JPS62241377A - Thin film transistor and manufacture thereof - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION TECHNICAL FIELD The present invention relates to a thin film transistor that enables self-alignment of a channel portion, and a method for manufacturing the same.

"Prior art and its problems" A thin film transistor (↑FT) is a type of field effect transistor (FET) and can be manufactured simply by forming an EtJ film on an insulating substrate. It has the advantage that a large number of elements can be formed on a large panel surface at once using a forming technique. In particular, since Si-based materials such as hydrogenated amorphous silicon have been used as semiconductor layers,
Active research has begun because it has become possible to improve reproducibility, controllability, and uniformity, which have traditionally been considered drawbacks.

One of the applications that is attracting attention for thin film transistors is
Examples include switching elements in liquid crystal televisions and the like. In other words, by adopting the so-called active matrix addressing method, in which a thin film transistor is formed corresponding to each pixel electrode of an LCD TV, and a voltage is applied to each pixel electrode via these TA thin film transistors, it is possible to overcome the conventional simple method. This is because contrast and resolution can be significantly improved compared to the matrix addressing method.

As an example of a thin film transistor, a one with an inverted stagger structure is shown. As shown in FIG.
A source electrode 15 and a drain electrode 16 are formed on the seventh layer of the semiconductor layer 14 with a channel portion 17 sandwiched therebetween. In this case, the semiconductor layer! 4 and the source electrode 15 and drain electrode 1B, in order to reduce the so-called Schottky resistance,
A highly doped layer 14a may also be provided. When a voltage is applied to the gate electrode 12, carriers e are formed in a portion of the semiconductor layer 14 close to the gate electrode 12, and a current flows from the drain electrode IB to the source electrode 15 through this carrier formation portion. ing.

In these thin film transistors, the gate electrode 12
Accurate alignment of the channel portion 17 and the channel portion 17 is extremely important due to its characteristics. The permissible range of this positional deviation is
For example, since it is on the order of several IL exposures or less, alignment is extremely difficult when using a photomask.

Therefore, a thin film transistor forming technique using self-alignment as shown in FIG. 8 has been proposed. That is, a gate electrode 12, a gate insulating film 13, and a semiconductor layer are formed on an insulating substrate 11! After laminating 4 and 4, this semiconductor layer!
4. Apply a positive resist on top. Then, when light is irradiated from the back side of the insulating substrate 11, the gate electrode 12
Only the portions blocked by the insoluble resist 18 remain. In this state, if necessary, the highly doped layer 14
After forming the resist 18, a metal film forming the source and drain electrodes is laminated and the resist 18 is removed by a lift-off method. It is patterned into IB. In this case, the channel portion 17 is the portion where the resist 18 is formed.

It exactly matches the gate electrode ai12.

However, in this thin film transistor manufacturing method, when the insulating substrate 11 is irradiated with light from the back side and cleaned to remove the resist 18 in the portion corresponding to the gate electrode 12, the entire resist 18 is removed. To prevent this from happening, cleaning can only be done by rinsing with water. For this reason, it is difficult to completely remove the resist (1B) other than the part corresponding to the gate electrode 12, which includes a highly doped layer on top of it. When forming the metal film that constitutes the source electrode 15 and the drain electrode 16, a semiconductor layer! 4 and the highly doped layer 14a or the metal film did not work well, which tended to cause malfunctions. This is also a common problem in lift-off methods.

``Object of the Invention'' In view of the above-mentioned problems with self-alignment using the lift-off method, an object of the present invention is to provide an sJ film transistor that enables self-alignment using a method other than the lift-off method, and a method for manufacturing the same. .

"Structure of the Invention" In the thin film transistor of the present invention, for example, as shown in FIG. The structure is such that a source electrode 25 and a drain electrode 2B are formed sandwiching a channel portion 27, and the source electrode 25 and the drain electrode 26 are made of a transparent conductive film. Note that the semiconductor layer 24
A highly doped layer 24a may be formed at the interface between the source electrode 25 and the drain electrode 26.

