JPH11150246A - Capacitor-insulating film of semiconductor device and its manufacturing method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a capacitor-insulating film that secures the capacitance of a capacitor and can maintain a proper insulation property, even when the capacitor is thinned in the case of a three-layer structure. SOLUTION: In the capacitor of a semiconductor device containing a capacitor-insulating film, a lower layer electrode 2 is formed by polysilicon which contains a high-concentration impurity on a substrate 1, an insulating film 3 with three-layer structure is formed on the lower layer electrode 2, and an upper layer electrode 4 is formed last on the insulating film 3 by polysilicon containing impurity as in the lower layer electrode 2. The insulating film 3 has the three-layered structure of N/O/N, in which a first silicon nitride film (Si3 N4 ) 3a, a silicon oxide film (SiO2 ) 3b, and a second silicon nitride film (Si3 N4 ) 3c are successively overlapped from the side of the lower layer electrode 2. The film thickness of the silicon oxide film 3b of 3 nm or more is secured, and the thickness of the first silicon nitride film 3a is set nearly equal to that of the second silicon nitride film 3b.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a structure of an insulating film of a capacitor included in a semiconductor device such as an IC, and a method of manufacturing the same.

[0002]

2. Description of the Related Art Capacitors included in semiconductor devices include:
An insulating film is formed on a lower electrode made of polysilicon containing impurities, and an upper electrode is formed of polysilicon containing impurities on the insulating film. Conventional insulating film
It consists of a combination of a silicon oxide film (SiO ₂ ) and a silicon nitride film (Si ₃ N ₄ ), and has a two-layer structure of O / N (oxide film / nitride film) or O / N / O (oxide film / nitride film) / Oxide film) 3
It has a layer structure. In any case, the thickness of the oxide film is 3 nm
The thickness of the nitride film is about 3 nm to 10 nm. The silicon nitride film is formed by low pressure chemical vapor deposition (LPCVD) using dichlorosilane (SiH ₂ Cl ₂ ) or monosilane (SiH ₄ ) and ammonia (NH ₃ ).

When dichlorosilane and ammonia are used in forming a silicon nitride film, the lower limit temperature of the reaction is about
Although the temperature is 600 ° C., the higher the temperature, the faster the film formation rate. Therefore, conventionally, the film is formed at 700 ° C. to 750 ° C. Also, the flow ratio of ammonia to dichlorosilane (NH ₃ / SiH ₂ C
l ₂ ) is set to about 10 to 100.

[0004]

As the size of the semiconductor device is reduced, a thin film is required for the insulating film in order to secure a large capacitance with a small electrode area. For this purpose, a predetermined film thickness is required. The above-described conventional insulating film having a three-layer structure of O / N / O has two layers of silicon oxide films, and thus the proportion of the oxide film in the entire insulating film is large, but the silicon oxide film is a silicon nitride film. Since the dielectric constant is lower than that of, the average dielectric constant of the entire insulating film is relatively low, and the capacitance obtained with a constant film thickness is relatively small. In a conventional insulating film having a three-layer structure, a silicon oxide film formed in contact with electrodes on both sides has a low blocking property against impurities and is weak against the mechanical strength and unevenness. When the impurities from the electrodes diffuse into the oxide film, when an external stress is applied, or when a three-dimensional structure electrode or an electrode having unevenness on the surface is used, the insulating property is reduced. When the thickness is thin, this decrease becomes remarkable.

On the other hand, if a thin insulating film is formed by a conventional manufacturing method in a conventional O / N two-layer structure, the life until the insulating film is broken by applying a voltage is short, and the life of the capacitor is reduced.
As a result, there is a problem that the life of a semiconductor device such as an IC including a capacitor is shortened.

The present invention has been made in view of the above-mentioned problems of the prior art, and in the case of a three-layer structure, a larger capacitance than the conventional one can be ensured at a predetermined film thickness, and good results are obtained. It is an object of the present invention to provide a method for manufacturing a capacitor insulating film which can maintain the insulating property and has a high durability even in a case where the capacitor insulating film has a two-layer structure and has a small thickness.

