Manufacturing Method of a Thin-Film Transistor

The present invention relates to a manufacturing method of a thin-film transistor of the field-effect type that is commonly used as a switching element for pixel electrodes of liquid crystal displays and other elements.

FIG. 4 is a plan view showing commonly used pixels on a TFT substrate for use in liquid crystal displays that is manufactured by using thin-film transistors of the field-effect type.

Signal lines 21 and gate lines 22 are installed on an insulating substrate so as to orthogonally intersect each other, and a thin-film transistor 20 having a source electrode 20a, a drain electrode 20b and a gate electrode 20c is placed in the vicinity of each of the intersections of the signal lines 21 and the gate lines 22. The source electrode 20a is connected to the corresponding signal line 21, the gate electrode 20c is connected to the corresponding gate line 22, and the drain electrode 20b is connected to the corresponding pixel electrode 23. Here, in FIG. 4, the reference numeral 24 represents a pixel storage capacitance.

The thin-film transistor 20 is a thin-film transistor of the so-called reversed stagger type wherein the gate electrode is placed right above the insulating substrate. Referring to FIGS. 5(a) and 5(b), an explanation will be given of a manufacturing method of a conventional thin-film transistor of the reversed stagger type. Here, FIG. 5(a) is a plan view of a thin-film transistor of the reversed stagger type that was manufactured in a conventional method, and FIG. 5(b) is a cross-sectional view taken along line V--V of FIG. 5(a).

First, a gate-electrode material layer is formed on an electrically insulating substrate 32, and the gate-electrode material layer is patterned into a predetermined shape by a photolithography technique consisting of coating of photoresist, a patterning process of the resist (consisting of an exposing process and a rinsing process), an etching process, a removing process of the resist, etc.; thus, gate electrodes 33 are formed. Next, the surfaces of the gate electrodes 33 are subjected to anodic oxidation so that a gate insulating film 34 is formed, and then a gate insulating film 35 is formed in a manner so as to cover the gate electrodes 33. Additionally, the gate insulating films 34 and 35 are omitted from FIG. 5(a).

Next, a semiconductor-material layer that subsequently serves as a semiconductor layer 36 and a contact-material layer 37 that subsequently serves as contact layers 37a and 37b are formed in this order, and the semiconductor-material layer and the contact-material layer 37 are patterned at the same time by the photolithography technique. In this case, since only the semiconductor layer 36 is first patterned, the pattern of a gap section 40 between the source electrode 38 and the drain electrode 39 has not yet been formed. Successively, the pattern of the gap section 40 is formed in the contact material layer 37 by the photolithography technique so that the contact layers 37a and 37b are formed (in FIG. 5(a), the contact layers 37a and 37b are indicated by cross-hatched regions). Here, there is a generally known manufacturing process in which at this time, an etching stopper layer is provided in the region of the gap section 40 between the semiconductor-material layer and the contact-material layer 37.

Thereafter, an electrode material that subsequently serves as a source electrode 38 and a drain electrode 39 is formed, and this electrode material is patterned by the photolithography technique so that source electrode 38 and the train electrode 39 are formed. The thin-film transistor of the reversed stagger type is manufactured by the processes as described above.

In this manner, the above-mentioned manufacturing method inevitably needs to use a specific resist pattern in order to form the gap section 40 during a patterning process of the gap section 40. This is also required in other conventional manufacturing methods similar to the above-mentioned manufacturing method.

In the current manufacturing processes of thin-film transistors, reduction of the number of processes has been a major problem to be solved in order to reduce the production costs and to improve the yield of desired products. However, in the above-mentioned conventional manufacturing methods, the production of the resist pattern used for the formation of the gap section further requires photolithography processes such as coating of resist and patterning of the resist (an exposing process and a rinsing process), resulting in a further problem of numerous processes.

The objective of the present invention is to provide a manufacturing method of a thin-film transistor that can reduce the production costs and improve the yield of desired products by reducing the number of processes.

