JP3352779B2 - Semiconductor device and manufacturing method thereof - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor integrated circuit device and a method of manufacturing the same, and more particularly to a metal wiring used in a semiconductor integrated circuit device and a method of manufacturing the same.

[0002]

2. Description of the Related Art As semiconductor devices have become more highly integrated, the width of metal wiring has been reduced to about 1 μm. As the wiring, aluminum or an aluminum alloy (these are sometimes collectively referred to as an aluminum-based material) are used. When the wiring width is reduced to about 1 μm, the wiring has a bamboo structure crossing the grain boundaries. When the wiring has a bamboo structure, the occurrence of wiring breakage due to electromigration decreases, but a new breakage due to stress (cutting due to stress migration) occurs (Journal of the Japan Institute of Metals, Vol.28, No.1) (1989), p. 40). As one of the measures against stress migration, a method of alloying elements such as Cu and Pd with aluminum of wiring material has been proposed (J. Vac. Sci. Technol.,
BZ (6) (Nov.-Dec. 1990) P.1232).

[0003]

SUMMARY OF THE INVENTION Reliability of a semiconductor device,
Prevention of disconnection of metal wiring has been a major issue for improving the life. The most common disconnection failure of aluminum wiring among metal wirings is mainly (1) the current density of the wiring increases due to the miniaturization of the wiring, which promotes the diffusion of atoms in the wiring and generates voids in the wiring. And (2) stress is generated in the film due to the process of wiring, and voids are generated in order to relieve the stress. SM)
Disconnection due to

[0004] These two phenomena have been studied in detail, and some countermeasures have been proposed. For example, it is said that a so-called bamboo structure, in which the grain size of the material constituting the wiring is increased to be larger than the wiring width, is effective in improving the EM resistance, but conversely, the SM resistance is degraded. It is said that the SM disconnection is related to the crystal grain boundary existing in the wiring and the (111) plane of the wiring material. In today's wiring forming process, the orientation plane of the wiring material is controlled by various methods, but it is not enough to control the direction of the crystal axis in the film.

[0005] As the density of semiconductor devices becomes higher and the manufacturing process becomes more complicated, disconnection due to SM will be a major problem in the future. A first object of the present invention is to provide a semiconductor device having a wiring with improved EM resistance and SM resistance in metal wiring. Another object of the present invention is to provide a method for forming such a metal wiring.

[0006]

The semiconductor device of the present invention has a metal wiring on a substrate, and the lowermost layer of the metal wiring is TiN.
The upper surface of the TiN thin film has a {111} plane orientation, and the <112> axis of the TiN thin film is oriented in the main longitudinal direction of the wiring, and is roughly aligned.
It is perpendicular to the crystal axis representing the 1 ° plane. In a preferred embodiment, the metal wiring is a two-layer metal wiring in which an aluminum-based thin film is laminated on a TiN thin film, and the orientation axis of the upper surface of the aluminum-based thin film and the crystal axis indicating the main longitudinal direction of the wiring are the same as those of the underlying TiN thin film. It has become.

In the manufacturing method of the present invention, when forming a wiring laminated film in which another metal wiring is laminated on a TiN thin film,
The film is formed by causing the Ti particles to fly from the direction perpendicular to the substrate, irradiating the substrate surface with a nitrogen ion beam from a plurality of directions during the film formation, and setting the directions of the nitrogen ion beams to approximately 120 ° from each other. And the direction of each nitrogen ion beam is approximately 54.degree. To the normal direction of the substrate.
7 °, and the in-plane direction of the substrate is one of three directions of a bisector having an angle of approximately 120 ° between the nitrogen ion beams and the main longitudinal direction of the wiring formed on the substrate. Without
And a step of forming a TiN thin film by arranging them so as to form a thin film.

The wiring of the present invention will be described with reference to FIG.
(A) is a lower layer TiN thin film metal wiring (hereinafter referred to as TiN wiring) formed on a substrate. In the drawing, the x direction indicates the width direction of the wiring, the y direction indicates the longitudinal direction of the wiring, and the z direction indicates the film thickness direction of the wiring. In the semiconductor device, the longitudinal direction of the wiring is not limited to one direction, but in general, the first direction and the second direction orthogonal to the first direction are centered and are often deviated to either one direction. The main longitudinal direction in the present invention refers to an average direction occupied by the longitudinal direction y of the wiring as the whole semiconductor device.

