JP3139468B2 - Semiconductor device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor device having a stack capacitor, a method of manufacturing the same, and an apparatus for manufacturing the same.

[0002]

2. Description of the Related Art In a dynamic random access memory (DRAM), which is one of silicon ultra-high-integrated circuits, a capacitor is formed including a stepped portion formed by a word line, thereby increasing the storage capacity. A stack capacitor technology for improving readout accuracy and soft error resistance is used.

A conventional method for forming a stack capacitor is described in, for example, Japanese Patent Application Laid-Open No. 63-318152. That is, as shown in FIG. 2, first, a gate insulating film 2 is formed on a P-type silicon substrate 1 by using a thermal oxidation method. Next, an N @ + -type polycrystalline silicon film is formed on the gate insulating film 2, and a word line 3 is formed by using a photolithography technique and a dry etching technique. Next, arsenic (As +) is ion-implanted into the silicon substrate using the word line 3 as a mask to form an N + type region 4 serving as a source / drain (S / D) connected to the charge storage electrode. Next, an interlayer insulating film 5A made of a silicon oxide film or the like is formed by a vapor deposition (CVD) method. After an interlayer insulating film is further formed, a sidewall 5B is formed on the side wall of the word line by using a dry etching technique. Next, after a polycrystalline silicon film 6 serving as a lower electrode for charge storage is formed, phosphorus is implanted to make it an N + type. After that, patterning is performed using a photolithography technique and a dry etching technique. Next, after the silicon nitride film 7 is formed on the surface of the lower electrode by the CVD method, the surface is oxidized to fill the pinhole. Next, a polycrystalline silicon film 8 is formed by a CVD method, phosphorus is introduced to make it an N + type, and patterning is performed to form an upper electrode (cell plate) for charge storage facing the lower electrode. Thereafter, an interlayer insulating film 9 made of PSG is formed, and a bit line 10 is formed to complete a DRAM cell.

In manufacturing such a capacitor, the polycrystalline silicon film 6 as a lower layer contains a high concentration of impurities, for example, arsenic or phosphorus, and a natural oxide film is easily grown on the surface. . Therefore, when the silicon nitride film 7 is deposited on this N + type polycrystalline silicon film by the CVD method, it is estimated that the oxide film on the polycrystalline silicon film further grows and its thickness is 2-3 nm. It is. The dielectric constant of the silicon oxide film is smaller than the dielectric constant of the silicon nitride film. Therefore, if there is a silicon oxide film between the silicon nitride film formed by the CVD method and the lower electrode,
The average dielectric constant of the insulating film sandwiched between the upper electrode and the lower electrode decreases. Therefore, the amount of charge that can be stored is reduced. To increase the amount of charge that can be stored,
The overall thickness of the insulating film must be reduced.
Since the thickness of the natural oxide film and the thickness of the thermal oxide film cannot be controlled, when the thickness of the silicon nitride film is reduced, the proportion of the silicon oxide film increases, and the amount of charge that can be stored does not increase so much even when the thickness is reduced.

[0005] In order to solve this problem, a method of thermal nitriding is sometimes used. The method is described in, for example, JP-A-2-16763. Specifically, first, as shown in FIG. 3, a polycrystalline silicon film 6 serving as a lower electrode is deposited. This polycrystalline silicon film 6 is doped with phosphorus at 1 × 10 201 / c by ion implantation or thermal diffusion.
Doping to about m2. After that, the natural oxide film formed on the surface of the polycrystalline silicon film 6 is rapidly thermally nitrided to be changed to the nitride film 17A. Rapid nitriding is at 950-1150 ° C,
Performed in an ammonia atmosphere. However, only by changing the natural oxide film having a thickness of 0.5 to 10 nm to a silicon nitride film, the leakage current is very large because the film thickness is small. In order to suppress the leakage current, CVD
A capacitor is formed by adding a silicon nitride film 17 having a required thickness by the method.

[0006]

SUMMARY OF THE INVENTION By thermally nitriding a natural oxide film, the growth of a thermal oxide film formed when a substrate is inserted into a CVD furnace is suppressed, and silicon nitride formed by thermal nitridation and CVD is used. The average dielectric constant of the entire nitride film is improved. However, in the conventional technique, oxygen contained in the natural oxide film remains in the film as it is, and is not completely turned into a silicon nitride film. Therefore, the dielectric constant is still lower than the intrinsic value of the silicon nitride film. Further, in the conventional technique, a silicon nitride film containing oxygen, that is, a silicon nitride oxide film is in contact with a polycrystalline silicon film serving as a lower electrode. When the silicon oxynitride film is in contact with polycrystalline silicon, electrical deficiencies such as traps are generated and reliability is reduced. Therefore, it is desirable that the silicon nitride film having a stoichiometric composition be in contact with polycrystalline silicon.