[0007]

A three-layer capacitor insulating film of a semiconductor device according to the present invention comprises a silicon oxide film and a silicon nitride film, and is provided between a lower layer and an upper layer electrode. In the capacitor insulating film,
A first silicon nitride film, a silicon oxide film,
The second silicon nitride film is sequentially laminated. Such an insulating film includes a step of forming a first silicon nitride film on the lower electrode, a step of forming a silicon oxide film on the first silicon nitride film, and a step of forming a second silicon nitride film on the silicon oxide film. And a step of forming a film.

In the above configuration, it is desirable that the thickness of the silicon oxide film is 3 nm or more, and that the first and second silicon nitride films have substantially the same thickness. After the first silicon nitride film is thermally nitrided on the lower electrode,
It can be formed by depositing a silicon nitride film by a CVD method, or a load lock type LPC.
It can be formed by depositing a silicon nitride film by the VD method. Further, in the step of forming the silicon oxide film, it is preferable to perform annealing in an oxidizing atmosphere after depositing the silicon oxide film by the CVD method, and more preferable to anneal in an oxidizing atmosphere after annealing in an ammonia gas.

Further, according to the method of manufacturing a capacitor insulating film having a two-layer structure of a semiconductor device according to the present invention, LPCVD using dichlorosilane and ammonia as raw materials on a lower electrode is provided.
In the range of 600 to 700 ° C., preferably 650 to 700 ° C.
Forming a silicon nitride film in a temperature range of 700 ° C. and forming a silicon oxide film on the silicon nitride film;

Further, the semiconductor device according to the present invention has a
Another method for manufacturing a capacitor insulating film having a layered structure is to use LP with dichlorosilane and ammonia as raw materials on a lower electrode.
The method includes a step of forming a silicon nitride film at a flow rate ratio of ammonia to dichlorosilane of 1 to 5 by a CVD method, and a step of forming a silicon oxide film on the silicon nitride film.

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, embodiments of a capacitor insulating film of a semiconductor device according to the present invention and a method of manufacturing the same will be described. As shown in FIG. 1, the capacitor of the semiconductor device including the capacitor insulating film of the first embodiment has a substrate 1
A lower electrode 2 is formed of polysilicon containing impurities at a high concentration, and an insulating film 3 having a three-layer structure is formed on the lower electrode 2.
Is formed, and finally the upper electrode 4 is formed on the insulating film 3 by the lower electrode 2.
It is formed of polysilicon containing impurities in the same manner as described above. The electrodes 2 and 4 may be formed of silicon.

The insulating film 3 is formed in the order of the first
Silicon nitride film (Si ₃ N ₄ ) 3a, silicon oxide film (SiO ₂ )
3b and a three-layer structure of N / O / N constituted by stacking a second silicon nitride film (Si ₃ N ₄ ) 3c. Silicon oxide film 3
The thickness of b is 3 nm or more, and the thicknesses of the first and second silicon nitride films 3a and 3c are set to be substantially equal.

The silicon nitride film has higher densities and hardnesses than the silicon oxide film, has a high blocking property against impurities and gases, and has a property of being resistant to irregularities. Therefore, by providing the silicon nitride films 3a and 3c at the positions in contact with the electrodes as in the first embodiment, the electrodes 2 and 4 can be formed.
Can be prevented from diffusing into the insulating film 3 and the resistance to mechanical stress applied from the outside can be increased. Deterioration of characteristics can be prevented.

Since the capacitance of a capacitor is inversely proportional to the distance between the electrodes and proportional to the dielectric constant of the insulating film, in order to increase the capacitance, it is necessary to make the insulating film thinner and increase the dielectric constant of the insulating film. It will be good. Dielectric constant of silicon oxide film 3.9
Since the dielectric constant of the silicon nitride film is as high as 6.9,
By increasing the proportion of the nitride film in the insulating film 3 as in the first embodiment, the average dielectric constant of the insulating film can be increased, and a large capacitance can be ensured even with the same thickness as in the related art. .

