JPH05171417A - Manufacture of tantalum metallic thin film - Google Patents

Abstract

PURPOSE:To provide the method for manufacturing a low resistance tantalum metallic thin film used for an integrated circuit element, an optical integrated circuit element, photoelectric converting circuit element and an optical display circuit element accompanied by fine working. CONSTITUTION:This is the method for manufacturing a thin film by a sputtering method characterized, for selectively obtaining the cubic crystals (alpha phase) of tantalum metal, by using a tantalum metal target 2 mixed with niobium metal or using tantalum metal and niobium metal as each independent target 2 or vapor-depositing tantalum metal on a niobium metal vapor-deposited film. Furthermore, it is executed in an atmosphere mixed with a trace amt. of nitrogen gas or nitrogen series gas as a manufacturing atmosphere.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a low-resistance tantalum metal thin film, and more particularly to an integrated circuit device, an optical integrated circuit device, a photoelectric conversion circuit device, and an optical display circuit device which require fine processing.

[0002]

2. Description of the Related Art Tantalum metal has excellent mechanical strength, Ta ₂ O ₅ which is an oxide film has extremely low dielectric loss and relatively high relative dielectric constant, and also has excellent acid resistance and alkali resistance. Therefore, it has a high utility value and has been widely used as a thin film wiring material that can withstand various processes.

On the other hand, tantalum has two phases of crystal structure, and in addition to a cubic crystal structure (α phase) showing a low resistivity (13 μΩcm), a tetragonal structure (β phase) having a remarkably high resistivity (up to 200 μΩcm). It is known to be metastable. Of these two phases, the β phase has a high resistivity and a small temperature change, and thus has application to precision resistors, while the low resistance α phase has been used as a thin film wiring material.

However, a high resistance β which is metastable in a thin film state
Various low-resistance α single-phase film forming methods have been proposed. Among them, the method of introducing nitrogen gas and sputter-depositing in a vacuum removes β phase relatively easily,
Since the α phase can be selectively formed, it has been often used as a wiring thin film forming process.

[0005]

However, when a tantalum thin film is manufactured by this nitrogen-added sputtering method, the appearance ratio (α / β) of both phases is determined by film forming conditions such as nitrogen gas partial pressure, same flow rate, sputtering power, It largely depends on the substrate temperature, the deposition rate, the shape of the film forming chamber, and the like. Especially the appearance rate of both phases (α / β)
Depends on the partial pressure of nitrogen gas, and for a tantalum thin film 10 ⁻⁶ to 10
^In the partial pressure region of ^-5 Torr or less, the β phase changes to the α / β mixed phase, and the α phase increases near 10 ^-5 Torr. When the partial pressure is further increased from 10 ^-5 Torr, in addition to metallic α and β phases, insulator nitrides TaN _0.1 , TaN _0.25 and Ta ₆ N are added.
_2.57 , TaN _0.5 , TaN _0.8 , TaN, Ta ₃ N ₄ etc. appear, and the resistance value increases again.

Therefore, in order to obtain the α phase, the nitrogen partial pressure is 1
It is necessary to control the nitrogen flow rate so that it is around 0 ^-5 Torr. However, in actual production, it is difficult to control this pressure over the whole substrate, and it becomes very difficult especially when the deposition area becomes large. Furthermore, in this method, an insulator film is mixed and formed in the tantalum metal thin film,
The obtained α-phase resistance value is the value of pure tantalum metal (13μΩ
It is inevitable that it will be 3 to 4 times higher than cm).

In addition to these, since a large amount of nitrogen atoms are present in the film in this method, the interval between tantalum atoms forming the thin film becomes large, which causes strain in the entire thin film.

[0008]

The present invention uses a tantalum metal target mixed with niobium metal, or a tantalum metal and niobium in order to selectively obtain a body-centered cubic crystal (α phase) of tantalum metal. The present invention relates to a thin film manufacturing method by a sputtering method, which is characterized in that metals are used as independent targets or tantalum metal is vapor-deposited on a niobium metal vapor deposition film. Further, the present invention relates to a method of carrying out in a production atmosphere in which a slight amount of nitrogen gas or nitrogen-based gas is mixed.

