JPH06216064A - Al contact structure and manufacture thereof - Google Patents

Abstract

PURPOSE:To provide an Al contact structure which is excellent in reliability and low in resistivity without barrier metal and can be easily manufactured for an Si device. CONSTITUTION:In a contact structure wherein Al is brought into direct contact with an Si substrate, an interface fluctuation is limited to four atomic layers per 10nm in a direction parallel with the interface. Or, an Al crystal is made to grow so as to make an orientation relation between an Si substrate and an Al contact satisfy a formula, Al<220>//Si<220>, in a plane parallel to an interface.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an Al contact structure of a device using a Si substrate.

[0002]

2. Description of the Related Art With the recent integration of devices, wiring technology for connecting elements has become more important. Particularly for wiring contacts, reducing resistance while maintaining reliability is an urgent issue. Further, the amount of material used for wiring has increased, and the structure has become complicated and the number of process steps has increased. However, it is also a big problem to realize a simple manufacturing process by utilizing the original property of the material. In the ohmic contact of a Si device using Al as a wiring material, a barrier metal structure in which a refractory metal such as Ti or W or a compound thereof is sandwiched between Al and Si is used. In this structure, although the thermal stability of the contact can be obtained, there is a problem that the resistance of the material is high or the manufacturing process is complicated and costly.
An object of the present invention is to realize an Al contact structure that simultaneously has high reliability, simplicity, and high performance of a wiring structure.

[0003]

According to a first aspect of the present invention, in an Al contact structure having a structure in which Al is directly contacted with a Si substrate, the fluctuation of the Si / Al interface is 4 per 10 nm in the direction parallel to the interface. It is an Al contact structure characterized by having a flat interface that is less than an atomic layer.

The second aspect of the present invention is to directly apply A to the Si substrate.
In an Al contact structure having a structure in which 1 is in contact with Al, the azimuth relationship between the Si substrate and Al is Al <220> // Si <220> in a plane parallel to the interface.
It is a contact structure. The relationship between Al and Si as described above is, for example, Al (110) // S for a Si (100) substrate.
i (100) and Al <220> // Si <220> are satisfied. For an Si (111) substrate, Al (111) // Si (11
1) and Al <220> // Si <220> or Al (100) //
It is realized by a relationship such that Si (111) and Al <220> // Si <220> are satisfied.

Further, in these Al contact structure manufacturing methods, the surface of the Si substrate is immersed in a hydrofluoric acid-based aqueous solution having a pH value of 4 to 8 so that the flatness of the Si surface is less than 4 atomic layers per 10 nm, and then It is characterized in that Al is deposited on this Si flat surface. Here, the Al contact is a contact containing Al as a main component, and includes Si, Cu,
A material such as Pd may be included.

[0006]

In the Al contact deposited by the sputtering method or the like which has been conventionally used, Si is converted into A by the heat treatment at 400 ° C. or higher.
Since a large amount of Al diffuses in 1 l, there is a problem that an Al spike is formed on the substrate side to cause a short circuit, and a re-precipitated Si layer is formed on the contact interface to increase the contact resistance. However, the present inventor has formed an Al contact on a Si substrate whose surface is flattened at an atomic level by a hydrofluoric acid solution treatment with controlled pH, using an vacuum deposition method that causes less damage to the surface. 1
It was found that no spikes were observed even after heat treatment for a long time and no deterioration in electrical characteristics occurred.

Therefore, the present inventors have found that the thermal stability of the interface is
It was hypothesized that the Al / Si interface has a close relationship with the flatness, and that a contact with sufficient reliability can be realized without a barrier metal by realizing a flatness above a certain level.

In order to verify this hypothesis, an Al / Si interface whose interface fluctuation was controlled was prepared, and an experiment was conducted to examine the correlation between the degree of fluctuation and thermal stability. First p
S whose surface is flattened with a hydrofluoric acid solution in which H is controlled
i (100) substrate was prepared, and Al was vapor-deposited on the substrate whose damage degree was changed by the irradiation amount of Ar ion beam in the ultra-high vacuum and the substrate which was not damaged, while keeping the substrate temperature at room temperature. did. The interface of the polycrystalline Al contact thus manufactured was observed with a high-resolution cross-sectional electron microscope, and it was confirmed that the size of the interface fluctuation varied depending on the degree of damage. As a result of investigating the thermal stability of this contact, alloy pits were not observed in the sample with interface fluctuation of less than 4 atomic layers in annealing in a nitrogen atmosphere at 450 ° C. for up to 1 hour.
The electrical characteristics evaluated by the method also showed ideal behavior, whereas in the other samples, deterioration of the surface morphology and deterioration of the electrical characteristics were already observed after annealing at 400 ° C. for 1 hour. From these facts, the above hypothesis that the thermal stability of the Al / Si interface is closely related to the interface flatness is proved, and the interface fluctuation is 10 nm in the direction parallel to the interface.
It has been found that a thickness of less than 4 atomic layers is desirable.

