JPH09289207A - Semiconductor device and its fabrication method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a semiconductor device including an oxide film in which a trouble is difficult to occur and accumulation of negative electric charges due to electron capture is difficult to occur. SOLUTION: A first silicon oxide film 3a is provided on a first electrode 1. A second silicon oxide film 3b having smaller specific gravity than the first silicon oxide film 3a is provided on the first silicon oxide film 3a. A second electrode 4 is provided on the second silicon oxide film 3b. In the second silicon oxide film 3b, contents of a chloride atom is larger than those of a hydrogen atom.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention generally relates to semiconductor devices, and more particularly to a semiconductor device improved so that a failure is less likely to occur. The present invention also relates to a method for manufacturing such a semiconductor device.

[0002]

2. Description of the Related Art Conventionally, metal-oxide film-semiconductor (Metal-Ox)
The gate oxide film of an ide-Semiconductor (MOS) type transistor has been formed by thermally oxidizing the surface of a silicon substrate with O ₂ gas or water vapor (H ₂ O). However, the literature of Yamabe et al. (K. Yamabe, K. Tanigu
chi, and Y. Matsushita, "Thickness dependence of d
ielectric breakdown failure of thermal SiO ₂ film
s, "Proc. 1983 International Reliability Physics S
ymposium, p.184), SiO ₂ obtained by thermally oxidizing the surface of a silicon substrate due to “microdefect” in the silicon substrate.
The membrane causes a "B mode failure". In order to reduce such a failure of the SiO ₂ film due to “microdefect” in the silicon substrate, J.
Lee et al. Used Si in a MOS structure by using a chemical vapor deposition method.
A method for forming an O ₂ film is proposed (J. Lee, IC
Chen, and C Hu, "Comparison between CVD and therma
l oxide dielectric Integrity, "IEEE Electron Divice
Letter, p.506, EDL-7, 1986).

In the CVD method, a "micro-deposition of a silicon substrate is performed.
SiO without being affected by “fect” _TwoCan form a film
Therefore, SiO that is hard to cause a failure_TwoCan get the membrane
You. J. The method proposed by Lee et al._FourGas and O
_TwoThis is a low pressure CVD method using gas as a raw material, and the growth temperature is 4
It is 50 ° C.

On the other hand, Y. H. Lee et al. Formed a SiO ₂ film grown by a thermal oxidation method, and further formed a SiH ₂ film on it.
Depressurized C at 900 ° C using Cl ₂ gas and N ₂ O gas as raw materials
It proposes a method of forming a SiO ₂ film by a VD method to form a SiO ₂ film having a laminated structure.

[0005]

However, the above-mentioned Y. H. It has been pointed out that the hot carrier characteristic deteriorates in the P-channel MOS transistor manufactured by the method of Lee et al. It is believed that this is because the SiO ₂ film formed by the CVD method has a high electron capture rate.

The cause of the high electron capture rate is SiH._TwoC
l_TwoGas and N_TwoH generated by reaction with O gas_TwoO is Si
O_TwoTo be incorporated into the film to form Si-OH bonds
Conceivable. The Si-OH bond becomes the center of the electron trap.
It is believed that. SiH _FourGas and O_TwoGas as raw material
Also in the case of the low pressure CVD method_TwoWhen the generation of O occurs
Conceivable. That is, SiH_TwoCl_TwoAnd SiH_FourSuch
Raw material containing hydrogen, N_TwoO or O_TwoContains oxygen such as
In the reaction with raw materials, H_TwoThe generation of O is inevitable
Yes. As a result, this method has a low electron capture rate of S.
iO_TwoIt is difficult to form a film.

Therefore, an object of the present invention is to provide a semiconductor device improved so that a failure is less likely to occur.

Still another object of the present invention is to provide a semiconductor device having a SiO ₂ film having a low electron capture rate.

Another object of the present invention is to provide a method of manufacturing a semiconductor device having a SiO ₂ film which is hard to cause a failure and has a low electron capture rate.

[0010]

A semiconductor device according to a first aspect of the present invention includes a first electrode. A first silicon oxide film is provided on the first electrode. A second silicon oxide film having a specific gravity smaller than that of the first silicon oxide film is provided on the first silicon oxide film. A second electrode is provided on the second silicon oxide film. In the second silicon oxide film,
The content of chlorine atoms is made larger than that of hydrogen atoms.