The first and second silicon nitride films 3a, 3a,
By setting the thickness of 3c to be substantially equal, the polarity dependency can be eliminated. As shown in the band diagram of FIG. 2, the current conduction in the silicon nitride film is mainly caused by pool Frenkel holes, so that silicon is provided on both electrode sides of the lower electrode (cathode) 2 and the upper electrode (anode) 4. Nitride films 3a, 3
By having c, electron conduction is suppressed in both cases of a negative bias and a positive bias. In addition, since the thickness of the silicon oxide film 3b is 3 nm or more, hole conduction is suppressed by the silicon oxide film 3b. Since the conduction of electrons and holes is suppressed as described above, leakage current can be suppressed.

Next, a method of forming the capacitor according to the first embodiment will be described. The wafer containing the capacitor has a CV
A low pressure chemical vapor deposition (LPCVD) process using monosilane (SiH ₄ ) as a raw material is performed at about 600 ° C. in a chamber of the D apparatus to form a polysilicon layer corresponding to the lower electrode 2 on the surface.

The wafer on which the lower electrode 2 is formed is subjected to a rapid thermal treatment using ammonia (NH ₃ ).
s; RTP) at a temperature of 800 ° C. or higher. The wafer having a thin layer of silicon nitride film formed on the surface by thermal nitridation is placed in a chamber of a CVD apparatus, and 700 ppm by LPCVD using dichlorosilane (SiH ₂ Cl ₂ ) and ammonia (NH ₃ ) as raw materials. 750 ° C., and a silicon nitride film is accumulated until a predetermined thickness is reached.

In order to form a nitride film having a predetermined thickness only by thermal nitriding, a long-time heat treatment at a high temperature is required. On the other hand, if the process is performed by the ordinary LPCVD method without passing through the RTP, the surface of the polysilicon layer is oxidized before the nitride film is formed, and an oxide film is formed between the lower electrode 2 and the silicon nitride film 3a. . Therefore, after a thin nitride film is once formed by RTP, the film is grown by LPCVD.

When a load-lock type LPCVD apparatus is used, the silicon nitride film 3a can be formed on the lower electrode 2 without forming an oxide film without performing RTP. Also in this case, LP is performed in a chamber using dichlorosilane (SiH ₂ Cl ₂ ) and ammonia (NH ₃ ) as raw materials.
The first silicon nitride film (Si ₃ N ₄ ) 3 a is formed on the polysilicon layer by processing at 700 to 750 ° C. by the CVD method.

Next, the wafer on which the first silicon nitride film 3a has been formed is placed in a chamber of a CVD apparatus.
LP using monosilane (SiH ₄ ) and nitrogen oxide (N ₂ O) as raw materials
The silicon oxide film (SiO ₂ ) 3b is formed on the first silicon nitride film 3a by processing at 700 to 800 ° C. by the CVD method. The silicon oxide film 3b can also be formed by processing at 600 to 700 ° C. by LPCVD using thermal decomposition of tetra-ethyl-ortho-silicate (TEOS).

As described above, the silicon oxide film 3b is formed by CVD.
When formed by the method, the film is sparse and may contain defects. Therefore, the wafer is processed by the annealing device after the formation of the silicon oxide film 3b. Annealing is performed using oxygen (O
₂ ) or in an oxidizing atmosphere containing nitrogen oxide (N ₂ O). At this time, if the annealing temperature is set to about 800 ° C., an increase in the film thickness can be prevented. When the atmosphere contains nitrogen oxide (N ₂ O), dangling bonds in the silicon oxide film 3b can be eliminated at a low temperature in a short time. After annealing in ammonia (NH ₃ ) gas, annealing may be performed in the above-described oxidizing atmosphere.

The silicon oxide film 3b has a CV as described above.
In addition to the formation using the method D, the formation may be performed using a thermal oxidation device. In the case of thermal oxidation, the surface of the first silicon nitride film 3a is oxidized in a wet atmosphere at 800 to 950 ° C. to form a silicon oxide film 3b. However, in this case, about の of the thickness of the first silicon nitride film 3a is converted to an oxide film. It is necessary to set the thickness at the time of formation of the layer larger than the final thickness.

