JPH06275577A - Method for forming contact hole in semiconductor device - Google Patents

Abstract

(57) [Summary] [Structure] After forming the SiO ₂ film 12 on the substrate 11, a rectangular contact hole 15 is formed by a photolithography process and an etching process, and then a low-viscosity resist 16 is applied to form a CF ₄ film. , CHF ₃ and He
And / or a mixed gas of Ar is used to etch the upper portion of the rectangular contact hole 15 to form a contact hole 17 having a taper angle. [Effect] Since the contact hole 17 having a taper angle can be formed by etching only the upper portion of the rectangular contact hole 15, the coverage is good and the conduction failure due to the filling failure in the contact hole 17 portion or the upper layer. It is possible to prevent disconnection in the wiring, and further, it is possible to obtain an effect that the controllability of the hole diameter and the fine workability are excellent.

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 a contact hole in a semiconductor device, and more particularly to a method for forming a contact hole by etching a SiO ₂ film in a semiconductor integrated circuit manufacturing process.

[0002]

2. Description of the Related Art Conventionally, in the manufacture of semiconductor devices (semiconductor integrated circuits), a technique combining photolithography and etching has been used to form a contact hole in a SiO ₂ film on the surface of a semiconductor substrate. The photolithography technique is a technique for transferring a mask pattern onto a resist, and the etching technique is a technique for processing a SiO ₂ film using the patterned resist as a mask.

A photolithography and etching process for forming a general contact hole will be described with reference to FIG. First, the SiO ₂ film 32 is formed on the Si substrate 31.
Then, a resist 33 made of a photosensitive polymer is applied, and then prebaking is performed to remove the organic solvent contained in the resist 33 (FIG. 3A). Next, the mask pattern 34 is transferred onto the resist 33 by exposure (FIG. 3B), and then the resist 33 is developed to form a pattern of the resist 33 corresponding to the mask pattern 34. Then, post-baking is performed to remove water contained in the resist 33 to cure the resist 33, and S
Adhesion with the iO ₂ film 32 is enhanced (FIG. 3C).
Further, the SiO ₂ film 32 is etched using the resist 33 as a mask to form a contact hole 35 (FIG. 3D). Next, the unnecessary resist 33 is melted and removed (FIG. 3E). As described above, the general photolithography and etching process is composed of the five main processes as shown in (FIGS. 3A to 3E).

The cross-sectional shape of the contact hole 35 formed by the above-mentioned photolithography and etching process is rectangular, but for application to a device, Si is used.
After etching the O ₂ film 32, it may be desirable to obtain a cross-sectional shape with a taper angle. For example, by making the cross-sectional shape of the contact hole of the insulating film (SiO ₂ film) in the multi-layered wiring taper, it is possible to prevent disconnection in the upper layer wiring, or improve the metal material embedding property to prevent conduction failure. This is the case. As a method of obtaining a contact hole having such a tapered shape, a method combining wet etching and dry etching, a method of performing dry etching while depositing a polymer on the sidewall of a resist pattern, and a method of being used as a mask material during etching There is a method of forming a taper angle on the resist.

First, a method of combining wet etching and dry etching will be described with reference to FIG. In this method, first, Si on the Si substrate 41
An O ₂ film 42 is formed, and a resist 43 made of a photosensitive polymer is applied on the SiO ₂ film 42. After that, pre-baking is performed to remove the organic solvent contained in the resist 43, and a pattern (not shown) on the mask is transferred onto the resist 43 by exposure and then developed. Next, post-baking is performed to cure the resist 43 and enhance the adhesiveness with the base (FIG. 4A). Further, using the resist 43 as a mask, for example, a 10: 1 BHF solution (HF,
The upper part of the SiO ₂ film 42 is isotropically etched by wet etching using a mixed solution of HNO ₃ and H ₂ O) to chamfer (FIG. 4B). After that, anisotropic etching is performed by dry etching to form a chamfered pattern on the SiO ₂ film 42 (FIG. 4).
(C)). Next, the unnecessary resist 43 is melted and removed (FIG. 4D).

Next, a method of performing dry etching while depositing a polymer on the side wall of the resist pattern will be described with reference to FIG. First, the SiO ₂ film 52 is formed on the Si substrate 51, and then the resist 53 is applied. After that, pre-baking is performed to remove the organic solvent contained in the resist 53, and a mask pattern (not shown) is transferred onto the resist 53 by exposure and then developed (FIG. 5).
(A)). Further, using the resist 53 as a mask, CCl ₂
Anisotropic etching is performed by reactive dry etching using a F ₂ / C ₂ H ₆ mixed gas system. In this case Si
At the same time when the O ₂ film 52 is etched, a polymer is deposited on the pattern side wall of the resist 53 to form a polymer film 54, and a pattern having a taper angle can be formed on the SiO ₂ film 52 (FIG. 5B. )). Next, the unnecessary resist 53 is melted and removed (FIG. 5C).

A method of forming a taper angle on a resist used as a mask material at the time of etching is to heat the resist after development to give a taper angle to the resist, and then perform etching to form the taper angle. The SiO ₂ film is formed.

