JP4170612B2 - Semiconductor device and manufacturing method thereof - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a semiconductor device including a member made of a silicon nitride film and a method for manufacturing the same, and more particularly, a semiconductor device in which an etching rate on a side surface of a member made of a silicon nitride film is controlled to be slower than an etching rate of a silicon oxide film. And a manufacturing method thereof.
[0002]
[Prior art]
In recent years, multi-layer wiring is often used in LSIs to increase the degree of integration. In this type of multilayer wiring, in order to realize wiring with a high degree of integration, a technique for directly connecting not only the wiring layers adjacent to each other up and down but also two or more layers apart is used.
[0003]
At this time, the plug that connects wirings separated by two or more layers and the wiring (intermediate wiring) existing between the wirings separated by two or more layers must be insulated. For this reason, multilayer wiring that directly connects two or more layers is usually designed with a sufficient margin so that the connection hole in which the plug is embedded does not reach the intermediate wiring due to misalignment between the layers. ing.
[0004]
On the other hand, in recent years, a method (SAC (Self-Aligned Contact) process) in which a plug is formed in a self-aligned manner with respect to the wiring has been performed in order to form a wiring with a higher degree of integration. This method will be described below with reference to FIG.
[0005]
First, as shown in FIG. 5A, a silicon oxide film 82 as a first interlayer insulating film is formed on the first wiring 81, and then the second wiring 83 and the first wiring are formed on the silicon nitride film 82. The silicon nitride film 84 is formed.
[0006]
Next, as shown in FIG. 5B, a second silicon nitride film (sidewall insulating film) 85 is formed on the side walls of the second wiring 83 and the first silicon nitride film 84, and then the second silicon nitride film (sidewall insulating film) 85 is formed. A silicon oxide film 86 as an interlayer insulating film is deposited on the entire surface, and then a contact pattern 87 made of a photoresist is formed on the silicon oxide film 86.
[0007]
Thereafter, using the RIE (Reactive Ion Etching) method, the silicon oxide etching rate is faster than that of silicon nitride, and the contact pattern 87 is used as a mask as shown in FIG. The oxide films 86 and 81 are selectively etched with respect to the silicon nitride films 84 and 85 to open the connection holes 88 reaching the first wirings 81 in a self-aligning manner.
[0008]
Thereafter, as shown in FIG. 5D, the contact pattern 87 is peeled off.
[0009]
Next, as shown in FIG. 5E, a metal film that becomes the third wiring and a plug (third wiring / plug) 89 that connects the third wiring and the first wiring 81 is formed in the connection hole. A third wiring / plug 89 is formed by depositing the metal film 88 on the silicon oxide film 86 and then patterning the metal film.
[0010]
According to such a method, since the silicon nitride films 84 and 85 function as a mask for the second wiring 83 in the etching process of FIG. 5C, the second wiring 83 is provided even if the contact pattern 87 is shifted. Is not etched. Therefore, it is not necessary to provide a margin between the connection hole 88 and the second wiring 83. That is, it is not necessary to increase the distance between the two second wirings 83 shown in the drawing.
[0011]
As a method for forming the silicon nitride film 85 covering the second wiring 83, the CVD method, particularly the LP-CVD method is preferable. As another method for depositing silicon nitride, a PE-CVD method is also generally used, but is significantly inferior to the LP-CVD method in terms of step coverage on the side surface of the second wiring 83.
[0012]
However, the LP-CVD method using ordinary SiH ₂ Cl ₂ (DCS) and NH ₃ as source gases requires a high-temperature heat process of 700 ° C. or higher. For this reason, the wiring material formed before this is not a low melting point material such as Al, but a high melting point material such as W is required.
[0013]
Furthermore, in the high-temperature heat process at 700 ° C. or higher, as shown in FIG. 6, the reaction between the metal constituting the first wiring 81 and the impurity diffusion layer 90 cannot be prevented by the barrier metal film 94. Problems such as an increase in contact resistance between the diffusion layer 90 and the first wiring 81 and an increase in leakage current occur. In FIG. 6, reference numeral 91 denotes a silicon substrate, 92 denotes an element isolation insulating film (STI), 93 denotes an interlayer insulating film, and 94 denotes a barrier metal film.
[0014]
In order to solve these problems, it has been proposed to use Si ₂ Cl ₆ (HCD) as a source gas. If this gas system is used, a silicon nitride film can be deposited even at a film forming temperature of 650 ° C. or lower.
[0015]
However, a silicon nitride film formed by LP-CVD using HCD as a source gas has a high etching rate with a liquid containing HF (HF solution) frequently used in the LSI manufacturing process.