The TiN wiring has two crystal grains 10 in the figure.
The grain boundary 103 has a so-called bamboo structure that exists across the width direction of the wiring. Each of the crystal grains 101 and 102 has a {111} plane orientation in which the (111) plane appears on the upper surface parallel to the substrate surface. Further, the crystal grains 101 and 102 have the <112> axis of the crystal axes representing the crystal structure roughly oriented in the longitudinal direction of the wiring. Here, the expressions {111} plane and <112> axis collectively represent equivalent planes and axes in the crystal structure. Therefore, FIG.
As shown in (A), the upper surface of the TiN crystal grain is changed to (11).
If expressed as 1) plane, the crystal axis in this direction is [111]
Axis, and the crystal axis in the longitudinal direction of the TiN wiring is [112]
Axis (or [112] axis) (the underline below the number should be placed above the number as shown in FIG. 1, but cannot be described, so it is underlined).

Next, the actual wiring is formed on the lower TiN wiring by A
This is a structure in which 1 alloy wiring is laminated, and is an Al alloy / TiN double layer metal wiring shown in FIG. this is,
This is a structure in which an Al alloy wiring is formed on the TiN wiring of (A) by inheriting the crystal structure of the underlying TiN wiring. That is, the crystal grains 104 and 105 constituting the Al alloy wiring (hereinafter referred to as Al wiring) are each oriented in the (111) plane (the [111] axis is oriented in the normal direction of the substrate), and are oriented in the longitudinal direction of the wiring. The <112> axis is roughly oriented. The grain boundary 106 between the crystal grains 104 and 105 is
Like the crystal grains 103 in the N wiring, they exist across the width direction of the wiring to form a bamboo structure.

The reason why the Al alloy / TiN double-layer metal wiring having such a structure improves the EM resistance and the SM resistance will be described. First, the reason for improving the EM resistance will be described. Al used in normal LSI formation process
The alloy / TiN two-layer metal wiring has a thickness of about 1 μm for an Al alloy thin film and about several hundred degrees for a TiN thin film, and the Al alloy thin film is much thicker. The resistivity of each material is about 2 μΩ · cm for the Al alloy, and about 100 μΩ · cm for TiN, and the resistivity of the Al alloy is sufficiently smaller. Thus, Al alloy / Ti
The electrical characteristics of the N double-layer metal wiring are determined by the Al alloy part.
The iN thin film is made of Al at the contact portion with the substrate silicon
It is used as a barrier metal for preventing diffusion of atoms. For this reason, it is important to study the prevention of wiring disconnection for the Al alloy.

Regarding the EM characteristics of the Al wiring, (11)
1) It is known that plane orientation is effective in improving EM resistance (and AK Sinha: Effect of Texture and Gr)
ainStructure on Electromigration in Al-0.5% Cu
See Thin Film, Thin Solid Film, 75, 253-259, 1981). Also, one crystal grain occupies the whole area of the wiring width,
It has also been reported that the so-called bamboo structure improves EM resistance (S. Vaidya, TT Shong and AK Sin
ha: Line-Width Dependence of Electromigration i
n Evaporated Al-0.5% Cu, Appl. Phys. Lett., 36,
464, 1980). However, these reports do not describe the direction of the crystal axis in the plane of each crystal grain.

In the present invention, attention is paid to the direction of the crystal axis to obtain higher EM resistance. That is, A
The two crystal grains adjacent to each other with the (111) -oriented crystal grains constituting the l-wiring are formed such that the crystal axes in the longitudinal direction of the wiring of the two adjacent crystal grains are controlled in substantially the same direction, and the crystal axis direction is <112. > Direction, higher EM resistance can be obtained. In order to show the reason, FIG. 2 shows a grain boundary portion of the Al wiring portion. The adjacent crystal grains 201 and 202 are formed such that their crystal axes [112] in the longitudinal direction of the wiring are shifted from each other by an angle θ. Considering the structure of the crystal grain boundary in such a case, when the grain boundary grows sufficiently by annealing or the like so as to form a bamboo structure, the crystal outline should be constituted by a crystal plane having the smallest surface energy. The crystal grows. Therefore, when adjacent crystal grains have substantially the same crystal axis direction in the plane as in the present invention, the crystal grain boundary is formed on the {111} plane having the smallest surface energy.

