JPH05102148A - Semiconductor device - Google Patents

Abstract

PURPOSE:To provide a semiconductor device having such a wiring structure that can prevent the diffusion of Ag atoms contained in Ag-metal wiring into an interlayer insulating film. CONSTITUTION:After forming an insulating film 12 on a silicon substrate 11 and boring a contact hole 13 through the film 12, a Ti film 14, TiN film 15 (diffusion preventing layer) 14, and Ag film 16 are successively formed on the film 12 by a DC magnetron sputtering method. Then, in order to form a contact wiring section and prescribed wiring section, the films 16, 15, and 14 are patterned. On these wiring sections, a silicon nitride film 18 is formed as a protective film by a plasma CVD method. Since the film 18 acts to inhibit the diffusion of Ag atoms, a highly reliable semiconductor device can be obtained.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention
The present invention relates to a semiconductor device including metal wiring.

[0002]

2. Description of the Related Art In recent years,
With the high integration of LSI, the electrode wiring tends to be miniaturized.
Aluminum (Al) or A as the electrode wiring material
Although Al alloys such as 1-Si and Al-Si-Cu are used, it is becoming difficult to ensure reliability against electromigration and stress migration as the line width decreases. If the Al alloy wiring that has been used up to now becomes wiring of 0.3 μm or less,
From the above problems, it is considered to be a limit in securing reliability. Therefore, introduction of a refractory metal such as W or Mo having high electromigration resistance as a wiring material replacing Al is being studied. However, its electric resistance is as high as twice as high as that of Al in bulk, and further higher in a thin film, which is disadvantageous in increasing the speed of the device.

In the next generation and VLSI, materials having high resistance to electromigration and stress migration and low resistance are required. Under such circumstances, Ag was considered to be suitable as a wiring material replacing Al. Ag is a material with the lowest resistance among metals (resistivity: 1.63 μΩcm), and is optimal for speeding up the device. Further, regarding electromigration, the Ag wiring has a longer average life time (MTF: Meantime to fa) than the Al-1% Si wiring.
ilure) is longer than 2 orders.

[0004] One reason why the Ag wiring with high electromigration resistance in the low resistance was not used in the LSI wiring material far, insulation such as SiO _2, PSG by heat treatment performed in a wafer process This is because Ag easily diffuses in the film.
When Ag diffuses into the insulating film layer, a minute leak current is generated between adjacent Ag wirings, and Ag atoms pass through the insulating film to form S atoms.
There is a problem that it diffuses into the i-substrate and deteriorates the device characteristics. In order to solve this problem, a wiring structure that does not cause diffusion of Ag into the insulating film is required.

The present invention was devised in view of these problems, and an object thereof is to obtain a semiconductor device having good element characteristics without diffusion from an Ag metal-based wiring to an interlayer insulating film. It is a thing.

[0006]

Therefore, according to the present invention, Ag selectively formed on a semiconductor substrate via a diffusion preventive layer.
In a semiconductor device having a metal-based wiring, forming a protective layer made of silicon nitride on the upper surface and the side surface of the Ag metal-based wiring is a means for solving the problem.

[0007]

The diffusion prevention layer prevents Ag atoms in the Ag metal-based wiring from diffusing to the substrate side and entering the p, n-type regions, for example. The protective layer formed of silicon nitride is Ag
It prevents Ag atoms from diffusing from the top and side surfaces of the metal-based wiring.

Since Ag has good oxidation resistance and high electrical conductivity, it is suitable as a wiring material for VLSI, and the electromigration characteristics of Ag are predicted from the melting point as follows.

(Electromigration Resistance of Ag Wiring) Generally, the life time due to electromigration is expressed by the following formula.

T ₅₀ = A · exp (Q _e / KT) (1) where Q _e is the activation energy for electromigration, K is the Boltzmann constant, and T is the absolute temperature.

