JP3559290B2 - Metal thin film and method for producing the same - Google Patents

Description

[0001]
[Industrial applications]
The present invention relates to a configuration of a low resistivity thin film of tantalum metal having good mechanical strength and chemical stability, and a method for manufacturing the same.
[0002]
[Prior art]
Various metals are used as wiring film materials in the field of electronics. Among them, tantalum metal is excellent in mechanical strength, and Ta ₂ O ₅ which becomes an oxide film thereof has a very small dielectric loss and a relative dielectric constant. Because of its relatively high electrical characteristics and excellent chemical stability of acid and alkali resistance, it becomes a thin film wiring that can withstand various device manufacturing processes and can increase the reliability of the device. It has high utility value and is heavily used.
[0003]
However, as the tantalum metal film becomes thinner, the tetragonal crystal structure (.about.200 .mu..OMEGA.cm) having a higher specific resistance (.about.200 .mu..OMEGA.cm) in the normal cubic crystal structure (.alpha. Phase) having a lower specific resistance (20.about.50 .mu..OMEGA.cm). It is known that (β phase) is generated and exists in a metastable state.
[0004]
Among the above two phases, the β phase having a high specific resistance of tantalum is used for precision resistors because its specific resistance has a very small change with temperature.
[0005]
On the other hand, low-resistivity α-phase tantalum has a specific resistance of about 1/10 of that of β-phase tantalum, so that it has been applied to various uses as a thin film wiring material having excellent characteristics. However, as the thickness of tantalum becomes thinner, it becomes easier to form a metastable β phase with a high specific resistance, and the resulting thin film wiring has a high resistance value and is not uniform. Various film-forming methods for forming only one have been proposed.
[0006]
In the above, the method of introducing a nitrogen gas during the deposition of a tantalum thin film by sputtering and forming the formed tantalum thin film into an alloy with nitrogen has historically been a result of research on a nitride alloy based superconductor material. However, it is relatively easy to prevent the generation of metastable β-phase with high resistivity and to selectively control the formation of low-resistance α-phase tantalum thin film. It is commonly used in forming processes.
[0007]
[Problems to be solved by the invention]
However, in the tantalum thin film formed by the sputtering method using nitrogen gas described above, the appearance rate (α / β) of two crystal structure phases having different specific resistances depends on the film forming conditions, for example, the nitrogen gas partial pressure and the like. Since it is known that it depends on the flow rate, the applied power of sputtering, or the temperature of the substrate, the material of the substrate, the film deposition rate, and the structure of the sputtering apparatus, various measures have been taken to stabilize the deposited film. Have been.
[0008]
Among the above film forming conditions, the magnitude of the partial pressure of nitrogen gas has a great influence on the appearance rate (α / β) of the phase. That is, when the partial pressure of nitrogen falls within the range of 10 ⁻⁶ to 10 ⁻⁵ Torr, the tantalum thin film changes from a high-resistivity β phase to a mixed phase of an α phase and a β phase, and further, at around 10 ⁻⁵ Torr. The α phase becomes rich with low specific resistance. _{Next, TaN 0 · 1, TaN 0} · 25 nitrogen gas partial pressure be at least ¹⁰ -5 Torr with the characteristics of said metallic α and β phases except for the _{insulator, Ta 6 N 2 · 75,} TaN _{0 · 5, TaN 0 · 8} , TaN, Ta 3 N 4 (ASTM: from American Standard and Testing Materials card) become like is formed, and the specific resistance comes increased again. Therefore, in order to form an optimal low-resistivity tantalum thin film by a nitrogen-added gas sputtering method, it is necessary to control the nitrogen flow rate so as to keep the nitrogen partial pressure at around 10 ⁻⁵ Torr. It is difficult to always maintain the entire substrate at the optimum film deposition conditions in the field, and it becomes more and more difficult if the film deposition area becomes large.
[0009]
In addition, since the thin film of tantalum metal formed by the above method has a structure in which an insulator is dispersed, even if it is possible to prevent the formation of a metastable β phase that forms a high-resistivity crystal structure, pure tantalum metal is used. It is unavoidable that the specific resistance value becomes 3 to 4 times higher than the low specific resistance value (13 μΩ) of the metal.
