JP2001049430A - Tantalum thin film and its production - Google Patents

Abstract

PROBLEM TO BE SOLVED: To easily produce a low-resistance film minimal in the dependence upon sputtering conditions, surface characteristics of a substrate to be coated, functions of a film forming apparatus, etc. by alternately laminating a tantalum nitride film and a tantalum film plural times. SOLUTION: It is preferable that, in the tantalum thin film, the film thickness of one layer of tantalum nitride film and that of one layer of tantalum film are regulated to about 50 Å and <=300 Å, respectively, and, in the course of film formation, argon gas is introduced and the introduction of nitrogen gas and its stoppage are repeatedly performed and, further, the flow rate of the nitrogen gas during the formation of tantalum nitride film is regulated so that it is 0.8-1.6% based on the flow rate of the argon gas. This tantalum thin film has a nitrided/unnitrided composition molulated multilayer-film structure and is divided by the tantalum film thickness within the range where epitaxial growth is made possible at the crystal lattice of α-phase by tantalum nitride, and as the result, the low-resistance film can be easily produced.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to a tantalum-based thin film used for a drive wiring or an electrode of a liquid crystal display device or an electronic device.

[0002]

2. Description of the Related Art In recent years, MIM (Metal Insulator Metal) elements, which are switching elements of liquid crystal display devices, and TF
Tantalum is widely used as a driving wiring or electrode material of a T (Thin Film Transistor thin film transistor) element. This is because tantalum can be anodically oxidized, and this oxide film (Ta2O5) has the advantage of being extremely excellent in insulating properties and also strong in corrosion resistance during the manufacturing process.

However, when a tantalum thin film is generally formed on an insulating substrate by sputtering or the like, a β phase different from a bulk crystal structure (α phase) is likely to be formed. This film has a high specific resistance of 170 to 220 μΩcm, and is not suitable for use as a driving wiring material.

On the other hand, it is known that when a tantalum film is formed while mixing a small amount of nitrogen, an α phase appears and the specific resistance decreases. However, in the film, TaN
Is also formed, so that the specific resistance substantially drops only to about 60 μΩcm. In addition, the range of the amount of nitrogen that minimizes the specific resistance is extremely small, and is very susceptible to the conditions at the time of film formation and the degree of cleanliness in the apparatus (the ultimate vacuum degree). It was very difficult to produce stably.

As a conventional technique for obtaining a low-resistance tantalum film, a method of forming a tantalum thin film on the basis of a tantalum nitride thin film is known.
No. 9091, JP-A-5-48097, JP-A-8-325721 and the like.

According to these, in order to obtain a low-resistance tantalum thin film, it is very important to precisely control the thickness of the tantalum nitride thin film as a base film, the nitrogen concentration, and the gas pressure of sputtering. That is, the state of formation of the tantalum nitride film greatly affects the reduction in resistance of the tantalum film.

[0007]

However, when the present inventors conducted a similar experiment, they found that a tantalum nitride thin film alone (1200 Å) was obtained under optimum sputtering conditions.
Although the resistivity decreased to about 60 .mu..OMEGA.cm, when the ultimate vacuum degree and the surface properties of the film-forming substrate were changed, the resistivity increased easily. Further, a laminated film (100 angstrom tantalum nitride / 1100 angstrom tantalum nitride) was prepared as in the prior art, but the α phase did not grow and a low specific resistance was not obtained.

[0008] Compared with the disclosed contents, the ultimate vacuum degree of the film forming apparatus (according to the disclosed technology, the ultimate vacuum degree is 10-
Although it is on the order of 7 Torr, in the experimental apparatus of the present inventors, 10-6
It was on the Torr level. ) And differences in the presence or absence of substrate heating. As described above, in order to obtain a tantalum nitride film or a tantalum nitride underlayer / tantalum laminated film having a low specific resistance, it is necessary to sufficiently optimize the sputtering conditions, the surface properties of a film-formed substrate, the performance of a film-forming apparatus, and the like. Did not.