On the other hand, in a thin film, Q _e is considered to be almost equal to the activation energy Q _b of the process because the material transfer is governed by grain boundary diffusion. The activation energy of diffusion has a correlation with the melting point T _{m of the} substance.
That is, Q _e ≈Q ₆ ≈7.4 × 10 ⁻⁴ T _m (2) Formulas (1) and (2) are combined to obtain t ₅₀ of substances 1 and 2.
The ratio of

[0012]

[Equation 1]

If (t ₅₀ ) ₁ is known from the equation (3), the electromigration characteristics of the substance 2 can be predicted from the melting point.

Predicting the MTF of the Ag wiring by using the MTF of the Al-1% Si wiring, which has already been obtained, is as follows.

Results of electromigration test of Al-1% wiring Melting point: 923 (K) MTF: 100 hours Test temperature: 250 ° C. Current density: 1 × 10 ⁶ A / cm ² ○ Electromigration prediction of Ag wiring Melting point: 1234 (K)

[0016]

[Equation 2]

That is, it is expected that the lifetime of Ag wiring due to electromigration is longer than that of Al—Si wiring by two orders of magnitude or more.

As described above, the Ag wiring has excellent electromigration resistance and low resistance, but the problem is that Ag atoms easily diffuse into the insulating film such as SiO ₂ .PSG.

3 was reported by McBrayer et al. (JC McBrayeret. Al J. El.
microchem. Soc. Vol. 133 No. 6
pp1242 (1986)) BTS test (test in which an appropriate temperature and electric field are applied to a MOS structure sample and left to stand: Bia
s Temperature Stress),
Ag, shows the Arrhenius plot of the diffusion amount of SiO ₂ in Cu. In the figure, the vertical axis represents the atomic weight piled up at the SiO ₂ / Si interface, and represents the degree of diffusion. From the figure, it can be seen that Ag diffuses more easily into SiO ₂ than Cu in the temperature range of 275 ° C. to 500 ° C. According to this report, the diffusion coefficient and activation energy are shown as follows.

Element Diffusion coefficient in SiO ₂ Temperature Activation energy Ag 4.5 × 10 ⁻⁵ cm ² / sec 300 ° C. 1.24 eV As described above, Ag has a high diffusion rate into SiO ₂ ,
SiO ₂ cannot be used as an insulating film for Ag wiring.

In order to solve the above problems, the silicon nitride (SiN) film proposed in the present invention may be used as a protective film for Ag wiring. The comparison data of SiN and SiO ₂ films formed by the plasma CVD method are shown.

Membrane type Density (g / cm ² ) Membrane stress (dyn / cm ² ) Hydrophilicity Crack resistance SiN 2.60 6 × 10 ⁹ compression large large SiO ₂ 2.20 3 × 10 ⁹ compression small small SiN It is a dense film that has a higher density than SiO ₂ and a low water permeability. The crystal structure is SiO ₂ OS
Whereas iN has a regular network structure, SiN has an amorphous structure in which Si—N bonds are complicatedly overlapped. In addition, the stress of the film is a strong compression, and cracks are less likely to occur. Due to the dense film structure of SiN, A in the insulating film
The diffusion of g can be prevented. By preventing the diffusion of Ag into the insulating film, a leak current between wirings does not occur, and a device malfunction does not occur. In addition, SiO ₂ or PSG
Silver atoms will not diffuse through the film to the p-type and n-type regions formed on the Si substrate, and the device characteristics will not deteriorate.

[0023]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The details of the semiconductor device according to the present invention will be described below with reference to the embodiments shown in the drawings.

(Embodiment 1) FIGS. 1A to 1D are sectional views showing a manufacturing process of Embodiment 1 of the present invention.

First, in this embodiment, as shown in FIG. 1 (A), an insulating film 12 is formed on a silicon substrate 11 as a semiconductor substrate on which predetermined elements are formed, and then a contact hole 13 is opened to form a contact. After removing the natural oxide film of the holes, the Ti film 14, Ti is formed by the DC magnetron sputtering method.
The N film 15 and the Ag film 16 are successively formed in this order using a multi-chamber type sputtering apparatus. The Ti film 14 is necessary to make ohmic contact with the silicon substrate 11, and the TiN film 15 is used as a diffusion prevention layer. Note that Ti
Film 14 is 300Å, TiN film 15 is 700Å, Ag film 1
No. 6 has a film thickness of 4000Å. These Ti film 14, Ti
The sputtering conditions for the N film 15 and the Ag film 16 are shown below. It should be noted that the film thickness and the following film forming conditions show recommended values and are not limited to these.

