Abstract:
It is possible to substantially remove a polymer residue from metal lines formed over a semiconductor device without damage to the metal lines. The disclosed method includes forming a metal layer over a lower layer. A photoresist film is formed over the metal layer, and then patterned. The metal layer is selectively etched, using the patterned photoresist film as an etch barrier, to form metal lines. A substantial portion of the photoresist film left on the metal lines is removed, leaving a polymer residue. Ultraviolet rays are irradiated onto the metal lines to degrade the polymer residue, and the residue is rinsed away.

Description:
[0001]    The present application claims priority under 35 U.S.C. 119 to Korean Patent Application No. 10-2007-0075046 (filed on Jul. 26, 2007), which is hereby incorporated by reference in its entirety. 
       BACKGROUND 
       [0002]    Various polymer-containing materials are used in the manufacture of electronic devices, for example, integrated circuits, disc drives, storage mediums, etc. Such polymer-containing materials may be found in photoresist film, anti-reflective coatings, via-filling layers, etch stop layers, etc. In modem techniques, a photoresist material is used to form a desired pattern on a substrate for lithography, to perform etching processes using the pattern, or to transfer the pattern to the material of the substrate. The photoresist material is deposited in the form of a film. As the photoresist film is exposed to light, a desired pattern is defined. The light-exposed region is dissolved by a suitable developing solution, to transfer the pattern to the substrate. After the transfer of the pattern to the substrate, the photoresist material is removed from the substrate, in order to prevent the photoresist material from adversely affecting or interfering with a subsequent treatment or process. 
         [0003]    The pattern definition (or pattern transfer) technique and polymer removal technique may often include at least one plasma processing procedure, for example, plasma etching, reactive ion etching, ion milling, plasma ashing, etc. In related cases, a plasma processing procedure is used in the manufacture of integrated circuits and other electronic devices. Generally, a polymer material is removed during the plasma processing procedure, irrespective of the amount of a polymer residue and other residues left on the substrate. 
         [0004]    The residues may include an incompletely removed photoresist film, a side wall polymer left on the side walls of a line structure or in a recess such as a via, and an organic metal polymer and metal oxides left on the upper surface of the line structure or on the bottom of the recess. Such post plasma residues cannot be completely removed, using related photoresist film removal methods and rinsing processes. 
         [0005]    The polymer residue left on metal lines may cause a bridge between the metal lines, and may adversely affect the electrical characteristics of the device. In particular, such problems may be more severe in a semiconductor device having a higher degree of integration. 
         [0006]      FIG. 1  is a flow chart illustrating a method for forming metal lines in a semiconductor device and a method for removing polymer residue. A metal layer forming process S 102  may be conducted to form a metal layer used to form metal lines over a lower layer. Thereafter, a photoresist film coating process S 104  is conducted, for the execution of photo-lithography. In the photoresist film coating process S 104 , a photoresist film is formed over the entire upper surface of the metal layer. 
         [0007]    Subsequently, a process S 106  for etching the metal layer and removing a photoresist film residue is conducted. In this process, a pattern on a mask or reticle is transferred to the photoresist film, which is uniformly coated over, for example, a wafer, using exposing equipment such as a stepper in accordance with a stepped projection/exposure process. The photoresist film is then subjected to a developing process, to form a two-dimensional photoresist pattern. Using the photoresist film pattern as an etch barrier, the metal layer is etched to form metal lines. Thereafter, a photoresist film residue is removed. 
         [0008]    A rinsing process S 108  is then conducted. After the process S 106  for etching the metal layer and removing the photoresist film residue, by-products in the form of polymer including carbon (C), silicon (Si), oxygen (O), etc. may be left on the metal lines. Such by-products may degrade the reliability of the product. For example, the by-products adversely affect the electrical connection of the lines. To this end, it is necessary to remove the by-products, through a rinsing process. 
         [0009]    In a 130 nm technology, the line width of metal lines is reduced to about 160 nm. This tends to increase RC delays. To maintain the RC delay at a desired value, it is necessary to effectively remove a polymer residue left on the metal lines. In particular, where a reduced design rule is used, there may be a problem in that the polymer residue is mainly left on the upper surfaces of the metal lines, but not on the side walls of the metal lines. 
         [0010]    If the metal line forming method and polymer residue removing method described above are used to remove the polymer residue as much as possible, the side walls of the metal lines, etc. may be damaged. This is because, although the maximal removal of the polymer residue can be achieved through an increase in the etching time or photoresist film removal time given in the metal layer etching/photoresist film residue removing process  106  or an increase in the rinsing time or rinsing intensity given in the rinsing process S 108 , damage to the side walls of the metal lines may also increase. 
       SUMMARY 
       [0011]    Embodiments relate to a method for removing a polymer residue from metal lines of a semiconductor device, and more particularly, to a method for removing a polymer residue formed in procedures of etching a metal layer for the formation of metal lines, removing a photoresist film, etc., without causing damage to the metal lines. Embodiments relate to a method for removing a polymer residue from metal lines of a semiconductor device, which is capable of removing a polymer residue formed in procedures of etching a metal layer for the formation of metal lines, removing a photoresist film, etc., without causing damage to the metal lines. 
         [0012]    A method for removing a polymer residue from metal lines of a semiconductor device according to embodiments includes: forming a metal layer over a lower layer; forming a photoresist film over the metal layer, and patterning the photoresist film; selectively etching the metal layer, using the patterned photoresist film as an etch barrier, to form metal lines; removing a substantial portion of the photoresist film left on the metal lines; irradiating ultraviolet rays onto the metal lines, from which the substantial portion of the photoresist film has been removed; and rinsing the ultraviolet-irradiated metal lines. 
     