As a result of many years of research conducted by the present inventors, the following surprising facts have been discovered. That is, the growth of a body-centered cubic lattice, which is a tantalum metal α phase, is dominated by heteroepitaxial heteroepitaxial growth via a high-order mirror plane such as (110) or (111) having a small interplane energy, and β phase. It was found to suppress the growth of tetragonal crystals. Metals having the same body-centered cubic crystal as tantalum (Ta) are Rb, V, N
b, Cs, Ba and the like.

Among them, niobium metal (Nb) has a crystal structure of body centered cubic lattice with a lattice constant of 3.303Å, and tantalum metal (Ta) α phase has a crystal structure of body centered cubic lattice with a lattice constant of 3.3058Å. Which is an extremely close lattice constant.
It has been found that it is extremely effective to apply niobium having a similar body-centered cubic lattice constant as a heteroatom of tantalum in heteroepitaxial growth, and the present invention has been completed.

The niobium metal has only to function as a nucleus for forming the tantalum metal α phase, and the amount thereof may be small.
Although the details will be discussed in the examples, the composition ratio of niobium metal in the tantalum metal in the sputtered vapor-deposited film is 0.1% in both the mixed metal target and the independent targets.
1% to 10% is preferable, and the pre-deposition thickness of niobium is 5
The range between 100 nm and 100 nm is good. Of these three methods, the mixed metal target method is recommended because of the ease of production.

Although the minimum value of niobium metal in the combined use system of niobium metal and nitrogen gas is not always clear, a mixing ratio of 0.1% in the tantalum thin film is sufficient, and a niobium vapor deposition film thickness of 10 nm or less is sufficiently effective. Exert. Although the minimum value of the amount of nitrogen gas added is not always clear,
If 5 sccm is added, a sufficient effect is exhibited.

Pure nitrogen gas is used as the added gas component.
In addition to gas, NH as a nitrogen-based gas ₃NH₂-NH
₂(Hydrazine) and the like. The spatter of this invention
The tantalum thin film produced by the
Flow rate is 4 to 6 sccm, and argon gas partial pressure is 0.2 to
0.6 Pa, the flow rate of argon gas is 40 to 80 sccm,
Sputtering voltage is -100 to -3000V, and substrate material is gas.
The substrate temperature of lath, silicon wafer, etc. is room temperature to 250
℃, vapor deposition rate 100 ~ 1000Å, base vacuum degree is 1
× 10^-FourIt is about Pa.

As the cathode target shape, an ordinary shape can be adopted, and a disk having a size of several cm to several tens of cm and a target metal purity of about 99.9% can be used.

[0015]

[Example] The following four manufacturing methods were proposed as specific methods for mixing niobium as a different atom of tantalum,
Discuss the details. I. Method without using nitrogen gas. 1. A method using a tantalum metal target mixed with niobium metal.

2. A method of using tantalum metal and niobium metal as independent targets. 3. A method for depositing tantalum metal on a niobium metal vapor deposition film. II. A method that uses a small amount of nitrogen gas together. 4. A method of mixing a trace amount of nitrogen gas or nitrogen-based gas in order to replenish the lack of niobium amount under the condition that the mixing of niobium metal into tantalum metal is minute.

Example 1 FIG. 11 shows the results when the metal composition ratio of the thin film was changed using a tantalum metal target in which the amount of niobium metal mixed was changed. The film formation was performed using an apparatus as shown in FIG. In FIG. 1, 1 is a substrate, 2 is a target, and 3
Is an exhaust port, 4 is a magnet, 5 is a DC power source, and 6 is an argon or nitrogen gas inlet.

The film forming conditions are: argon flow rate 50 sccm, nitrogen flow rate 0 sccm, pressure 0.4 Pa, input power 3.0 K.
W, the substrate is glass. In FIG. 11, the horizontal axis represents the thin film composition ratio of tantalum metal and niobium metal, and the vertical axis represents the appearance ratio (α / β) of both phases. As is clear from the figure, the appearance rate (α / β) of both phases is very poor when the tantalum metal is 100%, but when it exceeds 1%, almost only the α phase becomes stable and becomes stable. However, 0.1% is not always stable. On the other hand, in FIG. 12, the horizontal axis represents the thin film composition ratio of tantalum metal and niobium metal, and the vertical axis represents the resistivity of the tantalum film. As is clear from the figure, when the niobium metal content exceeds 10%, the resistivity of the tantalum film suddenly deteriorates. As is clear from these results, the composition ratio of niobium metal in tantalum metal is preferably 0.1% to 10%, and more preferably 1% to 10%.

