JPH06120220A - Wiring for semiconductor device and its forming method - Google Patents

Abstract

PURPOSE:To obtain wiring for a semiconductor device and its forming method wherein stress migration can be effectively restrained. CONSTITUTION:Wiring for a semiconductor device consists of a first layer 30 composed of metal or metal compound and a second layer 32 composed of aluminum-lithium based allay. The forming method of the wiring for a semiconductor device which wiring is composed of aluminum-lithium based alloy is constituted of a process for forming an aluminum layer or an aluminum alloy layer, and a process for forming an aluminum-lithium based allay layer by implanting lithium ions in the aluminum layer or the aluminum alloy layer.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor device wiring and a method for forming the same.

[0002]

2. Description of the Related Art With the high integration of semiconductor devices, dimensional rules in the manufacture of semiconductor devices are becoming finer, and wiring is required to have very high reliability. Usually, such a wiring for a semiconductor device includes aluminum-silicon (Al-S).
i) Alloys are used.

One of the problems with aluminum-based wiring is electromigration. Electromigration is a phenomenon in which, when a high-density current flows through an aluminum-based wiring, aluminum atoms move along with the flow of electrons, and the wiring eventually breaks. As a measure against electromigration, increasing the grain size of aluminum crystal grains or making the wiring a bamboo structure can be mentioned.

Further, stress migration has become a serious problem in recent years as a factor that lowers the reliability of wiring. Stress migration is a phenomenon in which a stress of an insulating film covering an aluminum wiring is applied to the aluminum wiring, diffusion of aluminum atoms occurs, and finally a disconnection occurs. That is, voids are generated in the aluminum crystal grains due to the stress received from the insulating film. Due to the movement of the holes, the aluminum atoms move and the wiring is broken.

As a measure against stress migration,
The addition of copper to aluminum-silicon alloys is being considered. It is said that the addition of copper captures the vacancies, so that the vacancies do not move and stress migration can be prevented. However, Al-
Even when the wiring is formed using the Si—Cu alloy, it cannot be said that the prevention of the stress migration is sufficient.

As a measure against electromigration, a wiring made of a Li-containing Al-based alloy is disclosed in Japanese Patent Laid-Open No. 2-2.
It is known from Japanese Patent No. 32927. It is considered that the addition of Li to Al can effectively suppress electromigration for the following reasons. (A) The intermetallic compound Al ₃ Li precipitated at the Al grain boundary is
Inhibits the movement of Al atoms. (B) The intermetallic compound Al ₃ Li has excellent compatibility with the Al metal lattice, and the interface between the precipitate and the Al metal lattice has a new Al.
Does not serve as an atomic diffusion path. (C) Since Al ₃ Li precipitated at the Al grain boundary has a function of increasing the tensile strength of the alloy, it suppresses the deformation of the wiring such as the generation of holes and the growth of protrusions due to electromigration.

[0007]

The use of aluminum-lithium alloy as the wiring material of the semiconductor device is effective from the viewpoint of preventing electromigration. However, JP-A-2-232927
In the wiring made of the Li-containing Al-based alloy disclosed in Japanese Patent Laid-Open Publication No. 2001-242242, the suppression of stress migration cannot be said to be sufficient.

In the process of manufacturing a semiconductor device, after forming wiring, a passivation film is deposited on the wiring. Then, heat treatment at about 400 ° C. is applied. At that time, the heat shrinkage of the passivation film causes defects (voids) in the wiring, resulting in stress migration.

Generally, it is considered that the higher the specific rigidity (= Young's modulus / specific gravity) of the wiring, the less likely it is that voids will occur in the wiring due to thermal contraction of the passivation film. Al-1
The Young's modulus of% Si or Al-1% Si-0.5% Cu is about 6.5 × 10 ¹⁰ Pa. By adding Li to Al, the Young's modulus of the Al-Li alloy is increased as shown in FIG. In addition, in FIG.
The change in specific gravity of the Al-metal alloy when added to 1 is shown. From FIG. 5, by adding Li to Al, A
The specific gravity of the 1-Li alloy is remarkably reduced. Li to Al
By increasing the addition amount, the Young's modulus of the Al-Li alloy becomes high and the specific gravity becomes small.
The specific rigidity of the alloy is high.

