In recent years, about semiconductor transistors, typical example of which are TFTs, the scope of articles to which the transistors are used tends to be enlarged with the development of display devices. In such a semiconductor transistor, its electrodes are connected to each other through the material of its semiconductor, so that the transistor fulfills a function as a switching element.
Hitherto, the semiconductor material used in the semiconductor transistor has been an inorganic semiconductor material such as silicon (Si), gallium arsenic (GaAs), or indium gallium arsenic (InGaAs). In recent years, semiconductor transistors in which such an inorganic material is used have been used in TFT array substrates for display, the use of which has been spreading in liquid crystal display devices.
As the semiconductor material, an organic semiconductor material made of an organic compound has also been known. The organic semiconductor material is low in process temperature, so that the material can be formed on a flexible plastic substrate. Thus, the material has advantages that the material is stable against mechanical impacts, and can be made light. Moreover, the material can be produced through a coating process such as printing, so that the material may be mass-produced into a larger area at lower costs than the inorganic semiconductor material. Accordingly, the following activities in which such organic semiconductor materials are objects have been actively made: applications of the organic semiconductor materials to next-generation display devices, such as flexible disks, typical examples of which are electronic papers; and researches in which print RFID tags are targeted.
At the time of manufacturing an organic transistor in which an organic semiconductor material is used, it is usually necessary to pattern its organic semiconductor layer. As a method for patterning the organic semiconductor layer, an ink-jetting method and others have been reported. However, the methods require the step of forming a hydrophilic/hydrophobic pattern on a substrate, the step of forming partition walls thereon, or some other step. However, the organic semiconductor material, in particular, of a low-molecular-weight type has a problem that when the organic semiconductor layer undergoes such a step, the material is declined in mobility.
Separately, attempts have been made for forming an organic semiconductor layer on the whole of a surface and then forming a protective layer thereon, and further inactivating its portion not protected by the protective layer as a mask, or removing the organic semiconductor layer partially (see, for example, Patent Literatures 1 to 4). As a method for the inactivation, investigations have been made about plasma treatment, the use of an oxidizer, and others. As a method for the removal, investigations have been made about laser radiation, and others.
However, when an organic semiconductor element is manufactured, these methods require the step of patterning its organic semiconductor layer by inactivating or removing the organic semiconductor layer, and further usually requires the step of forming a passivation layer separately. Thus, the process thereof becomes complicated, and costs are increased.