JP3058956B2 - 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 device and a method for manufacturing the same, and more particularly to a method for reducing contact resistance between a semiconductor substrate and a wiring material in a fine connection hole or the like.

[0002]

2. Description of the Related Art In recent years, as semiconductor devices have become more highly integrated, circuit miniaturization has been progressing, and even in MOS integrated circuits, connection between gate electrodes and source / drain diffusion layers and metal wiring has been required. Are very small.

As a result, an increase in contact resistance has become a major problem.

The value of the contact resistance per unit area is
Generally, it is determined by the difference in work function between a metal and a semiconductor and the concentration of electrically activated impurities in the semiconductor.
In order to reduce the contact resistance, it is desirable that the difference between the work functions is small and that the impurity concentration in the semiconductor is high.

In forming a contact, a technique using metal silicide is used for the purpose of reducing the resistance of the diffusion layer and forming a self-aligned contact. Normally, titanium is used as a metal forming silicide, but the problem with this technique is that the contact resistance to the p-type diffusion layer is high.

That is, boron in the p-type diffusion layer is sucked out by the titanium silicide, and the carrier concentration at the interface of the contact region is reduced, thereby increasing the contact resistance.

[0007]

As described above, the method using metal silicide for the contact has a problem that the contact resistance cannot be reduced due to a decrease in the carrier concentration due to the absorption of boron from the diffusion layer. .

The present invention has been made in view of the above circumstances, and has as its object to form a contact having a sufficiently small contact resistance even in miniaturization.

[0009]

SUMMARY OF THE INVENTION In a first aspect of the present invention, there is provided a semiconductor device in which an impurity region in which boron is introduced as an impurity is formed in a semiconductor substrate and a contact layer for contacting the region is formed. Is characterized in that the contact layer is made of a metal silicide whose free energy decreases more when forming a compound with silicon than with a compound with boron.

According to a second aspect of the present invention, in a method of manufacturing a semiconductor device for forming a contact with an impurity region formed by introducing boron as an impurity on a semiconductor substrate, the contact is formed on the semiconductor substrate. The method includes a step of forming a metal silicide in which the free energy decreases more when forming a compound with silicon than with a compound with boron.

[0011]

The problem that boron in the p-type diffusion layer is sucked out and the contact resistance becomes high is considered to be as follows.

That is, titanium boride (TiB ₂ ) and titanium silicide (TiSi ₂ ) have a larger negative free energy of formation than titanium boride. The boron diffused into the silicon substrate diffuses into the silicon silicide, and a titanium-boron bond is formed and stabilized.

Thus, TiSi ₂ / p ⁺ -Si
B existing at the interface is positively sucked into the TiSi ₂ film. Since the bonding ratio of Ti-B increases in proportion to the heat treatment temperature, the effect of sucking out B is accelerated by adding a high-temperature heat treatment step such as a gettering step or a melt step, and the decrease in interfacial boron concentration becomes remarkable. . As a result, it has not been possible to form a thermally stable low resistance contact with the prior art.

According to the present invention, a metal silicide having a larger free energy reduction when forming a compound with silicon than a compound with boron is formed at the interface of the contact, so that the silicide of this metal is formed. Is more stable,
This metal is very unlikely to react with silicon and with boron, so that almost no boron can be sucked out.

Preferably, vanadium V is used as a metal whose free energy decreases more when forming a compound with silicon than a compound with boron. Vanadium reacts with silicon to form a compound having the formula V ₂ Si. That is, only one Si atom is consumed for two vanadium atoms, and vanadium has a large atomic radius, so that Si is less eroded, and there is no danger of penetration even in a shallow diffusion layer. Further, even if it reacts slightly with boron, it forms a compound having the chemical formula of V ₂ B, so that the consumption of boron is small.

A tungsten layer may be formed on the vanadium silicide layer.

Further, when a contact having a blanket structure is formed, it is desirable to form a titanium nitride or vanadium nitride layer on the vanadium layer so as to reach the insulating film. This is because the adhesion between the electrode wiring layer such as a tungsten layer and the insulating film is not good. By thus interposing a layer such as titanium nitride or vanadium nitride as an intermediate layer between the electrode wiring layer and the insulating film, a more reliable contact can be formed.

