JPH04249358A - Semiconductor device and manufacture thereof - Google Patents

Abstract

PURPOSE:To provide a semiconductor device whose capacitor dielectric film is practically thin by a method wherein oxidation of a foundation film for forming a metal oxide film which is the capacitor dielectric film having a high specific inductive capacity is suppressed. CONSTITUTION:A process in which a titanium film 64 is formed on a polycrystalline silicon film 15 which is a lower electrode, a process in which a tantalum pentaoxide film is formed on the titanium film 64 and a process in which a natural oxide film 34 which is naturally formed on the polycrystalline silicon film 15 surface by heat or oxidizing agent contained in the titanium film 64 forming process, the tantalum pentaoxide film forming process or a wafer treatment process after them is reduced by the titanium film 64 and the titanium film 64 itself is oxidized and a titanium oxide film 65 is formed between the polycrystalline silicon film 15 and the tantalum pentaoxide film 24 are provided for forming a capacitor dielectric film.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor device and a method for manufacturing the same, and more particularly to a structure that can increase the capacitance of a capacitor in a semiconductor memory device equipped with a capacitor, and a method for manufacturing the same. be.

0002

2. Description of the Related Art Some semiconductor memory devices have a memory element composed of a series circuit of a MOSFET and a capacitor. Hereinafter, this type of semiconductor memory device will be referred to as a memory that requires a memory retention operation, abbreviated as a dynamic random access memory (Dynamic Random Access Memory).
It is called ``emory''.

FIG. 2 shows an example of the structure of a dynamic random access memory that has been commonly used in the past. In this figure, a first polycrystalline silicon film 5 is formed on a P-type silicon substrate 1, a first gate dielectric film 4 is provided below the first polycrystalline silicon film 5, and N+ diffusion layers 3 and 13 are formed on the silicon substrate 1.
This forms a MOSFET. Furthermore, this MOSFE
A capacitor is formed by the N+ diffusion layer 3 of T, the second gate dielectric film 14 provided thereon, and the second polycrystalline silicon film 15 formed thereon.

In recent years, with the increasing integration of semiconductor devices,
Even in this type of dynamic random access memory, there is a need to miniaturize individual elements. In the semiconductor device having the structure shown in FIG. 2, the second gate dielectric film 14 must be made thinner in order to miniaturize the capacitor part and ensure its capacitance. In a highly integrated dynamic random access memory, the second gate dielectric film 14 is obtained by thermally oxidizing the silicon substrate 1 at a temperature of about 800°C to 1000°C in an oxygen or water vapor atmosphere. The thickness is about 10 nm, and if the degree of integration increases further, it will be difficult to reduce the thickness of the silicon oxide film.

Therefore, in order to increase the area of the capacitor, instead of constructing the capacitor using the N-type diffusion layer 13 and the second polycrystalline silicon film 15 as electrodes as shown in FIG. 2, an example of this is shown in FIG. As shown in FIG.
A method of configuring a capacitor on top of an OSFET has also been proposed.

FIG. 3 shows a first polycrystalline silicon film 5 on a P-type silicon substrate 1, a first gate dielectric film 4 provided below it, and an N-type diffusion layer formed on the silicon substrate 1. 3 and 13 form a MOSFET. This MOS
A first interlayer insulating film 6 is provided on the FET, and a second polycrystalline silicon film 15, a third polycrystalline silicon film 25, and a second gate dielectric film 1 sandwiched therebetween are provided on the first interlayer insulating film 6.
4 constitutes a capacitor, which is connected to the MOSFET through the N-type diffusion layer 13.

[0007] Here, the second insulator film has an oxide film/nitride film structure obtained by thermally oxidizing a silicon nitride film formed using a low pressure vapor phase growth method or the like. A first conductive layer 7 made of tungsten silicide or the like is provided on the capacitor via a second interlayer insulating film 16,
This first conductive layer 7 is the N-type diffusion layer 3 of the MOSFET.
is connected to through a contact hole 18. A second conductive layer 17 made of an aluminum silicon alloy or the like is provided on the first conductive layer 7 with a third interlayer insulating film 26 interposed therebetween.

