Abstract:
The present invention concerns a method of forming a chalcogenide thin film for a phase-change memory. In the method of forming a chalcogenide thin film according to the present invention, a substrate with a pattern formed is loaded into a reactor, and a source gas is supplied onto the substrate. Here, the source gas includes at least one source gas selected from germanium (Ge) source gas, gallium (Ga) source gas, indium (In) source gas, selenium (Se) source gas, antimony (Sb) source gas, tellurium (Te) source gas, tin (Sn) source gas, silver (Ag) source gas, and sulfur (S) source gas. A first purge gas is supplied onto the substrate in order to purge the source gas supplied onto the substrate, a reaction gas for reducing the source gas is then supplied onto the substrate, and a second purge gas is supplied onto the substrate in order to purge the reaction gas supplied onto the substrate. At least one operation, namely changing the supply time of the first purge gas and/or adjusting the internal pressure of the reactor is performed in such a way as to ensure that the deposition rate at an inner portion of the pattern is greater than the deposition rate at an upper portion of the pattern. According to the present invention, it is possible to form a chalcogenide thin film having an excellent gap-fill property by changing the purge time of the source gas or adjusting the internal pressure of the reactor in such a way as to ensure that the film forming rate at the inner portion of the pattern is greater than the film forming rate at the upper portion of the pattern.

Description:
TECHNICAL FIELD 
     The present invention relates to a method of forming a thin film for use in a semiconductor device, and more particularly, to a method of forming a chalcogenide thin film. 
     BACKGROUND ART 
     With the remarkable development of information communication industry, needs for various memory devices are increasing. In particular, nonvolatile memory devices in which recorded data is not deleted even when power is cut off, are needed for portable terminals or MP3 players. A phase change random access memory (PRAM) device that uses a phase change phenomenon is being briskly researched as a nonvolatile memory device. Thus, a chalcogenide thin film in which a phase change phenomenon occurs, is being researched. Meanwhile, as semiconductor devices are highly integrated, a method of forming a chalcogenide thin film that has an excellent step coverage and an excellent gap-fill characteristic, in patterns having a large aspect ratio is required. 
     Conventional methods of forming a chalcogenide thin film may be performed by sputtering, chemical vapor deposition (CVD) or atomic layer deposition (ALD). When the chalcogenide thin film is formed by sputtering, a step coverage or gap-fill characteristic is deteriorated, and a small amount of carbon (C) or nitrogen (N) cannot be doped into the chalcogenide thin film. On the other hand, when the chalcogenide thin film is formed by CVD, the composition of patterns is not adjusted. In addition, when the chalcogenide thin film is formed by ALD, a deposition rate is reduced to about 0.3 Å/cycle and productivity is very low. 
     DETAILED DESCRIPTION OF INVENTION 
     Technical Problem 
     The present invention provides a method of forming a chalcogenide thin film that has an excellent gap-fill characteristic. 
     Technical Solution 
     According to an aspect of the present invention, there is provided a method of forming a chalcogenide thin film, the method including: loading a substrate in which a pattern is formed, into a reactor; supplying a source gas to the substrate; supplying a first purge gas to the substrate so as to purge the source gas supplied to the substrate; supplying a reaction gas that is used to reduce the source gas, to the substrate; supplying a second purge gas to the substrate so as to purge the reaction gas supplied to the substrate; and repeatedly performing a cycle comprising the supplying of the source gas through the supplying of the second purge gas, wherein the source gas is formed of one or more selected from the group including germanium (Ge)-based gas, gallium (Ga)-based gas, indium (In)-based gas, selenium (Se)-based gas, antimony (Sb)-based gas, tellurium (Te)-based gas, tartar (Sn)-based gas, silver (Ag)-based gas, and sulfur (S)-based gas, and wherein at least one of operations of varying time at which the first purge gas is supplied and adjusting pressure inside the reactor is performed so that a deposition rate of an inside of the pattern is greater than a deposition rate of an upper portion of the pattern. 
     Advantageous Effects 
     According to an exemplary embodiment, chalcogenide thin film having an excellent gap-fill characteristic may be formed. 
    
