Abstract:
A method of analyzing ions adsorbed on a surface of a mask for pattern formation of a semiconductor device, and an apparatus using the same are disclosed. The ion analyzing method includes: filling a heating container within a main chamber with a predetermined amount of a solvent; immersing a mask in the solvent-filled heating container; raising an internal pressure of the chamber to a predetermined level by supplying gas into the chamber; separating ions from a surface of the mask by heating the solvent within the heating container at a predetermined temperature for a predetermined period; and analyzing the ions by collecting the solvent.

Description:
CROSS-REFERENCE TO RELATED PATENT APPLICATION 
       [0001]    This application claims the benefit of Korean Patent Application No. 10-2007-0085576, filed on Aug. 24, 2007, in the Korean Intellectual Property Office, the disclosure of which is incorporated herein in its entirety by reference. 
       BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    The present invention relates to a method of and an apparatus for analyzing ions on a surface of a mask for semiconductor devices, and more particularly, to a method of and an apparatus for analyzing ions adsorbed on a surface of a mask using positive pressure effects. 
         [0004]    2. Description of the Related Art 
         [0005]    Circuit patterns on semiconductor devices are formed through a photolithography process. In such photolithography process, a photoresist film is deposited on a wafer, a pattern formed on a photomask is transcribed to the photoresist film by an exposure process, and the photoresist pattern is formed through a development process. Using the photoresist pattern, a film on the wafer is patterned to form a circuit pattern of the semiconductor device. In order to form the circuit pattern by the photolithography process, a mask, such as a photomask, is used. On a transparent substrate, such as light transmitting quartz, a shielding film such as light blocking chrome film is patterned on the photomask used for forming a circuit pattern in the photolithography process. 
         [0006]    In order to manufacture a semiconductor device, an exposure process is carried out with many wafers using one photomask. When such repetitive photolithography process is carried out, unstable ions are produced during the process, and the unstable ions adsorb to a surface of the photomask by static electricity or chemical bonding. The ions adsorbed on the surface of the photomask not only prevent accurate transcription of the photomask pattern onto the wafers during photolithography process, but also produce identical repetitive defects on many wafers that are manufactured using the photomask. 
         [0007]    Therefore, it is very important to remove the ions adsorbed on the surface of the photomask. Conventionally, ions adsorbed on surfaces of photomasks are removed by performing a cleaning process using sulfuric acid (H 2 SO 4 ). While the cleaning process using sulfuric acid may remove the ions adsorbed on the surface of the photomask, sulfuric acid residues such as SO 4   2−  still remain on the photomask. In this regard, a method of removing the sulfuric acid residues by neutralization using ammonium hydroxide (NH 4 OH) has been used, but such method produces salt such as (NH 4 ) 2 SO 4  when neutralizing with NH 4 OH. 
         [0008]    Therefore, in order to remove the adsorbed ions on the surface of the photomask through a cleaning process, the ions adsorbed on the surface of the photomask must be accurately analyzed. Conventionally, ions on the surface of the photomask are collected and analyzed by ion chromatography (IC). 
         [0009]    However, when using the conventional method for ion analysis, it is not only difficult to analyze ions accurately, but also the variation of analysis results is large, thereby making it difficult to determine the cleaning recipe for removing the ions. Moreover, a significant amount of time is spent on collecting the ions, thereby increasing the ion analysis time. 
       SUMMARY OF THE INVENTION 
       [0010]    Example embodiments of the present invention provide a method of and an apparatus for analyzing ions adsorbed on a surface of a photomask using positive pressure effects to accurately analyze the ions adsorbed on the surface of the photomask, thereby obtaining superior reproducibility of the analysis results. 
         [0011]    According to an aspect of the present invention, there is provided a method of analyzing ions adsorbed on a surface of a mask. First, a heating container within a chamber may be filled with a predetermined amount of a solvent. Then, a mask may be immersed in the solvent-filled heating container. An internal pressure of the chamber may be raised to a predetermined level by supplying gas into the chamber. The ions may be separated from the surface of the mask by heating the solvent within the heating container at a predetermined temperature for a predetermined period. The ions may then be analyzed by collecting the solvent. 
         [0012]    The gas may include a purge gas, such as N 2 , and the solvent may include deionized water. The amount of the solvent may be about 900 ml-1100 ml. The internal pressure of the chamber may be maintained at about 1-10 atm, and the temperature of the solvent may be kept at about 80-180° C. for about 5-10 minutes. 
         [0013]    Example embodiments of the present invention also provide an apparatus for analyzing ions adsorbed to a surface of a mask. The ion analyzing apparatus may include a main chamber having a gas inlet for supplying gas inside the main chamber, a gas outlet for discharging gas from the main chamber, and a door through which a photomask enters and exits out of the main chamber; a heating container may be disposed in the main chamber and may be filled with a solvent to immerse the photomask in solvent; and a hot plate may be disposed in the main chamber, an upper surface of which may be communicatively coupled to the heating container. 
         [0014]    The ion analyzing apparatus may further include a gas supply unit disposed outside of the main chamber, and configured to supply gas to the gas inlet of the main chamber in order to maintain a predetermined internal pressure in the main chamber. 
