JPH07130744A - Formation of connection hole - Google Patents

Abstract

PURPOSE:To form a connection hole in a normal tape shape, reduce the diameter thereof in size and flaten an insulation film. CONSTITUTION:In a first step, an insulation film 13 is so formed on a substrate 11 that the thickness is greater than a specified film thickness. An etching mask 14 is formed thereon and an opening 15 is further formed thereon. In a second step, the film 13 is etched from the opening 15 to form a connection hole 16 in a manner that its diameter becomes smaller as the opening 15 gets close to the substrate 11 side. In a third step, after only the mask 14 is removed, a flatening film 17 is formed on the upper side of the film 13 in a state that the hole 16 is filled in. In a fourth step, while an etchback treatment is so performed so as to leave the film 13 by only the film thickness, the films 13 and 17 are etched, and then the remaining film 17 in the hole 16 are removed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of forming connection holes in a semiconductor device manufacturing process.

[0002]

2. Description of the Related Art In recent years, as the design rules of semiconductor devices have become finer, the diameters of connection holes (contact holes) have become smaller. However, the film thickness of the interlayer insulating film has hardly changed in order to secure the withstand voltage. Therefore, the aspect ratio of the connection hole is increasing. When a wiring is formed only from aluminum in a connection hole having a large aspect ratio as described above, since aluminum has poor coverage at the step portion, poor conduction occurs in the connection hole. As a result, the reliability of the semiconductor device is reduced.

As measures against the above, for example, Japanese Patent Laid-Open No. 62-22
Japanese Patent No. 9959 discloses a so-called selective tungsten-which forms a connection hole and then selectively forms a tungsten (W) plug only inside the connection hole by utilizing a reduction reaction of tungsten hexafluoride (WF ₆ ). A CVD method is disclosed.

However, selective tungsten-CVD
The law is always difficult to obtain full selectivity. In principle, it is impossible to simultaneously fill the connection holes having different depths. Therefore, for example, in JP-A-62-229959, after forming a connection hole, tungsten (W) is formed.
By depositing a film on the entire surface and etching back this tungsten film, the tungsten film is left only inside the connection hole, so-called blanket tungsten-C.
The VD method is disclosed. In this method, the tungsten film can be formed relatively easily as compared with the selective tungsten-CVD method, and the tungsten film can be simultaneously embedded in the connection holes having different depths.
Further, since the tungsten film is formed by the CVD method, good coverage can be obtained even when the sidewall of the connection hole is formed substantially perpendicular to the substrate.

[0005]

However, in the above blanket tungsten-CVD method, in order to improve the adhesion between the tungsten oxide film and the silicon oxide (SiO ₂ ) film, which is an insulating film, the titanium-based material is used on the inner wall of the connection hole. A material layer [for example, a laminated film of a titanium (Ti) film and a titanium nitride (TiN) film] is formed. Since this titanium-based material layer is usually formed by the sputtering method, the coverage of the step portion of the connection hole is poor. Therefore, even if the sidewall of the connection hole is formed substantially perpendicular to the substrate, the titanium-based material layer is formed thick on the upper side of the connection hole and thin on the bottom side of the connection hole. Therefore, by forming the titanium-based material layer in the connection hole, the sidewall of the connection hole has a so-called reverse taper shape. When the tungsten film is formed in the connection hole in such a state, a cavity in which tungsten is not embedded occurs inside the connection hole. When the tungsten plug is formed from the tungsten film having the cavity as described above, the cavity remains inside the tungsten plug, so that a highly reliable wiring cannot be formed.

Therefore, blanket tungsten-CVD
In order to prevent the formation of voids inside the connection holes when forming the tungsten film by the method, it is necessary to form the tungsten film with a film thickness of the same value as the diameter of the connection hole. However, since the minimum diameter of the connection hole is limited by the limit value of the lithography technique when opening the connection hole, the diameter of the connection hole cannot be made sufficiently small. Further, when the diameter of the connection hole is large, the film thickness of the tungsten film must be increased. For this reason, the deposition time of the tungsten film becomes long. In addition, the time for the etch back process becomes long. Since the processing speed becomes slow in this way, the throughput decreases.

