JPH01264251A - Capacitor structure and its manufacture - Google Patents

Abstract

PURPOSE:To form an extremely thin dielectric insulating film with good controllability by a method wherein an Si oxynitride film formed by a heat treatment in an atmosphere of NH3 containing an oxidizing agent is used as a dielectric insulating film for capacitor use. CONSTITUTION:A switching MOS transistor which is composed of a gate insulating film 103, polycrystalline Si 104 to be used as a gate electrode and an n-type impurity diffusion layer 106 constituting a source and a drain is formed on an Si substrate 101. An Si film 107 is formed to be adjacent to a source region; it is patterned; a lower-part electrode for a capacitor is formed. An Si oxynitride film is formed on the surface of the Si film 107 by an NH3-O2 method; in addition, an Si film 109 to be used as an upper-part electrode is formed; the capacitor is formed. After that, phosphate glass 110 and an Al wiring part 111 are formed; a memory cell is formed.

Description

Detailed Description of the Invention [Field of Industrial Application] The present invention relates to a capacitor used in a memory LSI and a method for manufacturing the same, and particularly to a capacitor having an extremely thin dielectric insulation film of 5 nm or less and highly reliable. It relates to its formation method.

[Conventional technology]

The degree of integration of semiconductor memory LSIs has increased significantly in recent years, and in particular dynamic type RAM (R
andoIl+ Access Memory), a 16 megabit ultra-highly integrated LSI was developed at the research and development stage.
We have come to the point where we are considering the following. In order to increase the degree of integration of a memory LSI, the memory cell area must be reduced, but at this time the problem arises as to how to secure the capacitance of the capacitor. In conventional dynamic RAM (d-RAM), in order to secure the above-mentioned capacity, the dielectric insulating film has a high dielectric constant and is made thinner, and ■ the actual area does not decrease even if the planar area is reduced. Three-dimensional capacitor structures are being considered.

For the former, from a 5-inch single layer to a 5-inch Si nitride film and a 5-inch
It has changed to a multilayer thin film consisting of a combination with s,
Regarding the latter, planar type to stud capacitor (S
TC) type or Colgentirad capacitor cell (C
The a structure has changed to the CC) type.

However, even if these structures are used and a high dielectric constant thin film is used, an effective film thickness of 5 nm (converted to 5 ins with a dielectric constant of 3.8) is required for the 16 megabit d-RAM mentioned above. It has become.

Si oxynitride film and Si nitride film are one way to realize such an extremely thin dielectric film.

A method of forming a multilayer Si oxide film has been proposed, an example of which is described in Japanese Patent Laid-Open No. 62-2563.

[Problem to be solved by the invention]

The above-mentioned prior art describes a method of forming a dielectric insulating film through the following steps.

■The first step of forming a first Si nitride film on polycrystalline Si using the LPCVD method or direct nitriding method.■Converting the Si nitride film to a nitroxide film (Si oxynitride film) by oxidation treatment. a second step of forming a second Si nitride film by the LPCVD method;
(2) A fourth step of forming a second nitroxide film by oxidizing the surface of the second Si nitride film.

The following points are not considered in the WRWt body insulating film formed by the above procedure.

■When using the LPCVD method in the first step, due to the influence of the natural oxide film formed on the surface of the polycrystalline 81, the
For thin films, it becomes extremely difficult to control film quality and film thickness.

■In the first step, if a direct nitriding method is used to form the Si nitride film, the
At temperatures below 0° C., the film thickness is usually limited to 2 to 3 nm, and it is extremely difficult to control even thicker films.

(2) In the second step of oxidizing the Si nitride film.

In the case of the Si nitride film formed using the L PCV D method in the first step, if the Si nitride film is less than 6 nm thick, it has no oxidation resistance, and the underlying polycrystalline Si is oxidized. In the second step of oxidizing the Si nitride film, the first
The Si nitride film formed using the direct nitriding method in the process of 1.
The composition is an oxynitride film, and the film thickness is 2 to 3 nm.

Also, the distribution of N and 0 in the film thickness direction is not -like.

The distribution is such that N is segregated on the polycrystalline Si surface side.

Therefore, the oxidation treatment has no important meaning, and on the contrary, it is difficult to control the oxidation so that the lower layer does not become polycrystalline.