[0010]
On the other hand, it is known that the appearance ratio α / β of two phases in a tantalum metal thin film depends not only on the type of substrate on which the film is deposited but also on the surface state thereof. This is because β-phase, which has high resistance, is likely to be formed on the surface of a substrate made of an oxide or a material that easily forms an oxide, while the surface of the substrate is contaminated by adhesion of moisture or other molecules. Although there is a report that a low-resistance α-phase is likely to be formed, these are out of the range of empirical rules, and it has been difficult to continuously maintain the film deposition conditions in the manufacturing process.
[0011]
An object of the present invention is to provide a configuration of a low resistivity tantalum metal thin film and a production method thereof which solve the problems of the conventional method for producing a low resistivity tantalum metal thin film described above.
[0012]
[Means for Solving the Problems]
According to the present invention, the conventional sputtering method using a nitrogen gas for forming a low resistivity α-phase of a tantalum metal thin film has extremely severe film forming conditions, and has an insulating tantalum nitride formed by the sputtering conditions. In addition to preventing the formation of a, the α-phase tantalum thin film obtained by the above-mentioned nitrogen addition method forms an α-phase tantalum thin film having a lower resistivity than the α-phase tantalum thin film. It uses niobium metal having a structure.
[0013]
As a specific method for carrying out the above method, tantalum metal having acid resistance and alkali resistance similar to those of the tantalum metal of the present invention, being chemically stable, and in bulk and in a thin film state Without the metastable β phase as described above, the tantalum thin film also has the same crystal structure with niobium metal having only the same body-centered cubic crystal structure as the low resistivity α phase of tantalum.
[0014]
By adding this niobium metal into the tantalum deposited film by sputtering, the added niobium particles forcibly induce the adjacent tantalum metal layer to have the same body-centered cubic crystal structure. Utilizing the results, the deposited tantalum metal thin film is converted to the α phase.
[0015]
The forcing of the tantalum metal film to the body-centered cubic lattice structure at the boundary with the niobium metal as described above also occurs when the tantalum metal thin film is deposited on the niobium metal thin film. A tantalum thin film made of the α phase of resistance can be manufactured.
[0016]
[Action]
The induction of the crystal structure described above is based on the fact that niobium metal has a body-centered cubic lattice crystal structure with a lattice constant of 3.303 °, while tantalum metal with a low resistivity has the same crystal structure and a lattice constant of 3 .3058}, which is a very approximate value. In particular, heteroepitaxial growth between different atoms of a higher-order mirror surface at (110), (111) or the like having a small interplanar energy forcibly grows tantalum metal into a body-centered cubic lattice, and the other tetragonal lattice. The present invention finds an effect of inhibiting the growth of a β phase having a high specific resistance having a crystal structure, and utilizes this effect.
[0017]
According to the above-described method of the present invention, niobium having a specific resistance (14.2 μΩ) similar to that of tantalum metal is obtained without forming an insulator made of tantalum nitride which is inevitably formed when a conventional nitriding method is used. The use of a metal allows a low resistivity α phase to be formed without adversely affecting the resistivity of the tantalum metal thin film produced.
[0018]
【Example】
Hereinafter, embodiments of the present invention will be described with reference to the drawings.
[0019]
First, FIG. 4 shows an outline of the sputtering apparatus used for the film formation of the present embodiment and the film formation conditions.