    
     
       DESCRIPTION OF DRAWINGS 
         FIG. 1  is a view schematically showing a thin film deposition apparatus performing a method of forming a chalcogenide thin film, according to an embodiment of the present invention; 
         FIG. 2  is a flowchart illustrating a method of forming a chalcogenide thin film according to an embodiment of the present invention; 
         FIG. 3  schematically illustrates the shape of a pattern formed in a semiconductor substrate; 
         FIGS. 4 through 6  schematically illustrate an order of supplying a Ge-based gas, a Sb-based gas, a Te-based gas, a reaction gas, and a purge gas in the method of forming a Ge—Sb—Te compound thin film illustrated in  FIG. 2 , according to embodiments of the present invention; 
         FIG. 7  schematically illustrates a deposition rate of the Ge—Sb—Te compound thin film according to a purge time of the source gas and pressure inside the reactor in the method of forming the Ge—Sb—Te compound thin film illustrated in  FIG. 2 , according to an embodiment of the present invention; 
         FIG. 8  is a scanning electron microscopy (SEM) photo of the pattern when the pattern is gap-filled at the purge time of the source gas under pressure inside the reactor which correspond to a section A of  FIG. 7 , according to an embodiment of the present invention; 
         FIG. 9  is a SEM photo of the pattern when the pattern is gap-filled at the purge time of the source gas under pressure inside the reactor which correspond to a section B of  FIG. 7 , according to an embodiment of the present invention; 
         FIG. 10  is a SEM photo of the pattern when the pattern is gap-filled at the purge time of the source gas under pressure inside the reactor which correspond to a section C of  FIG. 7 , according to an embodiment of the present invention; 
         FIG. 11  schematically illustrates the deposition rate of the Ge—Sb—Te compound thin film according to a purge time of the source gas and pressure inside the reactor when a bias voltage is applied to the reactor, according to an embodiment of the present invention; and 
         FIG. 12  schematically illustrates the deposition rate of the Ge—Sb—Te compound thin film according to a purge time of the source gas and pressure inside the reactor when the surface of the semiconductor substrate is processed by using gas containing fluorine (F), according to an embodiment of the present invention. 
     
    
    