[0009]

According to the first aspect of the present invention, there is provided a tantalum-based thin film formed by vapor deposition or sputtering. According to a second aspect of the present invention, there is provided the tantalum-based thin film according to claim 1, wherein the tantalum-based thin film is formed by alternately laminating a film and a tantalum film a plurality of times. 4. The tantalum-based thin film according to claim 3, wherein the thickness of one layer is approximately 50 angstroms, and the thickness of one layer of the tantalum film is 300 angstroms or less.
According to the method for manufacturing a tantalum-based thin film according to claim 1 or 2, the tantalum nitride and the tantalum film are continuously formed using the same target or base material, and an argon gas is used during the film formation. And a method for producing a tantalum-based thin film characterized by repeatedly introducing and stopping nitrogen gas, and according to the invention of claim 4, the method of producing a tantalum-based thin film according to claim 3 is provided. In the manufacturing method, the flow rate of the nitrogen gas when forming the tantalum nitride is 0.8% to 1.6 times the flow rate of the argon gas.
% Of a tantalum-based thin film.

(Function) According to the tantalum-based thin film of the first aspect of the present invention, a multi-layer film structure in which the composition of nitridation / non-nitridation is modulated is formed, and epitaxial growth is performed on the α-phase crystal lattice by tantalum nitride. By dividing the thickness by a tantalum film thickness within the range in which a low resistance film can be obtained, it is possible to easily obtain a low-resistance film with little dependence on sputtering conditions, surface properties of a film formation substrate, performance of a film formation apparatus, and the like. According to the second aspect, by setting the nitrided layer of the multilayer film to about 50 Å and the non-nitrided layer to 300 Å or less, a film having a small specific resistance can be easily obtained.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the tantalum-based thin film of the present invention will be described below with reference to the drawings. FIG. 1 is a diagram showing the structure of a tantalum nitride / tantalum multilayer film 10 according to the present invention, and FIG. 2 is a tantalum-based thin film 10 according to the present invention.
FIG. 10 is a diagram for explaining a manufacturing process of the MIM element manufactured according to one embodiment in the order of processes.

First, referring to FIGS. 2 to 4, the steps of manufacturing a MIM element manufactured according to one embodiment of the tantalum-based thin film 10 of the present invention will be described in the order of steps.

First, a tantalum nitride 2 is formed to a predetermined thickness on a transparent insulating substrate 1 such as a synthetic resin, and then a tantalum film 3 is formed to a predetermined thickness without breaking vacuum.
These operations are repeated a plurality of times so that the total film thickness is set (FIG. 2).

Next, a multilayer film of tantalum nitride / tantalum is patterned into a shape of a predetermined signal wiring 4 by a photolithography process (FIG. 2).

Thereafter, the surface of the signal wiring 4 is anodized,
A Ta2O5 insulating film 5 is formed, on which a transparent electrode film such as ITO is formed and patterned (FIG. 3).

Finally, a titanium film is formed and patterned to form an upper electrode 7 (FIG. 4).

Here, the tantalum-based thin film forming the signal wiring 4 in the present invention will be described in detail with reference to the drawings. FIG. 1 is a view showing the structure of a tantalum nitride / tantalum multilayer film 10 according to the present invention. The tantalum nitride film 2 is provided as the lowermost layer, and serves as a base for the tantalum film 3 formed thereon to be oriented in the α-phase. Upper layer tantalum film 3
Is formed in a thickness range in which the growth of the α phase is maintained under the influence of the underlayer 2.

The tantalum nitride film 2 and the tantalum film 3 are successively formed thereon to the same thickness. This is repeated to obtain a predetermined film thickness of the signal wiring 4. In the experiment of forming a tantalum film in the present invention, a magnetron sputtering apparatus was used.

