JPH0745551A - Forming method of contact hole - Google Patents

Abstract

PURPOSE:To enhance the stepped part covering characteristics of a metallic wiring in a contact hole part by a method wherein a free-etching film is formed on an insulating film on a semiconductor substrate for wet etching the free- etching film and the insulating film using a photomask in a specific pattern further to dry-etch the insulating film only. CONSTITUTION:After the formation of an isolated region, a gate, diffused layer, etc., on a semiconductor substrate 1, an insulating film 2 is deposition-formed on one main surface of the semiconductor substrate 1. Next, after the formation and heat treatment of a spin-on-glass film 3 on the insulating film 2, a photomask 4 after a pattern having an aperture part 6 corresponding to a contact hole is formed. Next, the insulating film 2 and the spin-on-glass film 3 are wet-etched using a fluoric acid solution. Next, after dryetching the whole surface reaching the main surface of the semiconductor substrate 1 to form a contact hole 9, the photomask 4 is removed by plasma ashing process. Later, the whole body is cleaned up to remove the spin-on-glass film 3 for the formation of a metallic wiring 5.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for forming fine contact holes in a semiconductor integrated circuit device.

[0002]

2. Description of the Related Art Advances in microfabrication technology have dramatically improved the degree of integration of semiconductor integrated circuit devices. However, the thinning of the wiring and the insulating film has been delayed due to restrictions in terms of interlayer capacitance. That is, in terms of the degree of integration, the reduction in the direction perpendicular to the main surface of the semiconductor substrate lags the reduction in the surface direction. For example, although the size of the contact hole has been reduced, its depth has not decreased. The step coverage of the wiring in the contact hole portion deteriorates as the aspect ratio of the contact hole (the ratio of the depth of the contact hole divided by the size) gradually increases. If the step coverage deteriorates, the wiring may be broken at the step portion and the reliability may be reduced.

Generally, in order to improve the step coverage of wiring in the contact hole portion, a contact hole having a tapered side wall is used. A dry etching technique is usually used to form a contact hole in a fine semiconductor integrated circuit device. However, a silicon oxide film is used as the insulating film forming the contact hole. Since this is etched only by an ionic dry etching method, the cross-sectional shape of the side wall of the contact hole obtained is almost vertical to the main surface of the substrate. Therefore, wet etching, which is isotropic etching, is often used together in order to obtain a contact hole having a tapered sectional shape in the side wall portion. That is, a wet etching method is used to perform isotropic etching to some extent, and then a dry etching method is used to anisotropically perform etching. As a result, a contact hole having a tapered side wall is obtained.

2A to 2D are sectional views showing steps of forming a contact hole by a conventional method. After forming an isolation region, a gate, an impurity diffusion layer, and the like on the semiconductor substrate 1, an insulating film 2 is deposited and formed (FIG. 2A), and further, a photomask having a predetermined pattern is formed on the insulating film 2. 4 is formed by a known method (FIG. 2B). After that, the insulating film 2 is isotropically etched by a wet etching method using buffered hydrofluoric acid (FIG. 2C). Subsequently, the contact hole 9 is formed by opening to the bottom portion of the insulating film 2 by the dry etching method (FIG. 2D). After removing the photomask 4,
The metal wiring film 5 is formed by vapor deposition by the sputtering method (see FIG. 2).
(E)).

[0005]

According to the wet etching described above, the etching in the thickness direction of the insulating film 2 is mainly performed as shown in FIG. 2C, and the side wall of the contact hole 9 has a pointed portion. Are easily formed. When a metal wiring material is vapor-deposited in the contact hole 9 having the pointed portion by a sputtering method, a structure as shown in FIG. 2D is obtained. This is because a vapor-deposited film is more likely to be formed in the pointed portion than in other portions, so that it is difficult for the metal wiring material to enter the bottom portion of the contact hole 9 and the semiconductor substrate 1 exposed in the contact hole 9 is exposed. This lowers the reliability of the contact state between the surface and the metal wiring 5. Therefore, a forming method is desired in which no sharp portion is formed on the side wall of the contact hole 9.

An object of the present invention is to provide a method capable of easily forming a contact hole having a cross-sectional shape having a smooth taper without sharp points and improving the step coverage of metal wiring in the contact hole portion. Is.

[0007]

In order to solve the above-mentioned problems, a method of forming a contact hole according to the present invention provides a method for forming a contact hole on an insulating film on one main surface of a semiconductor substrate with an etching rate higher than that of an etching solution. A large easy-etching film is formed, a photomask having an opening of a predetermined pattern is formed thereon, and the easy-etching film and the insulating film are selectively wet-etched using this photomask, and then a further dry film is formed. The insulating film is selectively removed by an etching method.

[0008]

By using the present invention, a contact hole having an ideal tapered side wall portion is formed by a relatively simple method, and the step coverage of the metal wiring material is improved.

When the easily etchable film comes into contact with the etching solution at the opening of the photomask, it is removed in the substrate surface direction. A space 7 is formed between the photomask 4 and the insulating film 2 by etching the spin-on glass film 3, and the hydrofluoric acid solution enters into the space 7 to expand the space. The recesses 8 formed in the insulating film 2 are formed deeper while expanding in the surface direction according to the expansion of the etched portion of the spin-on glass film 3. As a result, the side wall portion of the recess 8 has a gentle taper shape, and the occurrence of the pointed portion seen in FIG. 2D of the conventional example is suppressed. Then, dry etching is performed until the main surface of the semiconductor substrate 1 is reached to form a contact hole 9 (FIG. 1D), and then the photomask 4 is formed.
Are removed by the plasma ashing method. Then, the RCA cleaning liquid (NH ₄ OH: H ₂ O ₂ : H ₂ O =
The spin-on glass film 3 is removed by washing with 1: 1: 8). After that, the metal wiring material is sputtered to 500 to 8
The metal wiring 5 is formed by vapor deposition to a thickness of 00 nm (FIG. 1E).