In the Al contact formed by the sputtering method or the like, in order to make an ohmic contact with the n-type substrate,
Annealing at about 400 ° C. is required. This is 400
The cause is that the Schottky barrier height of the contact is reduced by about 0.1 eV by annealing at about ° C. On the other hand, Al (1
11) It has been reported that the epitaxial single crystal contact shows a low Schottky barrier height of 0.7 eV without annealing, and that the value does not change due to annealing [I Triple E Transaction On・ Electron device (IEEE Transactio
n on Electron Devices), 1987, 34, 1018]. If this single crystal Al is used for ohmic contact, good electrical characteristics should be obtained without annealing. However, there is a problem that it is difficult to produce single crystal Al.

Therefore, the present inventor considers that the decrease in the barrier height is due to the stabilization of the Al / Si interface structure, and even if Al is polycrystalline, it has a structurally stable specific epitaxial relationship. A contact having a low Schottky barrier height of 0.7 eV without annealing,
Moreover, we hypothesized that this value does not change with annealing.

In order to verify this hypothesis, Si (100)
We have searched for a polycrystalline contact structure having the above-mentioned epitaxial relationship with an Al film formed on a Si (111) surface by an evaporation method in an ultrahigh vacuum. As a result, it was found by a plane electron microscope observation that an Al film having the above-mentioned epitaxial relationship and an Al film having no such epitaxial relationship can be obtained depending on the surface condition of the substrate. For Si (100) substrate, Al (110) // Si (100) and Al <220> // on a 2 × 1 surface superstructure
While a polycrystal composed of grains having an epitaxial relationship equivalent to Si <220> can be obtained,
On the hydrogen-terminated surface, polycrystals consisting of (110) -oriented grains, which were randomly rotated around an axis perpendicular to the substrate, were obtained. In Si (111) substrate, Al (111) // Si (111) and Al <22 on 7 × 7 surface superstructure
A single crystal having an epitaxial relationship of 0> // Si <220> has Al (111) // Si (111) and Al <220> // Si <220> or Al (100 ) //
Polycrystal composed of grains of Si (111) and grains having an epitaxial relationship equivalent to Al <220> // Si <220> (bicr
ystal) was obtained. On the other hand, on a clean surface with incomplete surface reconstruction, polycrystals of (111) -oriented grains, which were randomly rotated about an axis perpendicular to the substrate, were obtained. We investigated the change of the Schottky barrier height by annealing in a nitrogen atmosphere for up to 1 hour at 450 ° C for Al contacts having these five crystal orientation relationships, and found that Al <220> / in the plane parallel to the interface. / Si
All the samples having the <220> epitaxial relationship showed a barrier height of about 0.7 eV regardless of the annealing temperature, whereas all the samples having no epitaxial relationship showed the barrier height as the annealing temperature increased. The height was reduced from about 0.8 eV to about 0.7 eV. From the above results, in the plane where the epitaxial relationship is parallel to the interface,
The above hypothesis was verified to be correct when Al <220> // Si <220>.

[0012]

EXAMPLES Next, examples of the present invention will be described. Example 1 p-type Si (100) substrate (resistivity 10 to 20 Ωc
m, 4 inch φ), a Kelvin method test pattern for contact resistance measurement was prepared in the following manner, and Al / S
i The fine ohmic contact was evaluated. First, a field oxide film having a thickness of 0.5 μm was formed, the oxide film in the activated region was removed by ordinary photolithography, and a thermal oxide film for protection of 20 nm was grown, after which As ions were implanted. The implantation condition is a dose amount of 5 × 10 ¹⁵ c
m ⁻² , energy is 80 keV. 1000 in nitrogen
Activated by annealing at ℃ for 45 minutes, and further low pressure CVD
Method was used to form a 0.5 μm SiO ₂ layer. In order to completely remove the oxide film at the contact part by the second photolithography and subsequently to terminate the Si surface with hydrogen and at the same time planarize it in atomic order, buffered hydrofluoric acid (pH
Soak in ~ 4) for 1 minute. Immediately after rinsing with ultrapure water, the wafer was introduced into an MBE vacuum chamber with a back pressure of 10 ^-10 Torr and annealed at 700 ° C. for 10 minutes by the RTA method to form a 2 × 1 superstructure at the contact portion. It was After cooling the substrate temperature to 100 ° C., an Al film was formed using an effusion cell and sputtering as a source. The first 20 nm is 0.05 using an effusion cell.
Vapor deposition was performed at a rate of nm / sec, and subsequently a 0.8 μm Al layer was deposited by sputtering. A metal pattern was formed by the third photolithography.