As shown in FIGS. 5 and 8, for example, the method for manufacturing a thin film transistor of the present invention includes sequentially forming a gate electrode 22, a gate insulating layer 23, and a semiconductor layer 24 on an insulating substrate 21. After forming the highly doped layer 24a, a transparent conductive film 28 is formed on the entire surface of the semiconductor layer 24 or the highly doped layer 24a, and a negative resist 29 is further applied on the entire surface, and a light beam is applied from the back side of the insulating substrate 21. The source material is removed by irradiating the source with etching, cleaning to remove the portion of the resist 28 corresponding to the gate electrode 22, and etching to selectively remove the portion of the transparent conductive film 28 corresponding to the gate electrode 22. It is characterized in that an electrode 25 and the drain electrode 2B are formed.

In this way, in the present invention, the source electrode 25 is etched away by removing the transparent conductor M28 without using the lift-off method.
Since the drain electrode 26 is formed, the semiconductor layer 24
There is no presence of resist residue or the like at the interface between the source electrode 25 and the drain electrode 26, so that the yield can be improved. Then, by coating a negative resist 29 on the transparent conductive film 28 and irradiating light from the back side of the insulating substrate 21, the resist 29 in the portion corresponding to the gate electrode 22 is removed. , only the portion corresponding to the gate electrode 22 is etched, making self-alignment possible.

Embodiment of the Invention FIG. 1 shows an embodiment of the tI thin film transistor of the present invention, and FIGS. 2 to 8 sequentially show the manufacturing process of the same thin film transistor. The process will be explained below.

■Metal gate forming process As shown in FIG. 2, a gold f& film is formed on the entire surface of an insulating substrate 21 made of a transparent glass plate by means such as vapor deposition or sputtering, and photoetching is performed to form a gate electrode 22. . The material of the gate electrode 22 is required not to melt in the following process, so MOlCr,
High melting point metals such as W are preferred, but Ti, A1.
Ni, NiCr, etc. can also be used. Further, the thickness of the gate electrode 22 is equivalent to about 1000 people.

■Gate insulating film and semiconductor layer forming process As shown in FIG. 3, gate insulating film [5!23. Semiconductor layer 24, highly doped layer 2
4a is continuously deposited.

As the gate insulating film 23, for example, a SiNx (silicon nitride) film, a 5i(h (silicon dioxide) film, etc.) can be used, and in particular, 5i (silicon dioxide) film, which has a high dielectric constant, high breakdown voltage, and good surface characteristics, can be used.
NxljJ is suitable. The SiNx film can be formed by using SiH, +NH4+N2 as a reactive gas. The thickness of gate insulation $23 is 200
Approximately 0 people are eligible.

As the semiconductor layer 24, a Si-based material such as hydrogenated amorphous silicon (a-Si:H) is suitable, for example.

a-St:H is S I H4+ t as a reaction gas
(It can be formed by using 2. The thickness of the semiconductor layer 24 is about 1,000 layers.

Further, a highly doped layer 24a may be formed on the semiconductor layer 24, and when a-Si:H is used as the semiconductor layer 24, the highly doped layer 24a is n+a-8i:
H n+a-9i: H is S as a reaction gas
It can be formed by using jH,+PH3+112. The thickness of the highly doped layer 24a is suitable for about 100 people.

(2) Transparent conductive film forming step As shown in FIG. 4, a transparent conductive film 28 such as ITO is formed on the entire surface of the semiconductor layer 24 or the highly doped layer 24a by means of vapor deposition, sputtering, or the like. Its thickness is 20
Approximately 0.00 people are expected.

(2) Resist Formation Step As shown in FIG. 5, a negative resist 29 is applied over the entire surface of the transparent conductive film 28, and light is irradiated from the back side of the insulating substrate 21. Since the transparent conductive film 28 is light-transmissive, the resist 29 in the sun part of the figure is irradiated with light and becomes insolubilized, but the resist 29 in the part A is transparent to the gate electrode 22.
It is blocked by the light and becomes soluble. Then, by washing with water or other means, the resist 29 in the portion A is selectively removed, as shown in FIG.