In particular, a metal having a larger free energy reduction when forming a compound with silicon than a compound with boron is deposited, and boron ions are formed under such a condition that the maximum concentration of boron is located in the metal. By implanting and performing a heat treatment after the boron ion implantation so that the metal reacts with the semiconductor substrate, a contact can be formed simultaneously with the formation of the p-type diffusion layer. In addition, boron is favorably present in the metal layer, and an equilibrium state can be formed, so that the effect of sucking boron is reduced.

The ion implantation may be performed after the reaction between the metal and the semiconductor substrate, and then the diffusion layer may be formed by heat treatment.

Further, the metal thin film containing boron may be formed and heat-treated, and the metal silicide layer may be formed simultaneously with the formation of the p-type layer by boron diffusion. Furthermore, a metal silicide layer may be formed by forming this metal thin film on a substrate on which a diffusion layer has already been formed and performing heat treatment.

Furthermore, the metal used here is V
Alternatively, iron or the like may be used.

[0022]

Embodiments of the present invention will be described below in detail with reference to the drawings.

FIGS. 1A to 1D are cross-sectional views showing the steps of manufacturing a semiconductor device according to the first embodiment of the present invention.

First, as shown in FIG. 1A, after forming a field oxide film (not shown) on an n-type silicon substrate 1, an insulating film 2 is formed in an isolated element region. Contact window is opened and BF ₂ is accelerated at 30 ke
Ion implantation (mask is not shown) was performed under the conditions of V and an implantation dose of 5 × 10 ¹⁵ cm ⁻² ,
Heat treatment is performed at 0 ° C. for 1 hour. After forming the p-type diffusion layer 3 in this way, the substrate is set in a well-known magnetron sputtering apparatus.

After evacuating the chamber of the sputtering apparatus to a vacuum of 2 × 10 ⁻⁵ Pa or less,
Argon gas at a flow rate of ³ / min is introduced. At this time, the pressure in the chamber is maintained at 3.7 × 10 ⁻⁴ Pa. Then, the V target is sputtered with argon plasma generated at an applied voltage of 600 V and a target current of 5 A, and a vanadium layer 4 is deposited on the insulating film 2 so as to have a thickness of 60 nm.

Next, 100 cm ³ / min.
2. A nitrogen gas at a flow rate of 2.
It should be kept at 7 × 10 ^-1 Pa. Thereafter, a heat treatment is performed at 600 ° C. for 15 seconds using a tungsten halogen lamp provided on the back side of the substrate 1. By this heat treatment, the vanadium layer 3 becomes a vanadium silicide layer 5 in the contact region and a vanadium nitride layer 6 on the surface, as shown in FIG. Accordingly, in the contact region, a laminated structure of the vanadium silicide layer 5 and the vanadium nitride layer 6 is formed, while on the insulating film 2, a laminated structure of the vanadium layer 4 and the vanadium nitride layer 6 is formed. Note The vanadium nitride (VN _x) layer 6 with a thickness of about 10 to 50 nm, silicide vanadium (VSi _x) layer 5 is preferably formed to a thickness of about 20 to 80 nm.

Further, the semiconductor substrate 1 is selectively immersed in a solution in which sulfuric acid and hydrogen peroxide are mixed at a ratio of 1: 2 for 10 minutes to selectively etch the vanadium nitride layer 6 and the vanadium layer 4, thereby forming a vanadium silicide layer. A contact structure as shown in FIG.

Therefore, in order to measure the carrier profile near the interface of the contact portion, the contact interface between the vanadium silicide / p + diffusion layer of the embodiment of the present invention and the contact interface of titanium silicide / p + diffusion layer of the conventional contact structure was used. Figure 2 (a) and Figure 2 (a)
This is shown in (b). From these results, in the conventional contact structure, the carrier concentration sharply decreases near the surface and drops to about 2 × 10 ¹⁹ cm ⁻³ at the contact interface, whereas vanadium silicide as shown in FIG. It is maintained at 8 × 10 ¹⁹ cm ⁻³ or more at the interface with the / p + diffusion layer. These results are all obtained after the heat treatment at 850 ° C. for 1 hour. Thus, it was confirmed that the use of vanadium silicide instead of titanium silicide as the electrode material at the contact interface with the p + diffusion layer suppresses the absorption of boron into silicide.