As described above, since the Al--Li alloy has a high specific rigidity (= Young's modulus / specific gravity), it is considered that voids are less likely to occur as compared with ordinary Al--Si, etc., but no voids occur at all. However, even if the Al—Li alloy is used for the wiring of the semiconductor device, the suppression of stress migration cannot be said to be sufficient.

Therefore, it is an object of the present invention to provide a semiconductor device wiring capable of effectively suppressing stress migration and a method of forming the same.

[0012]

The above object is a wiring used in a semiconductor device, which is composed of a first layer made of a metal or a metal compound and a second layer made of an aluminum-lithium alloy. This can be achieved by the wiring for a semiconductor device of the present invention.

In a preferred embodiment of the wiring for a semiconductor device of the present invention, the lithium content of the aluminum-lithium alloy is 0.1% by weight to 4% by weight. Alternatively, germanium is contained in the aluminum-lithium alloy. In this case, in a more preferred embodiment, the germanium content is 0.1% by weight or more and 5% by weight or less.

Alternatively, the above-mentioned object is aluminum-
A method for forming a wiring for a semiconductor device made of a lithium-based alloy, comprising the steps of (a) forming an aluminum layer or an aluminum alloy layer, and (b) ion-implanting lithium ions into the layer.
It can be achieved by the method for forming a wiring for a semiconductor device of the present invention, which comprises the step of forming a lithium alloy layer.

[0015]

In the semiconductor device wiring of the present invention, the second layer made of the Al--Li alloy having a high specific rigidity is provided. Therefore, even if the passivation film is deposited on the wiring after the wiring is formed and then the heat treatment of about 400 ° C. is applied to the passivation film, the passivation film is thermally contracted. However, although stress migration is unlikely to occur, the prevention of stress migration is not completely achieved only by the second layer.

In the semiconductor device wiring of the present invention, the first layer made of a metal or a metal compound is formed below the second layer. The compressive stress of the passivation film is applied to the second layer, but by forming the first layer, tensile stress acts on the second layer from the first layer. As a result, the stress applied to the second layer is relaxed, voids do not occur at all, and stress migration can be prevented extremely effectively.

Li has poor workability, and if a large amount of Li is added to Al, depending on the etching process, Al-L
A Li residue may remain during the etching of the i-based alloy. In this case, the wiring made of Al-Li alloy is electrically short-circuited. FIG. 6 is a diagram in which the yield reduction of the semiconductor device caused by the short circuit in the wiring made of the Al—Li alloy is plotted against the Li content rate. From FIG.
When the Li content of the l-Li alloy is 5% by weight or more,
The residue of Li may cause a short circuit of the wiring, which may reduce the yield of the semiconductor device.

Therefore, considering the yield of the semiconductor device, the preferable range of the Li content of the Al--Li alloy is:
It is 0.1% by weight or more and 4% by weight or less.

The melting point of the Al--Si alloy is the melting point of Al (660 ° C.) as the amount of Si added to Al increases.
It drops more rapidly. The melting point of the Al-Ge alloy is
As the amount of Ge added to Al increases, it decreases more rapidly than when Si is added. In the high temperature sputtering method of aluminum alloy, the aluminum alloy is sputtered while the semiconductor element as the base is heated to a predetermined temperature. As a result, the wiring material made of aluminum alloy deposited on the base becomes fluid,
The deposition state of the wiring material on the base is improved. As a result, step coverage is improved.

Generally, in the high temperature sputtering method using pure aluminum, it is necessary to heat the underlying semiconductor element to about 550 ° C. or higher. When the heating temperature is increased in this way, the chamber of the sputtering apparatus becomes high in temperature, gas is desorbed from the side wall of the chamber, impurities such as oxygen enter into sputtered Al, and cloudiness occurs in the formed wiring, There is a problem that the surface of the wiring becomes rough. That is, many hillocks or the like are generated in the wiring, and a short circuit occurs between the minute wirings. Therefore, it is preferable that the temperature at which the wiring material is made to flow is as low as possible.

