JP5234892B2 - Thin film transistor substrate and display device - Google Patents

Description

  The present invention belongs to a technical field related to a thin film transistor substrate and a display device.

  In an active matrix liquid crystal display device such as a liquid crystal display, a thin film transistor (hereinafter also referred to as TFT) is used as a switching element. A schematic diagram of the TFT element is shown in FIG. The TFT element comprises a gate electrode formed on a glass substrate, a non-doped semiconductor silicon layer provided via a gate insulating film, and an impurity-doped semiconductor silicon layer in contact therewith. The impurity-doped semiconductor silicon layers are each electrically connected by a wiring metal such as an Al alloy. These wiring metals are called a source electrode and a drain electrode. The drain electrode is further connected to a transparent conductive film used in the liquid crystal display unit. As wiring metals (source electrode, drain electrode), various Al alloys have been conventionally proposed (for example, JP-A-7-45555, JP-A-2005-171378, etc.). At that time, the wiring metal and the TFT element (semiconductor silicon layer) or the wiring metal and the transparent conductive film (hereinafter also referred to as ITO film) used for the liquid crystal display unit are not directly in contact with each other as a barrier metal such as Mo, Cr. A structure in which a laminated film made of a refractory metal such as Ti, W is interposed is used.

Up to now, techniques for omitting the barrier metal existing between the wiring metal and the ITO film can be found in, for example, Japanese Patent Application Laid-Open Nos. 2004-214606, 2005-303003, and 2006-23388. Although various proposals have been made, the technology for omitting the barrier metal provided between the wiring metal and the TFT element (semiconductor silicon layer) has not yet been sufficiently studied.
JP 2004-214606 A JP 2005-303003 A JP 2006-23388 A

  The reason why the barrier metal is interposed between the wiring metal (source electrode and drain electrode) and the TFT element (silicon layer) is that the pure Al or Al alloy constituting the wiring and the semiconductor layer of the TFT element are in direct contact with each other This is to prevent adverse effects on the environment. As the semiconductor layer, amorphous silicon or polycrystalline silicon is used. The mechanism of the adverse effect on the device is as follows.

  That is, when a wiring process (pure Al or Al alloy) and a semiconductor layer (for example, silicon) are directly applied, a heating process such as CVD (Chemical Vapor Deposition) molding, sintering, annealing, etc. is applied in the TFT manufacturing process. The aluminum atoms (Al atoms) of the wiring thermally diffuse into the semiconductor silicon, or the silicon atoms (Si atoms) diffuse from the semiconductor silicon layer into the pure Al or Al alloy of the wiring. When Al atoms are thermally diffused into the semiconductor silicon, the semiconductor performance of the semiconductor silicon is significantly deteriorated. This causes an increase in leakage current, a decrease in on-current, a decrease in switching speed, and the like, and desired switching performance cannot be obtained. Further, even if Si atoms diffuse in the wiring, the semiconductor performance of the silicon semiconductor deteriorates, and the same switching performance deteriorates. That is, the performance and quality as a display deteriorate.

  Barrier metal is effective for suppressing interdiffusion of Al atoms and Si atoms, but on the other hand, a barrier metal forming step for forming this structure is indispensable. That is, in addition to a film forming apparatus required for forming an Al wiring or the like, an extra film forming apparatus for forming a barrier metal is required. As the cost of liquid crystal displays and the like is reduced due to an increase in the production amount, the increase in production cost due to the formation of the barrier metal cannot be ignored.

  The present invention has been made paying attention to such a situation, and the object thereof is to omit the formation of a barrier metal between the semiconductor layer of the thin film transistor and the source electrode and the drain electrode (the semiconductor layer of the thin film transistor). It is an object of the present invention to provide a thin film transistor substrate and a display device that do not require a barrier metal to be formed between a source electrode and a drain electrode.

  In order to achieve the above object, the present inventors have intensively studied, and as a result, completed the present invention. According to the present invention, the above object can be achieved.

