Thin film transistor device and method of manufacturing the same, and liquid crystal display device

1. A thin film transistor device manufacturing method comprising the steps of:

forming a first island-like semiconductor film and a second island-like semiconductor film on a substrate;

forming a first insulating film for covering the first island-like semiconductor film and the second island-like semiconductor film;

forming a first conductive film on an overall surface, and then selectively etching the first conductive film so as to form a first gate electrode on the first insulating film over the first island-like semiconductor film;

forming sequentially a second insulating film and a second conductive film on an overall surface;

forming a mask pattern on the second conductive film, and then side-etching the second conductive film while using the mask pattern as a mask so as to form a second gate electrode, which is narrower in width than the mask pattern;

applying an anisotropic etching to the second insulating film while using the mask pattern as a mask and also applying the anisotropic etching to the first insulating film while using the first gate electrode and the mask pattern as a mask so as to thus form a first gate insulating film made of the first insulating film under the first gate electrode and also form a second gate insulating film consisting of the first insulating film and the second insulating film under the second gate electrode;

removing the mask pattern;

forming high-concentration impurity regions on both sides of the first gate electrode by ion-implanting an impurity into the first island-like semiconductor film while using the first gate electrode as a mask, and also forming a pair of high-concentration impurity regions on both sides of the second gate electrode by ion-implanting the impurity into the second island-like semiconductor film while using the second gate electrode and the second gate insulating film as a mask; and

forming a pair of low-concentration impurity regions under the second gate insulating film on both sides of the second gate electrode by ion-implanting the impurity into the second island-like semiconductor film while using the second gate electrode as a mask and under a condition that the ion can transmit through the second gate insulating film in a peripheral portion of the second gate electrode.

2. A thin film transistor device manufacturing method according to claim 1 , wherein, in the step of applying an anisotropic etching to the second insulating film while using the mask pattern as a mask and also applying the anisotropic etching to the first insulating film while using the first gate electrode and the mask pattern as a mask, the first insulating film is left such that the first island-like semiconductor film and the second island-like semiconductor film are covered with the first insulating film.

3. A thin film transistor device manufacturing method according to claim 1 , wherein, in the step of forming a first conductive film on an overall surface and then selectively etching the first conductive film so as to form a first gate electrode on the first insulating film over the first island-like semiconductor, electric-field relaxation electrodes made of the first conductive film are formed in a region in which the second gate electrode is to be formed and on edges of the second island-like semiconductor film on both sides via the first insulating film.

4. A thin film transistor device manufacturing method according to claim 1 , wherein, in the step of forming a mask pattern on the second conductive film, and then side-etching the second conductive film while using the mask pattern as a mask so as to form a second gate electrode, which is narrower in width than the mask pattern, electric-field relaxation electrodes made of the second conductive film are formed over edges of the first island-like semiconductor film on both sides and the first gate electrode via the second insulating film.