[0016]
Therefore, for example, in the step of removing the natural oxide film with the HF solution performed after the step of FIG. 5C, the silicon nitride films 84 and 85 are etched, and the silicon nitride films 84 and 85 are thinned or eliminated. As a result, there arises a problem that it is difficult to maintain insulation between the third wiring / plug 89 and the second wiring 83.
[0017]
[Problems to be solved by the invention]
As described above, in the conventional SAC process, the LP-CVD method using HCD as the source gas is employed as a method for forming the silicon nitride film covering the wiring from the viewpoint of step coverage and film formation temperature.
[0018]
The silicon nitride film formed by this kind of method has a high etching rate with the HF solution used for removing the natural oxide film. Therefore, the silicon nitride film is thinned or disappeared in the process of removing the natural oxide film with the silicon nitride film as the sidewall insulating film exposed. As a result, there arises a problem that it is difficult to maintain insulation between the plug that connects the first wiring and the third wiring and the second wiring.
[0019]
The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a semiconductor device including an insulating member made of a silicon nitride film, which can prevent thinning and disappearance due to HF, and a method for manufacturing the same. There is to do.
[0020]
[Means for Solving the Problems]
Of the inventions disclosed in this application, the outline of typical ones will be briefly described as follows.
[0021]
That is, in order to achieve the above object, a semiconductor device according to the present invention includes a substrate and a member formed on the substrate, at least a part of the side surface of which is exposed, and formed of a silicon nitride film. When the surface layer including the side surface and the layer deeper than the surface layer are divided into two, the volume density of nitrogen in the surface layer has a distribution in the depth direction, and the layer deeper than the surface layer. The nitrogen in the surface layer is obtained by subtracting the volume density of nitrogen in a layer deeper than the surface layer from the volume density of nitrogen in the surface layer, wherein the volume density of nitrogen is substantially constant in the depth direction. A surface density of the surface layer obtained by integrating the volume density distribution of the surface layer in the depth direction of the surface layer is 1 × 10 ¹⁴ cm ⁻² or more and 5 × 10 ¹⁵ cm ⁻² or less , The member made of the silicon nitride film is 7 At 0 ℃ the following deposition temperature, characterized in that formed by the LP-CVD method using a hexachlorodisilane gas and NH ₃ gas.
[0022]
According to the present invention, by setting the nitrogen density of the exposed portion of the side surface of the member made of the silicon oxide film to 1 × 10 ¹⁴ cm ⁻² or more and 5 × 10 ¹⁵ cm ⁻² or less, etching with HF in the exposed portion is performed. A semiconductor device including a member made of a silicon nitride film and a method of manufacturing the same can be realized that can increase resistance and thereby prevent thinning and disappearance due to HF.
[0023]
The above and other objects and novel features of the present invention will become apparent from the description of the present specification and the accompanying drawings.
[0024]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention (hereinafter referred to as embodiments) will be described with reference to the drawings.
[0025]
(First embodiment)
When a silicon nitride film deposited by LP-CVD at 625 ° C. using HCD as a silicon source is wet etched with a liquid containing 0.25% HF, the etching rate of the silicon nitride film is formed by thermal oxidation immediately after deposition. The etching rate ratio to the thermal oxide film is about 0.45 times even after performing RTA in N ₂ at 900 ° C. for 20 seconds.
[0026]
However, the inventors' experiments have revealed that the etching rate can be sufficiently reduced by introducing a predetermined amount of nitrogen into the silicon nitride film.
[0027]
FIG. 1 shows a sample obtained by implanting nitrogen ions into a silicon nitride film deposited by LP-CVD at 625 ° C. using HCD and NH ₃ gas and performing RTA in N ₂ at 900 ° C. for 20 seconds. It is a figure which shows the relationship between the dose amount of nitrogen ion at the time of etching with 0.25% HF aqueous solution, and the etching rate of a silicon nitride film. For reference, FIG. 1 also shows the etching rate of the silicon nitride film into which nitrogen ions are not introduced.
[0028]
As can be seen from FIG. 1, when nitrogen ions are implanted so that the surface density is 1 × 10 ¹⁴ or more and 5 × 10 ¹⁵ cm ⁻² or less, the etching rate is lowered. On the contrary, the etching rate becomes faster at a nitrogen concentration of 1 × 10 ¹⁶ cm ⁻² , which is interpreted as the structure of the silicon nitride film being disturbed by physical stress.
[0029]
However, when the ion implantation method is used, the directivity of nitrogen ions is extremely high, so that nitrogen cannot be efficiently introduced into the side surface of the silicon nitride film. In addition, the silicon nitride film is easily damaged physically. In order to efficiently introduce nitrogen into the side wall portion, it is necessary to use particles containing nitrogen with low directivity.
