JPH05121376A - Dry-etching method and dry-etching device - Google Patents

Abstract

PURPOSE:To prevent excessive etching of a metallic film in the inside of a through hole and to prevent a short-circuit between wirings and between wiring layers when the wiring metallic film is etched to leave the metallic film only in the inside of the through hole. CONSTITUTION:In order to form a wiring metallic film and a poly Si film only in a groove of a through hole and a Si substrate 1 of a semiconductor device, after a thin film is formed using a selective CVD method or a wholesurface CVD method, a sample is anisotropically dryetched from the oblique direction. Thus, it becomes unnecessary to detect the terminal of the etching.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a dry etching method and apparatus for manufacturing semiconductor elements.

[0002]

2. Description of the Related Art A conventional thin film dry etching method is
It was customary to anisotropically etch from the direction perpendicular to the sample using the photoresist as a mask. For example,
This is because when the thin film is a metal film for wiring, the wiring layer is processed vertically to reduce the dimensional shift and form a fine pattern.

Further, as a method of forming a metal film only inside the through hole between the upper and lower wiring layers in order to secure the conduction reliability of the upper and lower wiring layers, there are disclosed in Japanese Patent Laid-Open Nos. 62-298110 and 62-243324. There is a metal burying in the through hole by the selective CVD method described in Japanese Patent Laid-Open Publication No. These methods are
When the selectivity is deteriorated, foreign particles of metal particles are also generated on the interlayer insulating film, which causes a short circuit between wirings and between wiring layers.

As a method for removing foreign matter from the metal particles, Japanese Patent Laid-Open No.
62-199034 and JP-A-63-44730. In these methods, a film of a material having etching characteristics different from that of the insulating material layer is previously deposited on the insulating material layer, a through hole is opened in this film and the insulating material layer, and then a through process is performed by a selective CVD method. A metal film is deposited only inside the hole. At that time, the metal particles on the film generated by the deterioration of the selectivity of the selective CVD method are removed simultaneously with the film by wet etching of the film. This method is capable of removing foreign matter from metal particles, but in a sample having a plurality of through holes having different depths, if a metal film is formed by the selective CVD method in accordance with the deepest through hole, the shallow through hole is formed. Then, a mushroom-shaped metal film protrusion is generated on the upper part of the surface. The size of the protrusion of the metal film is determined by the difference between the depth of the deepest through hole and the depth of the shallow through hole. If the protrusion is large, it causes a short circuit between wirings or between wiring layers.

There is also a method in which a metal film is formed on the inside of the through hole and on the interlayer insulating film by a full-scale CVD method or the like, and then only the metal film on the interlayer insulating film is etched to leave the metal film only inside the through hole. .. For example, in the method described in JP-A-62-229959, after forming a metal film, a flattening resist is applied, and then the flattening resist and the metal film are etched until the interlayer insulating film is reached. A metal film is formed only inside the hole. This method is difficult because it is necessary to set the etching selectivity between the planarizing resist and the metal film to 1. Further, since it is difficult to detect the end point of etching, it is difficult to form the shape of the metal film inside the through hole with good reproducibility. Further, there is a method in which the metal film is etched back without using a planarizing resist to form the metal film only inside the through holes. For example, the method described in Japanese Patent Laid-Open No. 61-237452 uses the entire surface C
The metal film is formed by the VD method, and then the metal film is etched until the surface of the interlayer insulating film is exposed to form the metal film only inside the through hole. This method
It is necessary to completely fill the through hole with a metal film and form the film until the surface of the metal film becomes flat. Therefore, when there is a through hole having a large diameter, it is necessary to form a thick metal film, and the etching amount must be increased accordingly. Further, when there is a step on the base of the sample, the metal film in the vertical direction on the step is thicker than the metal film on the flat portion. Therefore, if the etching is finished when the interlayer insulating film on the flat portion is exposed, the metal film on the step remains, which causes a short circuit between the wirings. Further, when the metal film on the step is completely etched, the metal film in the through hole is excessively etched, and the metal film embedded in the through hole remains only slightly.

