Abstract:
A method for forming a metal line in a semiconductor device, in which a resolution is improved for securing a design rule and minimizing a difference of critical dimensions, including the steps of (1) forming a first insulating film and a second insulating film on a substrate, (2) etching the second insulating film to form a second insulating film pattern, (3) depositing a third insulating film on the second insulating film pattern, (4) removing the second insulating film pattern, and (5) forming a metal line layer in a region having the second insulating film pattern removed therefrom.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a semiconductor device, and more particularly, to a method for forming a metal line in a semiconductor device. 
     2. Background of the Related Art 
     Referring to FIG. 1 a , in a related art method for forming a metal line, a metal layer  2  of aluminum is deposited on an oxide film  1 , and a positive photoresist  3  is coated on the metal layer  2 , and subjected to selective patterning by exposure and development using a dark tone mask so that the positive photoresist  3  masks a portion in which a metal line is to be formed. Then, as shown in FIG. 1 b , the patterned resist  3  is used as a mask in etching the metal layer  2 , to form a plurality of metal lines  2   a . Thereafter, the photoresist  3  is removed and the same process is repeated to form multilayered metal lines. 
     However, due to limitations in electrical properties of aluminum used for the metal line, copper has been used for a material of the metal. line. It is difficult to form a metal line of copper by a general method for forming a metal line due to a poor etchability of copper. Because of this reason, a process is employed in which an interlayer material is deposited firstly before formation of a metal line layer, a portion of the interlayer material in which the metal line layer is to be formed is etched, and a metal is stuffed in the etched portion, and planarized, which process is called a dual damascene process. 
     A related art method for forming a metal line by a dual damascene process will be explained with reference to the attached drawings. FIGS. 2 a ˜ 2   d  illustrate sections showing the steps of a related art method for forming a metal line in a semiconductor device. 
     Referring to FIG. 2 a , a second oxide film  12  is deposited on a first oxide film  11  having a via hole and a trench formed therein and a photoresist film  13  is coated on the second oxide film  12 . Then, the photoresist film  13  is removed by exposure and development to remove portions in which metal lines are to be formed only. The removal of the portions in which the metal lines are to be formed is called as a negative tone patterning. The negative tone patterning of the photoresist film  13  can be conducted in combination of a positive resist and a clear tone mask or a negative resist and a dark tone mask. As shown in FIG. 2 b , the patterned photoresist film  13  is used as a mask in etching the second oxide film  12  to form a negative tone structure. As shown in FIG. 2 c , the second oxide film  12  is used as a mask in depositing a metal layer  14  of, such as copper Cu, on an entire surface. As shown in FIG. 2 d , the metal layer  14  and the second oxide film  12  are planarized to form a metal line layer  14   a.    
     However, the related art method for forming a metal line in a semiconductor device has the following problems. 
     First, in a case when a negative tone form is formed in a positive photoresist film, it is difficult to remove the photoresist from the via hole or the trench completely by development. 
     Second, in a case when a negative tone form is formed in a negative photoresist film, a portion which is not exposed is dissolved to make a difference of critical dimensions the greater as a pattern density becomes the greater due to interference of incident lights in formation of a micron pattern. Because of this reason, there has been a limitation in a resolution in formation of the micron pattern and it is difficult to overcome optical proximity and to form a line form of pattern. 
     SUMMARY OF THE INVENTION 
     Accordingly, the present invention is directed to a method for forming a metal line in a semiconductor device that substantially obviates one or more of the problems due to limitations and disadvantages of the related art. 
     An object of the present invention is to provide a method for forming a metal line in a semiconductor device, in which a resolution is improved for securing a design rule and minimizing a difference of critical dimensions. 
     Additional features and advantages of the invention will be set forth in the description which follows, and in part will be apparent from the description, or may be learned by practice of the invention. The objectives and other advantages of the invention will be realized and attained by the structure particularly pointed out in the written description and claims hereof as well as the appended drawings. 
     To achieve these and other advantages and in accordance with the purpose of the present invention, as embodied and broadly described, the method for forming a metal line in a semiconductor device includes the steps of (1) forming a first insulating film and a second insulating film on a substrate, (2) etching the second insulating film to form a second insulating film pattern, (3) depositing a third insulating film on the second insulating film pattern, (4) removing the second insulating film pattern, and (5) forming a metal line layer in a region having the second insulating film pattern removed therefrom. 
     It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory and are intended to provide further explanation of the invention as claimed. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The accompanying drawings, which are included to provide a further understanding of the invention and are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and together with the description serve to explain the principles of the invention: 
     In the drawings: 
     FIGS. 1 a  and  1   b  illustrate sections showing the steps of a general method for forming a metal line in a semiconductor device; 
     FIGS. 2 a ˜ 2   d  illustrate sections showing the steps of a related art method for forming a metal line in a semiconductor device; 
     FIGS. 3 a ˜ 3   g  illustrate sections showing the steps of a method for forming a metal line in a semiconductor device in accordance with a preferred embodiment of the present invention; and, 
     FIGS. 4 a  and  4   b  respectively illustrate a graph and experimental data showing a comparison of a critical dimension difference of an isolated region and a concentrated region for different pattern critical dimensions in the related art and the present invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Reference will now be made in detail to the preferred embodiments of the present invention, examples of which are illustrated in the accompanying drawings. FIGS. 3 a ˜ 3   g  illustrate sections showing the steps of a method for forming a metal line in a semiconductor device in accordance with a preferred embodiment of the present invention, and FIGS. 4 a  and  4   b  respectively illustrate a graph and experimental data showing a comparison of a critical dimension difference of an isolated region and a concentrated region for different pattern critical dimensions in the related art and the present invention. 