The specifications such as sputtering conditions are as follows. Ultimate vacuum 6 × 10 −6 Torr or less Target diameter 3 inches Target-substrate distance 240 mm Power DC 0.4 A × 0.35 kV Deposition rate 55 Å / min Gas pressure 3 mTorr Argon (Ar) gas flow rate 24 ccm Nitrogen (N ₂ ) Gas flow rate 0 to 0.7 ccm Total film thickness 1200 angstrom Substrate # 100 manufactured by Matsunami Glass Co., Ltd. (substrate cleaning organic solvent cleaning only)

First, reactive sputtering was performed by introducing nitrogen during film formation, and the relationship between the specific resistance of the obtained film and the flow rate of nitrogen (N ₂ ) gas was examined. At this time, when nitrogen is continuously introduced during the film formation (Ta + N film), and nitrogen is introduced only into the initial layer of 100 angstroms, and then nitrogen introduction is stopped.
Both cases where 1100 Å film was formed (Ta + N / Ta two-layer film) were examined. The results of the relationship between the specific resistance and the flow rate of the nitrogen (N ₂ ) gas are shown in the graph of FIG.

The specific resistance value of the (Ta + N) film into which nitrogen was continuously introduced changes as shown by a solid line with a black square, and its minimum value is about 60 μΩcm (a flow rate of nitrogen (N ₂ ) gas of 0.1%). 08ccm)
And almost agrees with the results disclosed in JP-A-8-325721 and the like. However, the result when nitrogen was introduced only into the initial layer changes as indicated by the dotted line with a black circle, and the specific resistance hardly decreased regardless of the change in the flow rate of nitrogen.

When the crystal structure was examined by X-ray diffraction,
β phase was tantalum, and α phase was hardly precipitated (FIG. 6). At higher nitrogen flow rates,
The α (110) peak in the (Ta + N) film is almost eliminated, and tantalum cannot grow into the α phase in the (Ta + N / Ta) two-layer film.

As described above, it is considered that the cause different from the result of the prior art is due to a difference in the evacuation performance of the apparatus. That is, it is considered that the residual gas component hindered the growth of the α phase.

Next, when the power of the (Ta + N) film is increased to 0.8 A × 0.39 kV, and when the substrate is etched (reverse sputter cleaning) before film formation (power is 0.4 A). FIG. 5 is a graph showing the relationship between the specific resistance and the flow rate of the nitrogen (N ₂ ) gas.

When the powers are different, as shown by black squares in the graph of FIG. 7, the nitrogen flow rate at which the specific resistance is minimum is different, and the minimum value is also 100 μΩcm. Also, as shown by the black circles in the graph of FIG. 7, the flow rate of the nitrogen (N ₂ ) gas at which the specific resistance is minimized differs by etching before film formation, and the minimum value is also 120 μΩ.
cm.

As described above, the (Ta + N) film having a low resistance is very sensitive to the film forming conditions and the surface properties of the film formed substrate, and it is very difficult to manufacture the film stably. Similarly, it is very difficult to reduce the resistance in such a (Ta + N / Ta) two-layer film using the (Ta + N) film underlayer, including the effect of the device performance. It is.

A film was produced for the (Ta + N / Ta) multilayer film according to the present invention. Such a multilayer film can be easily manufactured simply by repeatedly introducing / stopping nitrogen (N ₂ ) gas during film formation.

FIG. 8 is a graph showing the change in specific resistance when the total film thickness of this multilayer film is 1200 Å and the film thickness per tantalum (Ta) layer is changed (the number of laminations is changed). . At this time, the flow rate of the nitrogen (N ₂ ) gas was fixed at 0.25 ccm, and the thickness of one (Ta + N) layer was 5 cm.
It was fixed at 0 Å. Further, the substrate 1 is etched before the film formation, and it is very difficult to reduce the resistance of the (Ta + N) film portion.

As can be seen from the figure, when the film thickness per tantalum layer is 250 Å or less, the specific resistance is 40 μΩcm, and it can be seen that the resistance is reduced. Here, it is easy to imagine that a film having a further lower resistance can be obtained by selecting the thickness of the (Ta + N) film portion and the conditions for lowering the resistance.

Further, one layer of tantalum nitride (Ta + N)
FIG. 7 is a graph showing the change in specific resistance when the flow rate of nitrogen was changed in the (Ta + N / Ta) × 6 laminated film when the thickness of the angstrom and tantalum Ta1 layer was 150 angstrom.