[0008]

[SUMMARY OF THE INVENTION] The method of combining the wet etching and dry etching using the case, the poor adhesion between the resist 43 and the SiO ₂ film 42, the interface between the resist 43 and the SiO ₂ film 42 The etching solution penetrates in the horizontal direction, and the etching spreads in the horizontal direction. Therefore, there is a problem that reproducibility and controllability are deteriorated and also disadvantageous in fine processing.

Further, in the case of the method of performing the dry etching while depositing the polymer on the side wall of the resist pattern,
Since the taper angle is formed on the SiO ₂ film 52 by utilizing the polymer film 54 formed on the side wall of the pattern of the resist 53, the etching rate decreases due to the influence of the polymer film 54 as the number of etching processes increases. There is a problem that reproducibility and controllability in each pattern are poor.

Further, in the case where the resist used as a mask material at the time of etching has a taper angle, the expansion and contraction caused when the resist is heat-treated is uniform due to the difference in pattern width and pattern density. Does not occur, and a difference occurs in the taper shape of the resist. Also,
There was also the problem of poor reproducibility and controllability.

The present invention has been invented in view of the above problems, and forms a contact hole having a taper angle excellent in step coverage, excellent in fine workability, controllability of hole diameter, and reproducibility. It is an object of the present invention to provide a forming method capable of forming the same.

[0012]

In order to achieve the above object, a method of forming a contact hole of a semiconductor device according to the present invention comprises a contact of a rectangular shape formed by a photolithography process and an etching process after forming a SiO ₂ film on a substrate. After forming a hole, apply a low viscosity resist,
The contact hole having a taper angle is formed by etching the upper part of the rectangular contact hole using a mixed gas of CF ₄ , CHF ₃ and He and / or Ar.

[0013]

According to the method for forming a contact hole of a semiconductor device described above, after the rectangular contact hole is formed by a photolithography process and an etching process, the low viscosity resist of about 12 to 15 cp (centipoise) is rotated at a high speed. in by applying, the one rectangular shape of the contact hole recess and thick resist film on the SiO ₂ film flat plane is formed, a thin resist film is formed on the SiO ₂ film in the periphery of the hole top. This is because the low-viscosity resist is likely to accumulate on the rectangular contact hole concave portion and the SiO ₂ film flat portion, but is less likely to accumulate on the periphery of the upper portion of the hole.

Baking is performed in this state, and then CF
Etching the upper part of the rectangular contact hole with a mixed gas of ₄ , CHF ₃ and He and / or Ar to etch the Si around the upper part of the hole.
The O ₂ film is etched to form a contact hole having a taper angle.

Since the contact hole has a taper angle, when Al (aluminum) is buried in the contact hole in a later step, stress around the upper portion of the hole is reduced and disconnection in the upper wiring is prevented.
Further, the burying property of the metal material is improved, the step coverage during wiring is improved, conduction failure is prevented, and the fine workability can be improved.

Further, after forming a SiO ₂ film on the substrate, a rectangular contact hole is formed by a photolithography process and an etching process, and then a low-viscosity resist is applied to CF ₄ , CHF ₃ and He and / or
Alternatively, since the upper portion of the rectangular contact hole is etched using a mixed gas of Ar, the conventional wet etching and dry etching are used together without increasing the lower diameter while giving a taper angle to the upper portion of the contact hole. It is possible to improve the controllability of the hole diameter as compared with the contact hole formed by the method or the method using the polymer film.

[0017]

EXAMPLES AND COMPARATIVE EXAMPLES Examples and comparative examples of a method for forming a contact hole of a semiconductor device according to the present invention will be described below with reference to the drawings. 1A to 1G are schematic cross-sectional views showing respective steps for explaining a method of forming a contact hole of a semiconductor device according to an example.

First, the SiO ₂ film 12 is formed on the substrate 31, then the resist 13 made of a photosensitive polymer is applied, and then prebaking is performed to remove the organic solvent contained in the resist 13 (FIG. 1). (A)). Next, the mask pattern 14 is transferred onto the resist 13 by exposure (FIG. 1B), and then the resist 13 is developed to form a pattern of the resist 13 corresponding to the mask pattern 14. Next, post-baking is performed to remove water contained in the resist 13 to cure the resist 13,
The adhesion with the O ₂ film 12 is enhanced (FIG. 1 (c)). Further, using the resist 13 as a mask, the SiO ₂ film 12 has a thickness of 1
The contact hole 15 having a rectangular cross section is formed by performing the etching process for the second time. Next, the resist 13 that is no longer needed is removed (FIG. 1D).

After that, the rectangular contact hole 15 is formed.
A low-viscosity resist 16 having a viscosity of about 15 cp is applied on the SiO ₂ film 12 having a thickness of about 6000 rpm so that the film thickness is about 5000 Å (FIG. 1 (e)). ). At this stage, a large amount of the low-viscosity resist 16 is applied to the concave portion of the rectangular contact hole 15 and the flat surface of the SiO ₂ film 12, but is applied thinly around the upper portion of the rectangular contact hole 15. Becomes

In this state, after baking at 110 ° C. for 2 minutes, the low-viscosity resist 16 is used as a mask for SiO 2.
_{The second} film 12 is subjected to a second etching process to form a contact hole 17 having a taper angle, and then the unnecessary low-viscosity resist 16 is removed (FIG. 1 (g)).
.