The wafer on which the silicon oxide film 3b is formed is set in a chamber of a CVD apparatus, and LPC is performed using dichlorosilane (SiH ₂ Cl ₂ ) and ammonia (NH ₃ ) as raw materials.
Treated at 700 to 750 ° C. by VD method. As a result, the second silicon nitride film (S
i ₃ N ₄ ) 3c is formed. The wafer on which the second silicon nitride film 3c has been formed is finally subjected to LPCVD using monosilane (SiH ₄ ) as a raw material in a chamber of a CVD apparatus.
The treatment is performed at about 00 ° C., and a polysilicon layer corresponding to the upper electrode 4 is formed on the surface.

FIG. 3 is a graph showing the results of a time-destruction (TDDB) test performed on Example 2 of Embodiment 1 described above and a comparative example of a conventional three-layer structure of O / N / O. is there. The test was conducted under the conditions of an electric field of 12.5 MV / cm and an electrode area of 0.
Are carried out under conditions of 14 mm ^2, graph stress time (horizontal axis, in seconds) Cumulative failure rate of the capacitor with respect to
(Vertical axis, unit:%).

In the first embodiment, after forming a 1.6 nm nitride film by RTP, L
A 3.9 nm nitride film is deposited by PCVD to form a first silicon nitride film 3a, a 8.1 nm silicon oxide film is formed by CVD, annealed in an oxidizing atmosphere, and 5.5 nm by LPCVD. Is formed by forming the second silicon nitride film 3c.

In the second embodiment, the silicon oxide film 3 of the first embodiment is used.
After formation of b in ammonia (NH ₃ ) gas at 850 ° C.
Anneal for 0 seconds, and further in an oxidizing atmosphere (oxygen (O ₂ )) for 85
It is formed by annealing at 0 ° C. for 60 seconds. 1st, 2nd
Of the silicon nitride films 3a and 3c,
Is the same as In the comparative examples, a 5.5 nm silicon oxide film, a 8.1 nm silicon nitride film, and a 5.5 nm
An insulating film is formed by laminating silicon oxide films each having a thickness of nm.

As shown in FIG. 3, the insulating film is N / O /
In any of the examples of the first embodiment including three layers of N,
The life is longer and the incidence of initial failure is lower than in the comparative example having the three-layer structure of O / N / O. Further, it can be understood that, when annealing the silicon oxide film 3b, the treatment is first performed using ammonia and then the treatment is performed in an oxidizing atmosphere, whereby the life is extended as compared with the case where the treatment is performed in an oxidizing atmosphere without the treatment with ammonia. .

FIG. 4 shows a capacitor according to the second embodiment.
In the second embodiment, the insulating film 6 disposed between the lower electrode 2 and the upper electrode 4 has a two-layer structure of N / O of a silicon nitride film 6a and a silicon oxide film 6b in order from the lower electrode 2 side. It is configured. The point that the silicon nitride film 6a is formed first is different from the conventional insulator having a two-layer structure.

A method for forming a capacitor according to the second embodiment will be described. The lower electrode 2 is made of an LPCV made of monosilane (SiH ₄ ) as a raw material in a chamber of a CVD apparatus as in the first embodiment.
This is a polysilicon layer formed by processing at about 600 ° C. by Method D. The wafer on which the lower electrode 2 has been formed is placed in a chamber of a load-lock type LPCVD apparatus, processed by LPCVD using dichlorosilane (SiH ₂ Cl ₂ ) and ammonia (NH ₃ ) as raw materials, and subjected to silicon nitride. The film 6a is formed. The temperature in the chamber during the formation of the silicon nitride film 6a is 600 to 700 ° C., and the gas flow ratio (N
H ₃ / SiH ₂ Cl ₂ ) is set within a range of 1 to 5.

The silicon oxide film 6b is formed by oxidizing the surface of the silicon nitride film 3a in a wet atmosphere at 800 to 950 ° C. using a thermal oxidation device. The upper electrode 4
Like the lower layer electrode 2, it is a polysilicon layer formed by processing at about 600 ° C. by the LPCVD method.

The feature of the second embodiment is that the silicon nitride film 6a
Is that the temperature at the time of formation is in the range of 600 to 700 ° C., and that the gas flow ratio (NH ₃ / SiH ₂ Cl ₂ ) at that time is set in the range of 1 to 5. When the thickness of the insulating film 6 is about 5 nm, by satisfying the above conditions, the life of the insulating film can be increased to 10 years or more.

