This application is based upon and claims the benefit of priority from prior Japanese Patent Application No. 2006-224319, filed Aug. 21, 2006, the entire contents of which are incorporated herein by reference.
1. Field of the Invention
The present invention relates to a method for manufacturing a semiconductor device.
2. Description of the Related Art
Owing to the demands of miniaturization of semiconductor devices, the thickness of photo-resist films is becoming increasingly smaller. Accordingly, it has become difficult to ensure a sufficient etching resistance only by a photo-resist film. In light of this problem, there has been proposed a pattern transferring technique utilizing a multilayer resist (for example, see Jpn. Pat. Appln. KOKAI Publication No. 2006-140222). In general, a multilayer resist is formed of a lower film, an intermediate film, and an upper film (photo-resist film).
However, along with a further decrease in the thickness of photo-resist films, a problem arises in that a photo-resist pattern disappears when the photo-resist pattern is used as a mask in dry etching of the intermediate film. In this case, since that portion of the intermediate film which serves as a mask is etched, it is difficult to form an adequate pattern at the intermediate film. If wet etching is used for the same purpose, the photo-resist pattern may be prevented from disappearing. However, since wet etching is isotropic etching, in which the etching proceeds in a lateral direction as well, the photo-resist pattern cannot be faithfully transferred to the intermediate film. Conventionally, because of such a reason, it is difficult to form an adequate pattern at the intermediate film, and thus is also difficult to reliably form a device pattern, such as an interconnection pattern, with high accuracy.
The problem described above is caused not only in a case where a multilayer resist is used for patterning an etching target film, but also in a case where a photo-resist pattern formed directly on an etching target film is used as a mask for etching the etching target film.
As described above, conventionally, there is a problem in that, when a photo-resist pattern is used as a mask for etching an underlying film, it is difficult to form an adequate pattern.
According to an aspect of the present invention, there is provided a method for manufacturing a semiconductor device, the method comprising: forming a photo-resist pattern above a first film; implanting a predetermined dopant that increases an etching rate of the first film into the first film using the photo-resist pattern as a mask, thereby forming an implantation layer in the first film; and etching a first portion of the first film, which is at least a part of the implantation layer, using the photo-resist pattern as a mask.
An embodiment of the present invention will now be described with reference to the accompanying drawings.
At first, as shown in
Then, a carbon film is formed as the lower film (second film) 14 of a multilayer resist on the etching target film 12 by a CVD method or coating method. The carbon film contains carbon as the main component and further contains oxygen and hydrogen. The thickness of the lower film 14 is determined in accordance with the etching selectivity ratio between the etching target film 12 and lower film 14.
Then, a silicon oxide family film, such as a BSG film or TEOS film, is formed as the intermediate film (first film) 16 of the multilayer resist on the lower film 14 by an LPCVD method. The thickness of the intermediate film 16 is set to be about 30 nm to 45 nm.
Then, a photo-resist film is formed as the upper film of the multilayer resist on the intermediate film 16 by a coating method. Thereafter, patterning is performed on the photo-resist film by photolithography to form a photo-resist pattern 18. After the photolithography, the thickness of the photo-resist film is about 40 nm to 65 nm. The photo-resist pattern 18 is arranged to form an interconnection pattern, and has a line width (interconnection line width) and a space width, each of which is set to be about 45 nm or less. Since the width of the photo-resist pattern 18 is narrow, the photo-resist pattern 18 can easily fall if the sidewalls of the photo-resist pattern 18 are vertical. Accordingly, the photo-resist pattern 18 is formed such that the sidewalls are inclined. Consequently, the photo-resist pattern 18 has skirt portions 18a formed along the surface of the intermediate film 16. Under ordinary circumstances, the skirt portions 18a are preferably not formed, but the inclined sidewalls of the photo-resist pattern 18 bring about the skirt portions 18a.
