JPH06232051A - Formation of ohmic contact - Google Patents

Abstract

PURPOSE:To surely form a low-resistance ohmic contact which has an excellent barrier property and is high in reliability. CONSTITUTION:The method contains a process in which a contact section 2 where the ohmic contact must be formed is coated with a metallic layer 5 for forming ohmic contact, a process in which an oxidation preventing film 5 is formed on the surface of the metallic layer 5, and a process in which a barrier metal layer 7 is deposited on the surface of the film 6 by the CVD method.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for forming an ohmic contact which is suitable for ohmic contact of wiring or electrodes of a semiconductor device.

[0002]

2. Description of the Related Art In various electronic devices such as semiconductor integrated circuits, the wiring or electrodes (hereinafter referred to as "wirings") have a multi-layered wiring structure with an interlayer insulating layer in order to reduce the size and increase the density. However, recently, there is an increasing demand for miniaturization and high density of electronic devices, and accordingly, fine patterning of wiring is being advanced.

For this reason, the wiring formed on the interlayer insulating layer through the contact holes such as contact holes and via holes formed in the interlayer insulating layer may be replaced with other wiring portions under the interlayer insulating layer or impurities in the Si semiconductor, for example. The diameter of the contact hole in the case of making ohmic contact with a semiconductor region such as a diffusion region (hereinafter referred to as a contact) is also inevitably small.

In this case. The interlayer insulating layer needs to have a predetermined thickness due to problems such as electrical reliability and parasitic capacitance, and the aspect ratio (depth / diameter) of the connection hole is large.

As described above, as a technique for burying an upper layer wiring or a so-called metal plug for the connection in a connection hole having a large aspect ratio, a blanket tungsten (hereinafter referred to as Blk) by a CVD (chemical vapor deposition) method is used.
-W) or high temperature Al sputtering.

In any of these cases of CVD of Blk-W, high temperature sputtering of Al, etc., the adhesiveness or A
A barrier metal layer is formed as an underlying layer for the purpose of, for example, preventing the semiconductor region from penetrating.

That is, as shown in FIG. 4 which is a sectional view of an essential part of the example, the interlayer insulating layer 3 formed on the surface of the base 1 is formed in the contact portion 2 of the semiconductor region of the base 1 made of a semiconductor substrate, for example. In the case of connecting the wiring through the connection hole 4 formed in the substrate, a CVD film of titanium nitride (TiN, TiON) film is formed as the barrier metal layer 7, and a metal layer such as Blk-W or Al described above is formed on the CVD film. 8 is formed.

The titanium nitride film as the barrier metal layer 7 itself needs to be deposited in the connection hole 4 as a high-quality film with good coverage.

That is, when the titanium nitride film itself of the barrier metal layer 7 has a problem in its adhesiveness and film quality, a void (cavity) is formed in the metal layer 8 as shown in the sectional view of the main part in FIG. Occurs, resulting in increased resistance and reduced mechanical and electrical reliability.

Titanium nitride as the barrier metal layer 7 is usually formed by a sputtering method, but in this sputtering method, there is a so-called step coverage in which sputtered incident particles do not penetrate deep into the bottom of the connection hole because the side wall of the connection hole is a shadow. There is a problem of being bad.

For this reason, it has been attempted to improve the coverage by a collimator (coherent) sputtering method in which the directivity of sputter incident particles is strengthened. However, even if a collimator is used, in the case of a connection hole having a diameter of 0.35 μm, Only about 20% coverage of the entire inner surface including the inner peripheral surface and the bottom surface can be obtained.

In order to form titanium nitride in a contact hole having a large diameter of 0.35 μm or less and a large aspect ratio with good coverage, it is formed by a CVD method which easily enters the fine portion due to a chemical reaction and is deposited. Will be needed.

By the way, even in the case of forming the barrier metal layer of titanium nitride, in order to lower the contact resistance, that is, to make good ohmic contact, the barrier metal layer is actually formed under the barrier metal layer. Furthermore, since the titanium Ti underlayer is formed as a metal layer for forming ohmic contact,
It is desirable that the Ti film of the metal layer for forming ohmic contact is also formed by the CVD method.

However, in the present situation, CVD of Ti is performed.
Is the only method of reducing TiCl ₄ with hydrogen plasma generated by ECR (electron cyclotron resonance) plasma, and in ordinary thermal CVD, a high temperature of about 2000 ° C. is required to reduce TiCl ₄ with hydrogen. It cannot be applied to the circuit LSI process.