By using this structure, the area occupied by the capacitor on the semiconductor substrate can be reduced, so it is possible to manufacture a semiconductor memory device with a higher degree of integration than the semiconductor memory device in which the capacitor is provided on the silicon substrate as shown in FIG. can.

However, when obtaining a degree of integration of 16 Mbit/chip or higher, even if the structure shown in FIG. 3 is used, sufficient capacitance cannot be obtained in the capacitor. In order to increase the capacitance of a capacitor, in addition to increasing the area of the electrodes, there are also ways to make the dielectric film inserted between the electrodes thinner, or to use a material with a higher dielectric constant as the material for this dielectric film. There is.

It is known that a dielectric film made of an oxide film and a nitride film, which has been conventionally used as a dielectric film, can be reduced in thickness to only about 6 nm in terms of oxide film. On the other hand, the dielectric constant is 10 to 20 compared to 9 for the nitride film.
The capacitance can be increased by using tantalum pentoxide (Ta2O5), which has a high This tantalum pentoxide can be deposited by depositing metal tantalum on the electrode by sputtering or the like, and then oxidizing it at a low temperature of about 500°C, or by reactive sputtering, which sputters tantalum in oxygen. , a method of forming using a vapor phase growth method in which a tantalum compound such as tantalum pentachloride and an oxidizing gas such as oxygen are reacted.

Of these methods, the vapor phase growth method, which is superior in film quality and step coverage, will be described below. FIG. 4 shows an example of a reduced pressure vapor phase growth apparatus used in the vapor phase growth method. Semiconductor wafer 107 is placed on a boat 106, usually made of quartz glass or silicon carbide, and placed in a reaction tube 108 made of a similar material, and reaction tube 108 is placed in a pressure vessel 102 made of a similar material. A flange 103 is provided below the pressure vessel 102 , and one or more source gas introduction pipes 104 and a vacuum exhaust device 105 are connected via an exhaust pipe 115 equipped with a valve 125 . pressure vessel 1
A heater 101 is placed outside of the reaction tube 108 to heat the inside of the reaction tube 108. The boat 106 is moved in and out of the reaction tube 108 using a boat holder 110. The raw material 121 for the tantalum pentoxide film is usually supplied as a liquid at room temperature, so it is stored in the raw material tank 120, and the raw material tank 120 is heated to a temperature of 50 to 300 °C by a heat-retaining heater 111.
It is maintained at a certain temperature. Carrier gas supply pipe 114
When a carrier gas such as nitrogen gas is supplied to the raw material gas tank, the carrier gas containing the raw material gas at a constant concentration flows into the raw material gas introduction pipe 104.

Next, a method for forming a tantalum pentoxide film using this reduced pressure vapor phase growth apparatus will be explained. First, the wafer 107 is inserted into the furnace from the flange 103. The wafer 107 inserted into the furnace is heated at normally 10 Torr while flowing an inert gas such as nitrogen gas until its temperature stabilizes.
After being maintained in the following reduced pressure state, the raw material gas tank 120
For example, tantalum pentachloride stored in the flange 103 is introduced into the pressure vessel 102 from a raw material gas introduction pipe 104 provided on the flange 103. At the same time, oxygen or the like is supplied as an oxidizing agent from the source gas supply pipe 124 into the reaction tube 108 . The raw material gas is fed into the reaction tube 10 for a time long enough to obtain the desired film thickness.
8 to form a tantalum pentoxide film on the wafer 107.

A method of manufacturing a semiconductor memory device using a tantalum pentoxide film as a capacitor dielectric film will be described below with reference to FIGS. 5, 6, and 7. First, Figure 5(a)
As shown in FIG. 2, an oxide film 2 for element isolation is first formed on a P-type silicon substrate 1. Then, as shown in FIG. 5(b), a first gate dielectric film (insulating film) 4 is formed, and a first polycrystalline silicon film 5 is formed thereon by low pressure vapor phase epitaxy. Furthermore, this first polycrystalline silicon film 5 is shaped, and N-type diffusion layers 3, 1 are formed on it in a self-aligned manner by ion implantation or the like.
form 3. After that, the first polycrystalline silicon film 5, N
M consisting of type diffusion layers 3 and 13 and first gate dielectric film 4
A first interlayer insulating film 6 is formed over the OSFET. Further, an opening is defined on this first interlayer insulating film 6 by photolithography, and an opening 8 is provided by reactive ion etching or the like (FIG. 5(c)).