The above etching treatment is performed by using CF ₄ , CHF ₃
And one or two mixed gases selected from He and Ar, and using the apparatus shown in FIG.
850 W, distance between electrodes: 1.0 cm, sample temperature: -30
It was carried out under the conditions of a temperature of 500 ° C and a pressure of 500 mTorr.

In the figure, 21 is an upper electrode, 22 is a lower electrode, 23 is a high frequency power source, 24 is a gas inlet, and 25 is a wafer.

Note that O ₂ may be added as an etching gas to the above mixed gas.

[0024]

[Table 1]

Table 1 shows contact holes 1 formed by the method for forming contact holes of the semiconductor device according to the embodiment.
7, and a contact hole formed by a method using both conventional wet etching and dry etching,
The results are shown by comparing the coverage by Al sputtering, the hole diameter controllability, and the fine workability between the contact hole formed by the conventional method using the polymer film 54.

As is clear from Table 1, in the case of the comparative example in which the wet etching and the dry etching are used together, the fine workability is very poor, and the coverage and hole diameter controllability by Al sputtering are also poor. .
Also, in the case of another comparative example using the method of using the polymer film 54, the hole diameter controllability is very poor and the fine workability is also poor. However, in the case of the example, it was confirmed that the coverage by Al sputtering, the fine workability, and the hole diameter controllability were all good.

As described above, in the method of forming a contact hole of a semiconductor device according to the embodiment, the rectangular contact hole 15 is formed and then the low-viscosity resist 16 is applied. The resist 16 is often applied to the concave portions of the rectangular contact hole 15 and the flat surface of the SiO ₂ film 12, but is hard to be applied to the periphery of the upper portion of the hole. Baking is performed in this state, and thereafter, the upper portion of the rectangular contact hole 15 is etched using a mixed gas of CF ₄ , CHF ₃ and He and / or Ar, so that SiO ₂ around the upper portion of the hole is etched.
The film 12 is etched so that the upper portion of the rectangular contact hole 15 can be provided with a taper angle, but the lower diameter is not widened, and the coverage is good and the taper angle is excellent in fine processability and hole diameter controllability. The contact hole 17 can be formed.

In the contact hole 17 having such a taper angle, the filling property of the metal material is good,
Further, since there is little stress in the vicinity of the upper part of the hole, it is possible to prevent conduction failure in the contact hole 17 part and disconnection in the upper layer wiring, and it is possible to improve fine workability.

In the mixed gas used for the second etching process, it is preferable to set the selection ratio of SiO _{2 to} the resist to be low so that the resist is also etched.

[0030]

As described above in detail, the semiconductor according to the present invention
The device contact hole formation method has a rectangular shape
After forming the contact hole of
Since the strike is applied at high speed, the low viscosity resist
Is the recess of the rectangular contact hole and SiO 2.₂ 
A large amount is applied on the flat surface of the film, but
SiO₂ Difficult to apply on the film. For this reason,
The SiO around the upper part of the hole₂ A thin resist film on the film
Can be formed. Then CF_Four , CHF ₃ Nara
And using a mixed gas of He and / or Ar, the rectangle
By etching the top of the contact hole
The SiO around the hole₂ Etching film
Can be above the rectangular contact hole
The lower caliber is widened while giving a taper angle to
Good coverage, fine processability and
Contact with taper angle with excellent controllability and reproducibility
Towholes can be formed.

In the contact hole having such a taper angle, the burying property of the metal material can be improved, and the stress in the periphery of the upper portion of the hole can be reduced, so that the contact hole portion can be reduced. It is possible to prevent conduction failure and disconnection in the upper layer wiring, and improve the fine workability.

[Brief description of drawings]

1A to 1G are schematic cross-sectional views showing an embodiment of a method for forming a contact hole of a semiconductor device according to the present invention in the order of each step.

FIG. 2 is a schematic cross-sectional view showing an etching apparatus used in an etching treatment process in an example.

3A to 3E are schematic cross-sectional views sequentially showing a contact hole forming process using a conventional resist pattern.

FIG. 4A to FIG. 4D are schematic cross-sectional views sequentially showing each step in forming a conventional contact hole having a taper angle.

5A to 5C are schematic cross-sectional views sequentially showing each step in forming a contact hole with a taper angle in another conventional example.

[Explanation of symbols]

11 substrate 12 SiO ₂ film 15 rectangular contact hole 16 low-viscosity resist 17 contact hole

Claims (1)

[Claims] 1. A contact hole having a rectangular shape is formed by a photolithography process and an etching process after forming a SiO ₂ film on a substrate, and then a low-viscosity resist is applied to CF ₄ , CHF ₃ and He and / or He and / or A method for forming a contact hole in a semiconductor device, comprising etching the upper portion of the rectangular contact hole using a mixed gas of Ar to form a contact hole having a taper angle.