In order to achieve the above-mentioned objective, the manufacturing method of thin-film transistors of the present invention has the following steps: a first step of forming a gate electrode on an electrically insulating substrate; a second step of forming a gate insulating film and a semiconductor layer on the gate electrode; a third step of forming a single contact-material layer on the semiconductor layer; a fourth step of forming an electrode-material layer by forming a conductive electrode material on the contact-material layer, as well as forming a source electrode and a drain electrode by patterning the electrode-material layer; and a fifth step of patterning a gap section that divides the contact-material layer into the source-electrode side and the drain-electrode side by an etching process using the source electrode and the drain electrode as masks so that a plurality of conductive contact layers are formed, in order to obtain a construction wherein the source electrode is connected to one side of the contact layer and the drain electrode is connected to the other side of the contact layer.

In the above-mentioned manufacturing method, the gap section is patterned in the contact-material layer by carrying out the etching process using the preliminarily formed source electrode and drain electrode as masks; therefore, it is not necessary to make a resist pattern in order to etch the gap section. Consequently, since the photolithography process is eliminated, it is possible to reduce the production costs. Moreover, since the elimination of the photolithography process reduces the formation of unwanted patterns, thereby making it possible to improve the yield of desired products.

For a fuller understanding of the nature and advantages of the invention, reference should be made to the ensuing detailed description taken in conjunction with the accompanying drawings.

FIG. 1(a) is a plan view showing a construction of a thin-film transistor that is commonly applied to embodiments 1, 2 and 3 of the present invention.

FIG. 1(b) is a cross-sectional view taken along line I--I of FIG. 1(a).

FIG. 2 is a cross-sectional view of the thin-film transistor that clearly shows a processed portion thereof in order to explain manufacturing processes of the thin-film transistor in Embodiment 1 of the present invention.

FIG. 3 is a cross-sectional view of the thin-film transistor that clearly shows a processed portion thereof in order to explain manufacturing processes of the thin-film transistor in Embodiments 2 and 3 of the present invention.

FIG. 4 is a plan view of a TFT liquid crystal display substrate wherein common thin-film transistors are used.

FIG. 5(a) is a plan view that shows a construction of a typical thin-film transistor of the prior art.

FIG. 5(b) is a cross-sectional view taken along line V--V of FIG. 5(a).

›EMBODIMENT 1!

Referring to FIGS. 1 and 2 the following description will discuss one embodiment of the present invention.

First, referring to FIGS. 1(a) and 1(b), an explanation will be given of a construction of a thin-film transistor of the present embodiment. FIG. 1(a) is a plan view of the thin-film transistor, and FIG. 1(b) is a cross-sectional view taken along line I--I of FIG. 1(a).

In this thin-film transistor, a strip-shaped gate electrode 3 is formed on an electrically insulating substrate 2, and on this is stacked a semiconductor layer 6 with first and second gate insulating films 4 and 5 sandwiched in between. On both sides of the semiconductor layer 6, a source electrode 8 and a drain electrode 9 are formed with contact layers 7a and 7b respectively sandwiched in between. The contact layers 7a and 7b are separated by a gap section 10 located between the source electrode 8 and the drain electrode 9.

Referring to a cross-sectional view of FIG. 2, the following description will discuss a manufacturing method of the above-mentioned thin-film transistor. FIG. 2 shows a cross-sectional view of the thin-film transistor during the formation process of the gap section 10 that is placed between the source electrode 8 and the drain electrode 9.

First, a gate-electrode material, which consequently serves as the gate electrode 3, is stacked on the substrate 2, and a resist pattern having a predetermined shape is formed on this material by a photolithography process. The gate-electrode material is etched by using this pattern so that the gate electrode 3 that is patterned into the predetermined shape is provided. Materials such as glass substrates, quartz and plastic are used as the substrate 2, and materials such as Ta, Al and Cr are used as the gate-electrode material.

Next, the gate electrode 3 is subject to anodic oxidation so that the first gate insulating film 4 is formed. Further, the second gate insulating film 5, a semiconductor-material layer that subsequently serves as the semiconductor layer 6, and a contact-material layer 7 that subsequently serves as the contact layers 7a and 7b are successively formed through the plasma CVD method. Here, materials such as SiNx and SiO.sub.2 are used as the gate insulating film 5, materials such as a-Si (amorphous silicon) and p-Si (poly-silicon) are used as the semiconductor layer 6, and materials such as a-Si (amorphus silicon) with n.sup.+ and .mu.c-Si (micro-crystal silicon) with n.sup.+ are used as the contact layers 7a and 7b.

Additionally, some constructions do not require the first gate insulating film 4 that is formed by anodic oxidation. Further, the second gate insulating film 5, the semiconductor-material layer and the contact-material layer 7 are not necessarily formed in a successive manner.