  The present invention thus completed and capable of achieving the above object relates to a thin film transistor substrate and a display device. The thin film transistor substrate according to claims 1 to 4 (thin film transistor according to the first to fourth inventions) Substrate) and a display device according to claim 5 (display device according to the fifth invention), which has the following configuration.

That is, the thin film transistor substrate according to claim 1 is a thin film transistor substrate having a semiconductor layer of a thin film transistor, a source electrode, a drain electrode, and a transparent conductive film, wherein the source electrode and the drain electrode are directly connected to the semiconductor layer of the thin film transistor. The source electrode and the drain electrode are made of an Al alloy thin film containing Ni: 0.1 to 6.0 atomic%, La: 0.1 to 1.0 atomic%, Si: 0.1 to 1.5 atomic%, the balance Al and inevitable impurities. A thin film transistor substrate characterized in that [First invention].

  The thin film transistor substrate according to claim 2 is the thin film transistor substrate according to claim 1, wherein the drain electrode has a structure directly connected to the transparent conductive film [second invention].

  The thin film transistor substrate according to claim 3 is the thin film transistor substrate according to claim 1 or 2, wherein the semiconductor layer is polycrystalline silicon [third invention].

  The thin film transistor substrate according to claim 4 is the thin film transistor substrate according to any one of claims 1 to 3, wherein the Al alloy thin film is formed by sputtering.

  The display device according to claim 5 is a display device in which the thin film transistor substrate according to any one of claims 1 to 4 is provided as a thin film transistor substrate [fifth invention].

  According to the present invention, it is possible to omit the formation of a barrier metal between the semiconductor layer of the thin film transistor and the source electrode and the drain electrode. That is, it is not necessary to form a barrier metal between the semiconductor layer of the thin film transistor and the source and drain electrodes.

  The inventors of the present invention formed an evaluation element using a thin film obtained by adding various elements to Al, Al / Si interdiffusion (interdiffusion between Al atom and Si atom), electric resistivity, hillock resistance. I investigated. As a result, we found that the addition of Ni, Si, and La is effective for the above characteristics.

  It is known that when Si is added to Al, the effect of suppressing interdiffusion between Al atoms and Si atoms is improved as the addition amount is increased. On the other hand, when these are used alone (when only Si is added), the upper limit of the temperature at which Al / Si interdiffusion can be suppressed is limited to about 250 ° C. at most. However, if Ni is added to the Al-Si alloy (Si is added to Al and Ni is further added) to form an Al alloy containing Si and Ni, the interdiffusion of Al / Si can be suppressed to higher temperatures. I found it.

  The mechanism for suppressing interdiffusion is considered as follows. First, as an effect of containing Si, it has an effect of preventing Si atoms from diffusing from the Si semiconductor layer into the Al film. That is, by adding atoms of the same type as Si atoms in advance in the Al film, the concentration difference that is the driving force for diffusion can be reduced. Further, the effect of containing Ni is considered to be that a diffusion preventing layer is formed at the interface between the Al alloy film and the Si semiconductor layer (Al alloy film / Si semiconductor layer interface). That is, Ni easily reacts with Si at a low temperature to form silicide. Once silicide is generated, it is considered that the silicide layer acts as a barrier and the interdiffusion does not proceed any further. These synergistic effects will drastically improve and Al / Si interdiffusion can be suppressed to higher temperatures.

  While Al / Si interdiffusion can be suppressed to higher temperatures, a film made of an Al—Si—Ni alloy does not have sufficient hillock resistance. However, it was found that hillock resistance was improved by adding La to the Al—Si—Ni alloy.