[0030]
As a method for efficiently introducing nitrogen into the side surface of the silicon nitride film using such particles having low directivity, a method using plasma containing nitrogen is conceivable.
[0031]
For example, after opening the connection hole 88 in the same manner as shown in FIGS. 5A to 5D, as shown in FIG. 2, for example, N ₂ or NH under a pressure of about 100 mTorr. _The substrate on which the silicon nitride film 85 is formed is exposed to the plasma 1 containing nitrogen generated by applying a high frequency of about 500 W to a gas containing nitrogen such as ₃ .
[0032]
Thereby, a high concentration nitrogen layer 2 having a nitrogen concentration of 1 × 10 ^{14 to} 5 × 10 ¹⁵ cm ⁻² , which is difficult by ion implantation, can be formed on the exposed side surface of the silicon nitride film 85. The high concentration nitrogen layer 2 is also formed on the exposed upper surface of the silicon nitride film 85. In the figure, reference numeral 3 denotes a high-concentration nitrogen layer 3 (surface layer) formed on the upper surface and side wall surface (side surface of the connection hole) of the silicon oxide film 82 by the plasma treatment.
[0033]
The nitrogen concentration (cm ⁻³ ) in the depth direction of the silicon nitride film 85 below the high-concentration nitrogen layer 2 is substantially constant. This is because the silicon nitride film 85 below the high-concentration nitrogen layer 2 has almost no nitrogen addition by plasma doping, and substantially contains only nitrogen inherent in the silicon nitride film.
[0034]
Further, since the silicon nitride film 85 in the portion below the high-concentration nitrogen layer 2 is hardly added with nitrogen by plasma doping, the nitrogen concentration in the silicon nitride film 85 in the portion below the high-concentration nitrogen layer 2 ( cm ⁻³ ) is lower than that of the high-concentration nitrogen layer 2.
[0035]
That is, when the method of this embodiment is used, the silicon nitride film 85 (a member made of a silicon nitride film) on which the high-concentration nitrogen layer 2 is formed is divided into a high-concentration nitrogen layer 2 and a deeper layer. The volume density of nitrogen in the high concentration nitrogen layer 2 has a distribution in the depth direction, and the volume density of nitrogen in a layer deeper than the high concentration nitrogen layer 2 is substantially constant in the depth direction, The volume density distribution of nitrogen in the high concentration nitrogen layer 2 obtained by subtracting the volume density of nitrogen in the layer deeper than the high concentration nitrogen layer 2 from the volume density of nitrogen in the high concentration nitrogen layer 2 is expressed as It was found that the surface density of the high-concentration nitrogen layer 2 obtained by integrating in the depth direction of 2 is 1 × 10 ¹⁴ cm ⁻² or more and 5 × 10 ¹⁵ cm ⁻² or less.
[0036]
After the high concentration nitrogen layer 2 is formed, if necessary, heating is performed at a relatively low temperature of about 600 ° C. for about 30 minutes to 60 minutes, or at a temperature of about 800 ° C. for about 20 to 30 seconds. By performing this heating, it becomes possible to introduce nitrogen more efficiently.
[0037]
Thus, according to the present embodiment, by forming the high-concentration nitrogen layer 2 on the exposed surface of the silicon nitride film 85 by nitrogen plasma treatment, for example, HF is used to perform cleaning for the purpose of removing a natural oxide film or the like. Even if the used wet etching is performed, the silicon nitride film 85 covering the side wall of the second wiring 83 can be prevented from being thinned, and the insulation between the third wiring / plug 89 and the second wiring 83 can be maintained. Will be able to.
[0038]
(Second Embodiment)
3 and 4 are cross-sectional views illustrating the manufacturing steps of the semiconductor device according to the second embodiment of the present invention.
[0039]
First, as shown in FIG. 3A, a gate insulating film 22 made of SiO ₂ or the like on a silicon substrate 21 and a semiconductor film made of silicon or silicon germanium having a thickness of 70 nm are made of B, As, P A low-resistance semiconductor film 23 to which a conductive impurity such as 1 × 10 ²⁰ cm ⁻³ or more is added, a thin W nitride film 24 having a thickness of about 5 nm, a W film 25, and a silicon nitride film 26 having a thickness of about 200 nm. A photoresist pattern 27 having a gate pattern is formed on the silicon nitride film 26 sequentially. Instead of the silicon substrate 21, an SOI substrate or a substrate containing silicon germanium may be used. The crystal structure of the semiconductor film 23 is, for example, polycrystalline.