FIG. 5 is a graph showing the results of a time-destruction (TDDB) test performed by changing the formation conditions of the silicon nitride film 6a in the two-layer structure shown in the second embodiment. When changed, (B) shows the gas flow ratio (NH ₃ / SiH
₂ shows the case where Cl ₂ ) was changed. In the test, it is assumed that the thickness of the insulating film 6 is 4.5 nm, the area of the electrode is 0.1 mm ² , and the upper silicon oxide film 6b is formed in a wet atmosphere at 800 ° C. for 30 minutes. The test is performed as an accelerated test to which a high voltage is applied. As shown in FIG. 6, the life (time until breakdown) at various voltages is plotted, and the power supply of the semiconductor device is extrapolated. Life expectancy at half the voltage of 3V, typically 1.5V applied to the capacitor.

In the test in which the forming temperature is changed, the flow ratio (N
H ₃ / SiH ₂ Cl ₂ ) is set to 5. As shown in FIG. 5A, when the temperature at the time of forming the nitride film is higher than about 720 ° C., the life is shorter than 10 years. The lower the formation temperature is, the longer the life is. However, since the lower limit temperature of the reaction between dichlorsilane and ammonia is about 600 ° C., a nitride film cannot be formed at a lower temperature. Therefore, the formation temperature is required to be in the range of 600 to 700 ° C. with some allowance at the upper limit. However, the film formation speed is higher as the temperature is higher. For example, when forming a silicon nitride film of 5 nm, about 90 minutes at 600 ° C. and about 40 minutes at 650 ° C.
Minutes, at 680 ° C., about 30 minutes. Therefore, 600
650 ° C. or higher, preferably 68 ° C.
When the temperature is set to about 0 ° C., the life and the time required for film formation can be balanced.

In the test for changing the gas flow ratio during formation, the formation temperature was set to 680 ° C. As shown in FIG. 5B, when the flow ratio is smaller than about 0.7,
And greater than about 8, the lifetime is less than 10 years. Therefore, the condition is that the flow rate ratio is in the range of 1 to 5 with some allowance for the upper and lower limits. If the flow rate ratio is smaller than the lower limit, the concentration of silicon in the silicon nitride film 6a becomes high, and when the silicon oxide film 6b is formed by thermal oxidation, oxidation may locally proceed rapidly. In such a case, since the silicon nitride film has a hole at a portion where the oxidation has progressed rapidly and the portion is also converted to the silicon oxide film, the insulating property of the insulating film 6 is deteriorated and the capacitance is reduced. Decrease.

[0035]

As described above, according to the present invention, the N / O
In the case where an insulating film having a three-layer structure of / N is used, diffusion of impurities contained in the electrode into the insulating film can be prevented, and mechanical stress applied from the outside and resistance to the uneven shape of the electrode can be prevented. And the deterioration of the characteristics of the insulating film due to entry of impurities and mechanical stress can be prevented. Further, since the proportion of the nitride film having a high dielectric constant occupies a large portion, the average dielectric constant of the insulating film can be increased, and a larger capacitance can be secured even with the same film thickness as in the related art. Further, when the thicknesses of the first and second silicon nitride films are set to be substantially equal, the polarity dependency can be eliminated. In addition, by setting the thickness of the silicon oxide film to 3 nm or more, Leak current can be suppressed.

In the case where an insulator having a two-layered structure of N / O is formed by the method of the present invention, the reaction temperature is increased when a silicon nitride film is formed by LPCVD using dichlorosilane and ammonia. In the range of 600 to 700 ° C. and / or a gas flow ratio (NH ₃ / SiH ₂ C
l ₂ ) is set in the range of 1 to 5 so that the film thickness 5n
The life of the insulating film of about m can be extended to 10 years or more, and the life of the capacitor, and the life of the semiconductor device including the capacitor can be extended.

[Brief description of the drawings]

FIG. 1 is a conceptual diagram showing a structure of a capacitor having a capacitor insulating film according to a first embodiment.