FIG. 3 shows a stereo projection of the (111) plane of the cubic crystal. From this stereo projection, the {111} plane is related in the <112> axis direction. Since the longitudinal direction is the [11 2 ] axis direction, the plane 203 representing the crystal grain boundary is configured around the (11 1 ) plane. In addition, as can be seen from the stereoscopic projection of FIG. 3, the (11 1 ) plane is orthogonal to the [11 2 ] axis, so that the crystal grain interface 203 also exists so as to be orthogonal to the long direction of the wiring. . Since the direction of the current in the Al wiring is the longitudinal direction, the crystal grain boundary 203 exists perpendicular to the current direction. In the case of such a relationship, the grain boundary diffusion of the atoms causing the cutting by EM is most unlikely to occur,
Therefore, high EM resistance is realized. The crystal axis orthogonal to the {111} plane is only the <112> axis, as is clear from the stereo projection of FIG. This is the reason why the wiring of the present invention in which the crystal axis in the longitudinal direction is the <112> axis exhibits high EM resistance.

Next, the reason why the wiring structure of the present invention improves the SM resistance will be described. Regarding the SM resistance of the Al wiring, the generation and growth of voids at the crystal grain boundaries of the wiring have been studied from the viewpoint of surface energy (for example, Nikkei Micro Devices, May 1990, 9th issue).
See pages 3-104). The cause of void generation in the Al wiring width, in other words, the force that causes the diffusion of Al atoms, includes the stress acting on the Al wiring from the outside and the Al
There is the grain boundary energy of the Al crystal grains forming the wiring. Among these, if the grain boundary energy of Al crystal grains can be reduced, the generation of voids at the grain boundaries is reduced. In the present invention, as shown in FIG. 2, since the adjacent Al crystal grains constituting the wiring have their [11 2 ] axes aligned substantially in the longitudinal direction of the wiring, the grain boundary energy at these grain boundaries is small. . Therefore, the structure is such that voids are hardly generated at the grain boundaries.

In the case where the crystal axes of adjacent crystal grains are substantially aligned as in the present invention, the energy of the grain boundary generated at the grain boundary can be calculated as follows. As shown in FIG. 4, when the crystal grains (1) and (2) are inclined by a small angle θ through the boundary, the grain boundary energy γ becomes γ = (Gb / 4π (1-ν)) θ (− logθ + logα) (1) Where G is the elastic modulus, ν is the Poisson's ratio,
b is the magnitude of the Burgess vector, and α is a constant (a value close to 1). The grain boundary energy γ is 0 when θ = 0, increases as θ increases, reaches a maximum value γm, and then decreases. The value of θm when indicating γm is substantially determined by the crystal form of the material, and in the case of a face-centered cubic material such as Al, θm is approximately 25 °. When γm is Al, G = 2.8 × 10 ¹¹ dyn / cm ² ν = 0.3 b = 4.049Å When α = 1, approximately γm = 480 erg / cm
^Get a value of ³ . When γm and θm are used in the above equation (1), γ / γm = (θ / θm) (1−log (θ / θm)) (2), and the change of γ / γm with respect to θ / θm The situation is as shown in FIG.

In the case of actually forming a wiring, it is preferable that the grain boundary energy is 0 or as small as possible. Even if energy exists at the grain boundary, it is desirable that the magnitude is 50% or less of the maximum value. , Θ / θm must be smaller than 0.2. Therefore, in the case of the present invention, the θm of Al is 2
Since it is 5 °, the range of θ is smaller than 5 ° according to the equation (2) or FIG. That is, in the present invention, the fact that the crystal axes are substantially aligned means that the deviation of the crystal axes is smaller than 5 °. As described above, the reason why the present invention has SM resistance and the range of θ at which such an effect is obtained are shown.

In the present invention, a TiN layer, an Al alloy / Ti
The N2 layer metal wiring defines only the crystal axis when used as a wiring, and has a wiring width, a film thickness, a layer configuration including a base or a protective film when forming the wiring, its material, and the wiring material. It does not specify various constants such as the degree of alloying, impurities, and resistivity. Materials and design values of Al-based wirings currently used can be used. Examples of the present invention will be described later, but it goes without saying that only the manufacturing method shown therein does not define the present invention. Various methods of producing TiN and Al films can be used to form the interconnects of the present invention.