[0007]

According to the present invention, there is provided a semiconductor device comprising:
In a semiconductor device having a capacitor formed of a lower electrode formed of a polycrystalline silicon film formed on a semiconductor substrate and a laminated film of a plurality of insulating films, and a capacitor formed of an upper electrode formed of a polycrystalline silicon film, The film includes a silicon nitride film in contact with the lower electrode, an insulating film different from the silicon oxynitride film and the silicon nitride film on the silicon nitride film, and an insulating film in contact with the upper electrode, wherein the silicon nitride film and the silicon The oxynitride film is characterized by being formed by rapid thermal nitridation of the polycrystalline silicon film forming the lower electrode and a natural oxide film on the surface thereof.

Further, the semiconductor device of the present invention is a semiconductor device having a capacitor formed on a semiconductor substrate and comprising a lower electrode made of a polycrystalline silicon film and a dielectric film and an upper electrode made of a polycrystalline silicon film. The dielectric film includes first and second silicon nitride films and a silicon oxynitride film sandwiched between the first and second nitride films;
The first silicon nitride film and the silicon oxynitride film sandwiched between the first and second silicon nitride films rapidly heat the polycrystalline silicon film forming the lower electrode and the natural oxide film on the surface thereof. It is formed by nitriding, and is characterized in that there is no silicon oxynitride film in contact with the lower electrode and the upper electrode.

[0009]

When the natural oxide film is nitrided by the rapid thermal nitridation method at a lower temperature range of 800 to 950 ° C. than the conventional one, nitridation starts from the interface between the natural oxide film and the polycrystalline silicon film. Thereafter, nitriding of the natural oxide film and nitriding of the polycrystalline silicon film progress, and a silicon nitride film having a stoichiometric composition is formed between the polycrystalline silicon film and the silicon nitride oxide film.

Further, oxygen in the silicon nitride film is reduced,
In order to bring the dielectric constant close to the intrinsic value of the silicon nitride film, after removing the native oxide film on the polycrystalline silicon film, immediately place the substrate in an atmosphere where the native oxide film does not grow again, and perform rapid thermal nitridation. Do. Next, on the surface of the silicon nitride film, the film is inserted into a CVD furnace in an atmosphere in which a natural oxide film does not grow, and a silicon nitride film and a polycrystalline silicon film serving as an upper electrode are continuously grown. According to such a manufacturing method, the influence of the natural oxide film on the polycrystalline silicon film serving as the lower electrode is eliminated. In addition, there is no formation of a thermal oxide film when the device is inserted into a CVD furnace for growing a silicon nitride film. Further, there is no growth of a thermal oxide film on the silicon nitride film when inserted into a CVD furnace for forming a polycrystalline silicon film. Therefore, a silicon nitride film containing no oxygen in the film can be formed.

[0012]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, the present invention will be described with reference to the drawings. FIGS. 1A and 1B are a sectional view of a semiconductor chip and an enlarged sectional view of a portion A for explaining a first embodiment of the present invention.

In FIG. 1A, a gate insulating film 2 having an opening is formed on a P-type (100) silicon substrate 1, on which a word line 3 and an interlayer insulating film 5A are formed.
And a side wall 5B. An N @ + region 4 serving as a source / drain (S / D) is formed in the silicon substrate 1 in the opening, and a 400 nm thick lower electrode made of a polycrystalline silicon film 6 is formed thereon. The structure so far can be formed by a conventional technique. A silicon nitride film 7 is formed on lower electrode 6. Hereinafter, the silicon nitride film 7 will be further described together with the manufacturing method. The silicon substrate shown in FIG. 1 is heated to 800 to 950 ° C. in an ammonia atmosphere using a rapid thermal nitridation apparatus (lamp annealer) to form a 2 nm-thick layer on the surface of the polycrystalline silicon film 6 doped with phosphorus at a high concentration. Was formed.

FIG. 4 shows the growth time dependence of the thermal silicon nitride film. The thickness that can be formed (including a film obtained by nitriding a natural oxide film) varies depending on the temperature. The silicon nitride film formed by rapid thermal nitridation is saturated with respect to the nitriding time as shown in FIG. Therefore, there is no point in heating for a long time, and adverse effects such as redistribution of impurity atoms are caused. A heating time of at most about 60 seconds is sufficient.
When the nitriding time is short, the controllability of the film thickness is poor, and at least 3
A nitridation time of about 0 seconds is required. The thickness of the formed silicon nitride film does not depend on the flow rate of ammonia constituting the atmosphere.

After the natural oxide film and polycrystalline silicon are nitrided at 850 ° C. for 30 seconds by rapid thermal nitridation,
A silicon nitride film 7C of 40 nm was deposited by the method. FIG.
(B) is a cross-sectional view of the silicon nitride film formed by the rapid thermal nitridation and the CVD, based on the result of composition analysis in the depth direction.

