| abstract |
An oxide semiconductor transistor with uniform characteristics is obtained in a memory device manufactured by stacking oxide semiconductor transistors. A first oxide semiconductor layer having a first channel formation region is formed over a first base insulating film, and a first heat treatment is performed on the first oxide semiconductor layer. A source electrode, a first drain electrode, a first gate insulating film, and a first gate electrode are formed, a first transistor is formed, an insulating layer is formed over the first transistor, and the insulating A second oxide semiconductor layer having a second channel formation region is formed over the layer, a second heat treatment is performed on the second oxide semiconductor layer, and a second source electrode and a second drain electrode are formed. The second gate insulating film and the second gate electrode are formed to form a second transistor, and the length of the first channel formation region is shorter than the length of the second channel formation region. It relates to the production of the device. [Selection] Figure 1 |