According to the graph of FIG. 9, when the flow rate of the nitrogen (N ₂ ) gas is in the range of 0.2 ccm to 0.4 ccm (the flow rate ratio of the argon (Ar) gas is 0.8% to 1.6%), the specific resistance is obtained. Is 50μ
Ωcm or less, indicating that there is little dependence on the flow rate of nitrogen (N ₂ ) gas. As described above, a large flow rate range of the nitrogen (N ₂ ) gas means that a permissible range in manufacturing is wide, which leads to an improvement in productivity and a yield.

[0032]

According to the tantalum-based thin film and the method of manufacturing the same of the present invention, a multi-layered structure is obtained in which the composition of nitride / non-nitride is modulated. By dividing by a tantalum film thickness within the possible range, a low resistance film with little dependence on sputtering conditions, surface properties of a film formation substrate, performance of a film formation apparatus, and the like can be easily obtained.

Further, by setting the nitrided layer of the multilayered film to approximately 50 Å and the non-nitrided layer to 300 Å or less, a film having a small specific resistance of 40 μΩcm or less can be easily obtained.

[Brief description of the drawings]

FIG. 1 is a view showing a structure of a low-resistance tantalum-based thin film (tantalum nitride / tantalum) multilayer film in one embodiment of the present invention.

FIG. 2 is a diagram for explaining a manufacturing process of the MIM element manufactured according to one embodiment of the present invention in a process order.

FIG. 3 is a diagram for explaining a manufacturing process of the MIM element manufactured according to one embodiment of the present invention in a process order.

FIG. 4 is a diagram for explaining a manufacturing process of the MIM element manufactured according to one embodiment of the present invention in a process order.

FIG. 5 is a diagram showing the relationship between the specific resistance of the (Ta + N) film and the (Ta + N / Ta) film and the flow rate of the nitrogen (N ₂ ) gas in one embodiment of the present invention.

FIG. 6 shows an X-ray diffraction of a (Ta + N / Ta) film in one embodiment of the present invention (at a nitrogen (N ₂ ) gas flow rate of 0.1 ccm).
FIG.

FIG. 7 shows an example of the (Ta + N) film in one embodiment of the present invention.
FIG. 7 is a diagram showing the relationship between the flow rate of nitrogen (N ₂ ) gas and the specific resistance when the power is changed and when etching before film formation is performed.

FIG. 8 shows (Ta + N / Ta) × n in one embodiment of the present invention.
FIG. 4 is a diagram showing the relationship between the film thickness per Ta layer and the specific resistance of the multilayer film.

FIG. 9 is a diagram showing the relationship between the flow rate of nitrogen (N ₂ ) gas and the specific resistance in a (Ta + N50 Å / Ta150 Å) × 6 laminated film in one embodiment of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Insulating substrate 2 Tantalum nitride film 3 Tantalum film 4 Signal wiring 5 Tantalum oxide film 6 Pixel electrode 7 Upper electrode 10 Tantalum thin film

Claims (4)

[Claims] 1. A tantalum-based thin film formed by vapor deposition or sputtering, wherein a tantalum nitride film and a tantalum film are alternately laminated a plurality of times. 2. The tantalum-based thin film according to claim 1, wherein the thickness of one layer of the tantalum nitride film is approximately 50 angstroms, and the thickness of one layer of the tantalum film is 300 angstroms or less. Tantalum-based thin film. 3. The method for manufacturing a tantalum-based thin film according to claim 1, wherein the tantalum nitride and the tantalum film are continuously formed using the same target and base material. A method of producing a tantalum-based thin film, comprising introducing argon gas and repeatedly introducing and stopping nitrogen gas. 4. The method of manufacturing a tantalum-based thin film according to claim 3, wherein the flow rate of the nitrogen gas when forming the tantalum nitride is 0.8% to 1.6% with respect to the flow rate of the argon gas. A method for producing a tantalum thin film.