[0020]
In FIG. 4, reference numeral 1 denotes a substrate, and when depositing a tantalum metal thin film, a glass plate, a silicon wafer or the like is generally used in many cases. Reference numeral 2 denotes a sputtering target. In this embodiment, a target of a niobium-added tantalum alloy or a combination of a niobium metal and a tantalum metal block is used according to the composition or configuration of the metal film to be deposited. A target having a pattern corresponding to an appropriate predetermined composition ratio or a target composed of only niobium metal and tantalum metal is used. Reference numeral 3 denotes an exhaust port connected to an exhaust system of the sputtering apparatus. In addition, a turbo pump, a heat diffusion pump, or the like can be used as an exhaust system (not shown) as long as the inside of the sputtering apparatus can be exhausted to a degree of vacuum of about 1 × 10 ⁻⁴ Pa. Reference numeral 4 denotes a coil for generating a magnetic field for confining the argon plasma generated by the discharge in the sputtering between the target and the substrate. The effective density of the argon plasma is controlled by the strength of the magnetic field generated by the coil 4. It has the advantage of increasing the film deposition rate by a factor of 100. However, film deposition is possible without this magnetic field. Reference numeral 5 denotes a DC power supply which is often used in a range of about -100V to -3000V. Although a direct current (DC) sputtering method is used in this embodiment, a high frequency (RF) sputtering method in which a control grid is provided in the apparatus may be used. Reference numeral 6 denotes a supply port for a sputtering gas, and in the embodiment, an argon gas to which a nitrogen gas is added is supplied. The amount of gas supplied to the gas supply port 6 and the degree of mixing / dilution thereof are precisely controlled by a flow control device. The thickness of the formed tantalum metal thin film was about 3000 °.
[0021]
(Reference Example 1) In the following reference example , a film was formed using the sputtering apparatus of FIG. 4 described above.
[0022]
In the film forming process of the embodiment, first, the gas supply port 6 of the apparatus is closed, the inside of the apparatus is evacuated to a degree of vacuum of about 1 × 10 ⁻⁴ Pa, and the attached gas and the like are exhausted. A gas was supplied so as to maintain the pressure at 0.4 Pa. The supply of this gas is 50 sccm with argon (Ar) gas. A glass plate (C7059) is used for the substrate 1, and the temperature for film deposition is room temperature. At the time of sputtering, power of 3.0 KW is supplied from the DC power supply 5.
[0023]
Under the above sputtering conditions, a film was formed using a target in which 1 to 10% by weight of niobium metal having the same cubic crystal structure as the α phase was added to tantalum metal.
[0024]
Each of the metal thin films formed as described above has a low specific resistance of 20 to 60 μΩcm, which is lower than that of a conventional α-phase tantalum thin film obtained by adding nitrogen.
[0025]
FIG. 1A shows the result of the X-ray diffraction measurement of the tantalum metal thin film of the above example. As can be seen from the above X-ray diffraction pattern, the thin film of the example is formed only of a low resistivity cubic crystal structure (α phase) of tantalum metal.
[0026]
FIGS. 1B, 1C, and 1D show X-ray diffraction patterns of a tantalum metal thin film manufactured by a conventional technique as a comparative example with respect to the above embodiment.
[0027]
The tantalum metal thin film measured in FIG. 1B was formed using a target consisting of only tantalum metal and supplying only an arcon gas as a sputtering gas.
[0028]
As can be seen from FIG. 1B, the tantalum thin film formed has a large metastable tetragonal crystal structure (β phase) with high specific resistance.
[0029]
The next X-ray diffraction pattern shown in FIG. 1C is deposited by adding ₂ sccm of nitrogen (N ₂ ) gas to the thin film forming conditions showing the X-ray diffraction pattern in the previous FIG. 1B. Of a thin tantalum metal thin film.
[0030]
As can be seen from FIG. 1C, the addition of nitrogen gas to the sputtering gas reduces the β phase and increases the low resistivity cubic crystal structure (α phase).
[0031]
Further, FIG. 1D shows an X-ray diffraction pattern of a tantalum metal thin film deposited by increasing the nitrogen gas to 4 sccm under the above-described film forming conditions. From FIG. 1 (D), it can be seen that the β phase has disappeared and only the α phase has remained.
[0032]
FIG. 2 shows the relationship between the amount of nitrogen added to the sputtering gas and the specific resistance of the formed thin film in the conventional deposition of a tantalum metal thin film with nitrogen addition. FIG. 2 shows that the specific resistance of the thin film is minimized when the added nitrogen gas is 4 sccm. As can be seen from FIGS. 1 and 2 described above, when the α phase is formed by the conventional method of adding nitrogen, it is necessary to essentially form the nitride insulator in the tantalum metal thin film. , And excess nitrogen addition increased the specific resistance of the thin film.