     BEST MODE 
     The present invention will now be described more fully with reference to the accompanying drawings, in which exemplary embodiments of the invention are shown. The invention may, however, be embodied in many different forms and should not be construed as being limited to the embodiments set forth herein; rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the concept of the invention to those skilled in the art. In the drawings, the thicknesses of layers and regions are exaggerated for clarity. 
     First, a method of forming a chalcogenide thin film according to the present invention may be performed using a thin film deposition apparatus  100  illustrated in  FIG. 1  according to an embodiment of the present invention. 
       FIG. 1  is a view schematically showing a thin film deposition apparatus performing a method of forming a chalcogenide thin film, according to an embodiment of the present invention; 
     Referring to  FIG. 1 , the thin film deposition apparatus  100  according to the present embodiment includes a reactor  110  having an inside, a substrate support  120 , which is installed at the inside of the reactor  110  to ascend thereon and on which a semiconductor substrate W is disposed, and a shower head  130 , which sprays gas so that a thin film is formed on the semiconductor substrate W disposed on the substrate support  120 . 
     The thin film deposition apparatus  100  is used to deposit the chalcogenide thin film onto the semiconductor substrate W such as a silicon wafer, and further includes a gas supply unit  140  that supplies a source gas into the reactor  110  via a gas line. In this case, the source gas may be formed of one or more selected from the group including germanium (Ge)-based gas, gallium (Ga)-based gas, indium (In)-based gas, selenium (Se)-based gas, antimony (Sb)-based gas, tellurium (Te)-based gas, tartar (Sn)-based gas, silver (Ag)-based gas, and sulfur (S)-based gas. The chalcogenide thin film may be formed of one or more material selected from the group including a Ge—Sb—Te compound, GaSb, InSb, InSe, Sb 2 Te 3  GeTe, Ge 2 Sb 2 Te 5 , InSbTe, GaSeTe, Sn S b 2 Te 4 , InSbGe, AgInSbTe, (GeSn)SbTe, GeSb(SeTe), and Te 81 Ge 15 Sb 2 S 2 . When the chalcogenide thin film is a Ge—Sb—Te compound thin film, the gas supply unit  140  includes a unit for supplying the Ge-based material, the Sb-based gas, and the Te-based gas into the reactor  110 . The gas supply unit  140  includes a unit for supplying a reaction gas and an inert gas, which are used to reduce the source gas, into the reactor  110 . 
     The thin film deposition apparatus  100  may further include another equipment (not shown in  FIG. 1 ) so as to form the chalcogenide thin film by chemical vapor deposition (CVD) or atomic layer deposition (ALD). In particular, in order for ALD to be used, the gas supply unit  140  may further include a unit for alternately supplying the source gas, the reaction gas, and the inert gas into the reactor  110 . 
     The thin film deposition apparatus  100  further includes a plasma generator  150 . The plasma generator  150  generates remote plasma and supplies the generated remote plasma into the reactor  110 . Except for including of the plasma generator  150  for generating plasma, the thin film deposition apparatus  100  may include a unit (not shown) for applying radio frequency (RF) and/or direct current (DC) power to the shower head  130  and/or the substrate support  120  to generate direct plasma in the reactor  110 . 
       FIG. 2  is a flowchart illustrating a method of forming a chalcogenide thin film according to an embodiment of the present invention. 
     Referring to  FIG. 2 , in operation S 210 , the semiconductor substrate W in which a pattern  310  is formed, is loaded into the reactor  110 .  FIG. 3  schematically illustrates the shape of the pattern  310  formed in the semiconductor substrate W. Next, in operation S 220 , the source gas is supplied to the semiconductor substrate W. In this regard, the source gas may be formed of one or more selected from the group including germanium (Ge)-based gas, gallium (Ga)-based gas, indium (In)-based gas, selenium (Se)-based gas, antimony (Sb)-based gas, tellurium (Te)-based gas, tartar (Sn)-based gas, silver (Ag)-based gas, and sulfur (S)-based gas. The chalcogenide thin film may be formed of one or more material selected from the group including a Ge—Sb—Te compound, GaSb, InSb, InSe, Sb 2 Te 3  GeTe, Ge 2 Sb 2 Te 5 , InSbTe, GaSeTe, Sn S b 2 Te 4 , InSbGe, AgInSbTe, (GeSn)SbTe, GeSb(SeTe), and Te 81 Ge 15 Sb 2 S 2 . 
     Hereinafter, a method of forming a Ge—Sb—Te compound thin film, which is a representative material of a chalcogenide compound, will be described. When a chalcogenide thin film to be formed is a Ge—Sb—Te compound thin film, the source gas is formed of one or more selected from the group including the Ge-based gas, the Sb-based gas, and the Te-based gas. In this regard, a metalorganic precursor may be used to form the Ge-based gas, the Sb-based gas, and the Te-based gas. When the metalorganic precursor is used to form the Ge-based gas, the Sb-based gas and the Te-based gas, the Ge-based gas, the Sb-based gas, and the Te-based gas contain carbon (C) and nitrogen (N). Thus, even though additional C and N doping is not performed, a small amount of C and N is doped into the Ge—Sb—Te compound thin film. 
     The Ge-based gas may be one or more selected from the group including compounds, among metalorganic precursors, represented by the following Formulae 1 through 4 
     
       
                 
         
             
             
         
      
     
     wherein R 1  through R 5  are each C n H 2n+1  or N(C n H 2n+1 .C m H 2m+1 ), R 6  through R 11  are each any one of H, C n H 2n+1 , and N(C n H 2n+1 .C m H 2m+1 ), and n and m are natural numbers. 
     In the related art, a compound Ge(C 4 H 9 ) 4  or GeH(C 4 H 9 ) 3  is used to form the Ge-based gas. The Ge-based gas used in the present invention has a form in which a ligand is substituted by hydrogen atoms. Thus, the volume of the Ge-based gas is smaller than that of a Ge-based gas used in the related art. Thus, the number of the Ge-based gas that can be chemically and physically absorbed into the surface of the semiconductor substrate W per unit area increases. The volume of the Ge-based gas reduces, and it is easy to absorb the Ge-based gas into an inside  320  of the pattern  310  having a large aspect ratio compared to the Ge-based gas used in the related art. 
     In addition, the Ge-based gas used in the present invention as described above has a form in which a ligand is substituted by hydrogen atoms. Thus, the Ge-based gas used in the present invention has a weak coherence with the semiconductor substrate W compared to the Ge-based gas used in the related art. Thus, a desorption coefficient of the Ge-based gas used in the present invention increases compared to the Ge-based gas used in the related art. Thus, a relatively large amount of the Ge-based gas used in the present invention compared to the Ge-based gas used in the related art is purged by a first purge gas in a purge process S 230  that will be described later. In particular, an upper portion  330  of the pattern  310  is well purged compared to the inside  320  of the pattern  310 . Thus, the deposition rate of the upper portion  330  of the pattern  310  is rapidly reduced due to the purge gas. On the other hand, the deposition rate of the inside  320  of the pattern  310  is relatively slightly reduced. As a result, when the compounds represented by Formulae 1 through 4 are used to form the Ge-based gas, the Ge—Sb—Te compound thin film having an excellent gap-fill characteristic may be formed. 
     The Sb-based gas may be a compound, among metalorganic precursors, represented by the following Formula 5. 
     
