JPH05217934A - Formation of contact hole - Google Patents

Abstract

PURPOSE:To improve step coverage of a wiring and to improve wiring reliability by carrying out isotropic etching and anisotropic etching by using a contact hole forming pattern as a mask, which is shaped to reduce a diameter of an opening part thereof gradually from an upper part to a lower part and to enlarge it gradually from the middle thereof. CONSTITUTION:An etching film 2 is formed in a semiconductor substrate 1. A contact hole forming pattern 3 is formed which is shaped to reduce a diameter of an opening part thereof from an upper part to a lower part gradually and to enlarge the diameter gradually from a part of a minimum diameter to an interface with the etching film 2. Isotropic etching is performed for the etching film 2 using the contact hole forming pattern 3 as a mask. Then, anisotropic etching is performed for the etching film 2 to open a contact hole of a large opening diameter and a small contact diameter in the etching film 2. After the contact hole forming pattern 3 is removed, a wiring film is deposited and such a desired process as patterning is carried out.

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 a contact hole, and more particularly, to improving step coverage of wiring,
The present invention relates to a method for forming a contact hole with improved wiring reliability.

[0002]

2. Description of the Related Art Conventionally, various demands have been made with the miniaturization of semiconductor devices. Particularly, in the rule of 0.5 μm or less, planarization of the semiconductor device is an essential element, and formation of a wiring film that makes good contact with a contact hole having a high aspect ratio is an important issue.

Therefore, the opening diameter of the contact hole (the diameter of the uppermost portion of the contact hole) so that the wiring film can sufficiently enter into the contact hole having the high aspect ratio.
The contact diameter (the diameter of the bottom of the contact hole)
There is provided a contact hole having a so-called round shape with a small size. The contact hole having the round shape is usually formed by forming a resist film having a contact hole forming pattern on an insulating film formed on a semiconductor substrate, and using the resist film as a mask to make the insulating film isotropic. It is formed by performing anisotropic etching after performing etching. That is, the contact hole having the round shape improves the step coverage of the wiring film, and as a result, the wiring film can secure good contact even for the contact hole having a high aspect ratio.

[0004]

However, in recent years,
As the miniaturization of semiconductor devices has progressed, the aspect ratio of the contact holes has also become higher. For this reason,
In the round-shaped contact hole formed by the method as in the conventional example, the opening diameter cannot fully correspond to the depth, and good step coverage of the wiring film cannot be obtained, resulting in contact failure and wiring reliability. There was a problem of lowering.

An object of the present invention is to solve such a problem and to form a contact hole in which the step coverage of the wiring is improved, good contact is secured, and the reliability of the wiring is improved. The purpose is to provide a method.

[0006]

In order to achieve this object, the present invention selectively removes the resist film formed on the film to be etched so that the diameter of the opening gradually increases from the upper part to the lower part. And a first step of forming a contact hole forming pattern having a shape in which the diameter gradually decreases toward the interface with the film to be etched from the middle thereof,
A second step of performing isotropic etching on the film to be etched using the contact hole forming pattern as a mask;
A method of forming a contact hole, comprising: a third step of performing anisotropic etching on the film to be etched using the contact hole forming pattern as a mask after performing the isotropic etching. To do.

[0007]

According to the present invention, in the contact hole forming pattern formed on the film to be etched, the diameter of the opening gradually becomes smaller from the upper part to the lower part, and the interface with the film to be etched is formed midway. The diameter of the opening at the interface with the film to be etched is relatively larger than that of the conventional contact hole forming pattern because the diameter gradually increases toward the contact hole. Therefore, when the film to be etched is isotropically etched using this as a mask, the film to be etched is etched starting from the opening edge portion at the interface. Therefore, the opening diameter of the contact hole formed in the film to be etched can be increased by the larger diameter of the opening portion at the interface. Further, in the anisotropic etching performed after the isotropic etching, a portion where the diameter of the opening portion of the contact hole forming pattern is the smallest is gradually etched. On the other hand, a difference in etching progress occurs. Therefore, in the film to be etched, the diameter of the opening becomes smaller as it approaches the bottom. Therefore, as compared with the conventional contact hole forming pattern, a contact forming pattern having a large opening diameter and a small contact diameter and having a good tapered shape can be obtained.

[0008]

Embodiments of the present invention will now be described with reference to the drawings. 1 to 5 are partial cross-sectional views showing a process of forming a contact hole according to an embodiment of the present invention. In the step shown in FIG. 1, a film to be etched 2 made of an oxide film having a film thickness of about 1.0 μm is formed on a semiconductor substrate 1. Then, a resist film having a thickness of about 1.2 μm is formed on the film to be etched 2. Here, PFI-15 (manufactured by Sumitomo Chemical Co., Ltd.) was used as the resist film, and prebaking was performed at 90 ° C. for 60 seconds. next,
The resist film is selectively exposed, and post-exposure bake (PEB) is performed at 110 ° C. for 60 seconds,
A contact hole forming pattern 3 made of the resist film is formed on the film to be etched 2. The exposure conditions and the development conditions were as follows.

Exposure conditions: exposure device NA = 0.42 g-line stepper Exposure time 490 msec (converted to 500 mW / cm ² ) Development conditions: Developer NMD-3 Development time 65 seconds (paddle development) Of the contact hole forming pattern 3 having a shape in which the diameter gradually decreases from the upper portion to the lower portion, and the diameter gradually increases from the portion having the smallest diameter toward the interface with the film to be etched 2. Formed.