Example 2 Next, the composition ratio of the thin film was changed using tantalum metal and niobium metal as independent targets. The apparatus used was almost the same as that shown in FIG. 1, except that it had two types of targets for tantalum metal and niobium metal. Similar to the above results using the mixed metal for the target by changing the input voltage force to the target and changing the metal composition of the thin film, the thin film composition, the appearance rate of both phases (α / β), the tantalum film The relationship of the specific resistance of was calculated. Similarly, in FIG. 13, the horizontal axis represents the thin film composition ratio of tantalum metal and niobium metal, and the vertical axis represents the appearance rate (α / β) of both phases. Further, in FIG. 14, the horizontal axis represents the thin film composition ratio of tantalum metal and niobium metal, and the vertical axis represents the resistivity of the tantalum film.

As clearly shown in FIG. 13, 100% tantalum metal
Then, the appearance rate (α / β) of both phases is very bad, but when it exceeds 1%, it becomes almost only the α phase and becomes stable. However, 1
If it is lower than 0.1%, it is not always stable. On the other hand, as clearly shown in FIG. 14, when the niobium metal content exceeds 10%, the specific resistance of the tantalum film suddenly deteriorates. As is clear from these results, the composition ratio of niobium metal in tantalum metal is 0.1% to 10%, preferably 1%.
It is similar to the above result that the range between 10% and 10% is preferable.

From this result, it can be seen that in the sputtering deposition thin film manufacturing method by the nitrogen-free method, the tantalum metal α-phase formation depends on the composition of the deposited film and is not largely influenced by the manufacturing method. Further, the selective sputtering observed when using the alloy target does not cause a big problem.

In the present embodiment, the metal composition was controlled by changing the input power of the independent target, but other methods such as changing the target area or changing the target arrangement may be used.

Example 3 Next, the results of evaporating tantalum on a substrate on which niobium was previously evaporated will be disclosed. In the manufacturing apparatus shown in FIG. 1, niobium having a thickness of 5 nm to 100 is previously formed on the glass of the substrate 1.
After vapor deposition up to nm, tantalum was vapor-deposited thereon under the above conditions, and the appearance rates of both phases (α / β) and the specific resistance of the tantalum film were measured.

FIG. 15 shows the relationship between the predeposition thickness of niobium and the appearance ratio (α / β) of both phases, and FIG. 16 shows the relationship between the specific resistance of the tantalum film. As is clear from FIG. 15, the appearance rate (α / β) of both phases is very poor with 100% tantalum metal without vapor deposition of niobium, but beyond 10 nm, almost only the α phase becomes stable. However, it is not always stable at 5 nm. As is clear from these results, the predeposition thickness of niobium is good between 5 nm and 100 nm. Here, the upper limit is a value determined by the device or process conditions.

The present invention is essentially a method of mixing niobium as a different atom of tantalum to grow a body-centered cubic lattice which is a tantalum metal α phase, and the amount of added nitrogen is zero or very small. That is, since it is not the conventional method of controlling the partial pressure of nitrogen, a large amount of nitrogen does not remain in the film, or the film is not distorted or warped by nitrogen. FIG. 8 shows α-T of tantalum formed by the present invention and the conventional nitrogen gas addition method.
The a (110) lattice constant is listed. In the figure, the horizontal axis is the nitrogen flow rate, and the value at the nitrogen flow rate 0 is α-Ta (110) = approximately 3.3.
2Å (marked with ●) is the present invention. In the conventional method, both α and β phases were mixed in a nitrogen flow rate range of 2 to 4 sccm, and the value of the α phase was selectively plotted. The flow rate of nitrogen is 6 sccm when all phases are α phase.
−Ta (110) = approximately 3.37Å. Clearly, nitrogen increases the interplanar spacing, and the value of the tantalum film of the present invention is close to the value of bulk metal (3.306Å), which is excellent.