A semiconductor device according to a second aspect of the present invention includes a semiconductor substrate. A silicon gate oxide film is provided on the semiconductor substrate. A gate electrode is provided on the silicon gate oxide film. Sidewall spacers formed of a silicon oxide film having a smaller specific gravity than the silicon gate oxide film are provided on the sidewalls of the gate electrode. In the above sidewall spacer, the content of chlorine atoms is made larger than the content of hydrogen atoms.

A semiconductor device according to a third aspect of the present invention includes a first electrode. A silicon nitride film is provided on the first electrode. A silicon oxide film is provided on the silicon nitride film. A second electrode is provided on the silicon oxide film. In the silicon oxide film, the content of chlorine atoms is larger than the content of hydrogen atoms.

In the method of manufacturing a semiconductor device according to the fourth aspect of the present invention, first, a first silicon oxide film is formed on the first electrode by thermal oxidation. A second silicon oxide film is formed on the first silicon oxide film by a chemical vapor deposition method using SiCl ₄ gas and an oxidizing gas. A second electrode is formed on the second silicon oxide film.

The operation and effect of the present invention will be described below. CVD using a raw material containing hydrogen such as SiH ₂ Cl ₂ and SiH ₄ and a raw material containing oxygen such as N ₂ O and O _2.
Since the SiO ₂ film formed by the method has a high electron capture rate, it is difficult to form a gate oxide film having excellent hot carrier characteristics for MOS transistors. Conventionally, it has been pointed out that the existence of water-related trap centers is a cause of such electron capture in the SiO ₂ film.

Furthermore, J. Lee and Y. H. In the method disclosed in Lee et al., SiH ₂ Cl ₂ gas and SiH ₄ gas are used as source gases when depositing a SiO ₂ film by the CVD method. When such a raw material gas containing hydrogen is reacted with an oxidizing agent such as O ₂ gas or N ₂ O gas, water (H ₂ O) is generated as a by-product. Therefore, it has been proved that trap centers caused by water are formed in the formed SiO ₂ film, and electron trapping easily occurs.

In the thin film forming method of the present invention, Si is used.
A SiO ₂ film is formed by a CVD method using Cl ₄ gas as a raw material. This raw material contains no hydrogen, in the SiO ₂ film is not formed is trapped around due to water, the trap center density lower SiO ₂ film can be formed. Also, CV
For using D method without being influenced by the "Mikurodefekuto" of the silicon substrate can be formed of SiO ₂ film, it is possible to obtain a hardly generated SiO ₂ film failure.

However, when SiCl ₄ gas is used, chlorine gas (Cl ₂ ) is generated as a by-product. Cl ₂ etches the silicon substrate and roughens the surface of the silicon substrate. Therefore, when the SiO ₂ film is formed on the surface of the silicon substrate by the CVD method using SiCl ₄ gas as a raw material, the formed SiO ₂ film has extremely low insulation.

In order to solve this problem, in the method of forming a thin film according to the present invention, the surface of the silicon substrate is thermally oxidized or thermally nitrided to form a thin SiO ₂ film or Si ₃ N ₄ film, and then SiCl. _{4C using} gas and oxidizer as raw materials
A VD method is performed to form a laminated insulating film. As a result, it is possible to obtain an insulating film in which a failure is unlikely to occur.

Further, the surface of the silicon substrate is thermally oxidized or thermal nitridation, even after forming a thin SiO ₂ film or Si ₃ N ₄ film by low pressure CVD using SiCl ₄ gas, the SiO ₂ film The following problems occur when the deposition is performed. That is, when the temperature is 1000 ° C. or higher, the SiO ₂ film or Si ₃ N ₄ film formed on the surface of the silicon substrate is locally etched, and pinholes are generated. Etching of the silicon substrate progresses in this pinhole portion to roughen the surface of the silicon substrate. Therefore, the insulating property of the formed SiO ₂ film is extremely low.
Therefore, in the preferred manufacturing method of the present invention, the surface of the silicon substrate is thermally oxidized or thermally nitrided, whereby S
After thinly forming the iO ₂ film or the Si ₃ N ₄ film,
CVD using l ₄ gas and an oxidizing agent as raw materials is performed at 1000 ° C. or lower to form a laminated insulating film. By doing so, an insulating film that is less likely to cause a failure can be obtained.