The contact structure thus obtained has a very low resistance of 25 Ω per 1 μm square. By the way, the contact structure using titanium silicide is 70Ω per 1μm square,
The comparison with this shows that the present invention is extremely effective.

In this embodiment, vanadium is used as the metal film. However, the metal film is not limited to vanadium, and the free energy when forming a compound with silicon is larger than a compound with boron such as iron. Any metal may be used.

The effect of the present invention was particularly remarkable for a sample having a high concentration of 3 × 10 ¹⁹ cm ⁻³ or more in surface concentration of a semiconductor substrate.

As described above, by forming a silicide of vanadium at the interface of the contact, which has a larger free energy reduction when forming a compound with silicon than a compound with boron, vanadium silicide is more likely to be formed. It is considered that since vanadium silicide is more stable than vanadium silicide, the possibility that this vanadium silicide reacts with silicon and reacts with boron is extremely small, and therefore, there is almost no absorption of boron.

The enthalpy of formation of silicides and borides of these metals was determined. The enthalpy of formation of vanadium disilicide was 75 kcal / mol, whereas that of vanadium boride was 31 kcal / mol. This indicates that boride is relatively difficult to form. For iron, 20 kcal / mol and 9 kcal / mo respectively
l, and had a similar tendency. On the other hand, in titanium, the enthalpy of formation of each of silicide and boride is 32.
kcal / mol and 70 kcal / mol, indicating that boride was easily formed.

The enthalpies of formation of silicides and borides of other metals, such as chromium, cobalt, tungsten, molybdenum, nickel, and tantalum, were also determined. A metal in which boride is relatively difficult to form was not found.

Next, a method for forming a wiring layer on the contact thus formed by using the selective CVD method will be described.

The substrate on which the vanadium silicide layer 5 of the contact is formed as shown in FIG.
Tungsten hexafluoride is flowed at a flow rate of 10 sccm and silane is flowed at a flow rate of 5 sccm, and a tungsten layer 8 is selectively deposited (approximately 300 nm) in a chamber maintained at 0.2 Torr so as to fill a contact hole (FIG. 1 (e) )). The deposition rate at this time was 120 nm / min. Here, the substrate temperature is 3
20 ° C. In this way, a buried contact having a sufficiently flat surface could be formed.

As shown in FIG. 3, a so-called blanket structure in which a wiring layer is formed from the opening to the insulating film 2 can be formed on the vanadium silicide layer formed by the method of the present invention.

[0038] That is, after forming the silicide vanadium layer 5 as shown in FIG. 3 (a), in a chamber of a sputtering apparatus, a nitrogen gas at a flow rate of 20 cm ³ / min and 20 cm ³ / min
, And the pressure in the chamber is maintained at 3.7 × 10 ^-1 Pa at this time, and a V target is sputtered with argon plasma generated at an applied voltage of 600 V and a target current of 5 A. And FIG.
As shown in (b), a vanadium nitride layer 6 is deposited on the entire surface to a thickness of about 20 nm.

Thus, a laminated structure of the vanadium nitride layer 6 / vanadium silicide layer 5 can be obtained.

Embodiment 2 Next, a second embodiment of the present invention will be described.

In the above embodiment, a vanadium layer was formed by a sputtering method using vanadium as a target, and a vanadium silicide layer was formed at the interface by heat treatment. In this example, however, 5% or less of boron was previously contained as a target material. A boron-containing vanadium layer is formed by a sputtering method using vanadium.

First, as shown in FIG. 4A, after forming a field oxide film (not shown) on an n-type silicon substrate 1, an insulating film 2 is formed in an isolated element region. After forming an opening as a contact window, the substrate is set in a well-known magnetron sputtering apparatus.