[0010]

EXAMPLE An example of the method of forming a contact hole according to the present invention will be described with reference to the sectional process drawing of FIG.

After forming an isolation region, a gate, a diffusion layer, etc. necessary for a semiconductor integrated circuit device on the semiconductor substrate 1, an insulating film 2 is deposited and formed on the main surface of the semiconductor substrate 1 (FIG. 1).
(A)). A spin-on glass film (SOG is formed on the insulating film 2.
Film 3 is spin-coated to a thickness of 50 to 100 nm, and is 400 to 600 in a nitrogen or oxygen atmosphere.
After heat treatment is performed for 30 to 60 minutes at a temperature in the range of ° C, a photomask 4 having a pattern having an opening 6 corresponding to a contact hole is formed (Fig. 1 (b)). The spin-on glass film 3 has the property that the heat treatment stabilizes the etching rate of the hydrofluoric acid solution as an etching solution.

Then, the insulating film 2 and the spin-on glass film 3 are formed according to the pattern of the photomask 4 using a hydrofluoric acid solution.
And wet etching. Insulating film 2 is photomask 4
The opening 6 comes into contact with the hydrofluoric acid solution, and etching in the thickness direction thereof starts. At the same time, the spin-on glass film 3 is also in contact with the etching solution at the opening 6 of the photomask 4, so that the etching starts.

Since the wet etching rate of the spin-on glass film 3 is higher than that of the insulating film 2, the spin-on glass film 3 is removed outward from the opening 6 portion of the photomask 4 as shown in FIG. Therefore, a space 7 formed by etching the spin-on glass film 3 is formed between the photomask 4 and the insulating film 2, and the hydrofluoric acid solution enters the space 7,
Further, the void 7 expands. As the void 7 expands, the etched region of the insulating film 2 expands outward from the opening 6. The opening edge side of the formed concave portion 8 spreads outward and becomes deeper. Due to the etching of the insulating film 2 in the thickness direction and the expansion of the etching region,
The side wall portion of the recess 8 has a gentle taper shape, and the generation of the pointed portion seen in FIG. 2D of the conventional example is suppressed.

Then, dry etching is performed until the main surface of the semiconductor substrate 1 is reached to form a contact hole 9 (FIG. 1D), and then the photomask 4 is removed by plasma ashing. Then, the RCA maintained at a temperature of 70 ° C.
The spin-on glass film 3 is removed by cleaning with a cleaning liquid (NH ₄ OH: H ₂ O ₂ : H ₂ O = 1: 1: 8). Then, a metal wiring material is deposited by sputtering to a thickness of 500 to 800 nm to form the metal wiring 5 (FIG. 1E).

As described above, according to this embodiment, the insulating film 2
A spin-on glass film 3 having a wet etching rate higher than that of the spin-on glass film 3 and the insulating film 2 are selectively removed with a hydrofluoric acid solution using a photomask 4 having a predetermined pattern. The sidewall portion 8 has a taper, and the dry etching which is subsequently performed forms a gently tapered contact hole 9 having no sharp portion on the sidewall portion in the insulating film 2. As a result, the step coverage of the metal wiring 5 in the contact hole 9 portion is remarkably improved, and the reliability of the wiring can be improved by applying it to the manufacture of a semiconductor integrated circuit device.

[0016]

According to the present invention, an easily-etchable film having an etching rate higher than that is formed on an insulating film on a semiconductor substrate, and the easily-etchable film is formed using a photomask having a predetermined pattern. Since the insulating film and the insulating film are selectively removed with a hydrofluoric acid solution and then the insulating film is removed by the dry etching method, a contact hole having a side wall portion with a gentle taper can be easily formed. Therefore, the step coverage of the metal wiring in the contact hole portion is improved, and the reliability of the semiconductor integrated circuit device can be improved.

[Brief description of drawings]

1A to 1C are cross-sectional views in order of steps for explaining an embodiment of a method for forming a contact hole according to the present invention.

2A to 2C are cross-sectional views in order of the processes, for illustrating a method of forming a contact hole in a conventional example.

[Explanation of symbols]

 1 Semiconductor Substrate 2 Insulating Film 3 Spin-on-Glass Film (SOG Film) 4 Photomask 5 Metal Wiring 6 Opening 7 Void 8 Recess 9 Contact Hole

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Office reference number FI Technical indication location H01L 21/3213 21/768 8826-4M H01L 21/88 C 8826-4M 21/90 B

Claims (2)

[Claims] 1. An insulating film on one main surface of a semiconductor substrate,
Forming an easy-etching film having a larger etching rate with an etching solution than the insulating film; forming a photomask having openings of a predetermined pattern on the easy-etching film; and using the photomask, A method of forming a contact hole, comprising: a step of selectively wet etching the easily-etchable film and the insulating film; and a step of selectively removing the insulating film by a dry etching method. 2. The method of forming a contact hole according to claim 1, wherein the etching solution is a hydrofluoric acid solution and the easily-etchable film is a spin-on glass film.