FIG. 9 shows the specific resistance of tantalum formed by the present invention and the conventional nitrogen gas addition method. In the figure, the horizontal axis is the nitrogen flow rate, and the value of the nitrogen flow rate of 0 is about 40 μΩcm for the specific resistance (marked with ●) of tantalum of the present invention. In the conventional method by controlling the partial pressure of nitrogen, the increase of the specific resistance is observed due to the mixture of β phase and the nitride. In the method according to the present invention, niobium is mixed as a heteroatom of tantalum, but the resistivity of body-centered cubic niobium (14.2 μΩcm) and that of tantalum (13 μΩcm) are very close to each other, which is similar to the conventional method. The phenomenon of resistance increase due to such nitrided insulator does not occur.

Example 4 Example 4 discloses an example using a tantalum metal and niobium metal mixed target. The conditions for producing the tantalum metal thin film were the same as the apparatus and the production conditions shown in FIG.

That is, the film forming condition is an argon flow rate of 50 scc.
m, nitrogen flow rate 0 sccm, pressure 0.4 Pa, input power 3.0 KW, substrate is glass, and niobium metal content is about 1%. As a result of X-ray diffraction analysis of the thin film produced under these conditions, as shown in FIG. 2, α-Ta (11
0), Bragg angle (2θ) = about 33.2 ° X-ray diffraction intensity was observed, and β-Ta (200) Bragg angle (2θ) = about 37.8 ° was not observed. Further, the specific resistance also shows a low value of 20 to 60 μΩcm, and supports the α-phase structure.

Comparative Example 1 In FIG. 10, as a comparative example, X was obtained by using a tantalum metal target which was not mixed with niobium metal under the same other conditions.
The line diffraction results are shown. Apparently, β-Ta (200) appears predominantly in addition to α-Ta (110). It has been found that a method of mixing niobium as a different atom of tantalum is extremely effective as a method of obtaining the α single phase.

Example 5 In Example 5, a mixture of tantalum metal and a small amount of niobium metal was used.
An example in which a get is used and a small amount of nitrogen gas is added is disclosed. The conditions for producing the tantalum metal thin film were the same as the apparatus and the production conditions shown in FIG.

That is, the film forming condition is an argon flow rate of 50 scc.
m, nitrogen flow rate 0.2 to 1 sccm, pressure 0.4 Pa, input power 3.0 KW, substrate is glass, and niobium metal content is about 0.1%. As a result of X-ray diffraction analysis of the thin film produced under these conditions, as shown in FIG.
Ta (110), Bragg angle (2θ) = about 33.2 °
X-ray diffraction intensity of β-Ta (200) B
The ragg angle (2θ) = about 37.8 ° was not observed. Furthermore, the specific resistance also shows a low value of 40 to 60 μΩcm, and supports the α-phase structure.

Further, as a result of analyzing both nitrogen in the metal thin film, the value was 0.1 to 1 atomic%, which was 1/10 to 1/2 of the value when the α phase was prepared by the conventional method.

Comparative Example 2 In FIG. 17, as a comparative example, a tantalum metal target not mixed with niobium metal was used, and the other conditions were the same.
The line diffraction results are shown. Apparently, β-Ta (200) is mixed with α-Ta (110). It has been found that a method of mixing niobium as a different atom of tantalum is extremely effective as a method of obtaining the α single phase.

Example 6 Example 6 discloses an example using independent targets of tantalum metal and niobium metal. The conditions for producing the tantalum metal thin film were the same as the apparatus and the production conditions shown in FIG. The difference from the above-mentioned Examples 4 and 5 was that two targets were provided, one for each tantalum metal and one for niobium metal.

That is, the film forming condition is an argon flow rate of 50 scc.
m, nitrogen flow rate 0 sccm, pressure 0.4 Pa, tantalum metal target input power 3 KW, niobium metal target input power about 2 KW, and substrate is glass. The target metal composition was 99.9% each. As a result of X-ray diffraction analysis of the thin film produced under these conditions, as shown in FIG. 4, α-Ta (110) and Bragg angle (2
θ) = only about 33.2 ° X-ray diffraction intensity is observed, β
-Ta (200) Bragg angle (2θ) = about 37.8 °
Was not observed. Furthermore, the specific resistance is 20 to 60 μΩ.
It shows a low value of cm and supports the α phase structure.