       
                 
         
             
             
         
      
     
     wherein, R 12  through R 14  are each any one of H, C n H 2n+1  and N(C n H 2n+1 .C m H 2m+1 ) and n and m are natural numbers. 
     The Te-based gas may be a compound, among metalorganic precursors, represented by the following Formula 6.
 
R 15 —Te—R 16   (6)
 
     wherein R 15  and R 16  are each any one of H, C n H 2n+1  and N(C n H 2n+1 .C m H 2m+1 ) and n and m are natural numbers. 
     In operation S 230 , the first purge gas is supplied to the semiconductor substrate W so as to purge the source gas. In this regard, the first purge gas may be N 2 , argon (Ar), helium (He), and a combination thereof. 
     Next, in operation S 240 , the reaction gas that is used to reduce the source gas is supplied to the semiconductor substrate W. In this regard, the reaction gas may be a compound containing hydrogen (H) and may be a H 2  gas, for example. When the reaction gas is supplied to the semiconductor substrate W, plasma may be generated in the reactor  110 . To this end, the plasma generator  150  included in the thin film deposition apparatus  100  generates remote plasma to supply the remote plasma into the reactor  110 . Direct plasma may be generated in the reactor  110  by using a unit (not shown) for applying radio frequency (RF) and/or direct current (DC) power to the gas supply unit  130  and/or the substrate support  120 . 
     In operation S 250 , a second purge gas is supplied to the semiconductor substrate W so as to purge the supplied reaction gas. In this regard, the second purge gas may be N 2 , argon (Ar), helium (He), and a combination thereof, like in the first purge gas. 
     In operation S 260 , it is checked whether a chalcogenide thin film is formed to a desired thickness. If the chalcogenide thin film is not formed to the desired thickness, operations S 220  through S 250  are sequentially repeatedly performed. If operations S 220  through S 250  are repeatedly performed, operation S 220  of supplying the source gas to the semiconductor substrate W may be varied. For example, when the Ge—Sb—Te compound thin film is formed, if in first operation S 220 , the Ge-based gas has been supplied to the semiconductor substrate W, in next operation S 220 , the Sb-based gas may be supplied to the semiconductor substrate W, and in next operation S 220 , the Te-based gas may be supplied to the semiconductor substrate W. In this way, when the Ge—Sb—Te compound thin film is formed, an order of supplying the Ge-based gas, the Sb-based gas, and the Te-based gas is shown in  FIGS. 4 through 6  according to other embodiments of the present invention. 
       FIGS. 4 through 6  schematically illustrate an order of supplying the Ge-based gas, the Sb-based gas, the Te-based gas, the reaction gas, and the purge gas in the method of forming the Ge—Sb—Te compound thin film illustrated in  FIG. 2 , according to embodiments of the present invention.  FIGS. 4 through 6  illustrate embodiments of a purge gas in which the first purge gas and the second purge gas are the same. 
     Referring to  FIG. 4  as an embodiment, first, the source gas formed of the Ge-based gas is supplied to the semiconductor substrate W (S 220 ), and the purge gas is supplied to the semiconductor substrate W so as to purge the Ge-based gas (S 230 ), and the reaction gas that is used to reduce the Ge-based gas is supplied to the semiconductor substrate W (S 240 ), and last, the purge gas is supplied to the semiconductor substrate W so as to purge the reaction gas (S 250 ). This procedure corresponds to a cycle A. Next, the source gas formed of the Te-based gas is supplied to the semiconductor substrate W (S 220 ), and the purge gas is supplied to the semiconductor substrate W so as to purge the Te-based gas (S 230 ), and the reaction gas that is used to reduce the Te-based gas is supplied to the semiconductor substrate W (S 240 ), and last, the purge gas is supplied to the semiconductor substrate W so as to purge the reaction gas (S 250 ). This procedure corresponds to a cycle B. Next, the source gas formed of the Sb-based gas is supplied to the semiconductor substrate W (S 220 ), and the purge gas is supplied to the semiconductor substrate W so as to purge the Sb-based gas (S 230 ), and the reaction gas that is used to reduce the Sb-based gas is supplied to the semiconductor substrate W (S 240 ), and last, the purge gas is supplied to the semiconductor substrate W so as to purge the reaction gas (S 250 ). This procedure corresponds to a cycle C. When the reaction gas is supplied to the semiconductor substrate W in each of the cycles A, B, and C (S 240 ), plasma is generated in the reactor  110 . 
