JP2000349283A - High withstand-voltage semiconductor device and its manufacture - Google Patents

Abstract

PROBLEM TO BE SOLVED: To control an interface state density so as to restrain a breakdown phenomenon from occurring between a source and a drain by a method wherein a protective film of an atom ratio Si/N which is set smaller than a specific value is formed on a semiconductor device provided on a semiconductor substrate. SOLUTION: A gate oxide film 1 is formed on the surface of a semiconductor substrate 10, a gate electrode 2 is formed thereon, ions are implanted using the gate oxide film 1 and the gate electrode 2 as a mask for the formation of source/drain regions 3 and 4. Then, an interlayer insulating film 5, a contact window is provided to the source/drain regions 3 and 4, and then a metal electrode 6 is formed by patterning. Lastly, a stoichimetric silicon nitride film whose atom ratio Si/N is smaller than 0.7 is grown as a protective film 7. By this setup, an electrolytic balance is less lost at an interface, and a breakdown phenomenon occurs less.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a high breakdown voltage semiconductor device and a method of manufacturing the same.

[0002]

2. Description of the Related Art Conventionally, polyimide, plasma nitride, or the like has been used as a protective film on the uppermost layer of a semiconductor, particularly a power transistor alone or an IC containing the same. The latter plasma nitride is extremely superior to the former in terms of moisture resistance and alkali ion resistance from the outside, and is often used as a protective film for general standard semiconductor devices.

FIG. 3 shows a process of manufacturing a protective film of a conventional high breakdown voltage semiconductor device including a high breakdown voltage MOS transistor.
As shown in FIG. 3A, a gate oxide film 1 and a gate electrode 2 are formed on a silicon substrate 10. Using the gate oxide film 1 and the gate electrode 2 as a mask, the source 3 and the drain 4 are formed as shown in FIG.

[0004] As shown in FIG.
After an interlayer insulating film 5 is formed so as to cover the drain 4 and the gate electrode 2, a contact hole is formed.
As shown in (d), the metal electrode 6 is formed in the contact hole. Finally, as shown in FIG. 3E, a protective film 7 is formed so as to cover the entire surface of the substrate in a nitrogen gas atmosphere, and a semiconductor device is formed.

In the manufacturing process of such a semiconductor device, a plasma nitride excellent in moisture resistance and alkali ion resistance is often used as the protective film 7, and this protective film 7 is composed of Si: N = 3: 4, that is, (Si /
N) = 0.7 and a stoichiometric composition of approximately Si ₃ N ₄ . The high breakdown voltage MOS transistor manufactured as described above is required to operate with desired characteristics during operation and has a gate voltage of 0 even during non-operation.
It is necessary that no current flows due to a voltage of several hundred volts applied between the source and the drain in a volt or open state.

[0006]

However, in the MOS transistor formed by the above-described conventional manufacturing method, as shown in FIG. 3E, an X mark is formed at the interface between the silicon substrate 10 and the interlayer insulating film 5. The indicated interface level 8 is easily formed. This interface state 8 is formed not only on the surface of a region where impurities are diffused at a high concentration such as the source 3 and the drain 4, but also on a surface of the silicon substrate 10 or a low impurity concentration region such as a channel region of a MOS transistor. In particular, in the low impurity concentration region, the influence of the interface state on the characteristics of the transistor increases.

That is, in the portion of the drain 4 close to the channel or in the low impurity concentration region, particularly in the channel region,
When the interface state is generated non-uniformly, when a high voltage of several hundred volts is applied between the source 3 and the drain 4, for example, the electric field intensity distribution in the horizontal direction becomes non-uniform, and the end of the drain 4 In the vicinity, the electric field intensity is emphasized and becomes maximum,
There is a problem that a breakdown phenomenon occurs and current flows between the source and the drain.

The breakdown phenomenon associated with the interface state 8 is as follows.
This is rarely a problem with a normal low-voltage-drive MOS transistor, but it is a significant problem with a high-breakdown-voltage device, particularly when the transistor is off. SUMMARY OF THE INVENTION It is an object of the present invention to provide a high-breakdown-voltage semiconductor device which solves the above-mentioned problems and controls the interface state to reduce a source-drain breakdown phenomenon, and a method of manufacturing the same.

[0009]

A high breakdown voltage semiconductor device according to the present invention is characterized in that components of a protective film covering the surface of a semiconductor substrate are controlled. According to the present invention, it is possible to solve an inherent problem caused by an interface state.

