Forming a thin transistor with a redundant source of drain electrode

A semiconductor device comprising:

• a gate electrode over a substrate;
• a gate insulating film over the gate electrode;
• a first source or drain electrode over the gate insulating film;
• an island-shaped semiconductor film including a channel forming region over the first source or drain electrode and the gate insulating film;
• an island-shaped impurity semiconductor film added with an impurity imparting one conductivity type over the island-shaped semiconductor film;
• and
• a second source or drain electrode over the island-shaped semiconductor film, the island-shaped impurity semiconductor film, and the first source or drain electrode,
• wherein a part of the second source or drain electrode is formed over and directly in contact with the first source or drain electrode,
• wherein the island-shaped semiconductor film and the island-shaped impurity semiconductor film are sandwiched between the first source or drain electrode and the second source or drain electrode, and
• wherein edges of the island-shaped semiconductor film are tapered.

A manufacturing method of a semiconductor device comprising the steps of:

• forming a gate electrode over a substrate;
• forming a gate insulating film over the gate electrode;
• forming first source or drain electrode over the gale insulating film;
• forming an island-shaped semiconductor film including a channel forming region over the first source or drain electrode and the gate insulating film;
• and
• forming a second source or drain electrode over the first source or drain electrode and the island-shaped semiconductor film,
• wherein a part of the second source or drain electrode is formed over and directly in contact with the first source or drain electrode,
• wherein the island-shaped semiconductor film is sandwiched between the first source or drain electrode and the second source or drain electrode, and
• wherein edges of the island-shaped semiconductor film are tapered.

A manufacturing method of a semiconductor device comprising the steps of:

• forming a first conductive film over a substrate;
• forming a gate electrode using the first conductive film;
• forming a gate insulating film over the gate electrode;
• forming a second conductive film over the gate insulating film;
• forming a first source or drain electrode using the second conductive film;
• forming a semiconductor film over the first source or drain electrode;
• forming an island-shaped semiconductor film including a channel forming region using the semiconductor film;
• forming a third conductive film over the first source or drain electrode and the island-shaped semiconductor film;
• and
• forming a second source or drain electrode using the third conductive film,
• wherein a part of the second source or drain electrode is formed over and directly in contact with the first source or drain electrode,
• wherein the island-shaped semiconductor film is sandwiched between the first source or drain electrode and the second source or drain electrode, and
• wherein edges of the island-shaped semiconductor film are tapered.

A manufacturing method of a semiconductor device comprising the steps of:

• forming a gate electrode over a substrate;
• forming a gate insulating film over the gate electrode;
• forming a first source or drain electrode over the gate insulating film;
• forming an island-shaped semiconductor film including a channel forming region over the first source or drain electrode and the gate insulating film;
• forming an island-shaped impurity semiconductor film added with an impurity imparting one conductivity type over the island-shaped semiconductor film;
• and
• forming a second source or drain electrode over the first source or drain electrode, the island-shaped semiconductor film, and the island-shaped impurity semiconductor film,
• wherein a part of the second source or drain electrode is formed over and directly in contact with the first source or drain electrode,
• wherein the island-shaped semiconductor film and the island-shaped impurity semiconductor film are sandwiched between the first source or drain electrode and the second source or drain electrode,
• wherein edges of the island-shaped semiconductor film are tapered.