When Al-1% Si is used as the wiring material, the wiring material can be reflowed by heating the base to 400 to 500 ° C. Furthermore, Al-5
In% Ge, the reflow of the wiring material becomes possible by heating the underlayer to 350 ° C (Ref., "Al-
Ge REFLOW SPUTTERING FOR SUBMICRON-CONTACT-HOLE FI
LLING ", K. Kikuta, ET AL., 1991 VLSI MULTILEVEL IN
TERCONNECTION CONFERENCE Proceeding (June 11-12, 1
991), pp. 163/169).

By the way, if Li is added to Al, Al
The melting point of the -Li alloy is slightly lower than that of pure Al. However, when the Li content is 4% by weight or less, the melting point is not significantly reduced. Therefore, when performing high temperature sputtering, reflow of a wiring material made of an Al-Li alloy is not possible unless the temperature of the base is raised to the same temperature as pure Al (about 550 ° C).

Therefore, when the high temperature sputtering method is adopted, it is desirable that the aluminum-lithium alloy contains germanium. In this case, the germanium content is more preferably 0.1% by weight or more and 5% by weight or less.

[0024]

EXAMPLES The present invention will be described below based on examples.
The steps of forming the semiconductor device wiring of the present invention based on the conventional method will be described in Examples 1 to 4, and in Example 5, the semiconductor device wiring of the present invention will be newly formed. The process of forming the film based on the method will be described.

(Example 1) Example 1 is an example in which the wiring of the present invention is applied to the manufacture of a MOS transistor. Less than,
The process of forming the semiconductor device wiring of the present invention will be described based on the process of manufacturing a MOS transistor. In Example 1, the first layer consists of Ti. The second layer is made of an Al-Li alloy (Al-0.5% Li) and is formed by a high temperature sputtering method.

[Step-100] First, an element isolation region 12 and a gate region 14 are formed on a semiconductor substrate 10 by a conventional method, and ion implantation is performed to form an LDD structure ((A in FIG. 1). )reference).

[Step-110] Next, a thickness of 250 is applied to the entire surface.
to form a SiO ₂ film of nm thickness. The conditions for forming the SiO ₂ film are
For example, it can be as follows. Gas used: SiH ₄ / O ₂ / N ₂ = 250/250/1
00 sccm Substrate temperature: 420 ° C. Pressure: 13.3 Pa Then, the entire surface is etched back to form the sidewall 16 in the gate region 14. The conditions of etch back,
For example, it can be as follows. Gas used: C ₄ F ₈ = 50 sccm RF power: 1200 W Pressure: 2 Pa After that, in order to form the source / drain regions 18,
Ion implantation of impurities is performed. Conditions for ion implantation are, for example, N channel: As ⁺ 20 KeV 5 × 10 ¹⁵ /
cm ² P channel: BF ₂ ⁺ 20 KeV 3 × 10 ¹⁵ /
It can be cm ² (see FIG. 1B).

[Step-120] Thereafter, for example, TEO
The interlayer insulating layer 20 having a film thickness of 400 nm and made of a CVD oxide film using S is formed under the following conditions, for example. Gas used: TEOS = 50 sccm Temperature: 720 ° C Pressure: 40 Pa Further, a BPSG film 22 having a thickness of 500 nm is formed on the interlayer insulating layer 20 under the following conditions ((C) in FIG. 1).
reference). Gas used: SiH ₄ / PH ₃ / B ₂ H ₆ / O ₂ / N ₂ = 80
/ 7/7/1000 / 32000sccm Temperature: 400 ° C Pressure: 1.0 × 10 ⁵ Pa

[Step-130] Next, after patterning the resist, an opening 24 is formed in the interlayer insulating layer 20 and the BPSG film 22 by dry etching. The conditions for dry etching can be set as follows, for example. Gas used: C ₄ F ₈ = 50 sccm RF power: 1200 W Pressure: 2 Pa

[Step-140] Next, the semiconductor device wiring of the present invention is formed. That is, first, metal, specifically T
The first layer 30 made of i is formed by the sputtering method (see FIG. 2A). The film forming conditions of the first layer 30 made of Ti can be set as follows, for example. Power: 4 kW Film formation temperature: 150 ° C. Process gas: Ar = 100 sccm Set film thickness: 70 nm As a result, the first layer 30 is formed on the BPSG film 22 and in the opening 24.