■Etching process When the transparent conductive film 2 is treated with an etching solution that selectively etches the transparent conductive film 28 in the state shown in FIG. A channel portion 27 is formed between the drain electrode 28 and the drain electrode 28 . Then, by completely removing the resist 29 using acetone, a peeling solution, or the like, the thin film transistor shown in FIG. 1 is obtained. Note that, if necessary, a passivation film may be formed on these layers. The passivation film may be, for example, a SiNx film formed by plasma CVD.

In this thin film transistor, the resist 29 in the portion corresponding to the gate electrode 22 is removed by performing back exposure shown in FIG. 5, and then etched, so that the positions of the gate electrode 22 and the channel portion 27 are accurately , so-called self-alignment is achieved.

Moreover, since the transparent conductive film 2 is formed on the semiconductor layer 24 or the highly doped layer 24a before applying the resist 28, the bonding surface between the transparent conductive film 29 and the semiconductor layer 24 or the highly doped layer 24a The bonding surface becomes clean, and malfunctions caused by resist residue or the like on the bonding surface can be avoided.

Note that the thin film transistor according to the present invention can be applied to various uses such as displays such as liquid crystal displays and thin film EL displays, image sensors, and logic integrated circuits.

"Effects of the Invention" As explained above, according to the present invention, by forming the source electrode and the drain electrode with a transparent conductive film, transparent conductive film can be formed on the semiconductor layer or the highly doped layer. After forming the tt film and applying a negative resist, the resist in the area corresponding to the gate electrode is removed by back exposure, and the source and drain electrodes can be patterned by selective etching, which eliminates the lift-off method. This method enables self-alignment. In addition, since a transparent conductive film is formed before applying the resist, the bonding surfaces between the semiconductor layer or highly doped layer and the source and drain electrodes are clean, and malfunctions due to resist residue can be avoided. , yield is improved.

[Brief explanation of drawings]

Figure i1 is a cross-sectional view showing an example of a thin film transistor according to the present invention, Figures 2, 3, 4, 5, and 6 are cross-sectional views sequentially showing the manufacturing process of the same B film transistor, and Figure 7 is a cross-sectional view showing an example of a thin film transistor according to the present invention.
The figure is a sectional view showing an example of a conventional fIIli) transistor, and FIG. 8 is a sectional view showing an example of a process for forming source and drain electrodes in a conventional thin film transistor. In the figure, 21 is an insulating substrate, 22 is a gate electrode, 22a is a metal film, 22b is a transparent conductive film, 23 is a gate insulating film, 2
4 is a semiconductor layer, 24a is a highly doped layer, 25 is a source electrode, 2B is a drain electrode, 27 is a channel portion, 28
2 is a transparent conductive film, and 29 is a resist. Figure 1 Figure 2 2'2 Figure 3 4th factor lZ 6th rJ! 1 Figure 7 Figure 8

Claims (4)

[Claims] (1) In a thin film transistor in which a gate electrode, a gate insulating film, and a semiconductor layer are sequentially laminated on an insulating substrate, and a source electrode and a drain electrode are formed on this semiconductor layer with a channel portion sandwiched therebetween, the source electrode and A thin film transistor, wherein the drain electrode is made of a transparent conductive film. (2) The thin film transistor according to claim 1, wherein a highly doped layer is formed at an interface between the semiconductor layer and the source and drain electrodes. (3) A method for manufacturing a thin film transistor in which a gate electrode, a gate insulating film, and a semiconductor layer are sequentially laminated on an insulating substrate, and a source electrode and a drain electrode are formed on this semiconductor layer with a channel portion sandwiched therebetween. After sequentially stacking the gate electrode, the gate insulating film, and the semiconductor layer on the insulating substrate, a transparent conductive film is formed on the entire surface, a negative resist is applied on the entire surface, and light is irradiated from the back side of the insulating substrate. Then, the source electrode and the drain electrode are removed by cleaning to remove the resist in the portion corresponding to the gate electrode, and etching to selectively remove the transparent conductive film in the portion corresponding to the gate electrode. 1. A method for manufacturing a thin film transistor, characterized by forming a thin film transistor. (4) The method for manufacturing a thin film transistor according to claim 3, wherein the transparent conductive film is formed on the entire surface after forming a highly doped layer on the upper layer of the semiconductor layer.