Dense Oxide Semiconductor Film via Sputtering
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Solution Overview
Problem
The challenge is to manufacture a semiconductor device with stable electric characteristics using an oxide semiconductor, where the film quality of the oxide semiconductor film significantly affects the electric characteristics and reliability of the transistor, and existing methods struggle to produce dense films with low impurity levels, especially on large glass substrates.
Innovation Solution
A method involving the use of a high-density polycrystalline sputtering target, controlled deposition conditions such as low back pressure and partial pressures of water and hydrogen, and optimized oxygen content in the deposition gas to form a dense oxide semiconductor film with a density above 6.0 g/cm3, which is close to single crystal, using a sputtering method with a substrate temperature above 200°C to achieve a c-axis aligned crystalline oxide semiconductor film.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Area of stationary object
If amorphous silicon is used to form transistors over large glass substrates, then the area of the substrate can be increased, but the field effect mobility decreases
Solution Approach 1:
The patent changes the material parameter from conventional silicon to oxide semiconductor (In-Ga-Zn-O), which enables formation of transistors with acceptable mobility characteristics over large-area glass substrates. The oxide semiconductor material inherently provides different electrical properties that resolve the mobility limitation when scaled to large substrates
Solution Approach 2:
The patent uses a composite structure combining oxide semiconductor layer with specific insulating layers (gate insulating layer, protective insulating layer) to achieve both large substrate compatibility and improved electrical characteristics. The multi-layer composite structure allows optimization of both area scalability and device performance
2Speed
If polycrystalline silicon is used to form transistors, then the field effect mobility increases, but they are not suitable for being formed over larger glass substrates
Solution Approach 1:
The patent changes the semiconductor material parameter from polycrystalline silicon to oxide semiconductor, which maintains compatibility with large-area substrate fabrication processes while achieving the desired mobility characteristics through material property optimization rather than relying on polycrystalline grain structure
3Reliability
If hydrogen is added to oxide semiconductor film to increase electrical conductivity, then the electrical conductivity increases by four to five orders of magnitude, but the threshold voltage control becomes difficult and reliability decreases
Solution Approach 1:
The patent extracts and removes hydrogen from the oxide semiconductor film through careful control of the deposition process and subsequent heat treatment in oxygen atmosphere. This extraction of hydrogen eliminates the harmful effect on threshold voltage stability while maintaining adequate electrical conductivity through proper oxygen stoichiometry control
Solution Approach 2:
The patent employs an oxygen-rich inert atmosphere during heat treatment and deposition processes to prevent hydrogen incorporation and to oxidize any hydrogen that may be present. This controlled oxygen environment ensures hydrogen-free oxide semiconductor film formation, stabilizing threshold voltage while maintaining reliability
4Ease of manufacture
If the oxide semiconductor film has low film density, then it is easier to manufacture, but hydrogen and oxygen diffusion increases and interface reaction occurs easily
Solution Approach 1:
The patent changes the deposition parameters (oxygen flow rate, power, pressure, substrate temperature) to achieve optimal film density. By adjusting these parameters, the oxide semiconductor film attains high density with reduced voids, preventing hydrogen and oxygen diffusion while maintaining manufacturability through standardized sputtering processes
Solution Approach 2:
The patent performs preliminary optimization of the sputtering process parameters before film deposition to ensure formation of dense oxide semiconductor films. The deposition conditions are pre-established to achieve the desired film density and crystalline structure, preventing subsequent diffusion and interface reaction issues
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 results in a semiconductor device with improved reliability and uniform electric characteristics, capable of being formed over large-area glass substrates, with reduced impurities and voids, leading to enhanced stability and performance.
Implementation Method 1
a method involving the use of a high-density polycrystalline sputtering target, controlled deposition conditions such as low back pressure and partial pressures of water and hydrogen, and optimized oxygen content in the deposition gas to form a dense oxide semiconductor film with a density above 6.0 g/cm3, which is close to single crystal, using a sputtering method with a substrate temperature above 200°C to achieve a c-axis aligned crystalline oxide semiconductor film
Data Source
AI summary
To manufacture a highly reliable semiconductor device by giving stable electric characteristics to a transistor. An oxide semiconductor film is deposited by a sputtering method with the use of a polycrystalline sputtering target. In that case, partial pressure of water in a deposition chamber before or in the deposition is set to be lower than or equal to 10−3 Pa, preferably lower than or equal to 10−4 Pa, more preferably lower than or equal to 10−5 Pa. Thus, a dense oxide semiconductor film is obtained. The density of the oxide semiconductor film is higher than 6.0 g/cm3 and lower than 6.375 g/cm3.