Further, for the purpose of flattening the surface of the sample, there is a method of forming a film on the surface of the sample in which holes are opened, and then etching the film formed first in an oblique direction with respect to the sample. .. For example, the method disclosed in JP-A-62-150724 forms a film on the micropores and the substrate by depositing film material particles on the substrate having micropores, and at the same time or after that, the film is formed on the substrate. The film is etched in an oblique direction. This method requires that the film thickness in the micropores and the film thickness on the substrate be approximately the same, and in addition, the film thickness must be formed to be approximately the same as the height of the micropores. It is very difficult to form a film by the vapor deposition method or the sputtering method. In particular, for minute holes having a large aspect ratio, when the film is formed by the vapor deposition method or the sputtering method, the film thickness at the bottom of the minute holes is significantly reduced as compared with the flat portion of the substrate. Furthermore, when the film formed on the substrate is completely etched once, if the thick film is etched from the direction oblique to the sample from the beginning, the etching rate is lower than the etching from the vertical direction. There is a problem that it takes a long time for etching.

Further, FIGS. 5 and 6 show a conventional etching method for a metal film formed around a hole. Figure 5 (a),
(b) and (c) are metal films 15 formed on the surface of the sample by the CVD method.
It shows the process of formation of the
At the end. As shown in FIG. 5C, when the formation of the metal film 15 is completed, the film quality of the central portion of the through hole is poor, and when the etch back is performed by the wet etching method, the result of
A cavity is easily generated in the central portion of the metal plug 17 as shown in (b). Further, when the metal film 15 is etched by the conventional dry etching method to form the metal plug 16, it is difficult to detect the end point of the etching.
It was extremely difficult to form the metal plug 16 with good reproducibility.

[0008]

In the conventional metal film etching method described above, it is difficult to detect the etching end point,
It was difficult to form the shape of the metal plug embedded in the through hole with good reproducibility. Further, when the metal film is etched by dry etching, there is a problem that the surface of the interlayer insulating film is easily damaged during overetching. Further, when forming a metal film by the CVD method, if there are a plurality of through holes having different depths in the selective CVD method, and if there are a plurality of through holes having different diameters in the full-scale CVD method, the It was difficult to embed metal. Further, when metal plugs are formed in a plurality of through holes having different depths by the selective CVD method, foreign matter of metal particles is generated on the surface of the interlayer insulating film due to deterioration of selectivity, and this foreign matter causes a short circuit between wirings or between wiring layers. It was the cause.

An object of the present invention is to eliminate the need for detecting the end point of etching in the dry etching method for a metal film and to form the shape of the metal plug buried in the through hole with good reproducibility.

A second object of the present invention is to reduce the damage on the surface of the interlayer insulating film which is exposed by etching the metal film by performing dry etching on the sample surface from an oblique direction.

A third object of the present invention is to obtain a metal plug which does not depend on the diameter and depth of the through hole in forming the metal plug in the through hole.

A fourth object of the present invention is to easily remove foreign matter of metal particles generated by deterioration of selectivity in forming a metal plug in a through hole by a selective CVD method without passing through a resist process. It is in.

[0013]

Means for Solving the Problems The above-mentioned objects are (1) in dry etching of a thin film, anisotropic dry etching is performed from an oblique direction with respect to a sample, (2) the above-mentioned dry etching is performed horizontally on a sample. 0 to 90 relative to the direction
(3) The thin film material to be dry-etched according to (1) and (2) above is a polysilicon film or a refractory metal film that is a metal thin film for wiring,
It is achieved by a dry etching method of a thin film, which is made of any one of a nitride film and a silicide film of a refractory metal, copper, aluminum, and an alloy film containing aluminum as a main component.