When the Al / Si interface of the above test pattern was observed using a high-resolution cross-sectional TEM method, the interface was steep on the atomic layer order, and the average interface fluctuation was 10 n.
The number of steps per atomic layer per m was extremely small, which was 2 or less. The orientation relationship between Al and Si is Al (110) // S
It was i (100) and Al <220> // Si <220>, and it was revealed that the grains consisted of two kinds of equivalent grains satisfying this. The electrical characteristics were evaluated by the IV method for the contact size of 1 × 1 μm.
Average specific resistance value of 100 contacts is 1 × 10 ^-7 Ω
cm ² or less, and an extremely low value was obtained without annealing. Further, when the same sample was annealed at 450 ° C. for 60 minutes in a hydrogen atmosphere and then the same electrical characteristics were evaluated, the average specific resistance value was hardly deteriorated. From the above results, it was proved that the Al / Si ohmic contact having the features of claims 1 and 2 has a low contact resistance even without annealing and has stable characteristics even at high temperature annealing.

Example 2 p-type Si (111) substrate (resistivity 10 to 20 Ωc
m, 4 inch φ), a Kelvin method test pattern for contact resistance measurement was prepared in the following manner, and Al / S
i The fine ohmic contact was evaluated. First, a field oxide film having a thickness of 0.5 μm was formed, the oxide film in the activated region was removed by ordinary photolithography, and a thermal oxide film for protection of 20 nm was grown, after which As ions were implanted. The implantation condition is a dose amount of 5 × 10 ¹⁵ c
m ⁻² , energy is 80 keV. 1000 in nitrogen
Activated by annealing at 45 ℃ for 45 minutes, and further low temperature CVD
Method was used to form a 0.5 μm SiO ₂ layer. In order to completely remove the oxide film at the contact portion by the second photolithography and subsequently to terminate the Si surface with hydrogen and at the same time planarize it on the atomic order, an aqueous solution of hydrofluoric acid (ammonium fluoride aqueous solution, pH ~ 8) Soak for 1 minute. After rinsing with ultrapure water, it was immediately introduced into a vacuum chamber with a back pressure of 10 ⁻⁷ Torr, and annealing was carried out at 400 ° C. for 10 minutes by the RTA method in order to desorb impurity gases other than surface-terminated hydrogen. After cooling the substrate temperature to 100 ° C., an Al film was formed by a collimating method using an effusion cell and a sputter as a source. The first 20 nm was vapor-deposited at a rate of 0.05 nm / sec using an effusion cell, and subsequently an Al layer of 0.8 μm was deposited by sputtering. A metal pattern was formed by the third photolithography.

When the Al / Si interface of the above test pattern was observed using a high-resolution cross-sectional TEM method, the interface was steep on the atomic layer order, and the average interface fluctuation was 10 n.
The number of steps per atomic layer per m was extremely small, which was 2 or less. The Al film is Al (111) /// with respect to the Si substrate.
Grain having a relation of Si (111) and Al <220> // Si <220>, or Al (100) // Si (111) and Al
It became clear that it consists of three types of grains equivalent to <220> // Si <220>. Evaluation of electrical characteristics
For contact size 0.5 × 0.5μm,
It was carried out using the IV method. The average specific resistance value of 100 contacts was 1 × 10 ⁻⁷ Ωcm ² or less, and an extremely low value was obtained without annealing. Further, when the same sample was annealed in a hydrogen atmosphere at 500 ° C. for 60 minutes and then the same electrical characteristics were evaluated, the average specific resistance value was hardly deteriorated. From the above results, it was proved that the Al / Si ohmic contact having the features of claims 1 and 2 has a low contact resistance even without annealing and has stable characteristics even at high temperature annealing.

[0016]

As described above, according to the present invention,
By the Al contact structure that does not use barrier metal,
An ohmic contact can be secured without annealing, and an excellent contact whose characteristics do not change with heat treatment to the extent used in the process can be realized. This was not possible with conventional Al contacts. Further, compared with the conventional barrier metal structure, it has many industrial advantages that the resistance of the material itself is low and the cost is low because the manufacturing process is easy.

Claims (3)

[Claims] 1. In an Al contact structure having a structure in which Al is directly contacted with a Si substrate, a flat interface having a fluctuation of the Si / Al interface of less than 4 atomic layers per 10 nm in a direction parallel to the interface is formed. Al characterized by having
Contact structure. 2. In an Al contact structure having a structure in which Al is directly contacted with a Si substrate, Al <220> // Si <220> in a plane in which the orientation relationship between the Si substrate and Al is parallel to the interface.
The Al contact structure is characterized by: 3. The surface of a Si substrate is immersed in an aqueous solution of hydrofluoric acid having a pH value of 4 to 8 so that the flatness of the Si surface is less than 4 atomic layers per 10 nm, and then Al is deposited on the Si flat surface. And a method for manufacturing an Al contact structure.