Further, a method of manufacturing a high withstand voltage semiconductor device according to the present invention is characterized in that a manufacturing process of a protective film is special. According to the present invention, the frequency of disruption of the electric field balance at the interface of the channel region or the like is reduced, and the breakdown is less likely to occur.

[0011]

According to a first aspect of the present invention, there is provided a high withstand voltage semiconductor device comprising a semiconductor element formed on a semiconductor substrate and having a ratio of the number of atoms of Si to N (Si / N) smaller than 0.7. A film is formed. According to a second aspect of the present invention, there is provided a high breakdown voltage semiconductor device according to the first aspect, wherein a ratio of the number of atoms of Si and N (Si / N) is provided on the semiconductor element formed on the semiconductor substrate.
N) is characterized in that a protective film having a thickness of 0.6 or less is formed.

[0012] High voltage semiconductor device according to claim 3 includes, on a semiconductor device formed on a semiconductor substrate, 2.5 × 10 ²²
A silicon hydride film containing hydrogen of atoms / cm ³ or more is formed as a protective film. Claim 4
The described high breakdown voltage semiconductor device is formed on a semiconductor element formed on an l-conductor substrate, and has a ratio of the number of atoms of Si and N (Si / N).
N) a first protective film having a value smaller than 0.7, and a second protective film formed on the first protective film and having a ratio of the number of atoms of Si and N (Si / N) of about 0.7. Is provided.

A method of manufacturing a high-breakdown-voltage semiconductor device according to claim 5, wherein the semiconductor substrate is formed in an inert gas containing at least 7% of hydrogen when a protective film is formed on a semiconductor element formed on the semiconductor substrate. Is subjected to heat treatment to reduce the density of interface states, and a protective film is formed on the semiconductor element after the heat treatment. The method of manufacturing a high withstand voltage semiconductor device according to claim 6, wherein the ratio of the number of atoms of Si and N (Si / N) is smaller than 0.7 on the semiconductor element formed on the semiconductor substrate. A protection film including a silicon hydride film containing hydrogen of × 10 ²² atoms / cm ³ or more is formed.

A method of manufacturing a high withstand voltage semiconductor device according to claim 7.
The method uses a protective film on a semiconductor element formed on a semiconductor substrate.
When forming an inert gas containing 7% or more hydrogen
Heat treatment of the semiconductor substrate in the
And adjust the ratio of monosilane gas to ammonia gas.
2.5 × 10 on the heat-treated semiconductor substrate ^{twenty two}
atoms / cm^ThreeSilicon hydride containing above hydrogen
A protective film including a film is formed.

9. The method of manufacturing a high-breakdown-voltage semiconductor device according to claim 8, wherein said semiconductor substrate is formed in an inert gas containing at least 7% of hydrogen when forming a protective film on a semiconductor element formed on the semiconductor substrate. Heat treatment to reduce the density of interface states, form a protective film on the semiconductor device after the heat treatment, and perform a heat treatment for diffusion on the protective film using an inert gas or a hydrogen-containing gas. It is characterized by the following.

According to a ninth aspect of the present invention, there is provided a method of manufacturing a high breakdown voltage semiconductor device according to the fifth or eighth aspect, wherein
The heat treatment is performed at a temperature of 00 ° C. Less than,
A high breakdown voltage semiconductor device and a method of manufacturing the same according to the present invention will be described based on a specific embodiment, taking a MOS transistor as an example of a high breakdown voltage semiconductor device. The same components as those shown in FIG. 3 showing the conventional example are denoted by the same reference numerals.

(Embodiment 1) FIG. 1 shows (Embodiment 1) of the present invention. In this (Embodiment 1), the conventional M
In order to suppress the breakdown phenomenon accompanying the interface level 8 more than the OS type transistor, the semiconductor substrate 10 is subjected to a heat treatment before the protective film 7 is formed on the semiconductor element formed on the semiconductor substrate 10. However, the other basic configuration is the same as that of FIG. 3 showing the above conventional example.

A specific example will be described below. As shown in FIG. 1A, a gate oxide film 1 having a thickness of about 40 nm was formed on the surface of a silicon substrate 10, and a gate electrode 2 made of a silicon film containing impurities and having a gate length of about 3 μm was formed thereon.
Using the gate oxide film 1 and the gate electrode 2 as a mask, ion implantation was performed to form a source 3 and a drain 4 having a junction depth of about 3 μm upon completion, as shown in FIG.

