Method for manufacturing semiconductor device
First Claim
1. A method for manufacturing a semiconductor device comprising the steps of:
- forming a first oxide semiconductor layer;
forming a second oxide semiconductor layer over the first oxide semiconductor layer;
performing a heat treatment on the first oxide semiconductor layer and the second oxide semiconductor layer to be dehydrated or dehydrogenated, whereby each of the first oxide semiconductor layer and the second oxide semiconductor layer has a carrier density of 1×
1018/cm3 or more;
etching a part of the second oxide semiconductor layer so as to expose a part of the first oxide semiconductor layer; and
forming an oxide insulating layer over and in contact with the part of the first oxide semiconductor layer, whereby the part of the first oxide semiconductor layer has a carrier density of less than 1×
1018/cm3.
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Abstract
It is an object to provide a highly reliable semiconductor device which includes a thin film transistor having stable electric characteristics. It is another object to manufacture a highly reliable semiconductor device at lower cost with high productivity. In a method for manufacturing a semiconductor device which includes a thin film transistor where a semiconductor layer having a channel formation region, a source region, and a drain region are formed using an oxide semiconductor layer, heat treatment (heat treatment for dehydration or dehydrogenation) is performed so as to improve the purity of the oxide semiconductor layer and reduce impurities such as moisture. Moreover, the oxide semiconductor layer subjected to the heat treatment is slowly cooled under an oxygen atmosphere.
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Citations
14 Claims
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1. A method for manufacturing a semiconductor device comprising the steps of:
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forming a first oxide semiconductor layer; forming a second oxide semiconductor layer over the first oxide semiconductor layer; performing a heat treatment on the first oxide semiconductor layer and the second oxide semiconductor layer to be dehydrated or dehydrogenated, whereby each of the first oxide semiconductor layer and the second oxide semiconductor layer has a carrier density of 1×
1018/cm3 or more;etching a part of the second oxide semiconductor layer so as to expose a part of the first oxide semiconductor layer; and forming an oxide insulating layer over and in contact with the part of the first oxide semiconductor layer, whereby the part of the first oxide semiconductor layer has a carrier density of less than 1×
1018/cm3. - View Dependent Claims (2, 3, 4, 5, 6)
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7. A method for manufacturing a semiconductor device comprising the steps of:
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forming a first oxide semiconductor layer; forming a second oxide semiconductor layer over the first oxide semiconductor layer; performing a first heat treatment on the first oxide semiconductor layer and the second oxide semiconductor layer to be dehydrated or dehydrogenated, whereby each of the first oxide semiconductor layer and the second oxide semiconductor layer has a carrier density of 1×
1018/cm3 or more;forming a conductive layer over the second oxide semiconductor layer; etching a part of the second oxide semiconductor layer so as to expose a part of the first oxide semiconductor layer, wherein the part of the second oxide semiconductor layer does not overlap the conductive layer; and forming an oxide insulating layer over and in contact with the part of the first oxide semiconductor layer, whereby the part of the first oxide semiconductor layer has a carrier density of less than 1×
1018/cm3. - View Dependent Claims (8, 9, 10, 11, 12, 13, 14)
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Specification