Thin film semiconductor device

A semiconductor device comprising:

• at least one first thin film transistor formed in a pixel portion over a substrate;
• a driving circuit including at least one circuit selected from the group consisting of a shift register, a buffer circuit and an analog memory, said circuit comprising at least one second thin film transistor formed over said substrate, said second thin film transistor comprising:
• a gate electrode comprising chromium formed over the substrate, wherein said gate electrode has tapered side edges;
• a gate insulating film formed on said gate electrode;
• a semiconductor film comprising crystalline silicon formed on said gate insulating film wherein said semiconductor film includes a channel forming region over said gate electrode, and a pair of impurity doped regions with the channel forming region interposed therebetween, wherein said substrate has a level upper surface.

A semiconductor device having at least one thin film transistor, said thin film transistor comprising:

• a gate electrode formed over a substrate wherein said gate electrode has tapered side edges;
• a gate insulating film formed on said gate electrode;
• a semiconductor film comprising crystalline silicon formed on said gate insulating film wherein said semiconductor film includes a channel forming region over said gate electrode, a pair of impurity regions with the channel forming region interposed therebetween and at least one lightly doped region interposed between said channel forming region and one of said pair of impurity regions wherein said lightly doped region is doped with an impurity at a lower concentration than said pair of impurity regions,
• wherein said gate insulating film has a multi-layer structure including at least a first layer comprising silicon oxide and a second layer comprising silicon nitride, and said second layer contacts said se miconductor film.

A semiconductor device comprising:

• at least one first thin film transistor formed in a pixel portion over a substrate;
• a driving circuit comprising at least one second thin film transistor formed over said substrate, said second thin film transistor comprising:
• a gate electrode formed over the substrate wherein said gate electrode has tapered side edges;
• a gate insulating film formed on said gate electrode;
• a semiconductor film comprising crystalline silicon formed on said gate insulating film wherein said semiconductor film includes a channel forming region over said gate electrode, a pair of impurity regions with the channel forming region interposed therebetween and at least one lightly doped region interposed between said channel forming region and one of said pair of impurity regions wherein said lightly doped region is doped with an impurity at a lower concentration than said pair of impurity regions,
• wherein said semiconductor film has a thickness of 100 to 300 Å.

A semiconductor device comprising:

• at least one first thin film transistor formed in a pixel portion over a substrate;
• a driving circuit including at least one circuit selected from the group consisting of a shift register, a buffer circuit and an analog memory, said circuit comprising a plurality of second thin film transistors formed over said substrate, at least one of said second thin film transistors comprising:
• a gate electrode formed over the substrate wherein said gate electrode has tapered side edges;
• a gate insulating film formed on said gate electrode;
• a semiconductor film comprising crystalline silicon formed on said gate insulating film wherein said semiconductor film includes a channel forming region over said gate electrode, a pair of impurity regions with the channel forming region interposed therebetween and at least one lightly doped region interposed between said channel forming region and one of said pair of impurity regions wherein said lightly doped region is doped with an impurity at a lower concentration than said pair of impurity regions,
• wherein said semiconductor film has a thickness of 100 to 300 Å.

A semiconductor device comprising:

• at least one first thin film transistor formed in a pixel portion over a substrate;
• a driving circuit including at least one circuit selected from the group consisting of a shift register, a buffer circuit and an analog memory, said circuit comprising at least one second thin film transistors formed over said substrate, each of said first and second thin film transistors comprising:
• a gate electrode formed over the substrate;
• a gate insulating film formed over said gate electrode;
• a semiconductor film formed on said gate insulating film, said semiconductor film including a channel forming region over said gate electrode, a pair of impurity regions with the channel forming region interposed therebetween, wherein said semiconductor film has a thickness of 100 to 300 Å,
• wherein the channel forming region of said first thin film transistor comprises amorphous silicon while the channel forming region of said second thin film transistor comprises crystalline silicon.

A semiconductor device comprising:

• at least one first thin film transistor formed in a pixel portion over a substrate;
• a driving circuit including at least one circuit selected from the group consisting of a shift register, a buffer circuit and an analog memory, said circuit comprising at least one second thin film transistors formed over said substrate, each of said first and second thin film transistors comprising:
• a gate electrode formed over the substrate;
• a gate insulating film formed over said gate electrode;
• a semiconductor film formed on said gate insulating film, said semiconductor film including a channel forming region over said gate electrode, a pair of impurity regions with the channel forming region interposed therebetween, wherein said semiconductor film has a thickness of 100 to 300 Å,
• wherein the semiconductor film of said second thin film transistor has a higher degree of crystallinity than the semiconductor film of said first thin film transistor that is not crystallized.

A semiconductor device comprising:

• at least one first thin film transistor formed in a pixel portion over a substrate;
• a driving circuit comprising at least one second thin film transistor formed over said substrate, said second thin film transistor comprising:
• a gate electrode comprising chromium formed over said substrate wherein said gate electrode has tapered side edges;
• a gate-insulating film formed on said gate electrode;
• and
• a semiconductor film comprising crystalline silicon formed on said gate insulating film wherein said semiconductor film includes a channel forming region over said gate electrode, a pair of impurity regions with said channel forming region interposed therebetween and at least one lightly doped drain region interposed between said channel forming region and one of said pair of impurity regions wherein said lightly doped region is doped with an impurity at a lower concentration than said pair of impurity region.

A semiconductor device comprising:

• at least one first thin film transistor formed in a pixel portion over a substrate;
• a driving circuit including at least one circuit selected from the group consisting of a shift resister, a buffer circuit and an analog circuit memory, said circuit comprising a plurality of second thin film transistors formed over said substrate, at least one of said second thin film transistors comprising:
• a gate electrode comprising chromium formed over said substrate wherein said gate electrode has tapered side edges;
• a gate insulating film formed on said gate electrode;
• and
• a semiconductor film comprising crystalline silicon formed on said gate insulating film wherein said semiconductor film includes a channel forming region over said gate electrode, a pair of impurity regions with said channel forming region interposed therebetween and at least one lightly doped drain region interposed between said channel forming region and one of said pair of impurity regions wherein said lightly doped region is doped with an impurity at a lower concentration than said pair of impurity region.