Further, the blanket tungsten-CV
When a tungsten film is formed by the D method and then the tungsten film is etched back to form a tungsten plug, if there is a step in the base, an etching residue occurs in the step. In order to eliminate this etching residue, sufficient over-etching is necessary. However,
When the step difference is large, when the etching residue is completely removed, the upper surface of the plug formed inside the connection hole is simultaneously etched. Therefore, when the wiring layer is formed on the upper surface of the plug, the coverage of the wiring layer on the plug is deteriorated.

Therefore, in order to apply the tungsten plug to the semiconductor device, it is necessary to reduce the step difference of the insulating film before forming the tungsten plug. In order to further increase the processing speed, it is necessary to make the diameter of the connection hole as small as possible and to form the shape of the connection hole in a so-called forward tapered shape.

It is an object of the present invention to provide a method of forming a connection hole, in which the connection hole is formed in a so-called forward taper shape, the diameter of the connection hole is reduced, and the insulating film is flattened. And

[0010]

SUMMARY OF THE INVENTION The present invention is a method for forming a connection hole, which has been made to achieve the above object. That is, in the first step, an insulating film having a thickness larger than a predetermined thickness is formed on the substrate, an etching mask is formed on the insulating film, and then an opening is formed in the etching mask.
Next, in a second step, the insulating film is etched from the opening to form a connection hole having a smaller diameter toward the substrate side. Subsequently, in a third step, after removing only the etching mask, a flattening film is formed on the upper side of the insulating film so as to fill the connection hole. Then, in a fourth step, the flattening film and the insulating film are etched by etching back so as to leave a predetermined thickness of the insulating film, and then the remaining flattening film embedded in the connection hole is removed. .

[0011]

In the method of forming the connection hole, the opening is formed in the etching mask by the lithography technique, the insulating film is etched from the opening to form the connection hole whose diameter becomes smaller toward the substrate side. Therefore, the smaller the thickness of the insulating film by etching back the upper surface of the insulating film, the smaller the diameter of the connection hole. Therefore, if the opening is formed with the limit value of the lithography technique, the diameter of the connection hole becomes smaller than the limit value of the lithography technique. The shape of the connection hole is a so-called forward taper shape. Further, since the insulating film is etched by the etch back process, the upper surface of the insulating film becomes substantially flat.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A first embodiment of the present invention will be described with reference to the forming process diagram of FIG.

As shown in FIG. 1A, a diffusion layer 12 is formed on the front surface side of a substrate (eg, silicon substrate) 11.

First, in the first step, the insulating film 13 having a thickness larger than a predetermined thickness is formed on the substrate 11 by, for example, the CVD method.
To form. The insulating film 13 is made of, for example, silicon oxide (SiO ₂ ), and is formed to have a predetermined film thickness of, for example, about 800 nm when a film thickness of 400 nm is required in consideration of withstand voltage. There is.

After that, the insulating film 1 is formed by a coating technique.
An etching mask 14 made of a resist is formed on the surface 3. Then, an opening 15 having a diameter of, for example, d1 is formed at a predetermined position of the etching mask 14 by a lithography technique (eg, photolithography technique). Here, since the connection is made with the diffusion layer 12, the diffusion layer 1
2 above the opening 1 in the etching mask 14
5 is provided.

Next, the second step shown in FIG. 1B is performed. In this step, the insulating film 1 below the opening 15 is etched by etching (for example, reactive ion etching).
3, a so-called forward taper-shaped connection hole 16 is formed in which the diameter becomes smaller toward the base body 11 side. The upper opening 16a of the connection hole 16 formed at this time
Has a shape in which the cross-sectional shape of the opening 15 is almost transferred. Therefore, the diameter d2 of the upper opening 16a is substantially equal to the diameter d1 of the opening 15.