[Step-150] Next, Al-Li (0.
A second layer 32 composed of 5%) is formed on the first layer 30 by a sputtering method (see FIG. 2B). An Al-Li alloy is used as the target. Second layer 32
The film forming conditions of can be set as follows, for example. Power: 22.5 kW Film forming temperature: 550 ° C. Process gas: Ar = 40 sccm Set film thickness: 500 nm After that, resist patterning and dry etching are performed to form wirings composed of a second layer and a first layer.
The conditions for dry etching can be set as follows, for example. Gas used: BCl ₃ / Cl ₂ = 60/90 sccm Microwave power: 1000W RF power: 50W Pressure: 0.016Pa

[Step-160] Further, the insulating film 4 is formed on the wiring.
0 is formed (see FIG. 2C). Therefore, first, a 100 nm-thickness SiN layer is formed under the following conditions, for example. Gas used: SiH ₄ / NH ₃ / N ₂ = 180/500 /
720 sccm temperature: 250 ° C. pressure: 2.5 Pa Furthermore, a PSG layer having a film thickness of 500 nm is further formed thereon, for example,
The film is formed under the following conditions. Gas used: SiH ₄ / PH ₃ / O ₂ / N ₂ = 80/7/1
000 / 32000sccm Temperature: 390 ° C Pressure: 1.0 × 10 ⁵ Pa

(Embodiment 2) Embodiment 2 is a modification of Embodiment 1. The second embodiment is different from the first embodiment in that the second layer 32 is
Of Al-0.5% Li-5% Ge, the second layer 3
2 is formed by a high temperature sputtering method at a lower temperature.

[Step-200] This step can be the same as [Step-100] to [Step-140] of Example 1. Through the above steps, the first layer 30 made of Ti is formed on the BPSG film 22 and in the opening 24.

[Step-210] Next, Al-0.5% L
A second layer 32 made of i-5% Ge is formed on the first layer by a sputtering method (see FIG. 2B). An Al-Li-Ge alloy is used as the target. Second
The film forming conditions of the layer 32 can be set as follows, for example. Power: 22.5 kW Film forming temperature: 400 ° C. Process gas: Ar = 40 sccm Set film thickness: 500 nm In Example 1, the film forming temperature is 550 ° C. In the second embodiment, the film forming temperature can be 400 ° C.
After that, resist patterning and dry etching are performed to form wirings composed of the second layer and the first layer.
This step can be performed in the same manner as in [Step-150] of Example 1.

[Step-220] This step of forming an insulating layer on the wiring can be the same as [Step-160] of the first embodiment.

(Embodiment 3) Embodiment 3 is also a modification of Embodiment 1. The third embodiment is different from the first embodiment in that a tungsten plug is embedded in the opening 24, and the first layer 30 and the second layer 32 are provided on the tungsten plug and the BPSG film 22.
There is a point to form on. Also, Al-1% Si-0.5
A second layer made of% Li-5% Ge is formed by a normal sputtering method.

[Step-300] This step can be the same as [Step-100] to [Step-130] of the first embodiment. Through the above steps, the interlayer insulating layer 20 and the BPS
An opening 24 is formed in the G film 22.

[Step-310] Next, the BPSG film 22
Tungsten is deposited on the top and in the opening 24 by the CVD method. The deposition conditions can be as follows, for example. Gas used: WF ₆ / H ₂ = 95/550 sccm Temperature: 450 ° C Pressure: 1.1 × 10 ⁴ Pa Film thickness: 400 nm Then, etch back is performed under the following conditions, for example, BP
Tungsten on the SG film 22 is removed, and the tungsten plug 26 is left only in the opening 24 (see FIG. 3A). Gas used: SF ₆ = 50 sccm Microwave power: 850W RF power: 150W Pressure: 1.33Pa

[Step-320] The steps of forming the first layer 30, forming the second layer 32, forming the wiring, and forming the insulating film 40 are the same as those in Example 1 from [Step-140] to [Step-140]. Process-1
60]. However, [Step-14
0], the first layer 30 made of Ti is formed on the tungsten plug 26 and the BPSG film 22 (see FIG. 3B). In addition, in [Step-150], Al-1% Si-0.5% Li- is formed on the first layer.
A second layer 32 made of 5% Ge is formed at a film forming temperature of 150 ° C. (see FIG. 3C).