[0014]

The dry etching method of the present invention will be described with reference to FIG. As shown in FIG. 1, a desired contact hole is formed in the first interlayer insulating film 2 on the Si substrate 1, a first wiring layer 3 is formed, and then a desired pattern is etched.
After that, the second interlayer insulating film 4 is formed, and the through holes are opened using the photoresist as a mask. Further, after removing the photoresist, a metal film is formed by using the chemical vapor deposition (CVD) method, and the metal film is embedded in the through hole. At this time, the CVD metal film 8 may be uniformly formed on the second interlayer insulating film 4 by the whole surface CVD method as shown in FIG. 2A, or as shown in FIG. 2B. The metal plugs 9 and 10 may be formed in accordance with the deepest through hole by the method to generate the protrusions of the metal plug 9 and the foreign matter 11.

While rotating the sample formed by this method, the metal film is dry-etched by using an etching method of extracting accelerated ions from the discharge chamber and irradiating the sample. At this time, the incident angle θ of the etching gas 7 with respect to the sample indicates the inclination of the sample with respect to the horizontal direction. When this incident angle θ is set in the angle range of 0 to 45 degrees and the dry etching of the metal film is performed, as shown in FIG.
The CVD metal film 8 on the second interlayer insulating film 4 shown in FIG. 2 is gradually etched to have the cross-sectional shape shown in FIG. Furthermore, the protrusion of the metal plug 9 and the foreign matter 1 as shown in FIG.
Regarding No. 1 as well, when dry etching is performed by the same method as described above, the cross-sectional shape shown in FIG.

Here, the shapes of the metal plugs 5 and 6 shown in FIG. 1 strongly depend on the incident angle θ of the etching gas 7. For example, the diameter of the through hole is D, and the etching gas 7
When the dry etching is performed with the incident angle of θ as θ, the metal plug 5 slightly recedes from the surface of the second interlayer insulating film 4. If this amount of retreat is χ, the equation of Dtan θ = χ holds. That is, when the diameter D of the through hole is constant,
By making the incident angle θ smaller, the metal plug 5
The retreat amount χ of can be reduced. Further, even when there are a plurality of through holes having different diameters D, the distance χ / D from the surface of the metal plug 5 to the surface of the second interlayer insulating film 4 with respect to the diameter D of the through hole (the metal plug is not embedded). The aspect ratio of the top of the through hole) becomes constant. This is because when forming the metal thin film of the second wiring layer in the next step, the aspect ratios of the upper portions of the through-holes in which the metal plugs 5 and 6 are not embedded become equal, so that the metal film coating shape of the second wiring layer is formed. Is almost constant, which is effective for improving the reliability of the wiring in the through hole portion and also for flattening the sample surface.

[0017]

Embodiments of the present invention will be described with reference to FIGS. FIG. 3 shows a dry etching method for a sample in which a through hole is selectively filled with a metal film by a selective CVD method. As shown in FIG. 3A, the first
Depending on the presence or absence of the first wiring layer 3 formed on the interlayer insulating film 2,
The depth of the through hole on the Si substrate 1 is deeper than the depth of the through hole on the first wiring layer 3. Here, when the metal plug 10 is formed in conformity with the deep through hole on the Si substrate 1, the metal plug 9 formed in the shallow through hole on the first wiring layer 3 becomes a projection shape on the upper part thereof, and further the selectivity is increased. Foreign matter 11 of metal particles is generated on the second interlayer insulating film 4 due to the deterioration.

Next, while rotating the sample of FIG. 3 (a),
When the incident angle θ of the etching gas with respect to the horizontal direction of the sample is fixed at 20 degrees and the metal plugs 9 and 10 and the foreign material 11 are dry-etched, the foreign material 11 is completely etched and the protrusion of the metal plug 9 can be reduced. .. At this time, the metal plug 10 slightly recedes from the surface of the second interlayer insulating film 4. This retreat amount is Dtan 20 ° = χ formula,
This is about 0.36 times the diameter of the through hole.