As described above, when a silicon oxide film is formed by CVD using SiCl ₄ gas and an oxidizing agent as raw materials, the obtained silicon oxide film contains almost no hydrogen atoms. On the other hand, some chlorine atoms remain in the silicon oxide film. Therefore, according to this method, a silicon oxide film having a chlorine atom content higher than a hydrogen atom content can be obtained. In this respect, those obtained by this method are the same as those described in J. It differs from that obtained by the method of Lee et al. That is, J. In the silicon oxide film obtained by the method of Lee et al., The content of hydrogen atoms is large, while chlorine atoms are not contained at all.

[0021]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the drawings.

First Embodiment FIG. 1 is a sectional view of a MOS capacitor according to the first embodiment of the present invention. The MOS capacitor has a silicon substrate-SiO ₂ film-n ⁺ polysilicon structure. MOS
S formed on the surface of a silicon substrate using a capacitor
The electron capture characteristics of the iO ₂ film 3 were examined. An n-type (100) silicon substrate was used as the silicon substrate 1. The specific resistance of the substrate is about 15 Ωcm. To fabricate a MOS capacitor, first, a 4000 Å isolation oxide film 2 was formed by the LOCOS method. After that, about 800 in steam atmosphere
A 300Å sacrificial oxide film was grown at a temperature of ° C, and the sacrificial oxide film was removed by a 1% HF solution. Subsequently, the gate oxide film 3 having a laminated structure was formed by the following five types of methods.

(1) By inserting the silicon substrate 1 into an electric furnace and thermally oxidizing it with steam at a temperature of 750 ° C. under a pressure of 760 Torr, Si of about 30 Å is obtained.
The O ₂ film 3a was grown. After that, the silicon substrate is inserted into another electric furnace, and the pressure is reduced to CV by using SiCl ₄ gas and N ₂ O gas at a temperature of 900 ° C. and a pressure of 1 Torr.
Deposit about 30Å of SiO ₂ film 3b by D method,
A SiO ₂ film 3 having a laminated structure of 0Å was formed.

(2) A sample having the gate oxide film 3 formed only by the thermal oxidation method was also prepared as a comparative example. The gate oxide film by the thermal oxidation method was obtained by growing it using O ₂ in an electric furnace at a temperature of 750 ° C. under a pressure of 760 Torr. The film thickness of the SiO ₂ film 3 was about 60Å.

(3) Using an electric furnace, the silicon substrate is thermally oxidized with water vapor at a temperature of 750 ° C. and a pressure of 760 Torr to obtain about 30 Å of SiO 2.
_Two films (3a in FIG. 1) were grown. Then, the silicon substrate was inserted into another electric furnace, and the pressure was reduced to about 850 ° C. under a pressure of 0.5 Torr using SiH ₂ Cl ₂ gas and N ₂ O gas by a low pressure CVD method. 30Å SiO ₂
A film (3b in FIG. 1) is deposited, and an S of about 60 Å is formed.
The iO ₂ film 3 was formed. This was also a sample used as a comparative example.

(4) Insert the silicon substrate into the electric furnace,
SiCl ₄ at a temperature of 900 ° C. and a pressure of 1 Torr
Gas and N ₂ O gas, about 60 by low pressure CVD method
A Å SiO ₂ film 3 was formed.

(5) By inserting the silicon substrate 1 into an electric furnace and thermally oxidizing it with steam at a temperature of 750 ° C. under a pressure of 760 torr, SiO _{2 of} about 30 Å is obtained.
Grow the film. Then, insert the silicon substrate into another electric furnace, and at a temperature of 1000 ° C. under a pressure of 1 Torr,
A SiO ₂ film was deposited by a low pressure CVD method using SiCl ₄ gas and N ₂ O gas to form a SiO ₂ film 3 having a laminated structure.