(Embodiment 4) Embodiment 4 is also a modification of Embodiment 1. The fourth embodiment differs from the first embodiment in that the second layer 32 is
A so-called co-sputtering method is used for forming the film.

[Step-400] This step can be the same as [Step-100] to [Step-140] of Example 1. Through the above steps, the first layer 30 made of Ti is formed on the BPSG film 22 and in the opening 24.

[Step-410] Next, a second layer 32 made of an Al--Li alloy is formed on the first layer 30 by a so-called co-sputtering method. That is, Al, Al-Si
Alternatively, a target made of Al-Ge-Si (hereinafter,
A target composed of Al-based target) and Li is installed in the chamber of the same sputtering apparatus. Then, both targets are simultaneously sputtered to form the second layer 32 made of an Al-Li alloy. Sputtering conditions for Al-based target Power: 22.5 kW Film forming temperature: 150 ° C Process gas: Ar = 40 sccm Set film thickness: 500 nm Sputtering conditions for Li target Power: 2 kW Film forming temperature: 150 ° C Process gas: Ar = 100 sccm Set film thickness: 10 nm After that, resist patterning and dry etching are performed to form wirings composed of the second layer 32 and the first layer 30. The dry etching conditions can be the same as those in [Step-150] of the first embodiment.

[Step-420] This step of forming an insulating layer on the wiring can be the same as [Step-160] of the first embodiment.

(Embodiment 5) Embodiment 5 relates to a method for forming a semiconductor device wiring according to the present invention. That is, the method includes: (a) forming an aluminum layer or an aluminum alloy layer; and (b) forming an aluminum-lithium alloy layer by ion-implanting lithium ions into the layer. To do.

[Step-500] This step can be the same as [Step-100] to [Step-140] of the first embodiment. Through the above steps, the first layer 30 made of Ti is formed on the BPSG film 22 and in the opening 24.

[Step-510] Next, on the first layer 30 made of Ti, an aluminum layer, an aluminum alloy layer made of Al-Si, or Al-Si-Ge (hereinafter referred to as an aluminum-based material) is formed by a sputtering method. (Also referred to as a layer). Power: 22.5 kW Film forming temperature: 150 ° C. Process gas: Ar = 40 sccm Film thickness: 500 nm Incidentally, the aluminum-based layer can be formed by a high temperature sputtering method.

[Step-520] Next, by adding Li ⁺ to the aluminum-based layer by an ion implantation method, Al
-Form a Li-based alloy layer. The conditions of ion implantation can be set as follows, for example. Ion source: LiCl is heated to 614 ° C. or higher for sublimation Acceleration voltage: 50 keV Dose amount: 1 × 10 ¹⁶ / cm ² or more After that, resist patterning and dry etching are performed to remove Al—Li alloy layer and Ti layer. Forming wiring. The dry etching conditions are, for example, those of Example 1.
[Step-150] of the above.

[Step-530] Further, the insulating film 4 is formed on the wiring.
Form 0. This step corresponds to [Step-16 of Example 1].
0].

The present invention has been described above based on the preferred embodiments, but the present invention is not limited to these embodiments. The first layer, the second layer, or the aluminum-based layer can be formed by a vapor deposition method, a chemical vapor deposition method, or an electron beam vapor deposition method as well as the sputtering method.
The first layer is not limited to Ti, but other metals or metal compounds,
For example, W, Mo, Cu, TiON, TiN, WN, T
It can also be composed of iSi ₂ , WSi ₂ , CoSi ₂ , NiSi ₂ , and NiSi. As the second layer, Al-1%
Si-1% Li, Al-1% Li-5% Ge, Al-1
% Si-1% Li-5% Ge etc. can be illustrated.