FIG. 2 is a band diagram at the time of a negative bias and a positive bias of the capacitor having the capacitor insulating film according to the first embodiment.

FIG. 3 is a graph showing a cumulative failure rate with respect to a stress time in Examples 1 and 2 of the capacitor insulating film according to the first embodiment and a comparative example.

FIG. 4 is a conceptual diagram showing a structure of a capacitor having a capacitor insulating film according to a second embodiment.

FIG. 5 is a graph showing a change in life when the (A) nitride film formation temperature and (B) gas flow ratio are changed in the configuration of the second embodiment.

FIG. 6 is a diagram illustrating a life test for the configuration according to the second embodiment.
The graph which shows the mode of the extrapolation at the time of predicting the lifetime at 5V.

[Explanation of symbols]

 2 Lower electrode 3 Insulating film 3a First silicon nitride film 3b Silicon oxide film 3c Second silicon nitride film 4 Upper electrode

Claims (13)

[Claims] 1. A capacitor insulating film of a semiconductor device comprising a silicon oxide film and a silicon nitride film and disposed between lower and upper electrodes, wherein a first silicon nitride film and a silicon oxide film are provided on the lower electrode. , Which are formed by sequentially laminating a second silicon nitride film.
A capacitor insulating film of a semiconductor device having a layer structure. 2. The capacitor insulating film according to claim 1, wherein said silicon oxide film has a thickness of 3 nm or more. 3. The capacitor insulating film according to claim 1, wherein said first and second silicon nitride films have substantially the same thickness. 4. A method of manufacturing a capacitor insulating film for a semiconductor device comprising a silicon oxide film and a silicon nitride film and disposed between lower and upper electrodes, wherein a first silicon nitride film is formed on the lower electrode. Forming, forming a silicon oxide film on the first silicon nitride film, and forming a second silicon nitride film on the silicon oxide film. A method for manufacturing a capacitor insulating film of a semiconductor device, the method being performed sequentially. 5. The capacitor insulating film according to claim 4, wherein, in the step of forming the first silicon nitride film, the lower electrode is thermally nitrided, and then a silicon nitride film is deposited by an LPCVD method. Production method. 6. The method according to claim 4, wherein in the step of forming the first silicon nitride film, a silicon nitride film is deposited by a load-lock type LPCVD method. 7. The method according to claim 4, wherein in the step of forming the silicon oxide film, the silicon oxide film is deposited by a CVD method and then annealed in an oxidizing atmosphere.
The method for manufacturing a capacitor insulating film according to any one of the above. 8. The method according to claim 4, wherein in the step of forming the silicon oxide film, after the silicon oxide film is deposited by a CVD method, annealing is performed in an ammonia gas, and then annealing is performed in an oxidizing atmosphere. 7. The method for manufacturing a capacitor insulating film according to any one of 6. 9. A method for manufacturing a capacitor insulating film of a semiconductor device comprising a silicon oxide film and a silicon nitride film and disposed between lower and upper electrodes, wherein dichlorosilane and ammonia are formed on the lower electrode. Forming a silicon nitride film at a temperature of 600 to 700 ° C. by LPCVD as a raw material; and forming a silicon oxide film on the silicon nitride film, wherein these steps are sequentially performed. A method for manufacturing a capacitor insulating film of a semiconductor device. 10. The method according to claim 9, wherein the step of forming the silicon nitride film is performed at a temperature of 650 to 700 ° C. 11. The step of forming a silicon nitride film, wherein a flow ratio of ammonia to dichlorosilane is 1%.
11. The method for manufacturing a capacitor insulating film according to claim 9, wherein the process is performed in a range of from 5 to 5. 12. A method of manufacturing a capacitor insulating film for a semiconductor device comprising a silicon oxide film and a silicon nitride film and disposed between lower and upper electrodes, wherein dichlorosilane and ammonia are formed on the lower electrode. A step of forming a silicon nitride film at a flow rate ratio of ammonia to dichlorsilane of 1 to 5 by LPCVD as a raw material; and a step of forming a silicon oxide film on the silicon nitride film. Are sequentially performed. 13. The method according to claim 12, wherein the step of forming the silicon nitride film is performed at a temperature of 600 to 700 ° C.