As the etching conditions, for example, a mixed gas of oxygen (O ₂ ) with a flow rate of ₃ sccm and trifluoromethane (CHF ₃ ) with a flow rate of 75 sccm is used as the etching gas, and the pressure of the etching atmosphere is 6.7 P.
a, set the high frequency power to 1 kW.

Subsequently, the third step shown in FIG. 1C is performed. In this step, only the etching mask 14 is removed by oxygen ashing or wet etching, for example. After that, by the coating technique, the connection hole 1
A flattening film 17 is formed on the upper side of the insulating film 13 so that the inside of 6 is embedded. The flattening film 17 is formed of, for example, a resist, and its upper surface is formed to be substantially flat.

Then, the fourth step shown in FIG. 1 (4) is performed. In this step, the insulating film 13 is etched back to a predetermined thickness (for example, 400 n in this case).
Then, the flattening film 17 (the part indicated by the two-dot chain line) and the insulating film 13 (the part indicated by the one-dot chain line) are etched while leaving only m). This etching is performed by using, for example, a reactive ion etching device, the flattening film 17 and the insulating film 1
The etching rate is the same as that of No. And in order to smooth the surface of the insulating film 13,
For example, the ratio of the etching rates of the flattening film 17 made of resist and the insulating film 13 made of silicon oxide (resist etching rate / silicon oxide etching rate) is set to about 0.5 to 2. Outside this range, the surface smoothness of the insulating film 13 deteriorates.

As the processing conditions, for example, oxygen (O ₂ ) having a flow rate of 15 sccm and an etching gas having a flow rate of 7 are used.
A mixed gas of 5 sccm of trifluoromethane (CHF ₃ ) is used, the pressure of the etching atmosphere is set to 6.7 Pa, and the high frequency power is set to 1 kW.

Thereafter, oxygen (O ₂ ) ashing or wet etching is performed to remove the remaining flattening film 17 (the portion shown by the broken line) embedded in the inside of the connection hole 16 and connect it to the insulating film 13. The hole 16 is formed.
By the etching, the upper opening 16 of the connection hole 16 is formed.
The diameter d3 of b is smaller than the diameter d1 of the opening 15.

In the method of forming the connection hole, the opening 15 is formed in the etching mask 14 by the lithography technique,
The base film 1 is formed on the insulating film 13 below the opening 15 by etching.
Connection hole 16 whose diameter decreases toward the 1 side
To form. Therefore, as the thickness of the insulating film 13 is reduced by etching back the upper surface of the insulating film 13, the diameter d3 of the connection hole 16 becomes smaller. Therefore,
If the opening 15 is formed with the limit value of the lithography technique, the diameter d3 of the connection hole 16 becomes smaller than the limit value of the lithography technique. The shape of the connection hole 16 is a so-called forward taper shape. Further, since the insulating film 13 is etched by the etch back process, the upper surface of the insulating film 13 becomes substantially flat.

Further, when flattening the insulating film 13 and forming the connecting hole 16, the insulating film 13 is first flattened before the connecting hole is formed, but in the above forming method, the connecting hole is formed. Since the flattening process is performed after forming the, the process load is not increased as compared with the conventional technique.

Next, a method of forming a tungsten plug by the blanket tungsten method in the connection hole 16 formed by the above method will be described with reference to FIG. In the figure, the same components as those described in FIG. 1 are designated by the same reference numerals.

As shown in FIG. 2A, first, the adhesion between the insulating film 13 and the tungsten film (23) described later is adhered to the inner wall of the connection hole 16 and the upper surface of the insulating film 13 by the sputtering method. A titanium (Ti) film 21 for improving is formed. Further, a titanium nitride (TiN) film 22 is formed on the surface of the titanium film 21 by the sputtering method. Thus, the titanium film 21 and the titanium nitride film 22 are formed by the sputtering method.
The wall surface of the titanium nitride film 22 formed on the side wall of the connection hole 16 is substantially perpendicular to the surface of the base 11.

Then, for example, a cold wall type CV
A tungsten (W) film 23 is formed on the surface of the titanium nitride film 22 including the inside of the connection hole 16 by a film forming method using a D device.

