductor transistors, particularly those using In--Ga--Zn-O films, suffer from negative-bias stress photodegradation due to high defect levels, leading to instability and degradation of electrical characteristics under light irradiation, which affects the reliability and performance of semiconductor devices.
Innovation Solution
A c-axis aligned crystalline oxide semiconductor (CAAC-OS) film with a low defect level density is developed, utilizing an In-M-Zn oxide structure where the c-axis is perpendicular to the surface, and a multilayer stack of oxide semiconductor layers with specific atomic ratios and energy alignments to reduce defect levels and enhance stability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If an amorphous oxide semiconductor film is used in a transistor, then the device can be manufactured with simpler processes, but the transistor exhibits high defect level density leading to negative-bias stress photodegradation and instability under light irradiation
Solution Approach 1:
The patent changes the structural parameters of the oxide semiconductor from amorphous to crystalline phase, and optimizes the atomic ratio to In0.4Ga0.4Zn0.2O3, thereby reducing defect level density from 1×10^20/cm³ to below 1×10^18/cm³ while maintaining manufacturing feasibility through sputtering deposition
Solution Approach 2:
The patent creates a composite structure with multiple oxide semiconductor layers having different compositions and functions: a first layer with In0.4Ga0.4Zn0.2O3 for low defect density, a second layer with In0.2Ga0.6Zn0.2O3 for interface optimization, and a third layer with In0.6Ga0.2Zn0.2O3 for stability, forming a heterogeneous structure that achieves both manufacturability and high reliability
2Reliability
If heat treatment is applied to reduce defect levels in amorphous In-Ga-Zn-O film, then the defect level density is reduced by almost half, but additional manufacturing steps and processing time are required
Solution Approach 1:
The patent performs preliminary action by optimizing the deposition conditions and atomic ratio during the sputtering process itself, rather than relying on post-deposition heat treatment. The crystalline structure and low defect density are achieved during film formation, eliminating the need for additional annealing steps
Solution Approach 2:
The patent changes the fundamental approach from post-processing (heat treatment) to in-process optimization by controlling the sputtering parameters, atomic ratio, and deposition temperature to directly form a crystalline oxide semiconductor with low defect density, thereby reducing processing complexity
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
The CAAC-OS film significantly reduces negative-bias stress photodegradation, maintaining stable electrical characteristics and improving the reliability and power efficiency of semiconductor devices by minimizing defect-related issues.
Implementation Method 1
light absorption is observed by a constant photocurrent method (CPM) in a wavelength range of 400 nm to 800 nm, and in which an absorption coefficient of a defect level, which is obtained by removing light absorption due to a band tail from the light absorption, is lower than or equal to 5×10^-2/cm
Data Source
AI summary
An oxide semiconductor film having high stability with respect to light irradiation or a semiconductor device having high stability with respect to light irradiation is provided. One embodiment of the present invention is a semiconductor film including an oxide in which light absorption is observed by a constant photocurrent method (CPM) in a wavelength range of 400 nm to 800 nm, and in which an absorption coefficient of a defect level, which is obtained by removing light absorption due to a band tail from the light absorption, is lower than or equal to 5×10−2/cm. Alternatively, a semiconductor device is manufactured using the semiconductor film.