  By adding these elements, it is possible to suppress the Al / Si interdiffusion and to improve the hillock resistance of the Al alloy film. On the other hand, increasing the added elements also increases the electrical resistivity of the wiring. There is a problem to do. In order to suppress Al / Si interdiffusion and improve the hillock resistance of the Al alloy film, while keeping the electrical resistivity low, the content of Ni, La, and Si is Ni: 0.1 to 6.0 atomic%. , La: 0.1 to 1.0 atomic%, Si: 0.1 to 1.5 atomic% are necessary. More preferably, they are Ni: 0.15-5.0 atomic%, La: 0.15-0.8 atomic%, Si: 0.1-1.0 atomic%.

  The present invention has been completed based on such knowledge, and it relates to a thin film transistor substrate and a display device. Of the thin film transistor substrate and display device according to the present invention thus completed, first, the thin film transistor substrate according to the present invention includes a thin film transistor semiconductor layer, a source electrode, a drain electrode, and a transparent conductive film. The source and drain electrodes (hereinafter also referred to as source / drain electrodes) have a structure in which they are directly connected to the semiconductor layer of the thin film transistor, and the source and drain electrodes are Ni: 0.1 to 6.0 atomic%, La: A thin film transistor substrate comprising an Al alloy thin film containing 0.1 to 1.0 atomic% and Si: 0.1 to 1.5 atomic%.

  The thin film transistor substrate according to the present invention has a structure in which the source / drain electrodes are directly connected to the semiconductor layer of the thin film transistor. The source / drain electrodes are Ni: 0.1 to 6.0 atomic%, La: 0.1 to 1.0 atomic%, Si : Since it is made of an Al alloy thin film containing 0.1 to 1.5 atomic%, as can be seen from the above knowledge, the Al / Si interdiffusion can be suppressed, and the hillock resistance of the Al alloy thin film is improved. The electrical resistivity of the thin film can be kept low.

  As can be seen from the above, the thin film transistor substrate according to the present invention has a structure in which the source / drain electrodes are directly connected to the semiconductor layer of the thin film transistor, so that there is no problem in terms of characteristics. In other words, Al / Si interdiffusion can be suppressed without forming a barrier metal between the semiconductor layer of the thin film transistor and the source / drain electrodes. At the same time, the hillock resistance of the Al alloy thin film is improved and the Al alloy thin film is improved. The electrical resistivity can be kept low.

  Therefore, according to the thin film transistor substrate of the present invention, it is possible to omit the formation of the barrier metal between the semiconductor layer of the thin film transistor and the source / drain electrodes. That is, it is not necessary to form a barrier metal between the semiconductor layer of the thin film transistor and the source / drain electrodes (source electrode and drain electrode).

In the thin film transistor substrate according to the present invention, the contents of Ni, La , and Si in the Al alloy thin film forming the source / drain electrodes are as follows: Ni: 0.1 to 6.0 atomic%, La: 0.1 to 1.0 atomic%, Si: 0.1 ~ 1.5 Atomic% (hereinafter also referred to as at%). The reason for this will be described below.

  Si: 0.1 to 1.5 at% is defined as follows. When Si is less than 0.1 at%, the effect of suppressing the Al / Si interdiffusion is reduced, and the suppression of the Al / Si interdiffusion is insufficient. If it exceeds%, the electrical resistivity will increase and the electrical resistivity cannot be kept low. Ni: 0.1 to 6.0 at%, if Ni: less than 0.1 at%, the effect of suppressing Al / Si interdiffusion is reduced and the suppression of Al / Si interdiffusion is insufficient, and Ni: 6.0 at% If it exceeds%, the electrical resistivity will increase and the electrical resistivity cannot be kept low. La: 0.1 to 1.0 at% is the reason why if La: less than 0.1 at%, the effect of improving hillock resistance is reduced and the hillock resistance is insufficient. If La: more than 1.0 at%, the electrical resistivity is low. This is because the electrical resistivity cannot be kept low by increasing.

  In the thin film transistor substrate according to the present invention, since the drain electrode is made of an Al alloy having the above-described composition, it can have a structure directly connected not only to the semiconductor layer of the thin film transistor but also to the transparent conductive film [second invention]. . This is because the contact resistance is low mainly by containing Ni.