(2) The Si nitride film formed in the third step grows a film that lacks oxidation resistance for the same reason as (2).

As a countermeasure to avoid the above problems, when using the t and pcvo method in the first step, the final effective film thickness is 9n.
It is difficult to reduce the final effective film thickness to 6 nm or less, and even when direct nitriding is used, it is difficult to reduce the final effective film thickness to 6 nm or less.

The object of the present invention is to have a film thickness of 10 nm or less, particularly 3 to 3.5 nm.
By forming a Si oxynitride film with a film composition of - nm with good controllability, v! It is an object of the present invention to provide a capacitor structure that can realize a large capacity by using a heavy insulating film, and a method for manufacturing the same.

[Means to solve the problem]

The above purpose is to use an oxidizing agent (Oz or H2O
) is achieved by using a Sl oxynitride film formed by heat treatment in an N 2 H8 atmosphere as a dielectric insulating film for the capacitor.

[Effect]

By heat treatment in a mixed gas of NHa and Oz,
A Si oxynitride film having a -like film composition can be obtained. Although the mechanism has not yet been fully elucidated, the following phenomenon can be said when the processing temperature is 950° C. or lower.

(2) 5iOz formed once is difficult to be nitrided.

■NHs sufficiently diffuses in SiOx.

■Si is nitrided.

(2) When Si is sufficiently nitrided and a film having a composition close to 5iaNa is formed, the film itself becomes a barrier to the diffusion of NHs, and the film is no longer formed.

It is considered that when N Hs and Ox coexist, the nitriding reaction and the oxidizing reaction proceed while maintaining a proper balance. However, even in this case, as long as 02 is used,
The film thickness that can be practically formed is 200 mm, and if a thicker film thickness is desired, HxO must be used.
Even if a large amount of 02 is contained, Hx
Although O is produced, NHs is a flammable substance and poses a risk of explosion, so it is not desirable to increase the O2 concentration excessively.

〔Example〕

The composition distribution and properties of the film formed by the above method were investigated by analysis using Auger electron spectroscopy and etching rate measurement using wet etching method.
Similar measurements were performed on samples such as a film formed by a direct nitriding method using only s and a Si nitride film formed by an LPCVD method, and the following was clarified.

In the direct nitriding method using only N Hs at temperatures below 0950°C,
5iOz is hardly nitrided, and the nitridation of the Si surface progresses. Further, the maximum thickness of the nitride film that can be formed on the Si surface is 15 people.

■Therefore, in the direct nitriding method using only NH3, for example, 3
It is difficult to obtain a Si oxynitride film having a thickness of 500 nm. In addition, in order to obtain that film thickness, 35 people's 5iOz
Even if direct nitridation is performed after forming SiO2, SiO2 is hardly nitrided, so a nitride film grows only at the interface between SiO2 and Si, and the composition distribution in the film thickness direction becomes extremely non-uniform.

■The quality of the Si nitride film formed by the LPCVD method significantly depends on the underlying material at the initial stage of film formation.
The etching rate is higher than that of N2, and the resulting film lacks oxidation resistance.

The above results will be explained in more detail based on experimental results. Figures 2 and 3 show the wet etching characteristics of a Si oxynitride film formed by the conventional method, and Figure 4 shows the N
The wet etching characteristics of the film formed in I-1g-02 mixed gas are shown. For wet etching, a solution with a composition of hydrofluoric acid (HF) to water (H2O) = 1:100 is used, and after etching for a certain period of time, an ellipsometer (
Manufactured by Gardner.

The procedure for measuring the remaining film thickness was repeated with L115A).

In addition, as an experimental sample, phosphorus was diffused into a (100) single-crystal Si substrate, and the surface impurity concentration was 3X10"C3I-
3, and the phosphorus glass formed on the surface was removed. In addition, in an ellipsometer, the optical constants of the Si substrate on which impurities are diffused at a high concentration change, so even when no film is formed on the surface, the
Showing people's values. This is why there are no values below 10 Å in the results shown each time. Therefore, the film thickness used in the following explanation is the value obtained by subtracting 10 people from the residual film thickness in the figure.