     The cycles A, B, and C constitute one super cycle, and the super cycle is performed until the chalcogenide thin film is formed to a desired thickness. In this way, the source gas formed of any one of the Ge-based gas, the Sb-based gas, and the Te-based gas is supplied to the semiconductor substrate W in one of the cycles A, B, and C so that the Ge—Sb—Te compound thin film can be formed. 
     Referring to  FIG. 5  as another embodiment, first, the source gas formed of a combination of the Ge-based gas and the Te-based gas is supplied to the semiconductor substrate W (S 220 ), and the purge gas is supplied to the semiconductor substrate W so as to purge the Ge-based gas and the Te-based gas (S 230 ), and the reaction gas that is used to reduce the Ge-based gas and the Te-based gas is supplied to the semiconductor substrate W (S 240 ), and last, the purge gas is supplied to the semiconductor substrate W so as to purge the reaction gas (S 250 ). This procedure corresponds to a cycle D. Next, the source gas formed of a combination of the Te-based gas and the Sb-based gas is supplied to the semiconductor substrate W (S 220 ), and the purge gas is supplied to the semiconductor substrate W so as to purge the Te-based gas and the Sb-based gas (S 230 ), and the reaction gas that is used to reduce the Te-based gas and the Sb-based gas is supplied to the semiconductor substrate W (S 240 ), and last, the purge gas is supplied to the semiconductor substrate W so as to purge the reaction gas (S 250 ). This procedure corresponds to a cycle E. Next, the source gas formed of a combination of the Ge-based gas and the Sb-based gas is supplied to the semiconductor substrate W (S 220 ), and the purge gas is supplied to the semiconductor substrate W so as to purge the Ge-based gas and the Sb-based gas (S 230 ), and the reaction gas that is used to reduce the Ge-based gas and the Sb-based gas is supplied to the semiconductor substrate W (S 240 ), and last, the purge gas is supplied to the semiconductor substrate W so as to purge the reaction gas (S 250 ). This procedure corresponds to a cycle F. When the reaction gas is supplied to the semiconductor substrate W in each of the cycles D, E, and F (S 240 ), plasma is generated in the reactor  110 . 
     The cycles D, E, and F constitute one super cycle, and the super cycle is performed until the chalcogenide thin film is formed to a desired thickness. In this way, the source gas formed of two of the Ge-based gas, the Sb-based gas, and the Te-based gas is supplied to the semiconductor substrate W in one of the cycles D, E, and F so that the Ge—Sb—Te compound thin film can be formed. 
     Referring to  FIG. 6  as another embodiment, first, the source gas formed of a combination of the Ge-based gas, the Te-based gas and the Sb-based gas is supplied to the semiconductor substrate W (S 220 ), and the purge gas is supplied to the semiconductor substrate W so as to purge the Ge-based gas, the Te-based gas and the Sb-based gas (S 230 ), and the reaction gas that is used to reduce the Ge-based gas, the Te-based gas and the Sb-based gas is supplied to the semiconductor substrate W (S 240 ), and last, the purge gas is supplied to the semiconductor substrate W so as to purge the reaction gas (S 250 ). This procedure corresponds to a cycle G. When the reaction gas is supplied to the semiconductor substrate W in the cycle G (S 240 ), plasma is generated in the reactor  110 . 
       FIG. 7  schematically illustrates a deposition rate of the Ge—Sb—Te compound thin film according to a purge time of the source gas and pressure inside the reactor  110 , in the method of forming the Ge—Sb—Te compound thin film illustrated in  FIG. 2 , according to an embodiment of the present invention. 
     Referring to  FIG. 7 , graph indicated by reference numeral  710  corresponds to the deposition rate of the Ge—Sb—Te compound thin film formed in the inside  320  of the pattern  310 . Graph indicated by reference numeral  720  corresponds to the deposition rate of the Ge—Sb—Te compound thin film formed in the upper portion  330  of the pattern  310 . In a section A of  FIG. 7 , the deposition rate of the Ge—Sb—Te compound thin film formed in the upper portion  330  of the pattern  310  is greater than that of the Ge—Sb—Te compound thin film formed in the inside  320  of the pattern  310 . In a section B of  FIG. 7 , the deposition rate of the Ge—Sb—Te compound thin film formed in the inside  320  of the pattern  310  is greater than that of the Ge—Sb—Te compound thin film formed in the upper portion  330  of the pattern  310 , and the deposition rate of the Ge—Sb—Te compound thin film formed in the inside  320  of the pattern  310  is greater than 0.5 Å/cycle. In a section C of  FIG. 7 , the deposition rate of the Ge—Sb—Te compound thin film formed in the inside  320  of the pattern  310  is smaller than 0.5 Å/cycle. 