[0051]

According to the wiring for a semiconductor device of the present invention,
Since the Al-Li alloy is used as the wiring material, not only the electromigration resistance is improved, but also
The specific rigidity is higher than that of a normal Al-Si alloy, and the stress migration resistance is improved.

Further, since the first layer made of Ti or the like is formed under the second layer made of Al--Li alloy,
Even under the influence of the thermal stress of the passivation film (insulating film) formed on the wiring, voids do not occur in the wiring, and stress migration can be suppressed very effectively.

In a preferred embodiment of the semiconductor device wiring of the present invention, the Li content of the Al--Li alloy is 4% by weight.
Since it is the following, the workability of the second layer made of the Al-Li alloy does not deteriorate as compared with the conventional Al-Si alloy,
A conventional dry etching process can be used. Therefore, the manufacturing cost of the semiconductor device does not increase, the reproducibility of the manufacturing process of the semiconductor device is good, and the manufacturing yield of the finally manufactured semiconductor device does not decrease.

In a preferred embodiment of the wiring for a semiconductor device of the present invention, since Ge is contained in the Al-Li alloy, the reflow temperature of the second layer in the high temperature sputtering method is compared with that of Al. It is possible to lower the temperature by 50 to 200 ° C.

Li has a high reactivity and therefore a high hygroscopicity. When Li is formed by the sputtering method, the target must be stored in a vacuum container or the like so that the target made of Li or an alloy containing Li does not come into contact with the atmosphere during maintenance of the sputtering apparatus, which makes maintenance of the target complicated. Becomes Further, when the vacuum container leaks, the target absorbs moisture, and as a result, the target cannot be used.

According to the method for forming a wiring for a semiconductor device of the present invention, LiCl is ion-implanted into the aluminum-based layer by an ion implantation method. Since LiCl is not as reactive as Li alone, the above-mentioned problems do not occur.

[Brief description of drawings]

FIG. 1 is a diagram for explaining a process of forming wiring for a semiconductor device according to a first embodiment of the present invention.

FIG. 2 is a diagram for explaining the process of forming the wiring for the semiconductor device in the first embodiment of the present invention, following FIG.

FIG. 3 is a diagram for explaining a process of forming a semiconductor device wiring according to a third embodiment of the present invention.

FIG. 4 is a diagram showing the relationship between the amount of Li added to Al and the Young's modulus of an Al—Li alloy.

FIG. 5: Al by adding various metals into Al
FIG. 6 is a diagram showing a change in specific gravity of a metal alloy.

FIG. 6 is a diagram showing the relationship between the yield of semiconductor devices and the Li content.

[Explanation of symbols]

 10 semiconductor substrate 12 element isolation region 14 gate region 16 sidewall 18 source / drain region 20 interlayer insulating layer 22 BPSG film 24 opening 26 tungsten plug 30 first layer 32 second layer 40 insulating film

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁵ Identification code Internal reference number FI Technical indication location 7514-4M H01L 21/88 N 7377-4M 29/78 301 X

Claims (5)

[Claims] 1. A wiring used for a semiconductor device, comprising a first layer made of a metal or a metal compound and a second layer made of an aluminum-lithium alloy. Wiring. 2. In the aluminum-lithium alloy,
The wiring for a semiconductor device according to claim 1, wherein the wiring contains lithium in an amount of 0.1% by weight to 4% by weight. 3. The wiring for a semiconductor device according to claim 1, wherein the aluminum-lithium alloy contains germanium. 4. The wiring for a semiconductor device according to claim 3, wherein the germanium content is 0.1% by weight or more and 5% by weight or less. 5. A method for forming a wiring for a semiconductor device made of an aluminum-lithium alloy, comprising: (a) a step of forming an aluminum layer or an aluminum alloy layer; and (b) ion implantation of lithium ions into the layer. And a step of forming an aluminum-lithium alloy layer, thereby forming a wiring for a semiconductor device.