JPS5833873A - Manufacture of thin film transistor - Google Patents

Abstract

PURPOSE:To enhance the performance and the operating range of a thin film transistor by individually forming a semiconductor film to become a channel and a noninsulating thin film to become a gate oxidized film, and subjecting the thin film to anodic oxidatin to form as a gate oxidized film. CONSTITUTION:The first layer thin semiconductor film 2 is formed on a substrate 1. Subsequently, patterned source and drain electrodes 3 are formed on the film 2. The electrodes 3 are utilized as the anode in case of subjecting an anodic oxidation, and are also used as source and drain electrodes 3 of a thin film transistor. Then, the second layer thin semiconductor film 4 is formed as a noninsulating film on the patterned electrodes 3 and the film 2, and is oxidized by an anodic oxidation. Thereafter, the film 4 is oxidized to form an oxidizied film 5. Successively, a gate electrode 7 is formed. As a result, a uniform can be formed at a low temperature, thereby enhancing the performance and the operating range of the thin film transistor.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to low-temperature formation of a gate insulating film that influences the switching characteristics of a thin film transistor (TFT).

The general structure of an insulated gate thin film transistor is a substrate--a semiconductor thin film--an insulating layer--a conductive layer. In order to take advantage of the large area and low cost characteristics of thin film transistors, it is possible to use glass, ceramics, etc. as the substrate, and in that case, high temperature processing is required. It becomes difficult.

Gate insulating films currently used in semiconductor technology include 8102 and the like, but at present, thermal oxidation is mainly used. However, if the temperature is restricted by the substrate, it is difficult to use commonly used thermal oxidation. Other insulating film forming methods include physical vapor deposition (PVD)
) and chemical vapor deposition (CVD), but these methods are inferior to thermal oxide films in terms of film uniformity, insulation, defects in the film, impurity density, interface state density, etc. Furthermore, in the case of gate insulating films using thermal oxidation, oxides of semiconductor films have been used.

The present invention utilizes anodic oxidation to form a film having film uniformity, insulation properties, impurity density, and interface state density comparable to those of thermal oxide films at low temperatures. Non-insulating thin films, such as semiconductor films, formed at low temperatures by PVD and CVD on an insulating substrate have a high sheet resistance, making it difficult to use conventional methods for anodic oxidation. , a first layer semiconductor thin film formed on a substrate is patterned, a second layer semiconductor thin film is formed on top of the first layer semiconductor thin film through a non-insulating thin film, the above electrode is used as an anode, and the second layer semiconductor thin film is patterned.
The layered semiconductor thin film is anodized and used as a gate insulating film.

In the case of conventional thermal oxidation, the oxide of the semiconductor film was used as the gate, but in the thin film transistor structure described above,
The gate insulating film can be formed without being affected by the composition of the semiconductor film, and the electrodes are made of materials that have been difficult to oxidize to date, and the voltage can be easily applied between the counter electrode and the source and drain electrodes. Therefore, by providing the first layer semiconductor thin film, it is possible to use the first layer semiconductor thin film.
The electrode-gate insulating film structure expands the scope of use of semiconductor films and gate insulating film materials, and provides high-performance thin film transistors. That is, in the present invention, a first layer semiconductor thin film is first formed on a substrate, patterned source and drain electrodes are formed on the semiconductor film, and a second layer semiconductor thin film, which is a non-insulating thin film, is formed on this. In this method, a thin film transistor is manufactured by forming a thin film transistor, and using the electrode as an anode and using anodic oxidation. In the present invention, a semiconductor film to become a channel and a non-insulating thin film to become a gate oxide film are separately formed, and the non-insulating thin film, for example, a semiconductor film, is anodized and formed as a gate oxide film. It has characteristics.

The present invention will be explained in detail below using the drawings.

All drawings show embodiments of the present invention, and FIGS. 1(A)(B)
)(C) and (D) show the manufacturing process of a thin film transistor. In the process of FIG. 1(A), 1 is a substrate, and a first layer semiconductor thin film 2 is formed on the substrate 1.

Next, patterned source and drain electrodes 3 are formed on the first layer semiconductor thin film 2. This electrode is used as an anode during anodic oxidation, and also as a source and drain electrode of a thin film transistor.

In the process shown in FIG. 1(B), 4 is the one in which a second layer semiconductor thin film as a non-insulating film is formed on the patterned electrode 6 and the first layer semiconductor thin film 2, and the anodic oxidation process is performed. Oxidized by

In the step shown in FIG. 1(C), the second layer semiconductor thin film 4 is oxidized to form an oxide film 5. 6 indicates an anticathode for anodic oxidation.

In the step shown in FIG. 1(D), a gate electrode 7 is formed.

Figure 2 shows an example of an actual anodic oxidation device, with a patterned electrode that also serves as an in-electrode, and is used as an anode.
25 is a non-insulating thin film to be anodized;
6 is a cathode, and 27 is a power source used for anodic oxidation.

For example, as the electrolytic solution 21, a solution of N-methylacetamide and 0.04N potassium nitrate, a mixed solution of nitrates and halides of tetrahydrofurfuryl alcohol and hyethylene glycol, and as the substrate and drain electrode, materials such as Mo and Ta can be used. High melting point metal, second layer semiconductor thin film 2
4 is a silicon film or the like, the cathode 6 is a platinum electrode, and the power source 27 is a constant current-voltage power source. Although this example dealt with anodic oxidation in the liquid phase,
Of course, it can also be used for anodic oxidation in the gas phase.

As described above, according to the present invention, the source and drain electrodes that are naturally required as the electrodes of the transistor are used instead of forming new electrodes for use in anodic oxidation, which contributes to the simplification of the process. By providing a single layer semiconductor thin film, problems such as electrode adhesion can be solved and the voltage applied between the electrodes during anodization can be made constant, and a second layer semiconductor thin film is provided to form an anodic oxide film. Therefore, it is possible to form an oxide film having the same composition as that of the first layer oxide film, or an oxide film having a different composition. By providing a layered semiconductor thin film, it is possible to form a uniform film at low temperatures, and the high performance and range of thin film transistors can be improved.

The present invention is a particularly effective technique for forming thin film transistors on display panel substrates using liquid crystals, etc., and is particularly suitable for display devices for small portable devices such as wristwatches.

[Brief explanation of the drawing]

FIGS. 1A, 1B, 1C, and 1D are manufacturing process diagrams of a thin film transistor showing an embodiment of the present invention, and FIG. 2 is a configuration diagram of an anodizing apparatus. 1.22... Substrate 2.26... First layer semiconductor thin film 3...
Patterned source and drain electrodes 4 and...second
Layer semiconductor thin film (non-insulating film) 5...Anodized non-insulating film 6.26...Counter electrode 7...
...Gate electrode 21... Electrolyte 27...
...Power supply Figure 1 χ1 (D) -.

Claims (1)

[Claims] (1) A step of forming a first layer semiconductor thin film on a substrate, a step of forming a patterned electrode on the semiconductor thin film, and a step of forming a second layer semiconductor thin film on the patterned electrode. and using the patterned electrode as an anode,
Claims characterized in that the thin film has a to-composition comprising the step of anodic oxidation of the second layer semiconductor thin film.Claims characterized in that the thin film has a to-composition. 2. A method for manufacturing a thin film transistor according to item 1.