[0040]
Next, as shown in FIG. 3B, the silicon nitride film 26 is etched by the RIE method using the photoresist pattern 27 as a mask, and the pattern of the photoresist pattern 27 is transferred to the silicon nitride film 26. As a result, a hard mask made of the silicon nitride film 26 is obtained.
[0041]
Next, as shown in FIG. 3C, after the photoresist pattern 27 is peeled off, a high frequency of about 500 W is applied to a gas containing nitrogen such as N ₂ or NH ₃ under a pressure of about 100 mTorr. The silicon substrate 21 on which the silicon nitride film 26 is formed is exposed to plasma containing nitrogen, and the surface of the silicon nitride film 26 has a high surface density of 1 × 10 ^{14 to} 5 × 10 ¹⁵ cm ^−2. A concentration nitrogen layer 28 is formed. The nitrogen concentration of the silicon nitride film 26 in the portion where the high concentration nitrogen layer 28 is not formed becomes a value lower than 1 × 10 ¹⁴ .
[0042]
At this time, a high-concentration nitrogen layer 29 is also formed on the surface of the W film 25, but the high-concentration nitrogen layer 29 is removed at the same step without affecting the subsequent RIE process.
[0043]
After the formation of the high-concentration nitrogen layers 28 and 29, if necessary, heating is performed at a relatively low temperature of about 600 ° C. for about 30 minutes to 60 minutes, or at a temperature of about 800 ° C. for about 20 to 30 seconds. Nitrogen can be introduced more efficiently by heating for a short time.
[0044]
Next, as shown in FIG. 3D, the W film 25, the W nitride film 24, and the semiconductor film 23 are formed using the silicon nitride film 26 (hard mask) having the high concentration nitrogen layer 28 formed on the surface as a mask. Etching is performed by RIE to form a gate electrode 30 composed of the W film 25, the W nitride film 24, and the semiconductor film 23. At this time, the high concentration nitrogen layer 29 formed on the surface of the W film 25 is removed.
[0045]
Next, for example, using a method disclosed in JP-A-59-132136, heat treatment is performed at about 800 ° C. in a mixed atmosphere of H ₂ and H ₂ O, and as shown in FIG. The side surfaces (gate sidewalls) of the semiconductor film 23 are oxidized without oxidizing the W film 25 and the W nitride film 24, thereby forming the oxide film 31. Thus, the reliability of the gate insulating film 22 can be improved by oxidizing the gate side wall and increasing the thickness of the oxide film in the portion in contact with the gate insulating film 22.
[0046]
Next, as shown in FIG. 4F, impurity ions are implanted into the substrate surface using the gate electrode 30 or the like as a mask to form an impurity diffusion layer 32 constituting source / drain extensions in a self-aligned manner.
[0047]
In all the steps from FIG. 3C to FIG. 4F, even if wet etching or wet cleaning is performed with a solution containing HF, the high-concentration nitrogen layer 29 is formed. The sheath width does not decrease.
[0048]
Next, as shown in FIG. 4G, a silicon nitride film 33 having a thickness of about 50 nm is deposited on the entire surface so as to cover the gate portion including the gate electrode 30 and the like.
[0049]
Next, as shown in FIG. 4H, the entire surface of the silicon nitride film 33 is etched by the RIE method, and the silicon nitride film 33 is selectively left on the side walls of the gate electrode 30 and the silicon nitride film 26. At this time, the high concentration nitrogen layer 28 formed on the upper surface of the silicon nitride film (hard mask) 26 is removed.
[0050]
Next, as shown in FIG. 4 (i), the substrate is exposed to nitrogen-containing plasma generated by applying a high frequency of about 500 W to a gas containing nitrogen such as N ₂ or NH ₃ under a pressure of about 100 mTorr. A high-concentration nitrogen layer 34 having a surface density of 1 × 10 ^{14 to} 5 × 10 ¹⁵ cm ⁻² is formed on the surfaces of the nitride film (gate sidewall insulating film) 33 and the silicon nitride film 26 (hard mask).
[0051]
After the formation of the high-concentration nitrogen layer 34, if necessary, heating is performed at a relatively low temperature of about 600 ° C. for about 30 minutes to 60 minutes, or at a temperature of about 800 ° C. for about 20 seconds to 30 seconds. Nitrogen can be introduced more efficiently by heating for a short time.
[0052]
Thereafter, a step of performing wet etching or wet cleaning with a solution containing HF continues, but the silicon nitride film (gate sidewall insulating film) 35 and the silicon nitride film (hard mask) 26 are formed with high-concentration nitrogen formed on the surfaces thereof. The layer 34 prevents thinning and disappearance, and as a result, insulation between the gate electrode 30 and the source / drain electrodes formed in the next process can be maintained.