    
     
       DRAWINGS 
         [0013]      FIG. 1  is a flow chart illustrating a related method for forming metal lines of a semiconductor device and a related method for removing a polymer residue. 
           [0014]      FIG. 2  is a flow chart illustrating a method for forming metal lines of a semiconductor device and a method for removing a polymer residue according to embodiments. 
           [0015]      FIGS. 3A to 3E  are sectional views illustrating a procedure for forming metal lines of a semiconductor device and removing a polymer residue from the metal lines in accordance with embodiments. 
           [0016]    Example  FIGS. 4A to 4C  illustrate scanning electron microscopy (SEM) images for the comparison of the results of the polymer residue removal according to embodiments with the results of the general polymer residue removal. 
       
    
    
     DESCRIPTION 
       [0017]      FIG. 2  is a flow chart illustrating a related method for forming metal lines of a semiconductor device and a related method for removing a polymer residue. In accordance with the related forming method, a metal layer forming process S 202  is conducted to form a metal layer over a lower layer, for the formation of metal lines. The metal layer may be made of Ti, AlCu, or TiN. 
         [0018]    Thereafter, a photoresist film coating process S 204  is conducted, for the execution of photo-lithography. In the photoresist film coating process S 204 , a photoresist film is formed over the entire upper surface of the metal layer. 
         [0019]    Subsequently, a process S 206  for etching the metal layer and removing a photoresist film residue is conducted. In this process, a pattern on a mask or reticle is transferred to the photoresist film, which is uniformly coated over, for example, a wafer, using exposing equipment such as a stepper in accordance with a stepped projection/exposure process. The photoresist film is then subjected to a developing process, to form a two-dimensional photoresist pattern. Using the photoresist film pattern as an etch barrier, the metal layer is selectively etched to form metal lines. Thereafter, a photoresist film residue is removed. 
         [0020]    For the photoresist film removing method, a dry ashing method using plasma may be used. For the selective etching of the metal layer, a reactive ion etching (RIE) method may be used. 
         [0021]    Thereafter, an ultraviolet irradiation process S 207  is conducted. When the ultraviolet irradiation is conducted after the metal layer etching/photoresist film residue removing process S 206 , but before a rinsing process for removing by-products such as a polymer residue, the polymer residue is deformed (or, in other words, degraded or decomposed) into a material capable of being easily removed without causing damage to metal lines. 
         [0022]    The patterning of the photoresist film and the etching of the metal layer are carried out with the amounts of Cl 2  and CHF 3  gas adjusted in accordance with the width and depth of the photoresist film. Since polymer such as Al x C y Cl z  produced in the form of by-products is hardened polymer, it is difficult to remove the polymer, even when the rinsing time in the subsequent rinsing process increases. In this case, damage to the metal lines may occur. 
         [0023]    When the rinsing time decreases, but the etching time for the metal layer increases, a line-shaped polymer may be formed on the metal lines, creating problems. To solve these problems, research on various gases usable in the etching process and various chemicals usable in the rinsing process has been conducted. However, most new methods developed to solve the above-mentioned problems cause another problem, for example, degradation in productivity, degradation in efficiency, or increases in costs. 
         [0024]    To this end, embodiments are directed towards an ultraviolet irradiation method. In embodiments, Ti, AlCu, and TiN are examples of the metal layer. The ultraviolet irradiation method will be described in conjunction with one example of the metal layer, for example, Ti. Since Ti can be easily oxidized, a TiO X  layer is formed to a thickness of about 10 Å to 20 Å over the metal layer. 
         [0025]    When ultraviolet rays are irradiated after the metal layer etching/photoresist film residue removing process S 206 , the TiO X  layer functions as a photo-catalyst layer on the surfaces of the metal lines formed in accordance with the etching of the metal layer. That is, the TiO X  layer reacts with a polymer residue left on the surface of the metal lines, thereby oxidizing the polymer residue into CO 2  and H 2 O. The CO 2  and H 2 O produced in accordance with the oxidation are materials capable of being easily removed in the subsequent rinsing process. In other words, the polymer left on the metal lines irradiated with the ultraviolet rays generates a photo oxidation, together with the photo-catalyst layer formed on the surfaces of the metal lines. 
         [0026]    In accordance with embodiments, a preliminary rinsing process may be additionally conducted between the metal layer etching/photoresist film residue removing process S 206  and the ultraviolet irradiation process S 207 . Thereafter, a rinsing process S 208  is conducted. This process is used to remove by-products left after the metal layer etching/photoresist film residue removing process S 206  and the ultraviolet irradiation process S 207  in accordance with a rinsing method. 