After forming the SiO ₂ film 3 by the above five methods, a doped polysilicon film of about 2000 Å was deposited by the low pressure CVD method. Next, the doped polysilicon film is processed into a predetermined pattern by photolithography and etching, and annealed in a nitrogen atmosphere at 900 ° C. to make the n ⁺ polysilicon electrode 4 having a phosphorus concentration of 6 × 10 ²⁰ cm ^−3. Was formed. Subsequently, a low pressure CVD method is used to deposit a silicon oxide film 5 of about 5000 Å,
Annealing was performed in a nitrogen atmosphere at 0 ° C. After that, a contact hole 6 was formed in the silicon oxide film 5 by photolithography and etching. Al-is formed by a sputtering method so as to be buried in the contact hole 6.
A Si—Cu alloy was deposited on the silicon substrate 1 and processed into a desired pattern by photolithography and etching to form an aluminum electrode 7. Finally, 450
Annealing was performed in a hydrogen atmosphere at ℃. The area of the formed MOS capacitor is 1.0 mm ² .

FIG. 2 shows a MOS capacitor having a gate oxide film (called a CVD oxide film (1)) formed by the method (1) and a gate oxide film formed by a thermal oxidation method (called a thermal oxide film (2)). FIG. 6 is a diagram comparing the performance with a MOS capacitor having a. In FIG. 2, the silicon substrate 1 is grounded, a positive voltage is applied to the polysilicon electrode 4, and +0.4 A / cm ^{2 is applied.}
3 is a graph showing the relationship between the cumulative failure rate (vertical axis) of a MOS capacitor that has failed due to dielectric breakdown and the voltage application time (horizontal axis) when a constant current of (1) is applied. In the case of the thermal oxide film (2), the failure occurs in the region where the voltage application time is short and 10 seconds or less, whereas the CVD oxide film (1)
Then, no trouble is seen. In addition, the above (4) and (5)
The gate oxide film created in step 2 has a low withstand voltage,
When a constant current of A / cm ² was applied, all the samples broke in less than 0.1 seconds. That is, the use of the CVD oxide film (1) was the most effective method for suppressing dielectric breakdown.

Next, another test was conducted using the MOS capacitor having the CVD oxide film (1), the CVD oxide film (3) and the thermal oxide film (2). Ground the silicon substrate 1,
A positive voltage is applied to the polysilicon electrode 4 and a constant current (current density 5 mA / cm ² ) is applied to change the gate voltage ΔVg.
Was measured.

The result of plotting the change ΔVg of the gate voltage against the current injection time is shown in FIG. Referring to FIG. 3, in the case of the CVD oxide film (3), the change ΔVg showed an increase. This indicates the following. That is, C
Electrons are trapped in the VD oxide film (3), whereby C
Negative charges are formed in the VD oxide film (3). This negative charge makes it difficult for the current to flow, and thus requires a higher voltage to flow a constant current. On the other hand, in the case of the CVD oxide film (1), the voltage is decreased, which indicates that positive charges are formed in the oxide film. That is, C
The use of the VD oxide film (1) was the most effective method for suppressing the accumulation of charges due to electron capture.

Embodiment 2 Embodiment 2 of the present invention relates to another method of forming an oxide film by the CVD method. First, a silicon substrate is thermally oxidized to form a SiO ₂ film. Then SiCl
10 by low pressure CVD method using ₄ gas and NO gas
A SiO ₂ film is deposited at a temperature of 00 ° C. or lower. Even if a laminated oxide film is formed by this method, the first embodiment of the invention
The same effect as in the case of is achieved.

Embodiment 3 In the embodiment of the invention described above, the case where the thermal oxide film is formed on the silicon substrate and then the oxide film is formed by the CVD method has been exemplified, but the present invention is not limited to this. Absent.

The silicon surface is treated with NH 3 at 900 ° C., for example.
Approximately 1 on the silicon surface by thermal nitriding in ₃ atmospheres
A 5Å Si ₃ N ₄ film is formed. After that, by using a low pressure CVD method using SiCl ₄ gas and NO gas, Si ₃ N
_A SiO ₂ film is deposited on the ₄ films at a temperature of 1000 ° C. or lower. Then, a gate oxide film having a laminated structure is formed. Also by this method, a semiconductor device having the same effect as that of the first embodiment of the present invention can be obtained.