[0053]
The present invention is not limited to the above embodiment. For example, in the above embodiment, the case of the silicon nitride film used during the SAC process or the gate process has been described. However, the present invention can be applied to a silicon nitride film used during other processes. Further, the deposition temperature of the silicon nitride film is preferably a low temperature of 700 ° C. or lower. Such a low film formation temperature can be easily realized by using an LP-CVD method using HCD as a source gas.
[0054]
Further, in the above embodiment, as a method of introducing a predetermined amount of nitrogen into the exposed side surface of the insulating member made of the silicon nitride film, a method of exposing to a plasma containing nitrogen, that is, the momentum distribution of nitrogen is not anisotropic. Although the insulating member made of a silicon nitride film was exposed to a rough environment, other methods may be used. For example, a method using oblique ion implantation is possible.
[0055]
Furthermore, the above embodiments include inventions at various stages, and various inventions can be extracted by appropriately combining a plurality of disclosed constituent elements. For example, even if some constituent requirements are deleted from all the constituent requirements shown in the embodiment, if the problem described in the column of the problem to be solved by the invention can be solved, the configuration in which this constituent requirement is deleted Can be extracted as an invention.
[0056]
In addition, various modifications can be made without departing from the scope of the present invention.
[0057]
【The invention's effect】
As described above in detail, according to the present invention, it is possible to realize a semiconductor device including an insulating member made of a silicon nitride film and a manufacturing method thereof that can prevent thinning and disappearance due to HF.
[Brief description of the drawings]
FIG. 1 shows a dose amount of nitrogen ions when a sample obtained by implanting nitrogen ions into a silicon nitride film deposited by LP-CVD using HCD and NH ₃ gas and etching RTA with an HF aqueous solution. FIG. 2 is a cross-sectional view showing a manufacturing process of a semiconductor device according to the first embodiment of the present invention. FIG. 3 is a diagram of manufacturing a semiconductor device according to a second embodiment of the present invention. FIG. 4 is a sectional view showing a manufacturing process of the semiconductor device following FIG. 3. FIG. 5 is a sectional view showing a conventional SAC process. FIG. 6 is a sectional view for explaining a conventional problem. [Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Plasma containing nitrogen 2, 3 ... High concentration nitrogen layer 21 ... Silicon substrate 22 ... Gate insulating film 23 ... Low resistance semiconductor film 24 ... W nitride film 25 ... W film 26 ... Silicon nitride film (hard mask)
27 ... Photoresist patterns 28, 29 ... High-concentration nitrogen layer 30 ... Gate electrode 31 ... Oxide film 32 ... Impurity diffusion layer 33 ... Silicon nitride film (gate sidewall insulating film)
34 ... High-concentration nitrogen layer

Claims (4)

A substrate,
A member made of a silicon nitride film, formed on the substrate, with at least a part of the side surface exposed, and the member divided into a surface layer including the side surface and a layer deeper than the surface layer If
The volume density of nitrogen in the surface layer has a distribution in the depth direction, and the volume density of nitrogen in the layer deeper than the surface layer is substantially constant in the depth direction, and the nitrogen density in the surface layer is substantially constant. The volume density of the surface layer obtained by integrating the volume density distribution of nitrogen in the surface layer obtained by subtracting the volume density of nitrogen in the layer deeper than the surface layer from the volume density in the depth direction of the surface layer. A member having a surface density of 1 × 10 ¹⁴ cm ⁻² or more and 5 × 10 ¹⁵ cm ⁻² or less, and the member made of the silicon nitride film is formed at a film formation temperature of 700 ° C. or less and hexachlorodisilane gas A semiconductor device formed by LP-CVD using NH ₃ gas .   2. The semiconductor device according to claim 1, wherein the member is a member made of a silicon nitride film formed on a side wall of the electrode, or a hard mask formed on the gate electrode and made of a silicon nitride film. The semiconductor device according to claim 2 , wherein the electrode is a gate electrode including a W film. Forming a silicon nitride film on the substrate at a film forming temperature of 700 ° C. or lower using LP-CVD;
Etching the silicon nitride film to form a member made of the silicon nitride film with at least a part of a side surface exposed;
Exposing the substrate on which the member is formed to plasma containing nitrogen, and introducing nitrogen of 1 × 10 ¹⁴ cm ⁻² or more and 5 × 10 ¹⁵ cm ⁻² or less into the exposed side surface of the member;
Have a step of removing the oxide film on the region including the member, a method of manufacturing a semiconductor device, characterized in that said the LP-CVD method is one using a hexachlorodisilane gas and NH ₃ gas.

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