Sample A shown in Figure 2 is a sample that has only been thermally oxidized.
The etching speed indicated by the slope of the straight line is approximately 30 people/m, in
It is. Sample B was obtained by directly nitriding a sample in which 10 native oxide films had grown for 20 minutes in an NHa atmosphere at 900°C. It can be seen that the etching rate is much slower than in A, indicating that it is nitrided. But 1000
Even when the same treatment is performed at a temperature of 100°C, almost the same etching characteristics are obtained, and no increase in film thickness is observed even when the temperature is raised. Therefore, it is substantially difficult to obtain a desired film thickness by direct nitridation alone at temperatures below 950° C., which limits the temperature range of the present invention.

Sample C was obtained by directly nitriding samples on which 30 thermal oxide films had been formed in advance under the above conditions. In this sample, the etching speed is fast immediately after the start of etching, and the etching speed of 5ins is almost the same, but as the etching time progresses, the etching speed slows down, and after 100 seconds, the Si nitride film formed thickly by the LPCVD method (see Fig. 3F) It shows an etching speed equivalent to that of .

That is, the nitriding reaction occurs intensively at the interface between 5iOz and Si, in other words, at the surface of Si.

This shows that S i Ox is hardly nitrided. Moreover, the thickness of the intensively nitrided layer is at most 10 layers. Therefore, at temperatures below 950°C, the preformed 5iOz film is converted into a Si′e11 film with a uniform composition distribution.
It is difficult to convert to nitride film.

The properties of a thin Si nitride film formed by the LPCV[) method will be explained with reference to FIG. In D, dichlorosilane C3iHxCQ was added to the sample in which 10 natural oxide films were formed.
z) and NHa as raw material gases, a thickness of 50 mm was obtained using the LPCVD method under the conditions of a pressure of 0.6 Torr and a temperature of 770°C.
An i-nitride film is formed. Although there is a region where the etching rate is extremely slow in the surface layer, the etching rate of the entire film is fast and is equivalent to 5iOz (straight line indicated by L), which is equivalent to that of the Si nitride film (straight line indicated by F), which originally has a slow etching rate. On the other hand, in E, the natural oxide film is 10
The human-formed sample was placed in an NHSP atmosphere at 900℃ for 2 hours.
Directly nitrided for 0 minutes, then LPCed at the same time as the subsequent sample.
A Si nitride film was formed by 50 people using the VD method. In this sample, the etching rate is quite slow, and the surface layer immediately after the start of etching shows an etching rate close to the F line. Thereafter, the etching rate increases as the etching time elapses, and finally a directly nitrided region appears that exhibits a slow etching rate comparable to F.

The difference between D and E in Figure 3 is that the quality of the Si nitride film formed thereon by the LPCVD method differs greatly depending on whether the base is 5iOz or a directly nitrided Si oxynitride film. It is shown that. This difference in film quality was also evident when thermally oxidized. B
, C, D, and E at the same time, only sample D had no oxidation resistance and a thick Si oxide film was formed.

B, C, and E showed sufficient oxidation resistance, and it became clear that the nitride layer of only about 1 layer existing on the Si surface was a film with extremely excellent oxidation resistance. LPCVD on the formed substrate
Even if a Si nitride film is formed by a method, it does not have the original properties of a Si nitride film (slow etching rate and excellent oxidation resistance).

It is practically difficult to use it for the purpose of thermal oxidation barrier. This is the reason for points (1) and (2) mentioned in the section on problems with the prior art.

On the other hand, FIG. 4 shows the etching characteristics of a film formed by the method that is the gist of the present invention. In this figure, the purpose of the vertical axis in FIGS. 2 and 3 is reduced to 1/2. J, shows Si nitride film and Sil! as a reference. It shows the etching characteristics of the dl film. G is 3% oxygen (
This sample was heat-treated for 35 minutes in an atmosphere of NH8+NZ (used as a carrier gas for Ox) containing Ox. The equipment is a normal horizontal electric furnace, and the natural oxide film is 10 Å.
Care was taken to prevent it from growing any further. The temperature is 900℃.