         [0015]    The ion analyzing apparatus may further include a temperature controller disposed outside of the main chamber, and which controls the temperature of the hot plate. 
         [0016]    The method of and the apparatus for analyzing ions according to example embodiments of the present invention use positive pressure effects to raise the boiling point of deionized water, which allows accurate separation of the ions adsorbed on a surface of the mask in a short time, thereby leading to accurate analysis results with superior reproducibility. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS  
         [0017]    The above and other features and advantages of the present invention will become more apparent by describing in detail exemplary embodiments thereof with reference to the attached drawings in which: 
           [0018]      FIG. 1  is a cross-sectional view illustrating an apparatus for analyzing ions adsorbed on a surface of a mask, according to the embodiment of the present invention; 
           [0019]      FIG. 2  is a perspective view illustrating a semiconductor testing apparatus including the ion analyzing apparatus of  FIG. 1 , according to an embodiment of the present invention; and 
           [0020]      FIG. 3  is a flow diagram of a method of analyzing ions adsorbed on a surface of a mask using the ion analyzing apparatus of  FIG. 1 , according to an embodiment of the present invention. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0021]    Hereinafter, the present invention will be described more fully with reference to the accompanying drawings, in which exemplary embodiments of the invention are shown. However, the embodiments described hereinafter are not intended to limit the scope of the present invention, and may be modified in other forms. The embodiments introduced here are provided to disclose the contents of the present invention more completely, and to sufficiently transfer the concept of the present invention to those of ordinary skill in the art. Therefore, figures of the components in the drawings and the like are exaggerated in order to emphasize a clear description. The same reference numbers represent the same components in the entire specification. 
         [0022]      FIG. 1  is a schematic cross-sectional view of an ion analyzing apparatus according to the embodiment of the present invention. Referring to  FIG. 1 , an ion analyzing apparatus  100  includes a main chamber  110 . The main chamber  110  includes on a sidewall a gas inlet  111  for supplying a purge gas, a gas outlet  113  for discharging the purge gas, and a door  115  through which a photomask  180  enters and exits from the main chamber  110 . The purge gas may include N 2  gas. The purge gas is provided through the gas inlet  111  in order to cause the main chamber  110  to have a nitrogen atmosphere during ion sampling. Once the ion sampling is completed, nitrogen is purged through the gas outlet  113 . 
         [0023]    Although not shown in any drawings, the ion analyzing apparatus  100  may further include a subchamber as a buffer through which the photomask  180  enters or exits from the main chamber  110 . 
         [0024]    The ion analyzing apparatus  100  may further include a gas supply unit  120  disposed outside of the main chamber  110 . The gas supply unit  120  supplies the purge gas to the gas inlet  111  through a gas channel  125  to raise the pressure in the main chamber  110  to a predetermined positive pressure. A solenoid valve  130  is disposed in the gas channel  125  such that gas supply from the gas supply unit  120  to the main chamber  110  may be controlled. Meanwhile, the gas outlet  113  may further include a gas channel (not shown) for gas discharge, and a solenoid valve (not shown) may further be disposed to control the gas discharge. 
         [0025]    A hot plate  150  is disposed within the main chamber  110 . The hot plate  150  may be disposed on a bottom portion of the main chamber  110 . Alternately, in order to prevent contamination of the ions to be sampled, the hot plate  150  may be supported by a stand  160  such that the hot plate  150  is placed at a predetermined distance from the bottom portion of the main chamber  110 . 
         [0026]    A heating container  140  is disposed on the hot plate  150 . The heating container  140  is composed of a quartz material. The heating container  140  may be covered by a lid member  145 . The lid member  145  may include a quartz material. A solvent such as deionized water  170  may be contained within the heating container  140 . A photomask  180  may be immersed in the deionized water  170  in the heating container to analyze the adsorbed ions. 
         [0027]    It is desirable that the photomask  180  be immersed in the deionized water  170  without overflowing the heating container  140 . For example, a predetermined amount of the deionized water  170  may be about 900-1100 ml. The deionized water  170  may be contained in the heating container  140  and heated through the hot plate  150  at a predetermined temperature, such as about 80-180° C. 
         [0028]    The ion analyzing apparatus  100  may further include a temperature controller  190  which controls the temperature of the hot plate  150 , in order to control the boiling point of the deionized water  170  within the heating container  140 . The temperature controller  190  may be disposed outside of the main chamber  110 , and may provide a control signal CS to control the temperature of the hot plate  150 . 
         [0029]      FIG. 2  is a perspective view illustrating a semiconductor testing apparatus according to an embodiment of the present invention. Referring to  FIG. 2 , a semiconductor testing apparatus  200  includes the ion analyzing apparatus  100  of  FIG. 1 , and may also include an apparatus to test semiconductor devices under a nitrogen atmosphere. 
         [0030]    The semiconductor testing apparatus  200  includes a chamber  210 , which corresponds to the main chamber  110  of  FIG. 1 . Inside the chamber  210 , as shown in  FIG. 1 , a heating container  140  may be disposed on the hot plate  150 , and the heating container  140  may be filled with deionized water  170  such that the photomask  180  for ion analysis can be immersed in the deionized water. 