The Al wiring in which the direction of the in-plane crystal axis is also controlled is formed by controlling the in-plane crystal axis of the underlying TiN thin film in the Al alloy / TiN two-layer metal wiring. You. In the Al alloy / TiN two-layer structure, the upper Al alloy thin film has a property of being easily formed by inheriting the crystallinity of the lower TiN thin film (see, for example, Spring 1990 1990 Preliminary Collection 28P-ZA-13). The control of the crystal growth direction of the TiN thin film is performed as follows. T
It is known that when an iN thin film is formed, the orientation of the TiN thin film changes when the film being formed is irradiated with an ion beam. Specifically, in the formation of TiN, when the supply of Ti atoms is performed by vacuum deposition of Ti using an electron beam and the supply of N atoms is used as an ion beam to form a TiN thin film on a substrate, the TiN thin film is formed by an N ion beam. Growing so that the (100) plane faces in the direction of incidence (Nuclear In
instruments and Methods in Physics Research, B39 (198
9) See pages 158-161).

Based on this result, the present invention has developed a technique for further controlling the direction of the in-plane crystal axis.
Referring again to the stereo projection of FIG. 3, the TiN thin film of the present invention has a {111} plane on the surface and the <112> axis oriented in the longitudinal direction of the wiring. the (111) plane, a longitudinal and [2 11] axis. When the relationship between the surface (111) plane and {100} at this time is viewed in a stereo projection, (100) plane has (10
0), (010), and (001), which are 120 ° from each other with respect to the crystal axis representing the (111) plane.
At an angle of °. Further, (001) is plane and (010) plane in a position symmetrical with respect to [211] axis, the angle is 60 °. (111) face and (10
0), (010), and (001) form an angle of 5
The expression of 4.7 ° is a stereo projection or an expression representing the angle between two planes in a cubic system.

(Equation 1) I understand more.

As described above, the cubic crystal (precisely, face-centered cubic) representing TiN has a crystal form of {111}.
There is a strict angular relationship between the plane, the {100} plane, and the <112> axis. That is, when a TiN thin film is formed on a substrate while irradiating nitrogen ions so as to maintain this angular relationship, a TiN thin film having a {111} plane orientation and the longitudinal direction of the wiring being the <112> axis can be formed.

FIG. 6 shows a conceptual diagram of the formation of such a TiN thin film. In the figure, reference numerals 601, 602 and 603 represent nitrogen ion beams. Reference numeral 604 denotes a substrate on which the TiN thin film is formed or a TiN thin film including the substrate, 605 denotes a source of titanium atoms, and 606 denotes the supplied titanium atoms. In the figure, θ _{1 to} θ ₄ represent angles formed by the three nitrogen ion beams 601, 602, and 603,
δ _{1 to} δ ₃ are three nitrogen ion beams 601, 602, 6
03 represents an angle formed with the normal direction of the substrate 604.
As described above, when setting θ ₁ = θ ₂ = 60 ° θ ₃ = θ ₄ (= 2θ ₁ ) = 120 ° δ ₁ = δ ₂ = δ ₃ = 54.7 °, the TiN thin film formed will $ 11
A 1｝ plane appears, and a TiN thin film is formed such that the direction indicated by the arrow in the drawing is the [112] axis.

[0023]

An embodiment of the manufacturing method will be described. As a substrate, a BPSG film is 1.0 μm on a (100) plane Si wafer.
Formed to a thickness of. Ti with controlled orientation
The N thin film was formed by a vacuum film forming apparatus equipped with three bucket type ion sources for generating an ion beam of nitrogen and an electron beam evaporation source of titanium. The nitrogen ion beams emitted from the three ion sources were arranged so as to satisfy the angle conditions described above. That is, three nitrogen ion beams 601,
Reference numerals 602 and 603 form an angle of 120 ° with each other, and the respective ion beams are arranged so as to enter the substrate 604 at an angle of 54.7 ° in the normal direction of the substrate. Further, the substrate 604 was arranged on the substrate holder such that the main longitudinal direction of the formed wiring coincided with the bisector of the angle formed by the nitrogen ion beams 601 and 602. The energy of each nitrogen ion beam is 1000 eV. Titanium vapor was generated by evaporating 3N pure Ti using an electron beam evaporation source. By adjusting the deposition rate from the electron beam evaporation source and the ion currents of the three nitrogen ion sources, the transport ratio Ti / N to the substrate was set to approximately 1. Membrane formation with back pressure of 5
The film was evacuated to a high vacuum of × 10 ⁻⁷ Torr or less, and the pressure during film formation was set to 3 × 10 ⁻⁵ Torr. No substrate heating was performed.

The formed thin film has a thickness of about 1000Å
And a TiN film whose surface had a {111} plane orientation by X-ray diffraction. Further, when the state of the crystal in the plane of the TiN thin film was examined by RHEED (high-speed electron diffraction method), a spot-like RHEED pattern was obtained.
It was found that the TiN thin film had uniform in-plane crystal axes over a wide range. Further, when the direction of the <112> axis was examined in the substrate plane from the RHEED pattern, it was found that the angle coincided with the bisector of the angle formed by the nitrogen ion beams 601 and 602. Thus, the TiN thin film of the present invention was formed.

