SEMICONDUCTOR DEVICE AND METHOD FOR MANUFACTURING THE SAME
First Claim
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1. A semiconductor device comprising:
- a gate electrode layer;
a gate insulating layer over the gate electrode layer;
a semiconductor layer over the gate insulating layer;
an oxide semiconductor layer over the semiconductor layer; and
a source and drain electrode layers over the oxide semiconductor layer, and electrically connected to the oxide semiconductor layer,wherein the oxide semiconductor layer contains indium, gallium, and zinc,wherein a thickness of the semiconductor layer is smaller than a thickness of the oxide semiconductor layer, andwherein an electrical conductivity of the semiconductor layer is higher than an electrical conductivity of the oxide semiconductor layer.
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Abstract
An object is to improve field effect mobility of a thin film transistor using an oxide semiconductor. Another object is to suppress increase in off current even in a thin film transistor with improved field effect mobility. In a thin film transistor using an oxide semiconductor layer, by forming a semiconductor layer having higher electrical conductivity and a smaller thickness than the oxide semiconductor layer between the oxide semiconductor layer and a gate insulating layer, field effect mobility of the thin film transistor can be improved, and increase in off current can be suppressed.
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Citations
17 Claims
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1. A semiconductor device comprising:
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a gate electrode layer; a gate insulating layer over the gate electrode layer; a semiconductor layer over the gate insulating layer; an oxide semiconductor layer over the semiconductor layer; and a source and drain electrode layers over the oxide semiconductor layer, and electrically connected to the oxide semiconductor layer, wherein the oxide semiconductor layer contains indium, gallium, and zinc, wherein a thickness of the semiconductor layer is smaller than a thickness of the oxide semiconductor layer, and wherein an electrical conductivity of the semiconductor layer is higher than an electrical conductivity of the oxide semiconductor layer. - View Dependent Claims (2, 3, 4, 5, 6)
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7. A semiconductor device comprising:
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a gate electrode layer; a gate insulating layer over the gate electrode layer; a semiconductor layer over the gate insulating layer; an oxide semiconductor layer over the semiconductor layer; a buffer layer having n-type conductivity over the oxide semiconductor layer; and a source and drain electrode layers over the buffer layer, and electrically connected to the buffer layer, wherein each of the oxide semiconductor layer and the buffer layer contains indium, gallium, and zinc, wherein a carrier concentration of the buffer layer is higher than a carrier concentration of the oxide semiconductor layer, wherein a thickness of the semiconductor layer is smaller than a thickness of the oxide semiconductor layer, wherein an electrical conductivity of the semiconductor layer is higher than an electrical conductivity of the oxide semiconductor layer, and wherein an electrical conductivity of the buffer layer is higher than the electrical conductivity of the semiconductor layer. - View Dependent Claims (8, 9, 10, 11, 12, 13)
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14. A method for manufacturing a semiconductor device comprising:
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forming a gate electrode layer over a substrate; forming a gate insulating layer over the gate electrode layer; forming a first oxide semiconductor film containing indium, gallium, and zinc over the gate insulating layer by a sputtering method; forming a second oxide semiconductor film containing indium, gallium, and zinc over the first oxide semiconductor film by a sputtering method; etching the first oxide semiconductor film and the second oxide semiconductor film to form a semiconductor layer and an island-shaped second oxide semiconductor film; forming a conductive layer over the semiconductor layer and the island-shaped second oxide semiconductor film; and etching the island-shaped second oxide semiconductor film and the conductive layer to form an oxide semiconductor layer and a source and drain electrode layers, wherein a proportion of a flow rate of an oxygen gas for forming the first oxide semiconductor film is made lower than a proportion of a flow rate of an oxygen gas for forming the second oxide semiconductor film. - View Dependent Claims (15, 16, 17)
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Specification