Next, as shown in FIG. 5(d), a second polycrystalline silicon film 15 is formed on this first interlayer insulating film 6 by low-pressure vapor phase epitaxy, and phosphorus and arsenic ions are added thereto. N-type impurity atoms are added by implantation or phosphorous deposition using phosphine or the like. This second polycrystalline silicon film 15 is also shaped using photolithography, reactive ion etching, etc. (FIG. 6(a)).

Then, a tantalum pentoxide film or the like is formed as the second gate dielectric film 14 by the already explained low pressure vapor phase growth method (FIG. 6(b)). When this tantalum pentoxide is placed between polycrystalline silicon films and is subjected to heat treatment at 800° C. or higher, it reacts with the polycrystalline silicon of the electrode, forming tantalum silicide and losing its insulating properties. For this reason, the upper electrode 25 of the capacitor is formed on the second gate dielectric film 14 using a high melting point metal such as tungsten by vapor phase growth or the like. Then, it is shaped as shown in FIG. 6(c) using photolithography and reactive ion etching.

Then, as shown in FIG. 7A, a second interlayer insulating film 16 is formed using a silicon oxide film or the like by vapor phase growth, a contact hole 18 is opened, and a first conductive film such as tungsten silicide is formed. Form layer 7. A third interlayer insulating film 26 is further formed on the first conductive layer 7 using a silicon oxide film or the like by vapor phase growth, and a second conductive layer 17 such as an aluminum silicon alloy is formed thereon (Fig. 7(b)).

[0017]

[Problem to be solved by the invention] By the way, Fig. 8(a)
As shown in the detailed cross-sectional view of the capacitor section shown in FIG. 2, when forming the tantalum pentoxide film 24, the polycrystalline silicon film electrode 15 is placed in an oxidizing atmosphere such as oxygen, regardless of whether the vapor phase growth method or the sputtering method is used. Therefore, a silicon oxide film 34 of about 1 nm to 4 nm is formed on the electrode 15 made of the polycrystalline silicon film. Therefore, the dielectric film using tantalum pentoxide is actually a composite film consisting of the silicon oxide film 34 on the electrode 15 and the tantalum pentoxide film 24, and considering the film thickness of the tantalum pentoxide itself, the total is equivalent to an oxide film. The film can only be made as thin as about 5 nm.

[0018] Therefore, by Shinki, Nishioka, Ouji, Murai, etc., I.E. Electron Devices, Volume 36, 1989, 328
9 pages (H. Shinnki┨. Nishioka, Y.
Ohji, and K. Mukai, IEEE El
ectron Devices vol. 36 (198
9) P. P. 3289), before forming the tantalum pentoxide film on the polycrystalline silicon film electrode 15, a silicon nitride film 54 is formed in advance by a vapor phase growth method, and the tantalum pentoxide film 24 is deposited on top of the silicon nitride film 54. By forming the tantalum pentoxide film, it is possible to prevent the electrode 15 made of polycrystalline silicon from being oxidized (FIG. 8(b)).
. However, in order to obtain a continuous silicon nitride film 54, a film thickness of at least 2 nm to 4 nm is required, and when inserting a semiconductor wafer into a vapor phase growth apparatus to form the silicon nitride film 54, Because of the oxygen, a 1 to 2 nm native oxide film 44 is formed between the silicon nitride film 54 and the electrode 15, and as a result,
The film thickness in terms of oxide film has been reduced to only about 4 nm.

As described above, the prior art has a problem in that when forming a capacitor using a metal oxide film having a high dielectric constant as a dielectric film, it is not possible to reduce the substantial film thickness.

[0020] This invention solves the above problems,
An object of the present invention is to provide a structure of a semiconductor device and a method for manufacturing the same, which can suppress oxidation of a base film when forming a metal oxide film having a high dielectric constant, and as a result can substantially reduce the thickness of a capacitor dielectric film. purpose.