     In the present invention, a dual damascene process is employed in which a positive tone form of photoresist film is formed and a nitride film is formed between the photoresist film and the oxide film as a sacrificial layer. The formation of a positive tone form of photoresist film implies that a metal line to be formed later will have the same form as the positive tone form. Therefore, if a negative tone form is formed, it implies that a metal line to be formed later will have a form opposite to the negative tone form. 
     Referring to FIG. 3 a , the method for forming a metal line in a semiconductor device in accordance with a preferred embodiment of the present invention starts with deposition of a nitride film  22 , which has an excellent selectivity over the first oxide film  21  in a wet etching, on a first oxide film  21 . Then, a positive photoresist film  23  is coated on the nitride film  22 , and subjected to selective patterning by exposure and development to leave only portions of the photoresist film  23  in which metal lines are to be formed later, to form a positive tone pattern. For reference, the positive photoresist film  23  has such a property that portions of the photoresist that is irradiated during the exposure are removed in development and, opposite to this, the negative photoresist film has such a property that portions of the photoresist that is not irradiated during the exposure are removed in development. As shown in FIG. 3 b , the patterned photoresist film  23  is used as a mask in subjecting the nitride film  22  to anisotropic etching to expose the first oxide film  21 , to have the nitride film  22  to be of the positive tone form. In order to form the nitride film  22  to be of the positive tone form, either a positive photoresist film and a dark tone mask are combined or a negative photoresist film and a clear tone mask are combined. As shown in FIG. 3 c , a second oxide film  24  is deposited on an entire surface to cover the etched nitride film  22 . As shown in FIG. 3 d , the second oxide film  24  is planarized until the nitride film  22  is exposed. As shown in FIG. 3 e , the second oxide film  24  is wet etched with phosphoric acid solution to leave the second oxide film  24  only in portions excluding regions in which metal lines are to be formed. In this instance, the nitride film  22  formed in the via hole in the first oxide film  21  is removed on the same time. Then, as shown in FIG. 3 f , a metal layer  25  is deposited on an entire surface. As shown in FIG. 3 g , the metal layer  25  and the second oxide film  24  are subjected to CMP(chemical mechanical polishing) or etch back, to planarize the metal layer  25  and the second oxide film  24 , to form metal lines  25   a . By repeating the aforementioned process, multilayered metal lines can be formed. 
     Difference of critical dimensions(c/d) between isolated regions and concentrated regions with respect to designed critical dimensions in the present invention and the related art will be explained referring to FIGS. 4 a  and  4   b . FIG. 4 a  illustrates a difference of process performances of the negative tone patterning and the positive tone patterning. The present invention employs the positive tone patterning and the related art employs the negative tone patterning. The black colored bars represent the positive tone patterning case and the dotted bars represent the negative tone patterning case. When delta of c/d between the concentration pattern and the isolated pattern for each size is compared, it can be known that in general the delta of c/d between the concentration pattern and the isolated pattern in the case the positive tone patterning is employed is smaller than the case the negative tone patterning is employed. Particularly, as the size of the critical dimension becomes the smaller, as the delta of c/d between the concentration pattern and the isolated pattern in the case the positive tone patterning is employed becomes the smaller than the case the negative tone patterning is employed significantly, it can be known that the positive tone patterning improves the resolution. 
     Critical dimensions which are limitations of resolutions and differences of the critical dimensions of the positive tone pattern form and the negative tone pattern form in concentrated region and isolated region are compared with reference to drawing. Under the same exposure conditions, a critical value of line/space, a limitation of the resolution, is 0.17 μm/0. 17 μm both for the positive tone patterning and the negative patterning done in a concentrated region. Opposite to this, under the same exposure, though a critical value of an isolated line dimension, a limitation of the resolution, is 0.17 μm for a positive tone patterning in an isolated region, a critical dimension of an isolated space, a limitation of the resolution, is 0.21 μm for a negative tone patterning in an isolated region. And, though a positive tone pattern form shows a difference of bias less than 0.02 μm for forming the critical dimension for both in a concentrated region and an isolated region, a negative tone pattern form shows a difference of bias less than 0.051 μm for forming the critical dimension for both in a concentrated region and an isolated region. 
     The method for forming a metal line in a semiconductor device of the present invention has the following advantages. 
     First, the improved resolution allows one to secure a design rule with ease. 
     Second, a difference of critical dimensions as a concentration of pattern becomes higher coming from optical proximity can be minimized. 
     It will be apparent to those skilled in the art that various modifications and variations can be made in the method for forming a metal line in a semiconductor device of the present invention without departing from the spirit or scope of the invention. Thus, it is intended that the present invention cover the modifications and variations of this invention provided they come within the scope of the appended claims and their equivalents.