[0033]
In contrast to the above-described conventional nitrogen addition, the tantalum thin film to which niobium is added using the target of the alloy with the tantalum metal to which 1 to 10% by weight of niobium metal of this embodiment is added is lower than that of the conventional method. It has been found that a tantalum thin film having a specific resistance can be stably formed with good reproducibility.
[0034]
In the first embodiment described above, the metal film formed by the sputtering method using the tantalum target to which niobium is added in an amount of 1 to 10% by weight has been described. It can be expected that the same effect can be obtained even with an alloy having a higher ratio than the embodiment.
[0035]
( Embodiment 1 ) In this embodiment, a target to be used is a tantalum target in which the addition amount of niobium metal is reduced to 0.1 to 10% by weight and the addition amount of niobium is reduced, and a sputtering gas is 0.2 to 1 sccm. Was added to form a film. The specific resistance of each of the prepared thin films was 40 to 60 μΩcm, which was lower than that of the conventional tantalum thin film.
[0036]
The X-ray diffraction pattern of the thin film formed as described above indicates that the thin film is a tantalum metal thin film having a single low resistivity cubic crystal structure (α phase) as shown in FIG. .
[0037]
FIG. 3B shows an X-ray diffraction pattern of a tantalum thin film formed as a comparative example of Example 2 using only a target as a target and only a tantalum metal target. FIG. 3B corresponds to the conventional case where the amount of nitrogen gas added is extremely small, and it can be seen that the metastable tetragonal crystal structure (β phase) with high specific resistance is significantly increased. .
[0038]
The method of adding a small amount of nitrogen to the sputtering gas according to the present embodiment is effective when it is necessary to limit the amount of niobium added to tantalum, and by adding a small amount of niobium, a tantalum thin film can be formed. It has been found that the amount of nitrogen for achieving a given specific resistance can be reduced.
[0039]
As a result of analyzing the amount of nitrogen in the metal thin film formed in Example 2, the amount was 0.1 to 1 atomic%, and the nitrogen amount was 1/10 to 1/2 of that obtained by the conventional nitrogen addition method. It can be seen that the cubic crystal structure (α phase) is remarkably formed.
[0040]
( Reference Example 2 ) In this reference example , the structure of the target was changed, and instead of a target of an alloy of tantalum and niobium as in Reference Example 1, a target in which the area ratio of tantalum and niobium on the surface was a predetermined ratio. In this case, a film is formed by a sputtering method using the method.
[0041]
The specific resistance of the produced metal thin film was as good as 20 to 60 μΩcm, and its X-ray diffraction pattern was almost the same as in FIG. 1A, indicating that it was formed of a single α phase. .
[0042]
In this embodiment, the atomic ratio of niobium in tantalum after film formation is controlled to be 1 to 10%. However, the present invention does not limit the niobium ratio, and it is possible to change the niobium ratio. It is.
[0043]
In the above, the embodiment of the method of changing the area ratio of the tantalum and the niobium on the target has been described. However, the targets of the tantalum and the niobium are configured to be independent from each other, and the power of the sputter applied to each target is controlled. May be used as the metal thin film.
[0044]
( Embodiment 2 ) In this embodiment, a film is formed by controlling the targets of tantalum and niobium independently, and supplying a small amount of nitrogen gas to the sputtering gas.
[0045]
The metal thin film formed as described above exhibited a low specific resistance of 40 to 60 μΩcm, and its X-ray diffraction pattern also indicated that it was a single 1α-phase tantalum metal thin film.
[0046]
This embodiment is effective when it is desired to reduce the amount of niobium in tantalum, and the amount of added nitrogen becomes effective at 0.1 to 1 atomic% as a result of analysis. It was found that the α phase can be formed remarkably at / 10 to ２.
[0047]
( Embodiment 3 ) In this embodiment , a metal film is formed by a sputtering method using a tantalum metal target and a niobium metal target.
[0048]
In this film formation, a niobium metal thin film of 10 to 100 nm is formed on a substrate by a niobium target, and then a tantalum thin film is formed on the niobium metal thin film by a tantalum target. The specific resistance of the metal film formed as described above was as low as 20 to 60 μΩcm, and the X-ray diffraction pattern of the thin film showed that it had a single α-phase configuration.