Further, an Al metal thin film was formed on the TiN thin film by MOCVD. That is, dimethyl aluminum halide (CH ₃ ) ₂ AlH was used as a raw material for Al. Hydrogen was used as a carrier gas for the raw material, the film formation pressure was 2.0 Torr, and the partial pressure of the raw material gas at this time was 5 × 10 ⁻³ T
orr, and the film formation temperature was 270 ° C. The thickness of the obtained Al thin film on the TiN film was 1.2 μm. It was confirmed by X-ray diffraction that the surface was oriented to the {111} plane, and the crystal axis was changed to the base Ti
It turned out to be almost the same as the N thin film. In this way, a two-layer metal wiring layer was formed in which the lower layer was a TiN thin film and the upper layer was an Al thin film.

[0026]

According to the wiring of the present invention, the lower layer is a TiN thin film, and the upper surface of the TiN thin film has a {111} plane orientation;
The <112> axis of the TiN thin film is oriented in the main longitudinal direction of the wiring , is approximately aligned, and is formed so as to be orthogonal to the crystal axis representing the {111} plane. The Al wiring has a crystal structure in which the EM resistance and the SM resistance of the Al wiring are maximized in terms of material mechanics. According to the manufacturing method of the present invention, when forming a TiN thin film, Ti particles fly from a direction perpendicular to the substrate to form a film, and a nitrogen ion beam is applied from a plurality of specific directions to the surface of the substrate during the film formation. , It is possible to form a TiN thin film that has a crystal structure in which the EM resistance and the SM resistance of the Al wiring formed thereon have the highest mechanical strength.

[Brief description of the drawings]

FIG. 1 is a diagram schematically showing a wiring of the present invention, and FIG.
Denotes a lower TiN layer, and (B) denotes an Al / TiN two-layer metal wiring.

FIG. 2 is a schematic perspective view showing a boundary portion of an Al alloy wiring portion.

FIG. 3 is a stereo projection of a (111) plane of a cubic crystal.

FIG. 4 is a diagram schematically showing a boundary between two crystal grains having an inclination θ.

FIG. 5 is a diagram showing the relationship between the inclination of a crystal grain and the grain boundary energy.

6A and 6B are diagrams showing the formation of a TiN film in one embodiment, in which FIG. 6A is a schematic bottom view showing a nitrogen ion beam in three directions, and FIG. 6B is a schematic front view showing the formation of a TiN film.

[Explanation of symbols]

 101,102 TiN crystal grains 104,105 Al crystal grains 103,106,203 Grain boundaries 601,602,603 Nitrogen ion beam 604 Substrate 606 Titanium particles

────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-4-256313 (JP, A) JP-A-3-262127 (JP, A) JP-A-5-193916 (JP, A) JP-A-1- 215966 (JP, A) (58) Field surveyed (Int. Cl. ⁷ , DB name) H01L 21/3205 H01L 21/321 H01L 21/3213 H01L 21/768

Claims (3)

(57) [Claims] A metal wiring is provided on a substrate, a lowermost layer of the metal wiring is a TiN thin film, an upper surface of the TiN thin film has a {111} plane orientation, and a <11
2> The axis is oriented in the main longitudinal direction of the wiring and roughly aligned
And a crystal axis orthogonal to a crystal axis representing a {111} plane. 2. The metal wiring is a two-layer metal wiring in which an aluminum-based thin film is laminated on a TiN thin film, and an orientation plane on the upper surface of the aluminum-based thin film and a crystal axis indicating a main longitudinal direction of the wiring are formed on the base TiN thin film. 2. The semiconductor device according to claim 1, which is the same. 3. When forming a wiring laminated film in which another metal wiring is laminated on a TiN thin film, a film is formed by causing Ti particles to fly from a direction perpendicular to a substrate, and a plurality of particles are formed during the film formation. The substrate surface is irradiated with a nitrogen ion beam from the direction of
An angle of 0 °, the direction of each nitrogen ion beam is set to be approximately 54.7 ° with respect to the normal direction of the substrate, and the direction in the plane of the substrate is formed on the substrate. A step of forming a TiN thin film by arranging the main longitudinal direction so as to face any one of three directions of a bisector having an angle of about 120 ° between the nitrogen ion beams. Device manufacturing method.