[0021]

[Means for Solving the Problems] A semiconductor device according to the present invention includes at least one layer of an insulating film provided on a semiconductor substrate having one conductivity type, and a semiconductor device that is provided on the insulating film and through an opening in the insulating film. A capacitor comprising a polycrystalline silicon film electrically connected to a semiconductor substrate, a dielectric film provided on the polycrystalline silicon film, and a conductive film provided on the dielectric film. The dielectric film is composed of a film made of an oxide, nitride, silicide, boride, carbide, or sulfide of a high melting point metal film, and a metal oxide film formed thereon.

Further, in the method for manufacturing a semiconductor device according to the present invention, at least one insulating film is formed on a semiconductor substrate having one conductivity type, and electrically connected to the substrate through an opening in the insulating film. In the process of forming a polycrystalline silicon film, forming a dielectric film thereon, and forming a conductive film on the dielectric film to form a capacitor, the formation of the dielectric film is Oxidation included in the process of forming a high melting point metal film on a crystalline silicon film, the process of forming a metal oxide film thereon, the high melting point metal film formation process, the metal oxide film formation process, or the subsequent wafer process. The high melting point metal film reduces the natural oxide film naturally formed on the surface of the polycrystalline silicon film using a chemical agent and heat, and oxidizes the high melting point metal itself, creating a bond between the polycrystalline silicon film and the metal oxide film. This method consists of a step of forming an oxide of the high melting point metal film.

[0023]

[Operation] In this invention, there is usually a natural oxide film of about 1 nm or less on the polycrystalline silicon film, but when a high melting point metal film such as Ti is formed on top of this, this high melting point metal film is removed by oxygen, etc. When the polycrystalline silicon film is placed in an oxidizing atmosphere, the surface of the high melting point metal film is oxidized, and the dense oxide film causes oxygen to diffuse inside. This prevents the polycrystalline silicon film from oxidizing. In addition, this high melting point metal reduces and removes the natural oxide film of 1 nm or less that exists on the polycrystalline silicon film, and at the same time it becomes a high melting point metal oxide film, preventing oxygen from diffusing into the polycrystalline silicon film. . Therefore, when a metal oxide film such as a tantalum pentoxide film is formed on the polycrystalline silicon film, a silicon oxide film is not formed on the polycrystalline silicon film. Therefore, even when a capacitor is formed using a metal oxide film as a dielectric film, a decrease in storage capacity can be prevented.

Furthermore, the Ti oxide film is a high dielectric film,
Moreover, since it has good insulation properties, tantalum pentoxide film and T
A capacitor using a composite film of i-oxide film has high reliability.

[0025]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the process of forming a capacitor using a tantalum pentoxide film will be described below as a method of manufacturing a semiconductor device according to an embodiment of the present invention with reference to FIG.

FIGS. 5(a) to (d) and FIG. 6(a)
As explained above, the process is the same as the conventional example until the second polycrystalline silicon film 15 is formed. After this second polycrystalline silicon film 15 is formed, as shown in FIG. Remove using. In this state, a natural oxide film 34 of about 1 nm or less is formed in the atmosphere at room temperature and still remains on the polycrystalline silicon film 15.

After this, a Ti film 64 is formed by a PVD method such as a sputtering method or a CVD method (FIG. 1(b)).
. This Ti film 64 is a natural substance formed on the polycrystalline silicon 15 by heat treatment or oxidizing agent during the formation of the Ti film 64, the formation of the tantalum pentoxide film to be formed later on it, or during the subsequent wafer process. Oxide film 3
At the same time as reducing Ti film 64, the Ti film 64 itself is oxidized and Ti
This becomes an oxide film 65 (FIG. 1(c)). Furthermore, at this stage, a thin Ti silicide film 66 is naturally formed at the interface between the Ti oxide film 65 and the second polycrystalline silicon film 15.

With the Ti oxide film 65 formed on this polycrystalline silicon film 15, a tantalum pentoxide film 24 is formed using a reduced pressure vapor phase growth apparatus as shown in FIG. The upper electrode 35 is made of tungsten or the like using
(Figure 1(d)).