When dry etching is continued in the same manner as this method, as shown in FIG. 3C, the protrusions of the metal plug 9 are completely etched, and the diameter of the through hole is reduced from the surface of the second interlayer insulating film 4. A recess corresponding to 0.36 times is generated, and the same shape as the upper portion of the metal plug 10 is obtained.

FIG. 4 shows a dry etching method for a sample on which the metal film 12 is formed by the full-scale CVD method. When the second interlayer insulating film 4 is not completely flattened as shown in FIG. 4A, the depth of the through hole on the first wiring layer 3 and the depth of the through hole on the Si substrate 1 are almost equal. .. As shown in FIG. 4B, while rotating this sample, the metal film 12 is dry-etched by making the etching gas 7 enter substantially perpendicularly to the sample, and the metal on the flat portion of the second interlayer insulating film 4 is etched. Dry etching is stopped until the film 12 is removed. At this time, an etching residue 14 of the metal film is generated in a portion where the surface of the second interlayer insulating film 4 is inclined. this is,
This is because when the metal film 12 is formed, the film thickness of the metal film 12 in the sample inclined portion becomes larger in the vertical direction than the film thickness of the metal film 12 on the flat portion.

Next, when the incident angle θ of the etching gas 7 with respect to the sample is changed to 20 degrees while the sample is rotated and the dry etching is continued, the etching residue 14 of the metal film is completely removed and the metal plug 13 is also removed. The shape slightly retreats from the surface of the second interlayer insulating film 4 and becomes the shape shown in FIG. still,
The amount of retreat of the metal plug 13 is about 0.
Since it becomes constant at 36 times, a substantially constant film coating shape can be obtained in any through hole in the wiring metal film formation in the next step, which is extremely effective in improving the reliability of the wiring.

In the present invention, the W film was etched by reactive ion etching using W (tungsten) as the metal film material and SF ₆ gas as the etching gas.

As a combination of another metal film material and an etching gas, CF ₄ , SF ₆ , NF ₃ is used as an F-based gas or Cl ₂ is used as a Cl-based gas for the refractory metal silicide film. If the metal film is made of Al, Cl ₂ gas such as Cl ₂ or BCl ₃ may be used.

The dry etching method of the present invention is also effective in forming trench isolation.

In the conventional trench isolation forming method, first, a Si substrate is thinly oxidized to form a SiO ₂ film, and a groove is formed by dry etching the oxide film and the Si substrate using the Si ₃ N ₄ film as a mask. And then oxidize again. Next, the poly-Si film is embedded in the groove of the Si substrate. There are two types of this embedding method, one of which is to form a poly-Si film on the entire surface of the sample and then etch back the poly-Si film to the surface of the Si substrate to leave the poly-Si film only in the groove of the Si substrate. deep. On the other hand, the SiO ₂ film on the bottom of the groove of the Si substrate is removed by dry etching, and S
By selectively forming a thick poly-Si film only on the exposed portion of the i-substrate and then etching back the Si-Si film,
The poly-Si film is left only in the groove of the substrate.

In the conventional method for forming trench isolation, the etch back of the poly-Si film is an essential condition, and it has been important to control the etch-back of the poly-Si film with good control. However, conventionally, since it was difficult to detect the end point of this etch back, there was no method other than controlling the etching by time, and it was extremely difficult to embed the poly-Si film with good reproducibility.

Using the dry etching method of the present invention, trench isolation can be formed with good reproducibility, as shown in FIGS. For example, when the poly-Si film 32 is formed on the entire surface of the sample (FIG. 7A), S
The poly-Si film 32 is etched until the i ₃ N ₄ film 31 is exposed. Up to this point, any etching method may be used. Next, the poly-Si film 32 is etched from an oblique direction by the dry etching method of the present invention, and S
The poly-Si film 32 is left only in the groove of the i substrate 1 (see FIG. 7).
(b)). The etching angle at this time was 20 ° with respect to the horizontal direction of the sample, and Cl ₂ was used as the etching gas. In this case, the etching gas is F-based gas, Cl-
F-based gas or the like can be used. Next, Si ₃ N ₄ film 3
After removing 1 and oxidizing the surface of the poly-Si film 32, a gate electrode 35 is formed (FIG. 7C). By thus etching the poly-Si film 32 using the dry etching method according to the present invention, the shape of the poly-Si film 32 embedded in the groove of the Si substrate 1 can be formed with good reproducibility.