  Since the temperature at which Al / Si interdiffusion begins is higher when the semiconductor layer is polycrystalline silicon, it is desirable that the semiconductor layer be polycrystalline silicon (third invention). In addition, the present invention can be applied to continuous grain boundary crystalline silicon as well as polycrystalline silicon.

  The Al alloy thin film of the source / drain electrodes is preferably formed by sputtering [fourth invention]. That is, when forming the Al alloy thin film of the source / drain electrodes, the formation method is not particularly limited, but it is desirable to apply the sputtering method. This is because according to the sputtering method, a desired composition can be easily obtained by adjusting the composition of the target to be used.

  The thin film transistor substrate according to the present invention can be used in various electronic devices, for example, as a thin film transistor substrate of a display device [fifth invention].

  Examples of the present invention and comparative examples will be described below. The present invention is not limited to this embodiment, and can be implemented with appropriate modifications within a range that can be adapted to the gist of the present invention, all of which are within the technical scope of the present invention. include.

[Example 1]
Evaluation elements (pn junction elements) according to examples and comparative examples of the present invention were manufactured. This process flow is shown in FIG. This manufacturing method will be described below.

As shown in FIG. 1, a polycrystalline silicon film having a thickness of 200 nm was first formed on a p-type low resistance silicon substrate by LPCVD [FIG. 1 (a)]. At this time, SiH ₄ was used as the source gas. Subsequently, BF ₂ ⁺ ions were implanted at 10 keV and 3e ¹⁵ / cm ² [FIG. 1 (b)]. Next, the material after this ion implantation was annealed at 800 ° C. for 30 minutes to form a p-type doped polycrystalline silicon film [FIG. 1 (c)]. Subsequently, an n-type doped polycrystalline silicon film having a thickness of about 40 nm was formed thereon [FIG. 1 (d)]. At this time, SiH ₄ and PH ₃ as a doping gas were used for film formation. As a result, a pn junction of polycrystalline silicon was formed.

  Then, an Al alloy film having a thickness of about 300 nm was formed on the polycrystalline silicon film by a sputtering method. Next, after a resist pattern was formed by photolithography, the Al alloy film was etched using the resist as a mask to form the evaluation element shown in the figure [FIG. 1 (e)]. The composition of the Al alloy film is as shown in the column of source / drain electrodes in Table 1 (Tables 1-a and 1-b). In the evaluation element shown in FIG. 1 (e), the Al alloy film corresponds to the source / drain electrode, and the n-type polycrystalline silicon film and the p-type polycrystalline silicon below (the part shown in FIG. 1 (c)). The film corresponds to a semiconductor layer of the thin film transistor. The source / drain electrodes (Al alloy film) and the semiconductor layer of the thin film transistor have a structure in which they are directly connected without interposing a barrier metal.

  The evaluation element (pn junction element) thus fabricated was annealed at a temperature of 250 to 400 ° C. for 30 minutes. The degree of mutual diffusion between Al atoms and Si atoms was examined by measuring current-voltage characteristics of the annealed pn junction element. That is, the diffusion phenomenon between Si atoms in the polycrystalline silicon (semiconductor layer) and Al atoms in the Al alloy film (source / drain electrodes) can be evaluated by measuring the current-voltage characteristics of the pn junction element. A device having a normal pn junction causes a current to flow by applying a negative voltage to the n-type region and a positive voltage (hereinafter referred to as a positive bias) to the p-type region, and conversely, a positive voltage to the n-type region. , Has a rectifying property of interrupting current by applying a negative voltage (hereinafter referred to as reverse bias) to the p-type region. However, if Al atoms diffuse from the Al alloy film (source / drain electrodes) into the pn junction region, normal rectification cannot be obtained. That is, even when a reverse bias is applied, the current cannot be cut off. Therefore, the influence of interdiffusion between Al atoms and Si atoms can be grasped by evaluating the magnitude of the current that flows during reverse bias (hereinafter referred to as leakage current). Therefore, the value of this leakage current was measured, and the degree of mutual diffusion between Al atoms and Si atoms was evaluated from the measured value of this leakage current. The size of the evaluated element has a pn junction area of 30 μm × 30 μm, and a current value when +1 V was applied as a reverse bias to this was defined as a leakage current.