As the film forming conditions, for example, hydrogen (H ₂ ) is used as a reaction gas for 1 to tungsten hexafluoride (W).
F ₆ ) was mixed in a ratio of 19 and a substrate 1 was used.
The temperature of 1 is set to 400 ° C., and the pressure of the reaction atmosphere is set to 867 Pa.

When the tungsten film 23 is formed under the above conditions, the tungsten film 23 grows from the side wall and the bottom surface of the connection hole 16. Therefore, the connection hole 16 can be filled by forming the tungsten film 23 so as to have a film thickness equal to or larger than 50% of the diameter of the connection hole 16. However, in order to eliminate the depression at the upper part of the connection hole 16, the tungsten film 23 is usually deposited so as to have a film thickness that is the same as or larger than the diameter of the connection hole 16.

Then, as shown in FIG. 2B, the tungsten film 23, the titanium nitride film 22 and the titanium film 21 indicated by the chain double-dashed line are etched by etch back until the insulating film 13 is exposed. And the connection hole 1
The tungsten film (23) and the titanium nitride film (2
2) and the plug 24 made of the titanium film (21) is formed.

As the etching back conditions, for example, a mixed gas of sulfur hexafluoride (SF ₆ ) having a flow rate of 40 sccm and chlorine (Cl ₂ ) having a flow rate of 30 sccm is used as the etching gas, and the pressure of the etching atmosphere is set to 6. 7P
a, high frequency power is set to 500W.

In this way, the plug 24 is placed inside the connection hole 16 having a diameter smaller than the limit value of the lithography technique.
Therefore, the formation area of the connection hole 16 is reduced. Further, for example, when the connection hole 16 is formed on a wiring (not shown), the width of the wiring and the distance between the wirings can be narrowed. Therefore, high integration of the semiconductor device can be realized.

Since the diameter of the connection hole 16 is small, the tungsten film 23 can be thinly formed. For this reason, the etch back processing time of the tungsten film is shortened.

In the above description, the case where tungsten is used as the material for filling the connection hole 16 is described, but the filling material is not limited to the tungsten plug, and for example, molybdenum (Mo), titanium (Ti), copper (Cu). ) Or a material containing aluminum (Al).

Next, as a second embodiment, a case where an insulating film is formed on a base having a step and a connection hole is formed in the insulating film, the process steps (No. 1) of FIG. Part 2)
Explained by. In the figure, the same components as those described in FIG. 1 are designated by the same reference numerals.

As shown in FIG. 3A, the element isolation region 3 is formed in a part of the upper layer of the substrate (eg, silicon substrate) 11.
1 is formed. The element isolation region 31 is made of, for example, a LOCOS oxide film. Further, the element isolation region 3
A wiring layer 32 is formed on the upper surface of 1. The wiring layer 32 is made of, for example, polysilicon. On the other hand, a diffusion layer 12 is formed on a part of the upper layer of the base 11 on which the element isolation region 31 is not formed.

First, in the first step, an insulating film 13 having a thickness larger than a predetermined thickness is formed on the base 11 so as to cover the wiring layer 32 by, for example, a CVD method. This insulating film 1
3 is made of, for example, silicon oxide (SiO ₂ ), and is set to have a predetermined film thickness, for example, a film thickness that ensures a dielectric strength.

Then, the insulating film 1 is formed by a coating technique.
An etching mask 14 made of a resist is formed on the surface 3. Then, the openings 33 and 34 are formed at predetermined positions of the etching mask 14 by a lithography technique (for example, a photolithography technique). here,
Since the connection is made with the diffusion layer 12, the opening 33 is provided in the etching mask 14 above the diffusion layer 12, and the opening 34 is provided in the etching mask 14 above the wiring layer 32.