After the step shown in
In order to solve the problem described above, according to this embodiment, as shown in
Then, as shown in
As described above, the first portion 16b is removed by wet etching. Since wet etching mainly utilizes a chemical etching effect, the etching selectivity ratio can be easily increased, but the etching proceeds in an isotropic manner in general. In this respect, according to this embodiment, the etching selectivity ratio has been increased by boron ion implantation, the etching proceeds substantially in an anisotropic manner even by wet etching. Thus, the first portion 16b is selectively etched while the portion below the photo-resist pattern 18 is scarcely etched. Consequently, the photo-resist pattern 18 is faithfully transferred to the intermediate film 16. Further, since wet etching is used, the first portion 16b of the intermediate film 16 is etched while the photo-resist pattern 18 is substantially not etched.
The skirt portions 18a of the photo-resist pattern 18 are removed by the ion implantation step shown in
Since the implantation layer 16a is formed by ion implantation, boron in the implantation layer 16a has a concentration distribution in the film thickness direction. Accordingly, in this embodiment, the implantation layer 16a is not entirely etched. The portion below the first portion 16b which contains boron at a low concentration is not etched. In other words, the implantation layer 16a is partly etched. However, where the entire implantation layer 16a contains boron at a high concentration, the entire implantation layer 16a can be etched.
Then, as shown in
As described above, in the wet etching step shown in
Then, as shown in
Then, as shown in
As has been described above, according to this embodiment, in the ion implantation step shown in
Since the first portion 16b has a sufficiently high etching rate (that results in a high etching selectivity ratio), the etching proceeds substantially in an anisotropic manner even by wet etching that proceeds in an isotropic manner under ordinary circumstances. Consequently, it is possible to reliably form an adequate pattern at the intermediate film 16 with high accuracy. Further, since wet etching is used, the first portion 16b of the intermediate film 16 can be etched while the photo-resist pattern 18 is scarcely etched.
According to this embodiment, the skirt portions of the photo-resist pattern 18 can be removed by the ion implantation step shown in
According to this embodiment, the modified layer 18b is formed in the surface area of the photo-resist pattern 18 by the ion implantation step shown in
Therefore, according to this embodiment, the third portion 16d of the intermediate film 16 can be reliably formed with high accuracy below the photo-resist pattern 18, so that the third portion 16d can serve as an etching mask with high reliability and high accuracy. Consequently, it is possible to form a pattern at the etching target film 12 with high accuracy.
In the embodiment described above, the multilayer resist has a three-layer structure formed of the lower film 14, intermediate film 16, and upper film (photo-resist film) 18. However, a multilayer resist having a two-layer structure including a photo-resist film may be used. Further, in place of use of a multilayer resist structure, the photo-resist pattern 18 may be formed directly on the etching target film 12. Also in these cases, the same method as described above with reference to the embodiment may be used.
In the embodiment described above, the photo-resist pattern 18 includes the skirt portions 18a. However, the same method as described above with reference to the embodiment may be applied to a case where the photo-resist pattern 18 includes no skirt portions 18a.
In the embodiment described above, the modified layer 18b is formed all over the surface area of the photo-resist pattern 18. However, it suffices if the modified layer 18b is formed at least in the upper surface area of the photo-resist pattern 18. If the modified layer 18b is present at least in the upper surface area of the photo-resist pattern 18, the photo-resist pattern 18 can have a sufficient anisotropic dry etching resistance, when the anisotropic dry etching is performed in the step shown in
In the embodiment described above, boron is used as a dopant in the ion implantation step shown in
In the embodiment described above, wet etching is used in the etching step shown in
In the embodiment described above, wet etching is performed in the step shown in
Additional advantages and modifications will readily occur to those skilled in the art. Therefore, the invention in its broader aspects is not limited to the specific details and representative embodiments shown and described herein. Accordingly, various modifications may be made without departing from the spirit or scope of the general inventive concept as defined by the appended claims and their equivalents.
Number | Date | Country | Kind |
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2006-224319 | Aug 2006 | JP | national |
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Number | Date | Country |
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2006-140222 | Jun 2006 | JP |
Number | Date | Country | |
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20080045026 A1 | Feb 2008 | US |