Fourth Embodiment Although a MOS capacitor has been illustrated in the above-described embodiments of the present invention, the present invention is not limited to this. FIG.
FIG. 9 is a sectional view of a MOS transistor according to a fourth embodiment of the present invention. Referring to FIG. 4, source / drain regions 8 are formed in the surface of silicon substrate 1 (first electrode). A silicon oxide film 3a formed by a thermal oxidation method is formed on the silicon substrate 1. A SiO ₂ film 3b formed on the silicon oxide film 3a by a low pressure CVD method using SiCl ₄ gas and N ₂ O gas.
Are formed. A gate electrode 9 (second electrode) is formed on the gate oxide film (3a, 3b). Referring to FIG. 4, the specific gravity of silicon oxide film 3a is larger than that of silicon oxide film 3b. Further, the content of chlorine atoms in the silicon oxide film 3b is made larger than the content of hydrogen atoms. That is, since SiCl ₄ gas is used as the source gas for forming the silicon oxide film 3b, hydrogen atoms are hardly contained in the silicon oxide film 3b. On the other hand, chlorine atoms remain in the silicon oxide film 3b.

By forming the gate oxide film of the MOS transistor in such a laminated structure, it becomes a gate oxide film which is less likely to cause a failure and less likely to accumulate negative charges due to electron capture.

When the thickness of the gate oxide film 3a is t ₁ and the thickness of the gate oxide film 3b is t ₂ , it is preferable to satisfy the following inequalities.

[0038]

[Equation 2]

That is, the total film thickness (t ₁ + t ₂ ) is 60Å
Then, t ₂ is preferably 30 to 50 Å.

Embodiment 5 FIG. 5 is a sectional view of a flash memory according to Embodiment 5 of the present invention. Referring to FIG. 5, source / drain regions 8 are formed in the main surface of silicon substrate 1.
A silicon oxide film 3a formed by thermal oxidation is formed on the silicon substrate 1. On the silicon oxide film 3a,
A silicon oxide film 3b formed by a low pressure CVD method using SiCl ₄ gas and N ₂ O gas is provided. The floating gate 10 is provided on the silicon oxide film 3b. A silicon oxide film 11a formed by thermal oxidation is provided on the floating gate 10. A silicon oxide film 11b formed by a low pressure CVD method using SiCl ₄ gas and N ₂ O gas is provided on the silicon oxide film 11a. Silicon oxide film 1
A control gate 12 is provided on 1b. A failure occurs when the insulating film between the silicon substrate 1 and the floating gate 10 has such a laminated structure and the insulating film between the floating gate 10 and the control gate 12 has such a laminated structure. It becomes an insulating film that is hard to prevent accumulation of negative charges due to electron capture, and the characteristics of the semiconductor device are improved.

Embodiment 6 The embodiment of the invention described above relates to a silicon oxide film sandwiched between the first electrode and the second electrode.
The present invention is not limited to this.

FIG. 6 shows a semiconductor device according to the sixth embodiment of the present invention.
FIG. 6 is a cross-sectional view of a body device. L on the main surface of the silicon substrate 1.
Source / drain regions 8 having a DD structure are provided.
Silicon formed on the silicon substrate 1 by a thermal oxidation method
The conoxide film 13 is formed. Silicon oxide film 13
Gate electrode 1 made of phosphorus-doped polysilicon on top of
4 are provided. On the side wall of the gate electrode 14, SiC
l_FourGas and N_TwoShaped by low pressure CVD method using O gas
Side wall spacer made of silicon oxide film
A sensor 15 is provided. Sidewall spacer 1
4, SiCl _FourGas and N_TwoReduced pressure CV using O gas
Negative charge due to electron capture is formed by the D method.
The load is less likely to accumulate. Obtained side
In the space spacer, the content of chlorine atoms is
Being larger than the content of offspring.

[0043]

As described above, according to the present invention,
On the surface of the silicon oxide film formed by thermal oxidation of silicon, a SiO ₂ film is deposited by a CVD method using SiCl ₄ gas and an oxidizing gas such as N ₂ O, NO, or O ₂ gas to form a laminated structure. Since the silicon oxide film is obtained, it is possible to obtain an oxide film in which failure is unlikely to occur and negative charges are less likely to be accumulated due to electron capture. As a result, there is an effect that a highly reliable semiconductor device can be obtained.