     In order to gap-fill the pattern  310  so as not to form voids or seams in the pattern  310 , the deposition rate of the Ge—Sb—Te compound thin film formed in the inside  320  of the pattern  310  may be greater than that of the Ge—Sb—Te compound thin film formed in the upper portion  330  of the pattern  310 . If the deposition rate of the Ge—Sb—Te compound thin film is smaller than 0.5 Å/cycle, it is not more advantageous than a deposition rate at which ALD is performed. Thus, the deposition rate of the Ge—Sb—Te compound thin film formed in the inside  320  of the pattern  310  may be greater than 0.5 Å/cycle. Thus, in order to form the Ge—Sb—Te compound thin film having an excellent gap-fill characteristic, a purge time and pressure inside the reactor  110  which correspond to the section B of  FIG. 7  are required. In  FIG. 7 , in order to form the Ge—Sb—Te compound thin film, the Ge-based gas is GeH 3 (C 4 H 9 ), the Sb-based gas is Sb(C 3 H 7 ) 3  and the Te-based gas is Te(C 3 H 7 ) 2 . In this case, the first purge gas is supplied to the semiconductor substrate W for 1 to 3 seconds under pressure inside the reactor  110  in the range from 1 to 3 torr. When other materials are used as the Ge-based gas, the Sb-based gas and the Te-based gas, specific values of the purge time and pressure inside the reactor  110  may be varied. 
       FIG. 8  is a scanning electron microscopy (SEM) photo of the pattern  310  when the pattern  310  is gap-filled at the purge time of the source gas under pressure inside the reactor  110  which correspond to the section A of  FIG. 7 , according to an embodiment of the present invention.  FIG. 9  is a SEM photo of the pattern  310  when the pattern  310  is gap-filled at the purge time of the source gas under pressure inside the reactor  110  which correspond to the section B of  FIG. 7 , according to an embodiment of the present invention.  FIG. 10  is a SEM photo of the pattern  310  when the pattern  310  is gap-filled at the purge time of the source gas under pressure inside the reactor  110  which correspond to the section C of  FIG. 7 , according to an embodiment of the present invention. In this regard, the Ge-based gas is GeH 3 (C 4 H 9 ), the Sb-based gas is Sb(C 3 H 7 ) 3  and the Te-based gas is Te(C 3 H 7 ) 2 . in each of the above-stated three cases, the pattern  310  is gap-filled for the same amount of time. 
     When the pattern  310  is gap-filled on condition of the purge time and pressure inside the reactor  110  which correspond to the section A of  FIG. 7 , the deposition rate of the Ge—Sb—Te compound thin film formed in the upper portion  330  of the pattern  310  is greater than that of the Ge—Sb—Te compound thin film formed in the inside  320  of the pattern  310 , as described above. Thus, a Ge—Sb—Te compound thin film  810  in which voids  820  are formed in the inside  320  of the pattern  310  is deposited, as illustrated in  FIG. 8 . 
     When the pattern  310  is gap-filled on condition of the purge time and pressure inside the reactor  110  which correspond to the section B of  FIG. 7 , the deposition rate of the Ge—Sb—Te compound thin film formed in the inside  320  of the pattern  310  is greater than that of the Ge—Sb—Te compound thin film formed in the upper portion  330  of the pattern  310 , as described above. Thus, a Ge—Sb—Te compound thin film  910  is hardly formed in the upper portion  330  of the pattern  310 , and the Ge—Sb—Te compound thin film  910  is deposited from the bottom of the inside  320  of the pattern  310  so that voids or seams are not formed in the pattern  310 , as illustrated in  FIG. 9 . 
     When the pattern  310  is gap-filled on condition of the purge time and pressure inside the reactor  110  which correspond to the section C of  FIG. 7 , the deposition rate of the Ge—Sb—Te compound thin film formed in the inside  320  or the upper portion  330  of the pattern  310  is smaller than 0.5 Å/cycle, as described above. Thus, a Ge—Sb—Te compound thin film  1010  is hardly formed in the inside  320  or the upper portion  330  of the pattern  310 , as illustrated in  FIG. 10 . Thus, when the pattern  310  is gap-filled on condition of the purge time and pressure inside the reactor  110  which correspond to the section C of  FIG. 7 , a long process time is required and thus, productivity is lowered. 