Next, as shown in FIG. 1C, a silicon oxide film as the interlayer insulating film 5 is formed by thermal CVD or plasma CVD.
After being deposited to a thickness of about 2 μm by a VD method and opening contact windows in the regions of the source 3 and the drain 4, as shown in FIG. An alloy metal electrode 6 was patterned. In FIG. 1E, a heat treatment, which is a characteristic step of the first embodiment, was performed at a temperature of about 400 ° C. for 30 minutes in a nitrogen atmosphere containing 7% or more of hydrogen.

Although the heat treatment temperature is set to about 400 ° C. here, 300 ° C. to 600 ° C. can be used if necessary. This temperature range is mainly determined by the thermal stability of the contact interface of the metal electrode 6, and when a thermally stable barrier metal or the like is formed at the interface between the metal electrode 6 and the source 3 or the drain 4, a heat treatment close to 600 ° C. It becomes possible.

Finally, as shown in FIG. 1F, a stoichiometric silicon nitride film was grown as the protective film 7 so that the atomic ratio was Si: N = 3: 4 as in the conventional case. . Specifically, monosilane and ammonia gas are grown by plasma CVD using a flow rate ratio of 1: 1, a growth temperature of 380 ° C., a growth time of 2 minutes, and nitrogen as a carrier gas. The protective film 7 having a rate of 2.05 was formed. The amount of hydrogen contained in the nitride film immediately after the deposition was 1.5 × 10 ²² atoms / cm ³ .

As described above, by performing the heat treatment in an atmosphere containing hydrogen before forming the protective film 7, the hydrogen easily diffuses into the interlayer insulating film 5 even at a relatively low temperature of about 400 ° C. Then, it can reach the interface between the source 3, the drain 4, and the silicon substrate 10. As a result, FIG.
The interface state 8 existing in (e) is repaired, and the electric charge of the interface state 8 disappears, and as shown in FIG.
The density of the interface states 8 can be reduced.

In the obtained MOS transistor, the frequency of the electric field balance at the interface of the channel region and the like is reduced, and the breakdown phenomenon is less likely to occur. A voltage of 600 volts is applied between the source 3 and the drain 4 of the MOS transistor in a direction opposite to the operation, and the source 3 is applied under a bias condition of applying 0 volt to the gate or in an open state and the substrate potential of 0 volt. As a result of a test on current leakage between the drain 4 and the drain 4, the yield was increased by 18% as compared with the conventional case.

In this (Embodiment 1), FIG.
The heat treatment (e) was performed in a nitrogen atmosphere containing 7% or more of hydrogen, but the present invention is not limited to this.
Any material may be used as long as heat treatment is performed in an inert gas containing 7% or more of hydrogen. Further, it is preferable that the hydrogen concentration in the inert gas is as high as the production conditions permit.
It is desirable to contain 0% or more of hydrogen.

Also, in the above (Embodiment 1), in the heat treatment before forming the protective film 7, it is sufficient that hydrogen entering the interlayer insulating film 5 reaches the interface between the source 3, the drain 4 and the silicon substrate 10. After performing heat treatment in a hydrogen atmosphere to the extent that hydrogen is contained in the interlayer insulating film 5 and forming a silicon nitride film as the protective film 7, an inert gas, a hydrogen-containing gas, or the like is removed. The heat treatment may be performed again to cause hydrogen in the interlayer insulating film 5 to reach the interface.

(Embodiment 2) FIG. 2 shows (Embodiment 2)
The manufacturing procedure of the protective film 7a is the same as that of FIG. 3 showing the conventional example, but the component configuration of the protective film 7a is different from that of the protective film 7 in the conventional example. When forming the protective film 7a on the semiconductor element formed on the semiconductor substrate 10, in the case of this (Embodiment 2), instead of nitrogen as a conventional carrier gas in FIG. Monosilane and ammonia gas, which are active gases, are used.

Then, the ratio between monosilane and ammonia gas is adjusted so that the ratio of the number of atoms of Si and N in the protective film 7a (Si / N) becomes smaller than 0.7, and
A silicon hydride film containing hydrogen of ²² atoms / cm ³ or more is formed as a protective film 7a. Such a protective film 7
When a is provided, hydrogen 9 easily diffuses in the interlayer insulating film 5 at a relatively low temperature, reaches the interface between the source 3, the drain 4, and the silicon substrate 10, and the interface state existing there. Is repaired, the density of the interface states 8 can be reduced.