Therefore, a method of depositing Ti as an ohmic contact forming metal layer in advance by a sputtering method and then depositing a barrier metal layer of titanium nitride by a CVD method can be considered.

However, in this method, after forming the Ti film of the ohmic contact forming metal layer by the sputtering method, the substrate is once taken out, and the barrier metal layer, that is, titanium nitride is CVD again by another device.
Therefore, the Ti film of the metal layer for forming ohmic contact is oxidized when taken out to the outside before the formation of titanium nitride, and the Ti film is formed on the Si semiconductor surface at the contact portion, for example. There is a problem that the reduction effect of Ti on the existing natural oxide film is obstructed and ohmic contact cannot be performed.

Even if the sputtering of Ti and the CVD of titanium nitride are carried out continuously in the same apparatus and clustered, Cl of TiCl ₄ which is a source gas of CVD titanium nitride is Ti. There is a problem that the film or the contact portion of, for example, a Si semiconductor is etched and the contact resistance increases.

[0018]

SUMMARY OF THE INVENTION The present invention solves the above-mentioned problems and provides a method for forming an ohmic contact capable of reliably forming an ohmic contact having excellent barrier properties, high reliability, and low resistance. It is a thing.

[0019]

According to the present invention, a step of depositing an ohmic contact forming metal layer on a contact portion where an ohmic contact is to be formed, and an anti-oxidation film on the surface of the ohmic contact forming metal layer. The step of forming and the step of depositing a barrier metal layer by CVD are performed thereafter.

Further, according to the present invention, in the above method, the ohmic contact forming metal surface is nitrided by nitriding annealing to form the above-mentioned antioxidant film.

Further, according to the present invention, the above-mentioned anti-oxidation film is made of refractory metal, refractory nitride or refractory metal silicide.

[0022]

In the method of the present invention, since the oxidation preventive film is formed on the surface of the ohmic contact forming metal layer at the contact portion where the ohmic contact is made, the barrier metal of titanium nitride is deposited by CVD. For example, reduction of the natural oxide film on the semiconductor surface at the contact portion, that is, conversion of TiSi ₂ with low resistance, due to oxidation of Ti of the metal layer, can be effectively generated, and a low resistance ohmic contact can be formed. At the same time, the presence of the Ti layer makes it possible to make a contact having an excellent barrier property.

[0023]

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

In each of the methods of the present invention, a connection hole is formed in a contact portion 2 of a substrate 1 made of a semiconductor substrate, for example, a semiconductor region made of an impurity diffusion region, and an interlayer insulating layer 3 formed on the surface of the substrate 1. This is the case where wiring is connected through 4.

In this case, in the present invention, the ohmic contact forming metal layer 5 is formed on the contact portion through the connection hole 4 of the interlayer insulating layer 3, and the oxidation barrier film 6 is formed on the surface thereof, and then the CVD barrier is formed. The metal layer 7 is deposited.

Example 1 In this example, the case where the antioxidant film is formed by nitriding the surface of the metal for ohmic contact formation by nitriding annealing will be described with reference to FIG.

In this case, first, as shown in FIG. 1A, after a connection hole 4 is formed in the interlayer insulating layer 3 by selective etching by photolithography of a well-known technique, a dilute hydrofluoric acid treatment is performed, and then a sputtering method is performed. Then, Ti is deposited to form the ohmic contact forming metal layer 5.

This ohmic contact forming metal layer 5
That is, the conditions for Ti deposition were a substrate temperature of 200 ° C., a pressure of 0.4 Pa, an Ar flow rate of 40 sccm, and an electric power of 1 kW (direct current).

Next, as shown in FIG. 1B, the surface 2 of the ohmic contact forming metal layer 5 was annealed by nitriding, that is, heated in an atmosphere containing nitrogen to form an anti-oxidation film 6 of titanium nitride TiN.

The nitriding annealing conditions are 600 to 900 ° C. and 30 to 120 in a nitrogen or ammonia atmosphere.
It was done for a second.

Thereafter, as shown in FIG. 1C, titanium nitride TiN is deposited and formed by a CVD method to form a barrier metal layer 7.

The conditions of this CVD are 450 ° C. and a pressure of 26.
At 60 Pa, 80 sccm, 300 sccm, and 5000 of each gas TiCl ₄ , NH ₃ , and N ₂ , respectively.
It was supplied with sccm.