Successively, a resist pattern is formed on the contact-material layer 7 by the photolithography process, and the semiconductor-material layer and the contact-material layer 7 are simultaneously patterned by an etching process using the resist pattern. The pattern, formed at this time, does not include a pattern of the gap section 10 located between the source electrode 8 and the drain electrode 9. Therefore, at this time, only the semiconductor layer 6 is formed by the patterning process.

Next, a conductive electrode material, which subsequently serves as the source electrode 8 and the drain electrode 9, is formed, and a resist pattern is formed on the resulting electrode-material layer by the photolithography process. The electrode-material layer is patterned by a wet-etching process using the resist pattern so that the source electrode 8 and the drain electrode 9 are formed. With respect to electrode materials of the source electrode 8 and the drain electrode 9, it is preferable to use ITO (indium tin oxide) that provides a great etch selectivity in respect to the aforementioned contact-material layer 7. Besides this, with respect to the electrode materials, materials containing Al, such as, for example, Al, Al/Ti and Al alloys, can be adopted. In particular, when the materials containing Al are used, dry etching makes it possible to provide a greater etch selectivity.

Then, after the resist pattern, which was used for the formation of the source electrode 8 and the drain electrode 9, has been removed, the contact-material layer 7 is etched by using the patterned source electrode 8 and drain electrode 9 as masks so that the pattern of the gap section 10 is formed in the contact-material layer 7. Thus, the contact layers 7a and 7b are formed (in FIG. 1(a), the contact layers 7a and 7b are indicated by cross-hatched regions). In the case when ITO is used as the electrode material for the source electrode 8 and the drain electrode 9, the following etching processes can be adopted: dry etching using HCl gases, dry etching using CF.sub.4 gases and other gases, and wet etching using a solution, such as a mixture of HF and HNO.sub.3 (hereinafter, referred to as HF+HNO.sub.3). Further, when Al is used, wet etching using solutions of phosphoric acid and dry etching using HCl gases or CF.sub.4 gases can be adopted; and in this case, dry etching makes it possible to provide a greater etch selectivity.

In this manner, the thin-film transistor is manufactured. Additionally, at last, a surface-protective layer, made of SiNx, etc., may be formed.

As described above, in the present embodiment, the patterning process of the gap section 10 is carried out by etching the contact-material layer 7 by the use of the pre-formed source electrode 8 and drain electrode 9 as masks. Therefore, different from conventional constructions, no resist pattern used for etching the gap section is required; thus, it becomes possible to eliminate the photolithography process.

Therefore, it is possible to reduce the production cost. Further, the elimination of the photolithography process reduces inferior patterns that used to be caused by the photolithography process, thereby making it possible to improve the yield of desired products of the thin-film transistors.

Here, in order to use the pre-formed source electrode 8 and the drain electrode 9 as masks, with respect to the electrode material used for forming the source electrode 8 and the drain electrode 9, it is necessary to use a material that has a great etch selectivity in respect to the material for forming the contact-material layer 7. When ITO is used, any of the above-mentioned dry etching process which uses HCl gases or CF.sub.4 gases and wet etching process which uses HF+HNO.sub.3 can provide a sufficiently great etch selectivity between ITO and the contact-material layer, thereby eliminating disadvantages that the source electrode 8 and drain electrode 9, used as masks, are simultaneously etched and that new product is generated.

›EMBODIMENT 2!

Referring to FIGS. 1 and 3 the following description will discuss another embodiment of the present invention. Here, for convenience of explanation, those members that have the same functions and that are described in the aforementioned Embodiment 1 are indicated by the same reference numbers and the description thereof is omitted.

The construction of the thin-film transistor of the present embodiment is the same as that of the thin-film transistor of Embodiment 1 shown in FIG. 1; therefore, the explanation thereof is omitted, and only the manufacturing method will be explained below with reference to the cross-sectional view of FIG. 3. FIG. 3 shows a cross-sectional view of the thin-film transistor during the formation process of the gap section 10 that is placed between the source electrode 8 and the drain electrode 9.