Specifically, when forming the protective film 7a, a gas of monosilane and ammonia is used as a carrier gas, and the flow ratio is adjusted to increase the ratio of monosilane: ammonia = 1: 8 to ammonia gas. The growth temperature is set to 380 ° C., the growth time is set to 1.5 minutes, and the plasma CV is further increased to a predetermined thickness by using nitrogen as a carrier gas.
Grown by method D.

The obtained protective film 7a has an atomic ratio of Si:
A film having a nitrogen-rich structure with N = 6: 10 (Si / N = 0.6) was obtained. When the film was formed under the condition of a film thickness of 800 nm, the refractive index automatically became 1.8. The amount of hydrogen contained in the nitride film immediately after the deposition was 3.0 × 10 ²²
atoms / cm ³ . In contrast, the silicon nitride film, which is the protective film 7 having the stoichiometric composition formed by the conventional manufacturing method shown in FIG.
05, the amount of hydrogen contained in the film immediately after deposition is 1.5 × 10 ²²
atoms / cm ³ .

Thus, by adjusting the composition of the carrier gas, the hydrogen content of the protective film 7a can be increased as compared with the conventional case. It is preferable that the atomic composition ratio (Si / N) of the nitrogen-rich silicon nitride film be smaller than 0.7 because the contained hydrogen amount becomes larger.
More preferably, the ratio of the number of atoms of Si and N (Si / N) is preferably 0.6 or less.

As described above, when a silicon nitride film containing a large amount of hydrogen is formed as the protective film 7a, hydrogen 9 easily diffuses in the interlayer insulating film 5 at a temperature of about 380 ° C. during the formation of the nitride film. The density of the interface state 8 can be reduced by reaching the interface between the source 3, the drain 4, and the silicon substrate 10 and repairing the interface state existing there.

This nitrogen-rich silicon nitride film is applied to a power MOS transistor having a withstand voltage of 600 volts, and a voltage of 600 volts is applied between the source and the drain of the transistor in a direction opposite to that of the operation, and a gate voltage is applied. Is 0 volts or an open state and the substrate voltage is 0 volts, the yield related to the source-drain leakage current is increased by 15% as compared with the conventional transistor.

[0033] In this Embodiment 2, although the hydrogen content has adopted a film of ^{3.0 × 10 22 atoms / cm 3} , substantially 2.5 × 10 ²² atoms / cm ³ or more The presence of hydrogen content has the effect of reducing interface states. Also, the protective film 7
Has a one-layer structure of a nitrogen-rich silicon nitride film. If the film has insufficient moisture resistance and alkali ion resistance, first, a conventional stoichiometric silicon nitride film is formed on the nitrogen-rich silicon nitride film. The protective film may have a two-layer structure covered with a nitride film.

That is, the ratio of the number of atoms of Si and N (Si /
N) a first protective film having a smaller value than 0.7, and a second protective film formed on the first protective film and having a ratio of the number of atoms of Si to N (Si / N) of about 0.7. May be used as a protective film having a two-layer structure. Even with such a configuration, moisture resistance and alkali ion resistance are improved by the second protective film.
The reliability of the MOS transistor can be further improved.

(Embodiment 3) In the above (Embodiment 1), before forming the protective film 7, the semiconductor substrate 10 is subjected to a heat treatment to form the protective film 7 having the same configuration as that of the conventional example. In this (Embodiment 3), after performing the heat treatment in the above (Embodiment 1), a protective film 7 having the same composition as the above (Embodiment 2) is formed.

That is, when forming the protective film 7 on the semiconductor element formed on the semiconductor substrate 10, hydrogen is
% Or more in an inert gas containing by heat-treating the semiconductor substrate 10 to reduce the density of interface states, then, monosilane gas and ammonia gas 2.5 × 10 on a semiconductor substrate having a specific heat-treated while adjusting the ²² A protection film 7 including a silicon hydride film containing hydrogen of atoms / cm ³ or more is formed.

With such a configuration, it is possible to reduce the breakdown phenomenon between the source and the drain by controlling the interface state, reduce the frequency of the electric field balance in the channel region, and further improve the quality. In the description of the above embodiments, an example of a power MOS transistor has been described, but the present invention is not limited to this.
In other elements such as a bipolar transistor, a thyristor, and an insulated gate bipolar transistor, a problem inherent to an interface state can be solved.