NHa flow rate 2Q/win pressure was atmospheric pressure. In this case, the thickness of the film formed was 75 mm, and the etching rate was also extremely uniform, with no fluctuations in the composition distribution in the film thickness direction. It can be seen that the film (K) has a value approximately in the middle of that of the film (K), indicating that it is a uniform Si oxynitride film. H is a sample heat-treated for 10 minutes under the same conditions. The thickness of the film formed at this time was 35 mm, showing exactly the same etching characteristics, and it was found that time control of film thickness and control of film quality could be realized extremely easily. ■ After heat treatment for 15 minutes under the same conditions, o
This sample was continuously heat-treated with NH3 alone for an additional 30 minutes with the supply of z stopped. In this case, a layer in which nitridation is concentrated only on the Si surface can be formed without changing the composition in the film at all.

Although we have explained the etching characteristics of wet etching above, we will also touch on an example of the results of Auger electron spectroscopy. Figure 5 shows the results of compositional analysis in the depth direction of sample B shown in Figure 2. This is what is shown. Although it is clear that the surface layer is a Si oxynitride film consisting of Si, N, and ○, the composition distribution in the depth direction is extremely ambiguous, and is unique to the analysis method in that it cannot correspond to the actual film thickness. There are some inconveniences. Therefore, there is always a problem in the veracity of the relationship between the film thickness (depth) indicated by the sputtering time and the composition distribution. For this reason, a wet etching method is used in the description of the present invention.

Next, we will discuss the problem of film thickness controllability of the Si nitride film formed by the LPCVD method. FIG. 6 shows the difference in film thickness controllability between a Si nitride film formed by the LPCVD method and a Si oxynitride film formed by the NH8-02 oxynitridation method, which is the gist of the present invention. In both cases, the film thickness was set using 35 people, and the relationship between the number of treatments when film formation was performed and the average film thickness on one sample is shown.

In the LPCVD method, the film thickness varies widely within the range of 30 to 40 people, whereas the N11s-0 film according to the present invention
In the 2 method, the variation is very small with only 2 people.

This shows that the controllability is extremely good. Conventionally, LPC
The VD method has been widely used in semiconductor manufacturing processes because it has a smaller film thickness distribution and better controllability than the normal pressure CVD method.
At present, it is difficult to control membranes as thin as a human being.

In the present invention, in order to avoid poor controllability of the Si nitride film formed by the LPCVD method, one of the main points is to form the dielectric insulating film for the capacitor without using the Si nitride film formed by the LPCVD method. are doing.

FIG. 7 is a cross-sectional view schematically showing the capacitor manufacturing process. Specific resistance 1Ω・■ with n-type (100) plane orientation
A 5iOz layer 202 having a thickness of 500 wafers was formed on a Si substrate 201 by a thermal oxidation method.

Next, a predetermined area is etched with 5iO using a well-known photoetching method.
Removed z. Further, a Si film 203 having a thickness of 2000 wafers was formed using the well-known LPCVD method, and then phosphorus was introduced into the Si film using a thermal diffusion method.

During thermal diffusion, phosphorus glass formed on the Si surface was removed (3). Next, a Si oxynitride film was formed by the NHa-Ox method. A horizontal electric furnace, which is commonly used for oxidation, was used as a heating device. When inserting the sample, care was taken to prevent a natural oxide film from growing on the surface of the Si film 203 due to air entrainment. After placing the sample in the furnace, NHa2Q
/win, 02100ce/win, Nz IQ/win as the o2 carrier gas and heat treatment at a temperature of 900° C. for 10 minutes to form a Si oxynitride film 204 with a thickness of 35 mm (b).

After that, a Si film 205 is formed again by the LPCI/[) method, and the Si film and 5iO
The z film was removed. Furthermore, phosphorus is introduced into the Si film 205 using a thermal diffusion method, buttering is performed by photoetching, and the upper part 1! A capacitor was constructed by forming poles.

The measurement is performed by keeping the Si substrate 201 at the ground potential as the lower electrode, and applying a positive (positive bias) or negative (negative bias) to the upper electrode.
This was done by sweeping the step wave voltage Va of (C
).

FIG. 8 shows an example of current-voltage characteristics.

The vertical axis represents leakage current normalized by area.

There is almost no dependence on positive or negative bias, the voltage leading to breakdown is high, and the leakage current is lower than that of the Si nitride film formed by the LPCVD method. Although it can withstand use as an insulating film, in order to further improve reliability, after forming a Si oxynitride film, it was
After forming a nitride layer at the interface between the Pa 203 and the Si oxynitride film 204, heat treatment may be performed in an oxidizing IJg atmosphere.

