Semiconductor device and method for manufacturing the same

A semiconductor device comprising:

• a pixel portion including a first thin film transistor over a substrate;
• and
• a driver circuit portion including a second thin film transistor over the substrate,
• the first thin film transistor comprising:
• a first gate electrode layer;
• a first gate insulating layer over the first gate electrode layer;
• a first semiconductor layer over the first gate insulating layer;
• and
• a first source electrode layer and a first drain electrode layer over the first semiconductor layer,
• the second thin film transistor comprising:
• a second gate electrode layer;
• a second gate insulating layer over the second gate electrode layer;
• a second semiconductor layer over the second gate insulating layer;
• and
• a second source electrode layer and a second drain electrode layer over the second semiconductor layer,
• wherein each of the first gate electrode layer, the first gate insulating layer, the first semiconductor layer, the first source electrode layer, and the first drain electrode layer has a light-transmitting property,
• wherein a material of the first gate electrode layer is different from a material of the second gate electrode layer,
• wherein resistance of the second gate electrode layer is lower than that of the first gate electrode layer,
• wherein a material of the first source electrode layer and the first drain electrode layer is different from a material of the second source electrode layer and the second drain electrode layer,
• wherein resistance of the second source electrode layer and the second drain electrode layer is lower than that of the first source electrode layer and the first drain electrode layer, and
• wherein the first semiconductor layer includes an oxide semiconductor.

A semiconductor device comprising:

• a pixel portion including a first thin film transistor over a substrate;
• and
• a driver circuit portion including a second thin film transistor over the substrate,
• the first thin film transistor comprising:
• a first gate electrode layer;
• a first gate insulating layer over the first gate electrode layer;
• a first semiconductor layer over the first gate insulating layer;
• and
• a first source electrode layer and a first drain electrode layer over the first semiconductor layer,
• the second thin film transistor comprising:
• a second gate electrode layer;
• a second gate insulating layer over the second gate electrode layer;
• a second semiconductor layer over the second gate insulating layer;
• and
• a second source electrode layer and a second drain electrode layer over the second semiconductor layer,
• wherein each of the first gate electrode layer, the first gate insulating layer, the first semiconductor layer, the first source electrode layer, and the first drain electrode layer has a light-transmitting property,
• wherein a material of the first gate electrode layer is different from a material of the second gate electrode layer,
• wherein resistance of the second gate electrode layer is lower than that of the first gate electrode layer,
• wherein a material of the first source electrode layer and the first drain electrode layer is different from a material of the second source electrode layer and the second drain electrode layer,
• wherein resistance of the second source electrode layer and the second drain electrode layer is lower than that of the first source electrode layer and the first drain electrode layer, and
• wherein the second semiconductor layer includes an oxide semiconductor.

A method for manufacturing a semiconductor device comprising a pixel portion including a first thin film transistor and a driver circuit portion including a second thin film transistor, comprising the steps of:

• forming a first light-transmitting conductive film over a substrate;
• forming a second conductive film over the first light-transmitting conductive film, wherein resistance of the second conductive film is lower than that of the first light-transmitting conductive film;
• forming a first resist mask including a first region and a second region whose thickness is smaller than that of the first region over the second conductive film;
• etching with the use of the first resist mask so that the second conductive film and part of the first light-transmitting conductive film in the pixel portion, and part of the second conductive film and part of the first light-transmitting conductive film in the driver circuit portion are removed, thereby forming a first gate electrode layer of the first thin film transistor and a second gate electrode layer of the second thin film transistor;
• forming a first gate insulating film over the first gate electrode layer and a second gate insulating film over the second gate electrode layer;
• forming a first semiconductor layer over the first gate insulating film and a second semiconductor layer over the second gate insulating film;
• forming a third light-transmitting conductive film over the first semiconductor layer and the second semiconductor layer;
• forming a fourth conductive film over the third light-transmitting conductive film, wherein resistance of the fourth conductive film is lower than that of the third light-transmitting conductive film;
• forming a second resist mask including a third region and a fourth region whose thickness is smaller than that of the third region over the fourth conductive film;
• and
• etching with the use of the second resist mask so that part of the third light-transmitting conductive film and the fourth conductive film and in the pixel portion, and part of the fourth conductive film and part of the third light-transmitting conductive film in the driver circuit portion are removed, thereby forming a first source electrode layer and a first drain electrode layer over the first gate insulating film, and a second source electrode layer and a second drain electrode layer over the second gate insulating film.