[0038]

As described above, according to the high breakdown voltage semiconductor device of the present invention, the semiconductor device formed on the semiconductor substrate is
By forming a silicon hydride film having a ratio of the number of atoms of Si and N (Si / N) smaller than 0.7 and containing hydrogen of 2.5 × 10 ²² atoms / cm ³ or more as a protective film,
The frequency at which the electric field balance at the interface is lost is reduced, so that the breakdown phenomenon can be reduced.

Further, according to the method of manufacturing a high breakdown voltage semiconductor device of the present invention, the density of interface states is reduced by heat-treating the semiconductor substrate in an inert gas containing 7% or more of hydrogen.
By forming a protective film on the semiconductor element after the heat treatment, hydrogen supplied from the protective film or the hydrogen atmosphere reduces an interface state formed at the interface between the silicon substrate and the interlayer insulating film, It is possible to easily realize a high withstand voltage semiconductor element in which the electric field balance is less frequently broken.

As a result, in a high withstand voltage semiconductor device having a reverse breakdown voltage of several hundred volts, it is possible to manufacture a semiconductor device in which the withstand voltage is reduced and the withstand voltage fluctuation is small due to the interface state existing on the semiconductor substrate surface.

[Brief description of the drawings]

FIG. 1 is a view showing a manufacturing process of a high breakdown voltage MOS transistor in (Embodiment 1);

FIG. 2 is a cross-sectional view of a high-breakdown-voltage MOS transistor according to Embodiment 1;

FIG. 3 is a diagram showing a manufacturing process of a conventional high breakdown voltage MOS transistor.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Gate oxide film 2 Gate electrode 3 Source 4 Drain 5 Interlayer insulating film 6 Metal electrode 7a Protective film 8 Interface state 9 Hydrogen 10 Silicon substrate

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 5F005 AH04 BB02 5F040 DA00 DA21 DC01 EB14 EB18 EL02 FC00 5F058 BA01 BD10 BF07 BF23 BF30 BJ01 BJ03

Claims (9)

[Claims] 1. A high breakdown voltage semiconductor device in which a protective film having a ratio of the number of atoms of Si and N (Si / N) smaller than 0.7 is formed on a semiconductor element formed on a semiconductor substrate. 2. The high breakdown voltage semiconductor device according to claim 1, wherein a protective film having an atomic ratio of Si and N (Si / N) of 0.6 or less is formed on the semiconductor element formed on the semiconductor substrate. . 3. A high breakdown voltage semiconductor device in which a silicon hydride film containing at least 2.5 × 10 ²² atoms / cm ³ of hydrogen is formed as a protective film on a semiconductor element formed on a semiconductor substrate. 4. A semiconductor device formed on a semiconductor substrate and having a ratio of the number of atoms of Si and N (Si / N) of 0.7
A smaller first protective film, and a ratio of the number of atoms of Si and N formed on the first protective film (S
A high withstand voltage semiconductor device provided with a second protective film having a ratio (i / N) of about 0.7. 5. When forming a protective film on a semiconductor element formed on a semiconductor substrate, the semiconductor substrate is heat-treated in an inert gas containing 7% or more of hydrogen to reduce the density of interface states. A method for manufacturing a high breakdown voltage semiconductor device, wherein a protective film is formed on a semiconductor element after the heat treatment. 6. A semiconductor device formed on a semiconductor substrate, wherein a ratio of the number of atoms of Si and N (Si / N) is smaller than 0.7 and is not less than 2.5 × 10 ²² atoms / cm ³ . A method for manufacturing a high-breakdown-voltage semiconductor device in which a protective film including a silicon hydride film containing hydrogen is formed. 7. When forming a protective film on a semiconductor element formed on a semiconductor substrate, the semiconductor substrate is heat-treated in an inert gas containing at least 7% of hydrogen to reduce the density of interface states. 2.5 × 10 ²² atoms / c on the heat-treated semiconductor substrate while adjusting the ratio of monosilane gas to ammonia gas.
A method for manufacturing a high withstand voltage semiconductor device for forming a protective film including a silicon hydride film containing hydrogen of m ³ or more. 8. When forming a protective film on a semiconductor element formed on a semiconductor substrate, the semiconductor substrate is heat-treated in an inert gas containing 7% or more of hydrogen. A method for manufacturing a high breakdown voltage semiconductor device, wherein a protective film is formed thereon, and a heat treatment for diffusion is performed on the protective film using an inert gas or a hydrogen-containing gas. 9. The method according to claim 5, wherein the heat treatment is performed at a temperature of 300 ° C. to 600 ° C.