After evacuating the chamber of the sputtering apparatus to a vacuum of 2 × 10 ⁻⁵ Pa or less,
Argon gas at a flow rate of ³ / min is introduced. At this time, the pressure in the chamber is maintained at 3.7 × 10 ⁻⁴ Pa. Then, a target made of vanadium containing 5% by mass of boron is sputtered with argon plasma generated at an applied voltage of 600 V and a target current of 5 A, and a boron-containing vanadium layer 7 is formed on the insulating film 2 to a thickness of 60 nm. To be deposited.

Next, 100 cm ³ / min.
2. A nitrogen gas at a flow rate of 2.
It should be kept at 7 × 10 ^-1 Pa. Thereafter, a heat treatment is performed at 600 ° C. for 15 seconds using a tungsten halogen lamp provided on the back side of the substrate 1. By this heat treatment, the boron-containing vanadium layer 7 becomes the vanadium silicide layer 5 in the contact region and the vanadium nitride layer 6 on the surface, as shown in FIG. Therefore, in the contact region, a laminated structure of the vanadium silicide layer 5 and the vanadium nitride layer 6 is formed, while on the insulating film 2, a laminated structure of the boron-containing vanadium layer 7 and the vanadium nitride layer 6 is formed.

Further, by performing a heat treatment at 850 ° C. for 30 seconds, a p-type diffusion layer 3 was formed on the substrate side of the vanadium silicide layer 5 as shown in FIG. 4C. Then p
The junction depth of the mold diffusion layer was 90 nm.

Further, the semiconductor substrate 1 is selectively immersed in a solution in which sulfuric acid and hydrogen peroxide are mixed at a ratio of 1: 2 for 10 minutes to selectively etch the vanadium nitride layer 6 and the vanadium layer 4, thereby forming a vanadium silicide layer. A contact structure as shown in FIG.

Thus, a contact structure with low contact resistance can be obtained simultaneously with the formation of the p-type diffusion layer.

Embodiment 3 Next, a third embodiment of the present invention will be described.

In the first and second embodiments, the vanadium layer is formed by the sputtering method and the vanadium silicide layer is formed at the interface by the heat treatment. In this embodiment, the vanadium layer is formed by the CVD method.

First, as in the second embodiment, as shown in FIG. 5A, a field oxide film (not shown) is formed on an n-type silicon substrate 1, and then an insulating film is formed in an isolated element region. 2 and an opening as a contact window is formed therein.

Then, the substrate was set in a cold wall type CVD apparatus, and the inside of the chamber of the apparatus was set to 2 × 10 5
After evacuation to ^-5 Pa or less, the temperature of the substrate is raised to 450 ° C. And hydrogen gas at a flow rate of 1000 cm ³ / min and 20
Vanadium chloride gas (VCl ^{3) at} a flow rate of 0 cm ³ / min
₅ ) and introduce. At this time, the pressure in the chamber becomes 3.
It should be maintained at 7 × 10 ⁻³ Pa. And FIG. 5 (b)
As shown in FIG. 1, a vanadium layer 4 is selectively deposited on the substrate surface exposed from the insulating film 2 so as to have a thickness of 60 nm.

Then, BF ₂ is ion-implanted (mask is not shown) under the conditions of an acceleration voltage of 25 keV and an implantation dose of 8.0 × 10 ¹⁵ cm ^-2 , at 850 ° C. in a dry nitrogen atmosphere.
Heat treatment is performed for 15 seconds. By this heat treatment, the vanadium layer 4 reacts with the substrate surface to form the vanadium silicide layer 5,
The vanadium nitride layer 6 is formed on the surface. On the substrate side of the vanadium silicide layer 5, a p-type diffusion layer 3 is formed.

Thus, a contact structure with low contact resistance can be obtained simultaneously with the formation of the p-type diffusion layer.

In this embodiment, vanadium silicide is formed by performing heat treatment after ion implantation. However, after performing heat treatment to obtain a laminated structure of vanadium silicide and vanadium nitride, B ions are implanted to perform p-type diffusion. A layer may be formed. Further, the vanadium layer may be formed in a blanket shape.