At this time, the substrate 1 is once taken out after the formation of the ohmic contact forming metal layer 5, and is then housed in a reaction vessel in which titanium nitride, that is, the barrier metal layer 7 is subjected to CVD. Since the oxidation preventing film 6 made of titanium nitride is formed on the surface of the forming metal layer 5, the surface of the ohmic contact forming metal layer 5, that is, the Ti layer is oxidized even when exposed to the outside air when taken out to the outside. Is avoided.

Thereafter, although not shown so as to fill the recess 10 formed by the connection hole 4 on the barrier metal layer 7, as described with reference to FIG. 4, for example, Blk-W by CVD,
Alternatively, the metal layer 8 of Al or the like is formed by high-temperature sputtering, and if necessary, etch back is performed to fill and form the metal plugs of these metal layers.

In the first embodiment, the formation of the anti-oxidation film 6 on the ohmic contact forming metal layer 5 is carried out by nitriding the surface of the ohmic contact forming metal layer 5 itself. The film 6 can also be formed by sputtering.

Example 2 In this example, the formation of the ohmic contact forming metal layer 5 and the formation of the titanium nitride anti-oxidation film 6 on the surface thereof are performed by continuous sputtering.

Also in this example, as in the case of the first embodiment, after the connection hole 4 is formed in the interlayer insulating layer 3 by selective etching by the well-known photolithography,
Dilute hydrofluoric acid treatment is performed, and then Ti is deposited by the sputtering method to form the ohmic contact forming metal layer 5. The thickness of this Ti ohmic contact metal layer 5 is 3
It was set to 0 nm.

Next, the oxidation preventive film 6 is formed by continuously sputtering titanium nitride TiN to a thickness of 30 nm by using the same sputtering device as the sputtering device in which the ohmic contact forming metal layer 5, that is, Ti is deposited. .

This TiN sputtering condition is that the substrate temperature is 2
00 ° C., pressure 0.5 Pa, N ₂ gas flow rate 50 sccm
The power was 3 kW (DC).

Then, as described in the first embodiment, C
The barrier metal layer 7 was formed by depositing titanium nitride TiN to a thickness of 40 nm by the VD method.

Also in this case, as in the case of Example 1, the substrate 1 is once taken out after the formation of the ohmic contact forming metal layer 5, and thereafter the titanium nitride, that is, the barrier metal layer 7 is subjected to CVD reaction vessel. However, since the antioxidation film 6 made of titanium nitride is formed on the surface of the ohmic contact forming metal layer 5, even if the ohmic contact is exposed to the outside air when taken out to the outside, ohmic contact formation is performed. Oxidation of the surface of the working metal layer 5, that is, the Ti layer is avoided.

After that, although not shown so as to fill the recess 10 formed by the connection hole 4 on the barrier metal layer 7, as described with reference to FIG. 4, for example, Blk-W by CVD,
Alternatively, the metal layer 8 of Al or the like is formed by high-temperature sputtering, and if necessary, etch back is performed to fill and form the metal plugs of these metal layers.

The characteristics of the ohmic contact formed by the forming method of Example 2 were measured.

FIG. 2 shows the voltage V applied to this contact portion.
Curve 21 is the case of Example 2 and curve 22 is the case of Comparative Example. In this Comparative Example, the same method as in Example 2 was used, but the Ti ohmic contact forming metal was formed. This is the case where no titanium nitride film, that is, the anti-oxidation film 6 is formed on the surface of the layer 5, and as is clear by comparing both curves 21 and 22, the example of the present invention shows excellent linearity. It can be seen that good ohmic contact is made.

FIG. 3 shows the measurement results of the contact resistance with respect to the same applied voltage V to the contact portion. The curve 31 is the case of Example 2, and the curve 32 is the metal for forming the Ti ohmic contact according to the comparative example described above. This is the case where no titanium nitride film, that is, the anti-oxidation film 6 is formed on the surface of the layer 5, and the embodiment of the present invention shows a low resistance value and excellent flatness with no change in resistance with respect to voltage. It can be seen that good ohmic contact is made. By the way, if no antioxidant film is provided,
Contact resistance Rc is 1030Ω at 0.512V
On the other hand, in the embodiment of the present invention, the contact resistance Rc was 135Ω.

In both cases of FIG. 2 and FIG. 3, the diameter of the connection hole is 0.4 μm and the aspect ratio is 2.

In each of the above-mentioned examples, the anti-oxidation film 6 on the ohmic contact forming metal layer 5 is made of a refractory metal, particularly titanium nitride which is a refractory nitride. 6 can be formed by, for example, sputtering W of a metal having oxidation resistance.