On the surface, a natural oxide film 1 of a silicon nitride film
There is one. Below that, there is a silicon nitride film 7C formed by the CVD method. Under the silicon oxynitride film 7B
There is. This layer was originally a natural oxide film on the polycrystalline silicon film 6 serving as a lower electrode, but was nitrided by rapid thermal nitridation to form a silicon oxynitride film. Further below the silicon nitride film 7 containing no oxygen
A was detected. This layer is formed by nitrogen passing through the oxide film and nitriding the polycrystalline silicon film 6 during rapid thermal nitridation.

On the other hand, if the condition of rapid thermal nitriding is 1000 ° C. for 30 seconds, which is the same as the conventional condition, oxygen diffuses and
The structure shown in (b) is broken, and the silicon oxynitride film 7B reaches the interface with the lower electrode made of the polycrystalline silicon film 6. Therefore, in order to form the silicon nitride film 7A containing no oxygen between the silicon oxynitride film and the lower electrode, the rapid heating condition needs to be 950 ° C. for 30 seconds at most. Under the heating condition of 800 ° C. or less, the formation of the silicon nitride film becomes insufficient and is not practical.

After the silicon nitride film is formed as described above, a facing upper electrode made of polycrystalline silicon having a thickness of 250 nm is formed by the CVD method in the same manner as in the prior art.
A DRAM cell was completed by forming an interlayer insulating film, forming a bit line, and forming a cover film. In the first embodiment, unlike the prior art, the nitride film is not oxidized. Nitride film oxidation is a method in which after a silicon nitride film is formed by a CVD method, the surface is oxidized, and a place where a leak current easily flows, such as a pinhole, is filled with a silicon oxide film. By performing the thermal nitridation according to the present embodiment, an insulating film having excellent electrical characteristics can be formed, and there is no need to oxidize the nitride film. This has the effect of increasing the amount of charge that can be stored.

FIG. 5 shows the results of evaluating the long-term reliability of the semiconductor device of the first embodiment by an accelerated test method. In the accelerated test method, the test temperature was 100 ° C., and the applied electric field was 12 MV /
cm. The vertical axis in FIG. 5 is the cumulative failure rate. Using the time when the cumulative failure rate becomes 50%, the reliability of the capacitor can be compared. The horizontal axis represents the time required for the accelerated test, which is the time required for dielectric breakdown. a is a capacitor formed by using the low-temperature thermal nitridation method according to the present embodiment. b is a capacitor formed by using the conventional high-temperature thermal nitriding method. c is a capacitor formed using only a normal CVD method. The solid line and the broken line show the difference in polarity of the applied voltage, and the solid line shows that a positive voltage is applied to the upper electrode. The broken line indicates that a negative voltage is applied to the upper electrode. It is clear from FIG. 5 that the present embodiment improves the reliability by one to two digits compared to the conventional example.

FIG. 6 is a block diagram of a manufacturing apparatus according to a second embodiment of the present invention.

In FIG. 6, a dry cleaning device 12 for removing a natural oxide film, a rapid thermal nitriding device 13 for forming a silicon nitride film, and a CVD device 14A for a silicon nitride film
And the CVD apparatus 14B for polycrystalline silicon film
5, the silicon substrate carried in from the entrance / exit chamber 16 is carried in / out of each device from the load lock unit 18 without being oxidized. Hereinafter, a method of manufacturing a semiconductor device using the second embodiment will be described as a third embodiment.

An apparatus for a continuous process shown in FIG.
A silicon nitride film was formed on the silicon substrate shown in FIG. The apparatuses for each process are connected via a gate valve, and transfer the substrate via the transfer chamber 15. The transfer was performed in a high-purity nitrogen atmosphere to prevent the growth of a natural oxide film. First,
A natural oxide film on the polycrystalline silicon film 6 serving as a lower electrode was selectively removed by a dry cleaning device 12 using anhydrous hydrogen fluoride gas. Dry cleaning conditions were such that nitrogen (5 L / min) was used as the carrier gas and anhydrous hydrogen fluoride gas (1 L / min) was used.

Next, the silicon substrate 1 was transferred to a rapid thermal nitriding apparatus 13 in a high-purity nitrogen atmosphere, and was thermally nitrided in the same manner as in the first embodiment. Thermal nitriding is performed in an ammonia atmosphere at 85
The test was performed at 0 ° C. for 30 seconds. Next, the silicon substrate 1 was transferred to a CVD apparatus 14A in a high-purity nitrogen atmosphere, and a silicon nitride film 7C was added. The raw material gases are dichlorosilane and ammonia, and the growth temperature is 800 ° C. and the growth pressure is 1 To.
Performed at rr. Flow rate is dichlorosilane; 1 liter /
Min, ammonia; 2.5 l / min. further,
The CVD apparatus 14
B, and a polycrystalline silicon film serving as an upper electrode was deposited using silane as a source gas.