Note that the subsequent steps other than the method of forming the capacitor are completely the same as those of the conventional example shown in FIG. 7, so the explanation thereof will be omitted.

Since the Ti oxide film 65 formed in this example has a masking effect against the oxidizing agent, the tantalum pentoxide film 3
Of the Ti film 64 formed on the polycrystalline silicon film 15 even though it was heat-treated in an oxidizing atmosphere during the formation of 5, the Ti oxide produced by reducing the natural oxide film 34 existing on the polycrystalline silicon film 15 Only the Ti that has not completely become the film 65 is oxidized, and the oxidation diffuses into the interior, so that the polycrystalline silicon film is not oxidized. Therefore, the capacitor insulating film according to the present invention includes the Ti oxide film 24 and the tantalum pentoxide film 35.
It has a two-layer structure.

As described above, according to this embodiment, there is usually a native oxide film 34 of about 1 nm or less on the polycrystalline silicon film 15, but if a Ti64 film is formed on this by sputtering or CVD, This Ti film 64 acts as a barrier to oxidizing agents such as oxygen, and when the polycrystalline silicon film 15 is placed in an oxidizing atmosphere, the surface of the Ti film 64 is oxidized and the Ti oxide film formed on the surface becomes dense. Therefore, oxygen cannot diffuse into the interior, thereby preventing the surface of the polycrystalline silicon film 15 from being oxidized.

Further, this Ti film 64 reduces the natural oxide film of 1 nm or less existing on the polycrystalline silicon film 15, and at the same time as this is removed, it itself is oxidized to become a Ti oxide film 65, thereby causing oxygen is the polycrystalline silicon film 15
prevent it from spreading.

Therefore, when the tantalum pentoxide film 65 is formed on the polycrystalline silicon film 15, there is no fear that a silicon oxide film will be formed on the polycrystalline silicon film 15, unlike in the conventional case.

Therefore, the thickness of the capacitor dielectric film can be determined only by the thickness of the two underlying layers, the Ti oxide film 24 and the tantalum pentoxide film 35, and the actual film thickness of the capacitor dielectric film can be determined by can be made thinner, and a decrease in capacitor storage capacity can be prevented.

Furthermore, since the Ti oxide film 65 itself is a high dielectric film like tantalum pentoxide, the gate dielectric film can be made thinner and more reliable than before, and the capacitor can be further miniaturized. This makes it possible to manufacture dynamic random access memory with a higher degree of integration than before.

In the above embodiment, the natural oxide film 34 on the polycrystalline silicon film 15 was first removed using an aqueous solution of hydrofluoric acid, but sputter etching or gaseous hydrogen fluoride was used during the Ti film formation. The natural oxide film is removed using acid, and Ti
A tantalum pentoxide film may be formed after forming the film.

Furthermore, in the above embodiment, Ti was formed after forming the polycrystalline silicon film, but in addition to this, W, Mo, and T were formed.
Similar effects can be obtained with high melting point metals such as a.

Furthermore, in order to prevent the polycrystalline silicon film from being oxidized by the oxidizing agent during the formation of the tantalum pentoxide film, a Ti oxide film was provided. It may also be an oxide, nitride, silicide, boride, carbide, or sulfide of a high melting point metal such as, and the same effects as in the above embodiment can be obtained in this case as well.

Further, in the above embodiment, an example was shown in which a tantalum pentoxide film was used as the dielectric film, but other than this, a metal oxide film such as a titanium dioxide film may also be used.

Further, the material of the upper electrode is not limited to tungsten, and may be made of other materials.