Example 3 In this example, similarly to Example 1, after the treatment with dilute hydrofluoric acid after forming the connection hole 4, Ti was deposited by sputtering to form the ohmic contact forming metal layer 5. .

Then, subsequently, in the same sputtering apparatus, tungsten W is sputtered on the surface of the ohmic contact forming metal layer 5 to form an oxidation preventing film 6.

This W sputtering deposition condition is that the substrate temperature is 2
00 ° C., pressure 0.4 Pa, Ar gas flow rate 50 sccm
The power was 3 kW (DC).

For tungsten W, for example, since the heat of formation ΔHf of the oxide is more positive than that of the Si semiconductor of the substrate 1, it is more stable when Si is oxidized than when W is oxidized. Is not easily oxidized. Therefore, this W functions as an antioxidant film.

Then, as described in the first embodiment, C
Titanium nitride TiN was deposited and formed by the VD method to form the barrier metal layer 7.

Also in this case, as in the case of the first embodiment, after forming the ohmic contact forming metal layer 5, the substrate 1 is once taken out, and then titanium nitride, that is, the barrier metal layer 7 is subjected to CVD. However, since the oxidation preventive film 6 made of tungsten W is formed on the surface of the ohmic contact forming metal layer 5, even if the ohmic contact is exposed to the outside air when taken out to the outside, ohmic contact forming is performed. Oxidation of the surface of the working metal layer 5, that is, the Ti layer is avoided. Moreover, since TiCl ₄ used in this TiN CVD is more volatile than WCl ₆ , W is less likely to be etched than Cl. Therefore, Cl is blocked by W and is used for forming an underlying ohmic contact. Ti of the metal layer 5 can be stably ohmic-contacted without being etched.

Thereafter, although not shown so as to fill the recess 10 formed by the connection hole 4 on the barrier metal layer 7, as described with reference to FIG. 4, for example, Blk-W by CVD,
Alternatively, the metal layer 8 of Al or the like is formed by high-temperature sputtering, and if necessary, etch back is performed to fill and form the metal plugs of these metal layers.

The antioxidant film formed on the ohmic contact forming metal layer 5 made of Ti is not limited to the above-mentioned example, but may be formed of a refractory metal silicide.

Further, the present invention is not limited to the case where the semiconductor region of the Si semiconductor substrate is used as the contact portion as described above, but other semiconductors, for example, the active region or the lower layer wiring by the polycrystalline silicon semiconductor layer, or other various contact portions. Various modifications can be made such as being applicable to ohmic contacts to.

[0057]

As described above, in the method of the present invention, the antioxidant film 6 is formed on the surface of the ohmic contact forming metal layer 5 at the contact portion where ohmic contact is made.
After forming the barrier metal layer 7 of titanium nitride,
Since it is deposited by D, it effectively avoids the reduction of the natural oxide film on the semiconductor surface at the contact portion, that is, the inhibition of the formation of TiSi ₂ with low resistance due to the oxidation of Ti of the ohmic contact forming metal layer 5. And a low resistance ohmic contact can be formed, and the presence of this Ti layer makes it possible to form a contact having an excellent barrier property.

[Brief description of drawings]

FIG. 1 is a process drawing of an example of the method of the present invention.

FIG. 2 is a measurement curve diagram of current-voltage characteristics of ohmic contacts formed by an example and a comparative example of the method of the present invention.

FIG. 3 is a measurement curve diagram of contact resistance-voltage characteristics of ohmic contacts formed by an example and a comparative example of the method of the present invention.

FIG. 4 is a configuration diagram of a conventional ohmic contact.

FIG. 5 is a configuration diagram of a conventional ohmic contact.

[Explanation of symbols]

 1 Base 2 Contact Part 3 Interlayer Insulation Layer 4 Connection Hole 5 Ohmic Contact Forming Metal Layer 6 Antioxidant Film 7 Barrier Metal Layer

Claims (3)

[Claims] 1. A step of depositing a metal layer for forming an ohmic contact on a contact portion where an ohmic contact is to be formed, a step of forming an antioxidant film on the surface of the metal layer for forming an ohmic contact, and thereafter. And a step of depositing a barrier metal layer by chemical vapor deposition, the method for forming an ohmic contact. 2. The method for forming an ohmic contact according to claim 1, wherein the surface of the metal layer for forming ohmic contact is nitrided by nitriding annealing to form the antioxidant film. 3. The method for forming an ohmic contact according to claim 1, wherein the anti-oxidation film is made of refractory metal, refractory nitride, or refractory metal silicide.