In this manufacturing method, the same processes as Embodiment 1 are carried out from the formation of the gate electrode 3 on the substrate 2 to the formation of the source electrode 8 and the drain electrode 9 that is carried out by patterning the electrode-material layer 7 through wet etching by the use of the resist pattern 11. With respect to the electrode materials, ITO and Al are used in the same manner as Embodiment 1; yet, besides these, Cr, Mo or other materials may be used.

Next, although in the aforementioned embodiment 1, the resist pattern 11, which was used for forming the source electrode 8 and the drain electrode 9, is removed, the resist pattern 11 is not removed in this embodiment, and the contact-material layer 7 is etched by using the resist pattern 11, as it is, so that the gap section 10 is patterned. In this case, the following etching processes are preferably adopted in the same manner as Embodiment 1: dry etching using HCl gases, dry etching using CF.sub.4 gases and other gases, or wet etching using a solution such as HF+HNO.sub.3. Thereafter, the same processes as Embodiment 1 are carried out.

As described above, the patterning process of the gap section 10 is carried out by etching the contact-material layer 7 by the use of the resist pattern 11, as it is, used for the pre-formed source electrode 8 and drain electrode 9. Therefore, in the same manner as Embodiment 1, no resist pattern which is to be used for etching the gap section is required; thus, it is possible to eliminate the photolithography process. As a result, it becomes possible to reduce the production cost, and the elimination of the photolithography process reduces inferior patterns that used to be caused by the photolithography process, thereby making it possible to improve the yield of desired products of the thin-film transistors.

Moreover, the present embodiment does not directly use the source electrode 8 and the drain electrode 9 as masks during the etching process, resulting in another advantage in that it becomes possible to expand the scope of selectivity of etching conditions and of electrode materials used for the source electrode 8 and the drain electrode 9, as compared with the method of Embodiment 1.

›EMBODIMENT 3!

Referring to FIGS. 1 and 3 the following description will discuss another embodiment of the present invention. Here, for convenience of explanation, those members that have the same functions and that are described in the aforementioned Embodiments 1 and 2 are indicated by the same reference numbers and the description thereof is omitted.

The construction of the thin-film transistor of the present embodiment is the same as that of the thin-film transistor of Embodiment 1 shown in FIG. 1; therefore, the explanation thereof is omitted, and only the manufacturing method will be explained below with reference to the cross-sectional view of FIG. 3.

In this manufacturing method, the same processes as Embodiment 1 are carried out from the formation of the gate electrode 3 on the substrate 2 to the formation of the electrode material layer. However, in the manufacturing method of the present embodiment, the source electrode 8 and the drain electrode 9 are formed by patterning the electrode-material layer through a dry etching process using the resist pattern 11 in a vacuum chamber. Here, materials, such as Ta, ITO, Al, Cr and Mo, are preferably used as the electrode materials of the source electrode 8 and the drain electrode 9.

Next, in order to pattern the gap section 10, the contact-material layer 7 is successively dry-etched in the same vacuum chamber by using the resist pattern 11, as it is, that was used for forming the source electrode 8 and the drain electrode 9. HCl gases or CF4 gases are used for the gas in this dry etching process. Thereafter, the same processes as Embodiment 1 are carried out.

In this way, the gap section 10 is formed by etching the contact-material layer 7 by the use of the resist pattern 11, as it is, used for the pre-formed source electrode 8 and drain electrode 9; thus, it is possible to obtain the same effects as the aforementioned Embodiment 2. Moreover, since the patterning process of the source electrode 8 and the drain electrode 9 and the patterning process of the gap section 10 in the contact-material layer 7 are continuously carried out in the same chamber without being exposed to the air, these processes are maintained in a vacuum state. Therefore, it becomes possible to avoid adhesion of foreign matters to the processed objects, and consequently to improve the yield of desired products. Moreover, since not only time loss caused by adjustments of the pressure difference between atmosphere and vacuum, but also time loss caused by transportation of the processed objects among devices during the respective processes, is minimized greatly as compared with conventional methods, this method is very effective from the standpoint of throughput.

Furthermore, instead of using the same chamber, another chamber may be provided that allows transportation of the processed objects in a vacuum state, and the dry etching processes may be continuously carried out between these chambers; this method also provides the same effects as described above.

The invention being thus described, it will be obvious that the same may be varied in many ways. Such variations are not to be regarded as a departure from the spirit and scope of the invention, and all such modifications as would be obvious to one skilled in the art are intended to be included within the scope of the following claims.