Next, in the step shown in FIG. 2, the etching target film 2 is isotropically etched using the contact hole forming pattern 3 obtained in the step shown in FIG. 1 as a mask. Here, since the contact hole forming pattern 3 has a large opening diameter at the interface with the etching target film 2, the etching target film 2 is etched starting from the opening edge portion at the interface. .. Therefore, the opening diameter of the contact hole formed in the etching target film 2 can be increased by the larger diameter of the opening portion at the interface.

Next, in the step shown in FIG. 3, the film to be etched 2 is anisotropically etched following the step shown in FIG. At this time, since the portion of the contact hole forming pattern 3 having the smallest diameter is gradually etched, a difference in etching progress occurs in the lateral direction of the film to be etched 2. Therefore, the diameter of the opening of the film to be etched 2 becomes smaller as it approaches the bottom.

Next, in the step shown in FIG. 4, anisotropic etching is performed successively to the step shown in FIG. 3 to form a contact hole having a large opening diameter and a small contact diameter in the film to be etched 2. Next, in the step shown in FIG. 5, the contact hole forming pattern 3 is removed. After that, a desired process such as depositing a wiring film and patterning is performed.

In the present embodiment, in the step shown in FIG. 1, the diameter of the opening gradually decreases from the upper portion to the lower portion, and the portion from the smallest diameter to the interface with the film to be etched 2 is formed. The contact hole forming pattern 3 having a shape in which the diameter gradually increases is formed, and the forming method includes the following four methods. (1) The etching target film 2 is made slightly hydrophilic (the adhesiveness between the etching target film 2 and the resist film is reduced). As this method, for example, a dry baking temperature of the film to be etched 2 is set to 200 ° C. or lower, and HMDS (hexamethy
l dilazan) The amount of treatment can be reduced. (2) The adhesiveness (adhesiveness) between the etching target film 2 and the resist film is reduced. As this method, for example, the pre-baking is performed at a temperature of 90 ° C. or lower, and the post-baking is performed by 1
And the like. (3) When developing the resist film, the temperature of the developer is 24 ° C.
The above, the development time to 60 seconds or more, to the developer,
For example, a surfactant such as NSD-TD (manufactured by Tokyo Ohka Kogyo) is added. (4) Use a resist film containing a large amount of low molecules (this example corresponds to this).

As described above, by performing at least one of (1) to (4), it is possible to form the contact hole forming pattern having the above-mentioned shape. The reason for this is as follows: J. Shingaku (C), J70-C, 3, 332-340 (Showa 62).
As described in (March, 2013), in the exposure performed when forming the contact hole pattern in the resist film, the light traveling toward the interface between the resist film and the film to be etched 2 is exposed in the resist film. , And the reflected light from the interface interferes with each other to generate a standing wave. Due to the standing wave, the intensity of light in the vertical direction in the resist film is periodically varied, and unevenness is caused in the photosensitivity. By carrying out this effect and the method described in the above (1) to (4), the resist film at the interface with the film to be etched 2 can be developed in a state of being bitten in the lateral direction. A contact hole having a shape in which the diameter of the opening gradually decreases from the upper portion to the lower portion, and the diameter gradually increases from the portion having the smallest diameter toward the interface with the film to be etched 2. Pattern 3 is formed. That is, as a condition for always being able to form the contact hole forming pattern 3 having the above-described shape, it is possible to execute at least one of the above (1) to (4).

[0015]

As described above, according to the present invention,
Since the contact hole forming pattern has a shape in which the diameter of the opening gradually decreases from the upper part to the lower part, and the diameter gradually increases from the middle toward the interface with the film to be etched. When the film to be etched is isotropically etched as a mask, the opening diameter of the contact hole formed in the film to be etched can be increased. Further, in the anisotropic etching performed after the isotropic etching, a portion where the diameter of the opening portion of the contact hole forming pattern is the smallest is gradually etched. On the other hand, a difference in etching progress occurs. Therefore, in the film to be etched, the diameter of the opening becomes smaller as it approaches the bottom. Therefore, as compared with the conventional contact hole forming pattern, a contact hole forming pattern having a large opening diameter and a small contact diameter and having a favorable tapered shape can be obtained. As a result, the step coverage of the wiring can be improved, a good contact can be secured, and a contact hole with improved wiring reliability can be obtained.

[Brief description of drawings]

FIG. 1 is a partial cross-sectional view showing a process of forming a contact hole according to an example of the present invention.

FIG. 2 is a partial cross-sectional view showing a step of forming a contact hole according to an example of the present invention.

FIG. 3 is a partial cross-sectional view showing a step of forming a contact hole according to the example of the present invention.

FIG. 4 is a partial cross-sectional view showing a step of forming a contact hole according to an example of the present invention.

FIG. 5 is a partial cross-sectional view showing a step of forming a contact hole according to the example of the present invention.

[Explanation of symbols]

 1 semiconductor substrate 2 film to be etched 3 contact hole pattern

Claims (1)

[Claims] 1. The resist film formed on the film to be etched is selectively removed so that the diameter of the opening gradually decreases from the upper part to the lower part, and from the middle thereof toward the interface with the film to be etched. And forming a contact hole forming pattern having a shape in which the diameter gradually increases,
A second step of performing isotropic etching on the film to be etched using the contact hole forming pattern as a mask;
A method of forming a contact hole, comprising a third step of performing anisotropic etching on the film to be etched using the contact hole forming pattern as a mask after the isotropic etching.