[0041]

As described above, according to the present invention, a polycrystalline silicon film is used as the lower electrode, and a high melting point oxide film such as Ti obtained by thermal or plasma oxidation and a metal oxide film such as tantalum pentoxide are used as the dielectric film. Since the capacitor is made of a high-melting point metal such as tungsten or a polycrystalline silicon film as the upper electrode, when forming the tantalum pentoxide film or annealing it in an oxygen atmosphere after formation, the tantalum pentoxide film and A Ti oxide film having a masking effect against the oxidizing agent is formed between the polycrystalline silicon films of the electrodes, so there is no fear that the polycrystalline silicon film will be oxidized and a silicon oxide film will be formed. Therefore, the film thickness of the dielectric film is determined only by the film thickness of the Ti oxide film and the two layers of tantalum pentoxide, which has the effect of reducing the actual film thickness. Furthermore, since the Ti oxide film itself is a high dielectric film like the tantalum pentoxide film, it is possible to make the gate dielectric film thinner and more reliable than in the past, allowing for smaller capacitors. This has the effect of making it possible to realize a dynamic random access memory with a higher degree of integration than before.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing a method for manufacturing a semiconductor device according to an embodiment of the present invention.

FIG. 2 is a diagram showing an example of a conventional dynamic access memory.

FIG. 3 is a diagram showing an example of another conventional dynamic access memory.

FIG. 4 is a diagram showing an example of a reduced pressure vapor phase growth apparatus.

FIG. 5 is a diagram illustrating an example of a conventional method for manufacturing a dynamic access memory.

FIG. 6 is a diagram illustrating an example of a conventional dynamic access memory manufacturing method.

FIG. 7 is a diagram illustrating an example of a conventional dynamic access memory manufacturing method.

FIG. 8 is a cross-sectional view of a capacitor according to the prior art.

[Explanation of symbols]

1 Semiconductor substrate 2 Element isolation oxide film 3, 13
N-type diffusion layer 4 First gate dielectric film 5
First polycrystalline silicon film 6
First interlayer insulating film 7 first
conductor film 8 first contact hole 14 second gate dielectric film 15
Second polycrystalline silicon film 16
Second interlayer insulating film 17 Second conductor film 18 Second contact hole 25
Third polycrystalline silicon film 24
Tantalum pentoxide film 26 Third interlayer insulating film 34, 44 Silicon oxide film 35 Capacitor upper electrode 64
Titanium oxide film 65 Titanium film 66 Titanium silicide film 101
Heater 102 Pressure vessel 103 Flange 104 Raw material gas introduction pipe 105 Vacuum exhaust device 106 Boat 107 Semiconductor wafer 108 Reaction tube 110 Boat holder 111 Heat retention heater 114 Carrier gas supply pipe 115
Exhaust pipe 120 Raw material tank 121 Tantalum pentoxide raw material 124
Raw material gas supply pipe 125 valve

Claims (3)

[Claims] 1. At least one insulating film is provided on a semiconductor substrate having one conductivity type, and a polycrystalline silicon film is provided on the insulating film and electrically connected to the semiconductor substrate through an opening in the insulating film. In a semiconductor device including a capacitor including a dielectric film provided on the polycrystalline silicon film and a conductive film provided on the dielectric film, the dielectric film is made of a high melting point metal. A semiconductor device comprising a film made of oxide, nitride, silicide, boride, carbide, or sulfide, and a metal oxide film formed thereon. [Claim 2] The high melting point metal is titanium, tungsten,
2. The semiconductor device according to claim 1, wherein the metal oxide film is made of molybdenum or tantalum, and the metal oxide film is made of tantalum pentoxide or titanium dioxide. 3. A step of forming at least one layer of an insulating film on a semiconductor substrate having one conductivity type, wherein polycrystalline silicon is electrically connected to the semiconductor substrate through an opening in the insulating film on the insulating film. In the method for manufacturing a semiconductor device having a capacitor forming step, the method includes a step of forming a film, a step of forming a dielectric film on the polycrystalline silicon film, and a step of forming a conductive film on the dielectric film. The dielectric film forming step includes a step of forming a high melting point metal film on the polycrystalline silicon film, a step of forming a metal oxide film on the high melting point metal film, and a step of forming the high melting point metal film, or the above steps. The high melting point metal film reduces the natural oxide film naturally formed on the surface of the polycrystalline silicon film using the oxidizing agent and heat included in the metal oxide film forming step or the subsequent wafer process. A method for manufacturing a semiconductor device, comprising the steps of: oxidizing the melting point metal itself to form an oxide of the high melting point metal film between the polycrystalline silicon film and the metal oxide film.