By performing the above-described processes continuously, thermal nitridation can be performed in a state where the natural oxide film on the lower electrode has been removed, and furthermore, the thermal nitride can be formed on the silicon nitride film and the polycrystalline silicon film. This eliminates the need for a thermal oxide film and allows the formation of only a silicon nitride film containing no oxygen in the film.

FIG. 7 shows that the standard value of the leakage current is 1 × 10 −8.
FIG. 4 is a graph showing the relationship between the electric field strength (vertical axis) and the equivalent oxide film thickness (horizontal axis) when A / cm 2 is set to A / cm 2, and a broken line indicates a voltage actually applied to the capacitor when the power supply voltage is 3.3V. The electric field intensity generated by the voltage of 1.65 V is shown. The oxide film equivalent film thickness is a film thickness determined using the relative dielectric constant of the oxide film in the measurement of the film thickness of the insulating film. The dashed line indicates the characteristics of the capacitor formed by the conventional rapid thermal nitridation method.

In the prior art, the power supply voltage is set to 3.3 V,
As long as the leak current density is 10-8 A / cm2 or less,
It cannot be made thinner than 4.9 nm. On the other hand, characteristics of the capacitor formed according to the third embodiment (solid line)
Shows that the thickness can be reduced to 4.5 nm. Since the physical thickness of the silicon nitride film of the solid line and that of the dashed-dotted line are the same, the equivalent oxide film thickness of the capacitor formed in the third embodiment is smaller. Means that the relative permittivity of the film is large. The value was about 8 at an oxide film equivalent thickness of 4.5 nm. At this time, the value of the conventional capacitor was 7.

[0027]

As described above, according to the present invention, since a polycrystalline silicon film serving as an electrode of a capacitor and a silicon nitride film having a stoichiometric composition are in contact with each other, a capacitor having improved long-term reliability by about one digit or more. Is obtained. According to the present invention, a silicon nitride film containing no oxygen can be formed.
The dielectric constant can be improved. As a result, according to the present invention, there is an effect that a semiconductor device having a capacitor with a large charge storage amount and excellent reliability can be realized.

[0028]

[Brief description of the drawings]

FIG. 1 is a sectional view of a semiconductor chip for explaining a first embodiment of the present invention.

FIG. 2 is a sectional view of a semiconductor chip for explaining a conventional example.

FIG. 3 is a sectional view of a semiconductor chip for explaining a conventional example.

FIG. 4 is a diagram showing a relationship between a nitriding time and a film thickness.

FIG. 5 is a diagram showing long-term reliability of an example and a conventional example.

FIG. 6 is a block diagram of a manufacturing apparatus according to a second embodiment of the present invention.

FIG. 7 is a diagram showing a relationship between an electric field strength for obtaining a dielectric constant and an equivalent oxide film thickness.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Silicon substrate 2 Gate insulating film 3 Word line 4 N + type region 5A Interlayer insulating film 5B Sidewall 6 Polycrystalline silicon film 7 Silicon nitride film 8 Polycrystalline silicon film 9 Interlayer insulating film 10 Bit line 11 Natural oxide film 12 Dry cleaning Apparatus 13 Rapid thermal nitriding apparatus 14A, 14B CVD apparatus 15 Transfer chamber 16 Entry / exit chamber 18 Load lock unit

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁷ , DB name) H01L 27/108 H01L 21/822 H01L 21/8242 H01L 27/04

Claims (2)

(57) [Claims] 1. A semiconductor device having a capacitor formed on a semiconductor substrate and including a lower electrode made of a polycrystalline silicon film and a dielectric film formed by laminating a plurality of insulating films and an upper electrode formed of a polycrystalline silicon film. Wherein the dielectric film is a silicon nitride film in contact with the lower electrode,
Oxynitride film and silicon nitride film on silicon nitride film
An insulating film that is in contact with the upper electrode and is different from the silicon nitride film and the silicon oxynitride film.
And the polycrystalline silicon film forming the lower electrode
Formed by rapid thermal nitridation of the natural oxide film on the surface
Wherein a has been made. 2. A semiconductor device having a capacitor formed on a semiconductor substrate and comprising a lower electrode made of a polycrystalline silicon film, a dielectric film and an upper electrode made of a polycrystalline silicon film, wherein the dielectric film is a First and second silicon nitride films, and a silicon oxynitride film sandwiched between the first and second nitride films.
And a silicon sandwiched between the first and second silicon nitride films.
The oxynitride film is formed by the polycrystalline silicon forming the lower electrode.
Rapid thermal nitridation of the silicon film and its native oxide film
And a silicon oxynitride film in contact with the lower electrode and the upper electrode does not exist.