The results are shown in the column of mutual diffusion in Table 1 (Tables 1-a and 1-b). The leakage current of a material in which Cr is interposed as a barrier metal between the source / drain electrodes (Al alloy film) and the semiconductor layer of the thin film transistor is 4.0 × 10 ⁻⁹ A, which is 10 times the value (4.0 × 10 ^-8 Compared with A), those having a small leakage current are indicated by ○, and those having a large leakage current are indicated by ×. That is, a leakage current of 4.0 × 10 ⁻⁸ A or less was good, and a leakage current of over 4.0 × 10 ⁻⁸ A was unsuitable.

Further, the generation of hillocks due to annealing was evaluated as follows. A 10 μm wide line and space pattern wiring was formed on the pn junction element sample, and vacuum heat treatment was performed at 350 ° C. for 30 minutes. Thereafter, the surface of the wiring was observed with an electron microscope, and the number of hillocks having a diameter of 0.1 μm or more was counted. Hillock density, 1 × 10 ⁹ pieces / m ² good following ones (○), and those of 1 × 10 ⁹ pieces / m ² than bad (×). The results are shown in the hillock resistance column of Table 1 (Tables 1-a and 1-b).

[Example 2]
An Al alloy film having a thickness of 300 nm was formed on a glass substrate by a sputtering method. Next, after forming a resist pattern by photolithography, the Al alloy film was etched using the resist as a mask, and processed into a stripe pattern shape having a width of 100 μm and a length of 10 mm. The composition of the Al alloy film is the same as that shown in the source / drain electrode column of Table 1 (Tables 1-a and 1-b).

  The Al alloy film after the etching was annealed at a temperature of 250 to 400 ° C. for 30 minutes. Then, the electrical resistivity of the annealed Al alloy film was measured by a four-terminal method. The results are shown in the electric resistivity column of Table 1 (Tables 1-a and 1-b). The electrical resistivity (3.3 × 1.3 = 4.3 μΩcm) 1.3 times the electrical resistivity of the pure Al film (3.3 × 1.3 = 4.3 μΩcm) is the standard. Those with a large are considered defective.

[Evaluation of results in Examples 1 and 2]
As can be seen from Table 1 (Table 1-a, Table 1-b), when the Al alloy film (source / drain electrode) is made of an Al—Si alloy, the annealing temperature is 250 ° C. or 400 ° C. The leakage current is large and inappropriate (x), and the mutual diffusion of Al atoms and Si atoms is not sufficiently suppressed (Nos. 3 to 7). The hillock resistance is also poor (x) and insufficient (No. 3 to 7).

  When the Al alloy film (source / drain electrode) is made of an Al-Si-Ni alloy, the leakage current is small and good (○) regardless of whether the annealing temperature is 250 ° C or 400 ° C. Although suppression of interdiffusion of Si atoms is sufficient, hillock resistance is poor (x) and insufficient (No. 13 to 18).

  In contrast, when the Al alloy film (source / drain electrode) is made of an Al-Si-Ni-La alloy, the leakage current is small and good regardless of whether the annealing temperature is 250 ° C or 400 ° C. In addition, the interdiffusion between Al atoms and Si atoms is sufficiently suppressed, and the hillock resistance is good (◯) (No. 25 to 29, 35 to 38, 43 to 46).

  Of these Nos. 25-29, 35-38, 43-46, No. 46 has too much Si in the Al alloy film, so the electrical resistivity is the reference value (the electrical resistivity of the pure Al film x 1.3 = 4.3 μΩcm), which is bad. In cases other than these, since the Al alloy film satisfying the composition of the Al alloy thin film in the thin film transistor substrate according to the present invention is used, the electrical resistivity is smaller than the reference value and good (No. 25 to 29, 35 to 38). 43-45).