Further, in the step shown in FIG. 5C, prior to the heat treatment for silicide formation, the chamber was evacuated to 2 × 10 ^-5 Pa or less while the substrate 1 was maintained at 450 ° C. after evacuating nitrogen gas at a flow rate of 500 cm ³ / min of the flow rate of hydrogen gas and 500 cm ³ / min and 200 cm ³ / min
Vanadium chloride (VCl ₅ ) gas is introduced at a flow rate of At this time, the pressure in the chamber was 3.7 × 10 ⁻³ Pa
And the vanadium nitride layer 6 of about 20 nm may be selectively formed on the vanadium layer 4. In the step of depositing vanadium nitride 6, 1
Nitrogen plasma may be generated by applying RF power of 3.56 MHz and 800 W to perform RF discharge.

Further, vanadium silicide is formed by using vanadium chloride, silane (SiH ₄ ) and active hydrogen, by exposing the semiconductor substrate or a metal silicide layer such as a vanadium silicide layer already formed by the method of the above-described embodiment. It may be performed by selectively growing vanadium silicide on the top or by growing the whole surface.

By the way, selective growth, vanadium chloride reacts with silicon in the initial stage, are formed silicide vanadium and silicon tetrachloride (SiCl _4), therefore when silicon tetrachloride is evaporated, Ya etch pits on the substrate surface Voids grow easily.

Therefore, it is preferable to suppress the reaction with the silicon substrate by using silane and active hydrogen and selectively grow vanadium silicide. By using the selective growth of vanadium silicide that does not erode the silicon substrate, 0.05%
Vanadium silicide can also be applied to p + / n and n + / p junctions as shallow as μm.

The above-mentioned vanadium silicide may be formed directly by a sputtering method.

The present invention is not limited to the embodiments described above. For example, as a heat treatment method, a method of instantaneously heating a silicon substrate, such as heating by irradiation with a laser beam, an ion beam, an electron beam, or the like, other than heating with a halogen lamp, may be used.

The electrode metal is not limited to tungsten, but may be other metals such as copper, aluminum and titanium.

[0062]

As described above, according to the present invention, the contact resistance in a semiconductor device can be greatly reduced.

[Brief description of the drawings]

FIG. 1 is a manufacturing process diagram of a semiconductor device according to a first embodiment of the present invention.

FIG. 2 is a diagram showing a carrier profile near the surface of a contact formed by the method of the embodiment and a contact formed by a conventional method.

FIG. 3 is a manufacturing process diagram of a semiconductor device which is a modification of the first embodiment of the present invention.

FIG. 4 is a manufacturing process diagram of a semiconductor device according to a second embodiment of the present invention.

FIG. 5 is a manufacturing process diagram of a semiconductor device according to a third embodiment of the present invention.

[Explanation of symbols]

 Reference Signs List 1 silicon substrate 2 silicon oxide film 3 impurity diffusion layer 4 vanadium layer 5 vanadium silicide layer 6 vanadium nitride layer 7 boron-containing vanadium layer 8 tungsten layer

──────────────────────────────────────────────────続 き Continuation of the front page (72) Inventor Kyoichi Suguro 1 Toshiba Research Institute, Komukai Toshiba-cho, Saiwai-ku, Kawasaki-shi, Kanagawa Prefecture (56) References JP-A-4-239126 (JP, A) JP-A-4-148533 (JP, A) JP-A-1-202860 (JP, A) JP-A-2-256238 (JP, A) JP-A-2-21622 (JP, A) JP-A-59-3978 (JP) , A) JP-A-57-177565 (JP, A) JP-B-3-6656 (JP, B2) (58) Fields investigated (Int. Cl. ⁷ , DB name) H01L 21/28 H01L 21/768

Claims (2)

(57) [Claims] In a semiconductor device, an impurity region in which boron is introduced as an impurity is formed in a semiconductor substrate, and a contact layer that contacts the region is formed. A semiconductor device comprising a metal silicide having a large decrease in free energy when forming a compound with silicon. 2. A method for manufacturing a semiconductor device, wherein a contact is formed with an impurity region formed by implanting boron as an impurity in a semiconductor substrate, wherein the contact is formed on the semiconductor substrate by a silicon rather than a compound with boron. A method of forming a metal silicide having a large decrease in free energy when forming a compound with the above.