Further, as shown in FIG. 8, a method similar to the above is applied to the structure (FIG. 8A) in which the poly-Si film 33 is selectively formed only on the exposed portion of the Si substrate 1. The trench isolation can be formed by. First,
After forming the poly-Si film 33, the poly-Si film 33 is etched by the dry etching method according to the present invention (FIG. 8B). Then, the Si ₃ N ₄ film 31 is removed, the surface of the poly Si film 33 is oxidized, and then the gate electrode 35 is formed, so that trench isolation as shown in FIG. 8C can be formed with good reproducibility. it can.

A well-known ion milling method or the like can be used for dry etching from an oblique direction with respect to the sample. However, in consideration of reduction of damage and high-speed processing, the following method was used in the present invention. Dry etching equipment is effective.

Therefore, the outline of the dry etching apparatus used in the present invention will be described with reference to FIG. As shown in FIG.
The microwave is generated by the microwave oscillator 101, and the microwave is introduced into the discharge tube 103 through the waveguide 102, and at the same time, the etching gas is introduced from the gas supply port 104 to discharge inside the discharge tube 103. The etching gas ions 109 generated by this discharge are introduced into the vacuum chamber 105 through the porous electrode 106. At this time, the etching gas ions 109 enter the porous electrode 106 substantially perpendicularly, are accelerated after passing through the porous electrode 106, and enter the sample 108 placed on the sample stage 107 without changing the directionality. Here, the sample stage 107 and the sample 108
The sample 10 is tilted with respect to the porous electrode 106.
The angle of the etching gas ions with which 8 is irradiated can be arbitrarily determined.

As shown in FIG. 10, the porous electrode 10
6, a grid electrode 110 is provided between the sample stage 107 and the sample stage 107 to generate a charge in the discharge tube 103.
It is possible to prevent the charged particles that have entered the inside 122 from advancing to the sample 108. Thereby, the grid electrode 11
Most of the particles that pass through 0 and enter the sample 108 become the etching gas neutral particles 111, and damage to the sample surface due to etching can be reduced. The incident angle of the etching gas neutral particles 111 to the sample 108 is
It can be determined by the angle of the sample stage 107 with respect to the grid electrode 110.

Further, as shown in FIG. 11, the etching gas is introduced into the gas activation chamber 112, and the temperature of the etching gas is raised there to activate the etching gas. The activated etching gas is introduced into the interior of the sample, and the sample 116 placed on the sample stage 115 is irradiated with the gas. At this time, the sample stage 1 against the etching gas that is activated and enters.
By tilting 15, the etching angle of the sample 116 can be arbitrarily determined. In this embodiment, Al
Since the film was etched with Cl ₂ gas, the etching conditions at that time are shown below. Cl _{2 in the} gas activation chamber 112
The gas is heated to 300 ° C. and the pressure in the vacuum chamber 114 is set to 1 Pa.
-5 mPa. Further, the sample stage 115 was tilted and rotated so that the incident angle of the etching gas with respect to the sample 116 was 20 degrees. In addition, the sample stage 115
A cooling liquid was circulated inside the sample to keep the temperature of the sample stage 115 constant at 0 ° C., thereby preventing the sample 116 from being heated to a high temperature. By using liquid nitrogen as the cooling liquid, the temperature can be controlled over a wide range of -100 ° C or lower. The etching rate of the Al film obtained by the above etching method was about 10 nm / min.