[Brief description of drawings]

FIG. 1 is a cross-sectional view of a MOS capacitor according to an embodiment of the present invention.

FIG. 2 is a graph showing the relationship between the cumulative failure rate of MOS capacitors and the voltage application time.

FIG. 3 is a graph chart in which a relationship between a change ΔVg in gate voltage and a current injection time is plotted.

FIG. 4 is a sectional view of a MOS transistor according to another embodiment of the present invention.

FIG. 5 is a sectional view of a flash memory according to still another embodiment of the present invention.

FIG. 6 is an MO according to still another embodiment of the present invention.
It is sectional drawing of SFET.

[Explanation of symbols]

1 silicon substrate, 3 gate oxide film, 4 polysilicon electrode.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Office reference number FI Technical indication location H01L 29/78 H01L 29/78 371 21/8247 29/788 29/792

Claims (13)

[Claims] 1. A first electrode, a first silicon oxide film provided on the first electrode, and the first silicon oxide film provided on the first silicon oxide film.
A second silicon oxide film having a smaller specific gravity than that of the silicon oxide film, and a second electrode provided on the second silicon oxide film. The semiconductor device, wherein the content is greater than the content of hydrogen atoms. 2. The film thickness of the first silicon oxide film is t1.
The semiconductor device according to claim 1, wherein the following inequality is satisfied, where t2 is the thickness of the second silicon oxide film. [Equation 1] 3. The semiconductor device according to claim 1, wherein the first electrode includes a semiconductor substrate, and the second electrode includes a gate electrode of a MOSFET. 4. The first electrode comprises a semiconductor substrate and the second electrode comprises a floating gate.
3. The semiconductor device according to claim 1. 5. The first electrode includes a control gate, and the second electrode includes a floating gate.
The semiconductor device according to claim 1. 6. A semiconductor substrate, a silicon gate oxide film provided on the semiconductor substrate, a gate electrode provided on the silicon gate oxide film, a sidewall provided on the gate electrode, and the silicon A sidewall spacer formed of a silicon oxide film having a specific gravity smaller than that of the gate oxide film, wherein the content of chlorine atoms in the sidewall spacer is larger than that of hydrogen atoms. 7. A first electrode, a silicon nitride film provided on the first electrode, a silicon oxide film provided on the silicon nitride film, and a silicon oxide film provided on the silicon oxide film. And a second electrode formed therein, wherein the content of chlorine atoms in the silicon oxide film is larger than the content of hydrogen atoms. 8. A method of manufacturing a semiconductor device including a silicon oxide film sandwiched between a first electrode and a second electrode, wherein a first oxide film is formed on the first electrode by thermal oxidation. A step of forming a silicon oxide film; a step of forming a second silicon oxide film on the first silicon oxide film by a CVD method using SiCl ₄ gas and an oxidizing gas; And a step of forming a second electrode on the silicon oxide film. 9. The method of manufacturing a semiconductor device according to claim 8, wherein N ₂ O gas is used as the oxidizing gas, and the second silicon oxide film is formed at a temperature of 1000 ° C. or lower by a low pressure CVD method. 10. The method of manufacturing a semiconductor device according to claim 8, wherein NO gas is used as the oxidizing gas, and the second silicon oxide film is formed at a temperature of 1000 ° C. or lower by a low pressure CVD method. 11. A step of forming a silicon nitride film on a first electrode, and a silicon oxide film is deposited on the silicon nitride film by a CVD method using a SiCl ₄ gas and an oxidizing gas. A method of manufacturing a semiconductor device, comprising: a step of forming a second electrode on the silicon oxide film. 12. The method of manufacturing a semiconductor device according to claim 11, wherein N ₂ O gas is used as the oxidizing gas, and the second silicon oxide film is formed at a temperature of 1000 ° C. or lower by a low pressure CVD method. 13. The method of manufacturing a semiconductor device according to claim 11, wherein NO gas is used as the oxidizing gas, and the second silicon oxide film is formed at a temperature of 1000 ° C. or lower by a low pressure CVD method.