     As such, as illustrated in  FIGS. 8 through 10 , when the Ge—Sb—Te compound thin film having an excellent gap-fill characteristic is formed to increase its deposition rate, the Ge—Sb—Te compound thin film may be formed on condition of the purge time and pressure inside the reactor  110  which correspond to the section B of  FIG. 7 . 
       FIG. 11  schematically illustrates the deposition rate of the Ge—Sb—Te compound thin film according to a purge time of the source gas and pressure inside the reactor  110  when a bias voltage is applied to the reactor  110 , according to an embodiment of the present invention. In this regard, the bias voltage may be applied to the reactor  110 . Alternatively, the bias voltage may be applied to the shower head  130  or may be applied to the reactor  110  after a grid (not shown) is disposed between the shower head  130  and the substrate support  120 . The bias voltage is applied to the reactor  110  so as to vary the characteristic of plasma. Thus, the bias voltage is applied to the reactor  110  in an operation of generating plasma in the reactor  110 , i.e., in operation S 240  of supplying the reaction gas. 
       FIG. 11  illustrates both the case where the bias voltage is not applied to the reactor  110  ( 710 ,  720 ) and the case where the bias voltage is applied to the reactor  110  ( 1110 ,  1120 ). Referring to  FIG. 11 , graphs indicated by reference numerals  710  and  1110  correspond to the deposition rate of the Ge—Sb—Te compound thin film formed in the inside  320  of the pattern  310 . Graphs indicated by reference numerals  720  and  1120  correspond to the deposition rate of the Ge—Sb—Te compound thin film formed in the upper portion  330  of the pattern  310 . In other words, if the bias voltage is applied to the reactor  110 , graph showing the deposition rate of the Ge—Sb—Te compound thin film formed in the inside  320  of the pattern  310  varies as arrow indicated by reference numeral  1115  ( 710 → 1110 ). Graph showing the deposition rate of the Ge—Sb—Te compound thin film formed in the upper portion  330  of the pattern  310  varies as arrow indicated by reference numeral  1125  ( 720 → 1120 ). 
     As such, if plasma is generated in the reactor  110  and the bias voltage is applied to the reactor  110  in operation S 240  of supplying the reaction gas, the deposition rate of the Ge—Sb—Te compound thin film formed in the inside  320  or the upper portion  330  of the pattern  310  increases, as illustrated in  FIG. 11 . However, the deposition rate of the Ge—Sb—Te compound thin film formed in the inside  320  of the pattern  310  increases more than three times compared to the Ge—Sb—Te compound thin film formed in the upper portion  330  of the pattern  310 . Thus, the deposition rate of the Ge—Sb—Te compound thin film formed in the inside  320  of the pattern  310  is greater than that of the Ge—Sb—Te compound thin film formed in the upper portion  330  of the pattern  310 , and a process window in which the deposition rate of the Ge—Sb—Te compound thin film corresponds to 0.5 Å/cycle, increases. In other words, as the deposition rate of the Ge—Sb—Te compound thin film increases, the range of condition of an allowable purge time and pressure inside the reactor  110  becomes wide. Thus, productivity is improved and a defective rate is reduced. 
       FIG. 12  schematically illustrates the deposition rate of the Ge—Sb—Te compound thin film according to a purge time of the source gas and pressure inside the reactor  110  when the surface of the semiconductor substrate W is processed by using gas containing fluorine (F), according to an embodiment of the present invention. Processing of the surface of the semiconductor substrate W by using the gas containing F is performed between operations S 210  and S 220 . The gas containing F may be NF 3 . 