Further, other etching devices can be used. As shown in FIG. 12, the etching gas is introduced into the vacuum chamber 118 through the gas supply port 119. At this time, since the gas is not activated only by the etching gas, the sample 121 cannot be etched.
Therefore, the light from the light source lamp 117 assists the etching so that only the portion irradiated with the light is etched. At this time, the etching angle of the sample 121 can be determined by the inclination of the sample stage 120 with respect to the incident angle of light. As the etching assist beam, an electron beam can be used instead of light.

[0034]

According to the present invention, in the method of etching back a metal film embedded in a through hole, the end point of etching is detected by anisotropically dry-etching the metal film while rotating the sample. Unnecessary and
Further, the shape of the metal plug embedded in the through hole can be formed with good reproducibility.

Further, since the metal film is anisotropically dry-etched from the oblique direction, the damage on the surface of the interlayer insulating film can be reduced as compared with the dry etching from the vertical direction.

By etching back the metal film formed by the CVD method by the dry etching method of the present invention, a metal plug can be formed in the through hole without depending on the diameter or depth of the through hole.

Further, when the metal film is formed by the selective CVD method, the foreign matter of the metal particles generated due to the deterioration of the selectivity can be easily removed without a resist process, and a short circuit between wirings or between wiring layers can be avoided. ..

Further, when forming trench isolation, poly S is formed by the dry etching method according to the present invention.
By etching back the i film, it is possible to form trench isolation having excellent shape reproducibility.

[Brief description of drawings]

FIG. 1 is an explanatory view of a hole portion by a dry etching method of the present invention.

FIG. 2 is a sectional view of a metal embedded in a through hole by a CVD method.

FIG. 3 is an explanatory diagram of a dry etching method according to an embodiment of the present invention.

FIG. 4 is an explanatory diagram of a dry etching method according to an embodiment of the present invention.

FIG. 5 is an explanatory diagram of a conventional etching method for a metal film formed around a hole portion.

FIG. 6 is an explanatory view of a conventional etching method for a metal film formed around a hole portion.

FIG. 7 is an explanatory view of an embodiment of trench isolation formation according to the present invention.

FIG. 8 is an explanatory view of an embodiment of trench isolation formation according to the present invention.

FIG. 9 is a sectional view of a dry etching apparatus.

FIG. 10 is a sectional view of a dry etching apparatus.

FIG. 11 is a sectional view of a dry etching apparatus.

FIG. 12 is a sectional view of a dry etching apparatus.

[Explanation of symbols]

1 ... Si substrate, 2 ... First interlayer insulating film, 3 ... First wiring layer,
4 ... Second interlayer insulating film, 5 ... Metal plug, 6 ... Metal plug, 7 ... Etching gas.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Hisashi ▲ Rei ▼ Tokuo 1-280, Higashi Koikekubo, Kokubunji City, Tokyo Inside the Central Research Laboratory, Hitachi, Ltd. (72) Inventor Akihiro Shimizu 5-chome, Kamimizumoto-cho, Kodaira-shi, Tokyo No. 20-1 Hitate Super LSI Engineering Co., Ltd.

Claims (4)

[Claims] 1. A dry etching method for a thin film, which comprises anisotropically etching the sample obliquely from an oblique direction. 2. The dry etching method for a thin film according to claim 1, wherein the dry etching is performed in an angle range of 0 to 45 degrees with respect to the horizontal direction of the sample. 3. The high-melting-point metal film which is a polysilicon film or a metal thin film for wiring, a nitride film and a silicide film of a high-melting-point metal, copper,
A dry etching method for a thin film which is one of aluminum and an alloy film containing aluminum as a main component. 4. The beam source of any one of ions, electrons, neutral particles, and light for accelerating an etching reaction according to claim 1 or 2, and optionally at an angle range of 0 to 45 degrees with respect to the beam. A dry etching system consisting of an adjustable sample stage.