At this time, the mixing ratio of niobium metal to tantalum metal was about 5%. Similarly, as a comparative example, when only the tantalum metal target was used and the other conditions were the same, the X-ray diffraction results were measured, and α-Ta (110) was obtained.
In addition, β-Ta (200) appeared predominantly. It has been found that a method of mixing niobium as a different atom of tantalum is extremely effective as a method of obtaining the α single phase.

Example 7 Example 7 discloses an example in which independent targets of tantalum metal and niobium metal are used, and a trace amount of nitrogen gas is further added. The conditions for producing a tantalum metal thin film are as shown in FIG.
It was carried out by a method similar to the apparatus and manufacturing conditions shown in. The difference from Example 6 is that a slight amount of nitrogen gas was added.

That is, the film forming condition is an argon flow rate of 50 scc.
m, nitrogen flow rate 0.2 to 1 sccm, pressure 0.4 Pa, input power for tantalum metal target 3 KW, input power for niobium metal target about 2 KW, substrate is glass. The target metal composition was 99.9% each. As a result of X-ray diffraction analysis of the thin film prepared under these conditions, as shown in FIG. 5, α-Ta (110) and Bragg having a cubic crystal structure were obtained.
Only the X-ray diffraction intensity of the angle (2θ) = about 33.2 ° is observed, and β-Ta (200) Bragg angle (2θ) = about 3
7.8 ° was not observed. Furthermore, the specific resistance is 40-
It shows a low value of 60 μΩcm and supports the α-phase structure.

At this time, the mixing ratio of the niobium metal to the tantalum metal was about 2%, and the result of analyzing the amount of nitrogen in the metal thin film was 0.1 to 1 atomic%.
The value was 1/10 to 1/2 of that at the time of phase preparation. As a comparative example, when only tantalum metal target was used and other conditions were the same, X-ray diffraction was measured, and α-Ta (1
In addition to 10), the mixture of β-Ta (200) was observed.
It has been found that a method of mixing niobium as a different atom of tantalum is extremely effective as a method of obtaining the α single phase.

Example 8 Example 8 discloses an example in which tantalum metal is epitaxially vapor-deposited on a substrate on which niobium metal is vapor-deposited in advance. The conditions for producing the tantalum metal thin film were the same as the apparatus and the production conditions shown in FIG.

That is, the film forming condition is an argon flow rate of 50 scc.
m, nitrogen flow rate 0 sccm, pressure 0.4 Pa, input power 3.0 KW, substrate was glass, and niobium metal was vapor-deposited on the substrate in advance at about 5 to 100 nm. As a result of X-ray diffraction analysis of the thin film produced under these conditions, as shown in FIG. 6, cubic crystal structure α-Ta (110) and Bragg angle (2θ) = about 3
Only the X-ray diffraction intensity of 3.2 ° was observed, and β-Ta (2
00) Bragg angle (2θ) = about 37.8 ° was not observed. Further, the specific resistance also shows a low value of 20 to 60 μΩcm, and supports the α-phase structure.

Similarly, as a comparative example, when only tantalum metal target was used and the other conditions were the same, the X-ray diffraction results were measured. In addition to α-Ta (110), β-T was obtained.
a (200) appeared predominantly. It has been found that a method of mixing niobium as a different atom of tantalum is extremely effective as a method of obtaining the α single phase.

Example 9 Example 9 discloses an example in which tantalum metal is epitaxially vapor-deposited on a substrate on which niobium metal has been vapor-deposited in advance in an atmosphere in which a slight amount of nitrogen gas is mixed. The conditions for producing the tantalum metal thin film were the same as the apparatus and the production conditions shown in FIG. The difference from Example 8 is that a trace amount of nitrogen gas is mixed.

That is, the film forming condition is an argon flow rate of 50 scc.
m, nitrogen Flow rate 0.2 to 1 sccm, pressure 0.4 Pa,
The input power was 3.0 kW, the substrate was glass, and niobium metal was vapor-deposited on it in a thickness of about 5 to 100 nm in advance. As a result of X-ray diffraction analysis of the thin film produced under these conditions, as shown in FIG. 7, cubic crystal structure α-Ta (110) and Bragg angle (2θ) were obtained.
= Only about 33.2 ° X-ray diffraction intensity was observed, and β-T
The a (200) Bragg angle (2θ) = about 37.8 ° was not observed. Furthermore, the specific resistance is 40 to 60 μΩcm.
Shows a low value, and supports the α-phase structure.