       FIG. 12  illustrates both the case where processing of the surface of the semiconductor substrate W is not performed ( 710 ,  720 ) and the case where processing of the surface of the semiconductor substrate W is performed ( 1210 ,  1220 ). Referring to  FIG. 12 , graphs indicated by reference numerals  710  and  1210  correspond to the deposition rate of the Ge—Sb—Te compound thin film formed in the inside  320  of the pattern  310 . Graphs indicated by reference numerals  720  and  1220  correspond to the deposition rate of the Ge—Sb—Te compound thin film formed in the upper portion  330  of the pattern  310 . In other words, if processing of the surface of the semiconductor substrate W is performed, graph showing the deposition rate of the Ge—Sb—Te compound thin film formed in the inside  320  of the pattern  310  varies as arrow indicated by reference numeral  1215  ( 710 → 1210 ). Graph showing the deposition rate of the Ge—Sb—Te compound thin film formed in the upper portion  330  of the pattern  310  varies as arrow indicated by reference numeral  1225  ( 720 → 1220 ). 
     As such, if the surface of the semiconductor substrate W is processed by using the gas containing F between operations S 110  and S 220 , the deposition rate of the Ge—Sb—Te compound thin film formed in the inside  320  or the upper portion  330  of the pattern  310  is reduced, as illustrated in  FIG. 12 . However, the deposition rate of the Ge—Sb—Te compound thin film formed in the inside  320  of the pattern  310  is slightly reduced compared to the Ge—Sb—Te compound thin film formed in the upper portion  330  of the pattern  310 . On the other hand, the deposition rate of the Ge—Sb—Te compound thin film formed in the upper portion  330  of the pattern  310  is rapidly reduced compared to the Ge—Sb—Te compound thin film formed in the inside  320  of the pattern  310 . Thus, the deposition rate of the Ge—Sb—Te compound thin film formed in the inside  320  of the pattern  310  is greater than that of the Ge—Sb—Te compound thin film formed in the upper portion  330  of the pattern  310 , and a process window in which the deposition rate of the Ge—Sb—Te compound thin film corresponds to 0.5 Å/cycle, increases. In other words, the deposition rate of the Ge—Sb—Te compound thin film is the same, and the range of condition of an allowable purge time and pressure inside the reactor  110  becomes wide. Thus, productivity is improved and a defective rate is reduced. 
     When the Ge—Sb—Te compound thin film is formed according to the present invention, the temperature of the semiconductor substrate W may be set to 150° C. to 400° C., and pressure inside the reactor  110  may be maintained in the range from 0.5 to 10 torr. When the temperature of the semiconductor substrate W is lower than 150° C., reaction is not briskly performed, and the deposition rate of the Ge—Sb—Te compound thin film is so low, and a large amount of C and N is contained in the Ge—Sb—Te compound thin film so that the matter property of the Ge—Sb—Te compound thin film is deteriorated. When the temperature of the semiconductor substrate W is higher than 400° C., an increase in the deposition rate of the Ge—Sb—Te compound thin film causes deterioration of a step coverage, and the matter properties of other thin films formed before the Ge—Sb—Te compound thin film is formed may be deteriorated. 
     If pressure inside the reactor  110  is smaller than 0.5 torr, the deposition rate of the Ge—Sb—Te compound thin film is rapidly reduced, and if pressure inside the reactor  110  is greater than 10 torr, the deposition rate of the Ge—Sb—Te compound thin film increases and the step coverage may be deteriorated. 
     Meanwhile, time at which the first purge gas is supplied to the semiconductor substrate W may be set in the range from 0.1 to 5 seconds. If the time at which the first purge gas is supplied to the semiconductor substrate W is less than 0.1 second, a purging operation of the source gas is not sufficiently performed, and ALD is not smoothly performed. If the time at which the first purge gas is supplied to the semiconductor substrate W exceeds 5 seconds, a deposition process is delayed, and productivity is lowered, and desorption of a precursor absorbed into the surface of the semiconductor substrate W occurs, and the deposition rate of the Ge—Sb—Te compound thin film is reduced. 
     As described above, in the method of forming the chalcogenide thin film according to the present invention, time at which a source gas is purged and pressure inside a reactor are adjusted so that speed at which the chalcogenide thin film is formed inside patterns can be greater than speed at which the chalcogenide thin film is formed on the patterns. As such, the chalcogenide thin film having an excellent gap-fill characteristic can be formed. 
     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.