Then, the second step shown in FIG. 3B is performed. In this step, a so-called forward-tapered connection hole 35, whose diameter becomes smaller toward the base 11 side, is formed in the insulating film 13 below the openings 33, 34 by etching (for example, reactive ion etching). Three
6 is formed. The upper openings 35a, 36a of the connection holes 35, 36 formed at this time have a shape in which the cross-sectional shapes of the openings 33, 34 are almost transferred. The etching conditions are set to the same conditions as described in (2) of FIG. 1, for example.

Subsequently, the third step shown in FIG. 4C is performed. In this step, only the etching mask 14 is removed by oxygen ashing or wet etching, for example. After that, by the coating technique, the connection hole 3
A flattening film 17 is formed on the upper side of the insulating film 13 so that the inside of each of 5, 5 is filled. The flattening film 17 is formed of, for example, a resist, and its upper surface is formed to be substantially flat.

Then, the fourth step shown in FIG. 1 (4) is performed. In this step, for example, the insulating film 13 on the element isolation region 31 is left in a state of a predetermined film thickness by an etch back process, and the flattening film 17 (portion indicated by a chain double-dashed line) and the insulating film 13 (1 And the part indicated by the dotted chain line). This etching is performed by using, for example, a reactive ion etching apparatus under the processing condition that the flattening film 17 and the insulating film 13 have substantially the same etching rate. The processing conditions are, for example, (4) in FIG.
The conditions are set to the same as those described in.

Thereafter, the connection holes 35 and 36 are formed by oxygen (O ₂ ) ashing treatment or wet etching.
The remaining flattening film 17 (the part indicated by the broken line) embedded in the inside of the substrate is removed, and the connection holes 35 and 36 are formed in the insulating film 13.
To form.

Also in the forming method described in the second embodiment, as in the first embodiment, the connection holes 35, 36 having a diameter smaller than the diameter of the openings 33, 34 that can be formed by the lithography technique. Is formed. Moreover, since the insulating film 13 is etched by the etch-back process, the upper surface of the insulating film 13 becomes substantially flat.

When the tungsten plugs are formed in the connection holes 35 and 36 formed as described above, the same method as described with reference to FIG. 2 may be used. In this case, since the surface of the insulating film 13 is substantially flattened even if there is a step in the base, etching residue does not occur in the step as in the conventional case. Therefore, it is not necessary to perform over-etching as in the conventional case in the etch-back process of the tungsten film.

[0044]

As described above, according to the present invention,
The insulating film is etched from the opening formed in the etching mask to form a connection hole whose diameter becomes smaller toward the substrate side. Since the flattening film is formed on the insulating film, the upper surface side of the insulating film is etched back together with the flattening film. Therefore, the thinner the insulating film is, the smaller the diameter of the connection hole becomes. Therefore, if the opening is formed with the limit value of the lithography technique, it is possible to form the connection hole having a diameter smaller than the limit value of the lithography technique. As a result, the formation area of the connection hole can be reduced, so that the semiconductor device can be highly integrated. Moreover, since the insulating film is etched by the etch-back process, the upper surface of the insulating film can be formed to be substantially flat.

[Brief description of drawings]

FIG. 1 is a process drawing of forming a connection hole according to a first embodiment.

FIG. 2 is a process drawing of forming a plug.

FIG. 3 is a process diagram (1) of forming a connection hole of the second embodiment.

FIG. 4 is a process diagram (No. 2) of forming a connection hole of the second embodiment.

[Explanation of symbols]

 11 substrate 13 insulating film 14 etching mask 15 opening 16 connection hole 17 flattening film

Claims (1)

[Claims] 1. A first step of forming an insulating film having a thickness larger than a predetermined thickness on a substrate, forming an etching mask on the insulating film, and then forming an opening in the etching mask by a lithography technique. A second step of etching the insulating film from the opening to form a connection hole having a smaller diameter toward the substrate side, and removing the etching mask only, and then filling the connection hole A third step of forming a flattening film on the upper side of the insulating film; and etching the flattening film and the insulating film in a state where the insulating film remains by a predetermined film thickness by an etch-back process, and then the connecting hole And a fourth step of removing the remaining flattening film embedded therein.