         [0027]    Example  FIGS. 3A to 3E  are sectional views illustrating a procedure for forming metal lines of a semiconductor device and removing a polymer residue from the metal lines in accordance with embodiments. Referring to example  FIG. 3A , a metal layer  304  is formed over a lower layer  302  formed over a semiconductor substrate, and a photoresist film  306  is then coated over the metal layer  304 . Thereafter, the photoresist film  306  is patterned to form a metal line pattern, as shown in example  FIG. 3B . Using the patterned photoresist film  306  as an etch barrier, the metal layer  304  is then selectively etched to form metal lines, as shown in example  FIG. 3C . 
         [0028]    Thereafter, the photoresist film  306  left after the formation of the metal lines is removed, as shown in example  FIG. 3D . In this state, a polymer residue  308  is left mainly on the upper surface of the patterned metal layer  304 , namely, the upper surfaces of the metal lines. In order to effectively remove the polymer residue  308 , the whole area is irradiated with ultraviolet rays  310 . 
         [0029]    The irradiation of the ultraviolet rays  310  is conducted with power at 0.5 mW/cm 2  to 1.3 mW/cm 2  and a wavelength of 220 nm to 365 nm. The metal layer  304  may be made of Ti, AlCu, or TiN. Where the metal layer is made of, for example, Ti, a TiO X  layer is formed to a thickness of about 10 Å to 20 Å over the metal layer because Ti can be easily oxidized. 
         [0030]    The ultraviolet rays  310  activate a photo oxidation on the surface of the metal layer  304  to remove the polymer residue  308 . The use of power at 0.5 mW/cm 2  to 1.3 mW/cm 2  and a wavelength of 220 nm to 365 nm correspond to minimal energy causing the TiO X  layer present on the surface of the patterned metal layer  304  to react with the ultraviolet rays  310 . 
         [0031]    When the irradiated ultraviolet rays  310  have a wavelength of 365 nm or shorter, electrons are excited from a valence band to a conduction band, even when they have optical band gap energy. As a result, the electrons and holes are activated. Using energy generated in accordance with the activation, the TiO X  layer conducts a photo oxidation with the hardened polymer residue  308  left on the surfaces of the metal lines through a catalyst reaction. At this time, no reaction occurs at the TiO X  layer itself. Thus, the polymer residue  308  is oxidized into CO 2  and H 2 O. The ultraviolet rays  310  may have a wavelength of 220 nm to 380 nm. 
         [0032]    The residue left after being subjected to the above-described process can be easily removed in the subsequently rinsing process, using many chemicals. Referring to example  FIG. 3E , it can be seen that the surfaces of the patterned metal layer  304 , in particular, the upper surface, are in a cleaned state without any polymer residue, after being subjected to the rinsing process. 
         [0033]    Example  FIGS. 4A to 4C  are illustrations of scanning electron microscopy (SEM) images for the comparison of the results of the polymer residue removal according to embodiments with the results of the general polymer residue removal. Example  FIG. 4A  is an illustration showing the state after the etching of the metal layer, but before the removal of the photoresist film. Referring to example  FIG. 4A , the photoresist film is left on the patterned metal layer, namely, on the upper surfaces of the metal lines, but no or little photoresist film is left on the side walls of the metal lines. If the etching of the metal layer is changed to increase the etch depth, in order to effectively remove the photoresist film, damage to the metal lines formed in accordance with the etching of the metal layer may occur. Otherwise, a variation in profile occurs. Also, if the subsequent rinsing process is conducted at a higher intensity, damage to the metal lines may occur. 
         [0034]    If the etch depth or rinsing intensity is reduced to prevent the side walls of the metal lines from being damaged, a large amount of polymer residue is left on the upper surfaces of the metal lines, as shown in example  FIG. 4B . In this case, the reliability of the semiconductor device is degraded. 
         [0035]    When ultraviolet rays are irradiated after the removal of the photoresist film, and a rinsing process is conducted in accordance with embodiments, to solve the above-described problems, there is no polymer residue left on the upper surfaces of the metal lines, as shown in example  FIG. 4C . In this case, it is possible to optimize the process without any damage to the metal lines. As apparent from the above description, the metal line polymer residue removing method according to embodiments can remove a polymer residue as much as possible without causing damage to the metal lines, by conducting an ultraviolet irradiation process after the etching of the metal layer and the removal of the leftover photoresist film. 
         [0036]    It will be obvious and apparent to those skilled in the art that various modifications and variations can be made in the embodiments disclosed. Thus, it is intended that the disclosed embodiments cover the obvious and apparent modifications and variations, provided that they are within the scope of the appended claims and their equivalents.