In this case as well, since the LPCVD method is not used, a highly reliable capacitor can be formed without deteriorating film thickness controllability.

FIG. 1 shows a cross-sectional structure when the present invention is applied to a dielectric insulating film of a capacitor constituting a 5TCp dynamic RAM. Si with p-type (100) plane orientation
A switching MOS transistor is formed on a substrate 101, consisting of a gate insulating film 103, a polycrystalline 5i 104 serving as a gate electrode, and an n-type impurity diffusion layer 106 forming a source and a drain, and a Si film 107 is formed in contact with the source region. It was buttered to form the lower electrode of the capacitor. A Si oxynitride film was formed on the surface of the Si film 107 by the NHs-02 method, and a Si film 109 serving as an upper electrode was further formed to form a capacitor.

Thereafter, phosphorus glass 110 and AQ wiring 111 were formed to form a memory cell. Further, the present invention can be applied to a CCC structure in which a capacitor is formed by forming a groove in a Si substrate, and there are no structural restrictions at all.

〔Effect of the invention〕

According to the present invention, it is possible to form an extremely thin dielectric insulating film with uniform film quality and high reliability with good controllability by simply using an electric furnace that is normally used as a processing device. I can do it. In addition, Si
Since no nitride film is required, there is no need for expensive processing equipment, and there is a great economic advantage. By forming a thin dielectric insulating film as described above, it is possible to reduce the planar area of the memory cell by half or less compared to the case where 50 insulating films are used, which is effective in improving the degree of integration.

[Brief explanation of the drawing]

FIG. 1 shows an S using a capacitor which is an embodiment of the present invention.
A cross-sectional view of the TC structure, FIGS. 2 and 3 are etching characteristic diagrams of a dielectric insulating film according to the prior art, and FIG. 4 is an etching characteristic diagram of a silicon oxynitride film in an embodiment of the present invention.
Figure 5 is a graph showing the analysis results of silicon oxynitride film by Auger electron spectroscopy, and Figure 6 is a graph showing the results of analysis using LPCVD method and NHs
A graph showing film thickness controllability by the Oz method, FIG. 7 is a cross-sectional view for explaining a capacitor forming process according to an embodiment of the present invention, and FIG. 8 is a graph showing a capacitor according to an embodiment of the present invention.
l Fig. 27 Knee, 'l-'-7'' to the leaves 1 (total) Fig. 4 JLX) h Engineering,・■ Now〉Fginma (-t') Kun early 5 Fig. Matata Hersoku〉2''11'＋M<l>n茅 ム dent′ “茅′7 figure 乎8reason

Claims (1)

[Claims] 1. Semiconductor substrate or S formed on the semiconductor substrate
In a capacitor structure configured by using the i-layer as a first electrode, forming a dielectric insulating film on the electrode, and further forming a second electrode, the dielectric insulating film serves as the first electrode, A capacitor structure comprising at least a Si oxynitride film (oxynitride) obtained by heat treatment in an atmosphere containing at least an oxidizing agent (O_2, H_2O, N_2O, etc.) and ammonia (NH_3). 2. The capacitor structure according to claim 1, wherein the dielectric insulating film includes at least a Si oxynitride film obtained by thermally oxidizing the Si oxynitride film. 3. The first step of forming a Si layer that will become the first electrode on the semiconductor substrate, and forming the Si layer on the surface of the first electrode by thermal nitridation in an atmosphere of 950°C or lower containing an oxidizing agent and NH_3.
a second step of forming a dielectric insulating film including an oxynitride film;
A method for manufacturing a capacitor structure, comprising a third step of forming a second electrode on the dielectric insulating film. 4. The first step is to form a Si layer that will become the first electrode on the semiconductor substrate, and the surface of the first electrode is thermally nitrided to a desired thickness in an atmosphere of 950°C or lower containing an oxidizing agent and NH_3. After forming the Si oxynitride film, a layer with a high nitrogen content is formed at the interface between the first electrode and the Si oxynitride film by including a step of stopping the supply of an oxidizing agent and performing heat treatment,
A method for manufacturing a capacitor structure, the method comprising: a second step of performing heat treatment in an oxidizing atmosphere to form a dielectric insulating film; and a third step of forming a second electrode.