As a comparative example, when only tantalum metal target was used and the other conditions were the same, X-ray diffraction was measured, and in addition to α-Ta (110), β-Ta (20
A mixture of 0) was observed. As a method to obtain α single phase,
It was found that the method of mixing niobium as a different atom of tantalum is extremely effective.

[0046]

The present invention is essentially a method of mixing niobium as a different atom of tantalum to grow a body-centered cubic lattice which is a tantalum metal α phase, and the amount of added nitrogen is zero or very small. That is, since it is not the conventional method of controlling the partial pressure of nitrogen, a large amount of nitrogen does not remain in the film, or the film is not distorted or warped by nitrogen.

That is, TaN _0.1 and TaN which are insulators
_0.25 , Ta ₆ N _2.57 , TaN _0.5 , TaN _0.8 , Ta
This is a method of forming an α-phase tantalum thin film having a low resistance by eliminating a metal nitride such as N, Ta ₃ N ₄ . Furthermore, the sputter deposition method is characterized in that nitrogen in the film, which is a main cause of thin film distortion, can be reduced as much as possible.

Further, in the method according to the present invention, although niobium is mixed as a different atom of tantalum, the resistivity of body-centered cubic niobium (14.2 μΩcm) and that of tantalum (13 μΩcm) are very close to each other. The high resistance phenomenon due to the nitrided insulator unlike the conventional method does not occur.

[Brief description of drawings]

FIG. 1 is a schematic view of a sputtering apparatus.

2 is an X-ray diffraction diagram of Example 4. FIG.

FIG. 3 is an X-ray diffraction pattern of Example 5.

4 is an X-ray diffraction pattern of Example 6. FIG.

5 is an X-ray diffraction diagram of Example 7. FIG.

6 is an X-ray diffraction pattern of Example 8. FIG.

FIG. 7 is an X-ray diffraction pattern of Example 9.

FIG. 8 is a relationship between a nitrogen flow rate and a lattice constant in the production of a tantalum thin film.

FIG. 9 is a relationship between nitrogen flow rate and specific resistance in the production of tantalum thin film.

FIG. 10 is an X-ray diffraction diagram when niobium metal is not mixed.

FIG. 11: Tantalum / niobium composition ratio and appearance rate of both phases (α
FIG. 6 is a relationship diagram of / β).

FIG. 12 is a relationship diagram of the tantalum / niobium composition ratio and the specific resistance of the tantalum film.

FIG. 13: Tantalum / when using an independent target
It is the relationship between the niobium composition ratio and the appearance rate (α / β) of both phases.

FIG. 14: Tantalum when using an independent target /
This is the relationship between the niobium composition ratio and the specific resistance of the tantalum film.

FIG. 15 is a relationship between the tantalum / niobium composition ratio and the appearance ratio (α / β) of both phases when preliminarily vapor-depositing niobium.

FIG. 16 shows the relationship between the tantalum / niobium composition ratio and the specific resistance of the tantalum film when niobium was pre-deposited.

FIG. 17 is an X-ray diffraction diagram when a trace amount of nitrogen gas is mixed without mixing niobium metal.

[Explanation of symbols]

 1 Substrate on which a tantalum metal thin film is deposited 2 Sputtering gate 3 Vacuum exhaust port 4 Magnet 5 DC power supply 6 Sputtering gas inlet

Claims (2)

[Claims] 1. When a tantalum metal thin film is formed by a sputtering method, i) tantalum metal mixed with niobium metal is simultaneously vapor-deposited as a target, or ii) tantalum metal and niobium metal are simultaneously used as separate targets. A method for producing a tantalum metal thin film, which comprises performing vapor deposition, or performing vapor deposition of niobium metal in advance and then performing vapor deposition of tantalum metal to preferentially form a body-centered cubic tantalum metal thin film. 2. The manufacturing method according to claim 1, which is carried out in an atmosphere in which nitrogen gas or a nitrogen-based gas is mixed.