(Sputtering condition of Ti film 14) ○ Sputtering gas ... Ar ○ Pressure ... 5 mTorr ○ DC power ... 5 kw ○ Substrate temperature ... 150 ° C. (Sputtering condition of TiN film 15) ○ Sputtering gas ... Ar-60% N ₂ ○ Pressure: 5 mTorr ○ DC power: 7 kw ○ Substrate temperature: 150 ° C. (sputtering condition of Ag film 16) ○ Sputter gas: Ar ○ Pressure: 5 mTorr ○ DC power: 10 kw ○ Substrate temperature: 300 ° C. A desired resist pattern 17 is formed on the Ag film 16. Next, the Ag film 16 is etched by the ion beam etching method using Ar gas. As an example, the etching conditions at this time are shown below.

(Conditions of Ion Beam Etching) ○ Etching gas… Ar ○ Pressure… 1 × 10 ^-4 Torr ○ Acceleration voltage… 1000 V (DC) ○ Ion current density… 1 × 10 ^-5 A / cm ² ○ Substrate temperature… 80 ° C. Under the above etching conditions, the Ag film 16 is etched at a rate of about 500 Å / min. Then, the underlying TiN film 1
5, when the Ti film 14 is etched by a reactive ion etching method using a chlorine-based gas, a shape as shown in FIG. 1B is obtained. Further, when the resist 17 is removed by the resist ashing process, a shape as shown in FIG. 1C is obtained.

The etching conditions and the resist ashing conditions for the TiN film 15 and the Ti film 14 are shown below.

(Conditions for Reactive Ion Etching) Etching gas and its flow rate Boron trichloride (BCl ₃ ) ... 60 _SCCM Chlorine gas (Cl ₂ ) ... 90 _SCCM ○ RF power ... 40 W ○ Pressure ... 40 mTorr (resist ashing conditions ) Ashing gas ... Oxygen (300 _SCCM ) ○ Pressure ... 2 Torr ○ Microwave power ... 400 W After resist ashing, as shown in FIG. 1D, a silicon nitride (Si ₃ N ₄ ) film 18 is used as a protective layer by plasma CVD.
7,000 Å by the method As an example, formation conditions are shown below.

(Conditions of Plasma CVD) ○ Gas and its flow rate Silane (SiH ₄ ) ... 180 _SCCM Ammonia (NH ₃ ) ... 500 _SCCM Nitrogen (N ₂ ) ... 720 _SCCM ○ RF power ... 430 W ○ Pressure ... 300 mTorr Then nitrogen Sinter at 400 ° C. for 60 minutes in the atmosphere. Even after sintering, the diffusion of Ag is prevented by the silicon nitride film 18, which is a SiN protective layer, so that the device characteristics are not deteriorated. This structure makes it possible to apply Ag wiring devices and has high electromigration resistance.
A device with low resistance can be realized.

(Embodiment 2) Next, S is formed on the protective layer of silver wiring.
A _second embodiment in which an iO ₂ -based planarizing interlayer insulating film is formed will be described.

The second embodiment shows an example in which a laminated protective film of SiN and another insulating film is formed. Since Si ₃ N ₄ has a strong compressive stress as described above, a strong tensile stress is applied to the wrapped wiring. This stress may cause stress migration in the wiring and cause disconnection. This problem can be solved by using the Si ₃ N ₄ / PSG laminated structure described in this embodiment. Si ₃ by PSG film is laminated to have a tensile stress Si ₃ N ₄
It is possible to cancel the stress of N ₄ . That is, Si ₃ N
_{By using} a laminated structure of ₄ and PSG, the stress applied to the wiring can be reduced.