[0049]
In this embodiment, tantalum is deposited on a very thin niobium thin film (10 to 100 nm) having the same structure as the low resistivity cubic crystal structure (α phase) of tantalum, and forced induction by the niobium thin film is performed. The tantalum thin film deposited thereon is aligned with the α phase.
[0050]
In the above embodiment, the thickness of the niobium thin film previously deposited is set to 10 to 100 nm. However, the thickness of the niobium thin film is not limited to this range in the present invention, and the subsequently deposited tantalum thin film can be guided to the α phase. Any thickness is acceptable.
[0051]
( Embodiment 4 ) Also in this embodiment, first, a niobium thin film of 1 to 100 nm is deposited using a niobium target, and subsequently, a tantalum is added by using a sputter gas to which a small amount of nitrogen (0.2 to 1 sccm) nitrogen gas is added. Deposits a thin film.
[0052]
The specific resistance of the metal thin film formed as described above was as good as 40 to 60 μΩcm, and the X-ray diffraction pattern of the thin film showed that it was a single low specific resistance α phase.
[0053]
The above example is effective when it is desired to reduce the thickness of the niobium thin film deposited first, and it has been found that the effect is obtained even when the thickness of the niobium thin film is about 1 nm.
[0054]
Although the various embodiments described above show that the tantalum thin film of the present invention can be stably formed at a low specific resistance, the present invention is not limited to the embodiments. A stacked film formed by continuously forming niobium and tantalum in a chamber for use may be formed by a plurality of chambers via a transfer gate valve. Film formation can be performed by changing the combination or the number of layers, and the film formation conditions can be changed depending on the purpose.
[0055]
【The invention's effect】
The tantalum thin film according to the present invention is formed by adding niobium to the thin film or forming a niobium thin film and depositing the thin film on the tantalum thin film so that the formed tantalum thin film has a low resistivity cubic structure (α phase). It is. Further, since the thin film made of the tantalum metal of the present invention can be manufactured by using a conventional sputtering apparatus, it can be used as a stable conductive thin film, especially for ICs, optical ICs, photoelectric conversion devices, optical devices requiring fine processing. It can be widely used in the field of electronics such as display devices.
[Brief description of the drawings]
FIG. 1 is a diagram showing X-ray diffraction patterns of a tantalum thin film to which niobium is added and a conventional tantalum thin film to which nitrogen is added.
FIG. 2 is a diagram showing a change in specific resistance depending on the amount of nitrogen added to a tantalum thin film.
FIG. 3 is an X-ray diffraction pattern diagram showing the effect of the present invention in film formation in which a small amount of nitrogen is added to a sputtering gas.
FIG. 4 is a cross-sectional view showing an outline of a sputtering apparatus used for film formation in an example.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Substrate 2 Target 3 Exhaust port 4 Magnetic field generating coil 5 DC power supply 6 Gas supply port

Claims (4)

A metal thin film mainly composed of tantalum metal and used as a conductor,
Elemental nitrogen was added, and, Ri in that it consists of adding an alloy niobium metal having the same crystal structure as α-phase tantalum, specific resistance of a metal thin film of 40～60Myuomega, the amount of the nitrogen element 0.1 A metal thin film , wherein the amount of the niobium metal is 0.1 to 10% by weight . A metal thin film characterized in that a tantalum thin film containing a nitrogen element is formed on a niobium metal thin film to form a laminated structure. The metal thin film according to claim 2 , wherein the thickness of the niobium metal thin film is in a range of 10 nm to 100 nm. When manufacturing a metal thin film mainly containing tantalum metal by adding nitrogen gas to the sputtering gas,
Niobium metal having the same crystal structure as α-phase tantalum, be added to the deposited film of tantalum, a tantalum metal film deposited Ri name in the α-phase, a nitrogen content of 0.1 to 1 atomic% And obtaining a metal thin film containing tantalum metal as a main component and having a niobium metal content of 0.1 to 10% by weight and a specific resistance of 40 to 60 μΩ .

Images