  Therefore, when the Al alloy film (source / drain electrode) is made of an Al alloy film satisfying the composition of the Al alloy thin film on the thin film transistor substrate according to the present invention, the leakage temperature is 250 ° C. or 400 ° C. The current is small and good (○), the interdiffusion between Al atoms and Si atoms is sufficiently suppressed, the hillock resistance is good (○), and the electrical resistivity is also small and good. confirmed.

[Example 3]
The contact property (contact resistance) when the Al alloy electrode and the transparent conductive film were directly connected was examined.
Samples in which ITO films were formed on various Al alloy electrodes shown in Table 2 (Table 2-a and Table 2-b) were formed under conditions of a pressure of 3 mTorr and a temperature of 200 ° C. in an Ar gas atmosphere. As the ITO film, indium oxide added with 10% by mass of tin oxide was used.

The contact resistivity was measured by a four-terminal method by preparing a Kelvin pattern having a 10 μm square contact hole. A contact resistivity of 2 × 10 ⁻⁴ Ωcm ² between the Cr thin film and ITO was taken as a reference value, a value below this reference value was good (◯), and a value exceeding the reference value was bad (×). The evaluation results are shown in Table 2 (Table 2-a and Table 2-b).

  In the case where the Al alloy electrode is made of an Al—Si alloy, the contact resistivity is large and it is defective (×) (No. 3 to 7).

  On the other hand, when the Al alloy electrode is made of an Al—Si—Ni—La alloy, the contact resistivity is small and good (◯) (No. 25 to 29, 35 to 38, 43 to 46). Even when the Al alloy electrode is made of an Al—Si—Ni alloy, the contact resistivity is small and good (◯) (No. 13 to 18).

  Since the thin film transistor substrate according to the present invention does not need to form a barrier metal between the semiconductor layer of the thin film transistor and the source / drain electrodes, the thin film transistor substrate is excellent in economy and can be suitably used as a thin film transistor substrate for a display device or the like. it can.

It is a figure which shows the outline | summary of the preparation process of the element for evaluation (pn junction element) which concerns on an Example, (a) of FIG. 1 is what formed the film | membrane of the polycrystalline silicon on the p-type low resistance Si substrate, FIG. 1 (b) shows the situation of BF2 + ion implantation into the polycrystalline silicon film, and FIG. 1 (c) shows that the polycrystalline silicon film after the BF2 + ion implantation is annealed to form a p-type polycrystalline silicon film. FIG. 1 (d) shows an n-type polycrystalline silicon film formed on the p-type polycrystalline silicon film. FIG. 1 (e) shows an Al alloy film on the n-type polycrystalline silicon film. It is a figure which shows the element for evaluation (pn junction element) formed by etching, after forming a film | membrane. It is a schematic diagram which shows the outline | summary of a TFT (thin film transistor) element.

Claims (5)

A thin film transistor substrate having a semiconductor layer of a thin film transistor, a source electrode, a drain electrode, and a transparent conductive film, wherein the source electrode and the drain electrode are directly connected to the semiconductor layer of the thin film transistor, and the source electrode and the drain electrode A thin film transistor substrate comprising: an Al alloy thin film containing Ni: 0.1-6.0 atomic%, La: 0.1-1.0 atomic%, Si: 0.1-1.5 atomic%, the balance Al and inevitable impurities .   The thin film transistor substrate according to claim 1, wherein the drain electrode has a structure directly connected to the transparent conductive film.   3. The thin film transistor substrate according to claim 1, wherein the semiconductor layer is polycrystalline silicon.   The thin film transistor substrate according to claim 1, wherein the Al alloy thin film is formed by a sputtering method.   5. A display device comprising the thin film transistor substrate according to claim 1 as a thin film transistor substrate.

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