In the same procedure as in Example 1, Ag / TiN / T
A wiring pattern of i is formed. Thereafter, as shown in FIG. 2, a silicon nitride (Si ₃ N ₄ ) film 21 (3000 Å) and a SiO ₂ -based insulating film PSG were formed by a plasma CVD method.
The film 22 (7000 Å) is formed in this order. The forming conditions are shown below.

(Conditions for Plasma CVD of Silicon Nitride Film 21) Gas and Flow Rate Silane (SiH ₄ ) ... 180 _SCCM Ammonia (NH ₃ ) ... 500 _SCCM Nitrogen (N ₂ ) ... 720 _SCCM ○ RF Power 430 W ○ Pressure … 300 mTorr (conditions for plasma CVD of PSG film 22) ○ Gas and its flow rate Silane (SiH ₄ )… 80 _SCCM Phosphine (PH ₃ )… 7 _SCCM Oxygen (O ₂ )… 1000 _SCCM Nitrogen (N ₂ )… 32000 _SCCM ○ RF power ... 500 W Pressure ... Normal pressure The film thickness and forming conditions under the above-mentioned conditions are recommended values. Then, sintering is performed at 400 ° C. for 60 minutes in a nitrogen atmosphere. As long as the silicon nitride film is formed directly on the Ag wiring as in the present embodiment, Ag can be formed even after sintering.
Since the diffusion of Ag is blocked by silicon nitride, the deterioration of device characteristics due to Ag diffusion does not occur. In addition to this, a combination of laminated structures may be SiN / CVD-SiO ₂ SiN / BPSG SiN / SiC SiN / Al ₂ O ₃ . further. You may form a protective film in three or more layers. This structure makes it possible to apply Ag wiring devices with improved stress migration resistance, realize highly reliable devices, and is industrially very useful.

The first and second embodiments have been described above.
The present invention is not limited to these, and it goes without saying that the present invention can be modified in various ways associated with the gist of the configuration and can be applied to semiconductor devices of various structures.

[0036]

As is apparent from the above description, according to the present invention, Ag is prevented from diffusing from the Ag metal wiring to the interlayer insulating film side, and the deterioration of device characteristics such as inter-connection leakage is prevented. Have.

Further, Ag is added to the p and n type regions in the semiconductor substrate.
Since atoms do not enter, there is an effect of surely preventing deterioration of device characteristics in addition to the above effects.

Furthermore, it becomes possible to realize Ag metal-based wiring, and particularly in a VLSI having a wiring width of 0.3 μm or less, a wiring structure having a low resistance and a high electromigration resistance which cannot be obtained by the conventional Al wiring technology. Is obtained.

Further, in particular, in the invention described in claim 2, it has an effect of further reducing the stress applied to the Ag wiring.

[Brief description of drawings]

1A to 1D are cross-sectional views showing each step of a first embodiment of the present invention.

FIG. 2 is a sectional view of a second embodiment of the present invention.

FIG. 3 is a graph showing an Arrhenius plot of diffusion amounts of Ag and Cu in SiO ₂ .

[Explanation of symbols]

11 ... Silicon substrate, 12 ... Insulating film, 14 ... Ti film, 1
5 ... TiN film (diffusion prevention layer), 16 ... Ag film, 18 ... Silicon nitride film.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁵ Identification code Internal reference number FI technical display location H01L 29/46 R 7738-4M

Claims (2)

[Claims] 1. A semiconductor device having an Ag metal-based wiring selectively formed on a semiconductor substrate via a diffusion prevention layer, wherein a protective layer made of silicon nitride is provided on an upper surface and a side surface of the Ag metal-based wiring. A semiconductor device characterized by being formed. 2. A semiconductor device having an Ag metal-based wiring selectively formed on a semiconductor substrate via a diffusion prevention layer, wherein a protective layer made of silicon nitride is formed on an upper surface and a side surface of the Ag metal-based wiring. And a SiO ₂ -based flattening layer is formed on the protective layer.