         [0031]    In an upper part of another wall of the semiconductor testing apparatus  200 , a window  230  through which the inside of the chamber  210  can be seen with the naked eye is disposed. The window  230  may be fixed by a fixing member  240  made of metallic plate material. The fixing member  240  may be fastened by a fastening element  245  such as a screw. Gloves  235  may be arranged in a lower portion of the outer wall of the chamber below the window  230 . It is desirable that the gloves  235  be arranged corresponding to the heating container arranged inside the chamber  210 . 
         [0032]    Moreover, a gas channel  225 , which corresponds to the gas channel  125  of  FIG. 1 , may be installed on an outer wall of the chamber, and a valve  221 , which corresponds to the solenoid valve  130  of  FIG. 1 , may be installed in the gas channel  225 . In addition, a gauge  223  that can display the amount of gas supplied to the chamber  210  may be installed in the gas channel  225 . The gas channel  225  may be connected to the gas supply unit  120  as in  FIG. 1 . Furthermore, a gas outlet may be disposed in the chamber  210 . 
         [0033]    Additionally, a door  215 , which corresponds to the door  115  of  FIG. 1 , may be arranged in the outer wall below the gas channel  223  so that the photomask  180  can enter and exit from the chamber  210 . 
         [0034]      FIG. 3  is a flow diagram of a method of analyzing ions adsorbed on the surface of the photomask using the ion analyzing apparatus  100  of  FIG. 1 . 
         [0035]    First, the heating container  140  is disposed on the hot plate  150  within the main chamber  110  of the ion analyzing apparatus  100 . A predetermined amount of the solvent  170  is added to the heating container  140  (S 110 ). The solvent  170  may include deionized water. The solvent  170  is sufficiently filled in the heating container  140  such that the photomask  180  is completely immersed therein, while not letting the solvent  170  overflow from the heating container  140  during heating. For example, about 900-1100 ml of the solvent  170  is contained in the heating container  140 . 
         [0036]    The photomask  180  is transported through the door  115  of the main chamber  110 , and immersed in the heating container  140  filled with the solvent  170  (S 120 ). The heating container  140  is covered with the lid member  145  (S 130 ). The door  115  of the main chamber  110  is locked such that the inside of the main chamber  110  is isolated from external air. 
         [0037]    Sequentially, the purge gas is supplied from the gas supply unit  120  to the gas inlet  111  of the main chamber  110  through the gas channel  125 , thereby raising the pressure in the main chamber  110  to a predetermined level (S 140 ). The purge gas may include N 2  gas. Therefore, the inside of the main chamber  110  is maintained at a predetermined positive pressure. The internal pressure in the main chamber  110  may be maintained at about 1-10 atm. 
         [0038]    While the main chamber  110  is maintained at the predetermined positive pressure, the heating container  140  is heated using the hot plate  150  to keep the solvent  170  at a predetermined temperature for a predetermined time. The temperature  170  of the solvent may be maintained at about 80-180° C. for about 5-10 minutes. 
         [0039]    The solvent  170 . which may be deionized water, comes to a boil in the heating container  140  at about 100° C. when the internal pressure of the main chamber  110  is about 1 atm. As the pressure rises, the boiling point of the deionized water increases, and as the pressure drops, the boiling point decreases. 
         [0040]    When the internal pressure of the main chamber  110  is positively increased and the solvent  170  in which the photomask  180  for ion measurement is immersed is heated using the hot plate  150 , the boiling point of the solvent  170  increases with the internal pressure of the main chamber. There is a binding energy between a film photomask  180  and the ions adsorbed on the surface of the film. The binding energy is weakened as the temperature of the solvent  170  in which the photomask  180  is immersed rises, thereby allowing easy separation of the ions adsorbed on the surface of the photomask  180 . Therefore, when the internal pressure of the main chamber  110  is positively increased to sufficiently raise the temperature of the solvent  180  to the point that the bond between the film photomask  180  and the adsorbed ions is broken, the ions adsorbed on the surface of the photomask  180  are separated from the photomask  180  and dissolved in the solvent  170 . 
         [0041]    The purge gas within the main chamber  110  may be discharged through the gas outlet  113  to decrease the internal pressure of the main chamber  110  to the original state (S 160 ). The solvent  180  is collected and the ions adsorbed on the photomask  180  may be analyzed using ion chromatography (S 170 ). 
         [0042]    In some example embodiments of the present invention, the ions adsorbed on the surface of the photomask are completely separated from the photomask and dissolved in deionized water by sufficiently increasing the temperature of the solvent, thereby allowing an accurate analysis of the ions and a decrease in the variation of the analysis results. Example embodiments of the present invention provide an efficient determination of an accurate cleaning recipe. Moreover, by sufficiently separating the ions adsorbed on the surface of the photomask in a very short time, the ion analysis time can be shortened. 
         [0043]    While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it will be understood by those of ordinary skill in the art that various changes in form and details may be made therein without departing from the spirit and scope of the present invention as defined by the following claims.