Abstract:
A semiconductor element has an upper wiring layer and a lower wiring layer. These layers communicate with each other via a via-hole. The via-hole is filled with W. Before W is filled in the via-hole by a CVD process to connect the lower wiring layer to the upper wiring layer, a cleaning gas is supplied into the via-hole to remove particular substances, which would otherwise result in high resistance. Subsequent to the cleaning step, the W portion is formed in the via-hole. Since the high resistance substances are removed from the via-hole before the formation of the W portion, the semiconductor element (or the via-hole) has a low resistance and high reliability.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    1. Field of the Invention  
           [0002]    The present invention generally relates to a method of manufacturing semiconductor elements, and more particularly to a method of fabricating semiconductor elements having a multi-wiring-layer structure (multi-level interconnection structure), with a metal-filled low-resistance via-hole being formed in an interlayer dielectrics.  
           [0003]    2. Description of the Related Art  
           [0004]    A conventional method for fabricating semiconductor elements is disclosed in, for example, Japanese Patent Kokai (Laid-open Publication) No. 11-260823.  
           [0005]    [0005]FIG. 6 of the accompanying drawings illustrates a cross sectional view of a semiconductor element fabricated by such conventional method.  
           [0006]    In this figure, reference numeral  1  designates a Si substrate, reference numeral  2  designates an insulating film (thin layer), reference numeral  3  designates a first wiring layer, reference numeral  4  designates an interlayer dielectrics (insulating film), reference numeral  5  designates a via-hole, reference numeral  6  designates an adhesive layer, reference numeral  7  designates a W plug, and reference numeral  8  designates a second wiring layer.  
           [0007]    As understood from FIG. 6, the insulating layer  2 , the first wiring layer  3 , and the interlayer dielectrics  4  are formed on the Si substrate  1  in this order. The interlayer dielectrics  4  has the via-hole  5  formed by a photolithographic process and an etching process. The wall of the via-hole  5  is covered with the adhesive layer  6 , and the W plug  7  is formed in the via-hole  5 . After the via-hole  5  is filled with the W plug  7 , the second wiring layer  8  is formed.  
           [0008]    A process for forming the W plug  7  has two major steps. One step is a W nucleus (seed) forming step and another step is a W main portion forming step (i.e., W fill-in step).  
           [0009]    [0009]FIG. 7 of the accompanying drawings illustrates a flowchart of a process for forming the W plug with supplied gases.  
           [0010]    The first step is a nucleation step for forming a W nucleus for the W plug  7  (sub-steps S 1  and S 2 ). In this step, layers are formed using WF 6 , SiH 4 , and H 2 , which are the main raw materials.  
           [0011]    Specifically, in the first step, a wafer (Si substrate) is placed in a chamber (device for forming the W plug) and is then heated to a temperature suitable for the W plug formation. Subsequently, a raw material gas SiH 4  is fed to the chamber to form a Si layer on an adhesive layer, and then another raw material gas WF 6  is additionally fed to the chamber to form a thin W film on the Si layer. This thin W film is called a W nucleus or seed. The WF 6  gas and SiH 4  gas form the thin W film on the Si layer. It should be noted that the combination of the Si layer and thin W film may be referred to as “W nucleus.” 
           [0012]    The second step is a step for forming a main W portion (sub-step S 3 ). In this step, the supply of the SiH 4  gas is stopped, and the W plug  7  is formed using WF 6  and H 2  as the main raw materials.  
           [0013]    In this procedure, after W films are formed in and over the via-hole  5  by a CVD process, the surface is etched back to have only the W plug  7  remained in the via-hole  5 .  
           [0014]    When the via-hole  5  is provided on the first wiring layer  3 , undesired substances  9 , such as TiOx, which result in high resistance, often remain on the first wiring layer  3 . If these substances  9  remain in the via-hole  5  (or between the adhesive layer  6  and the W plug  7 ), the resulting semiconductor element (or the via-hole) has a high resistance.  
         SUMMARY OF THE INVENTION  
         [0015]    It is an object of the present invention to provide a method for manufacturing a semiconductor element that can eliminate high resistance substances from a via-hole so that the semiconductor element has a low resistance and high reliability.  
           [0016]    According to a first aspect of the present invention, there is provided an improved method for manufacturing a semiconductor element. The semiconductor element has a lower wiring layer and an upper wiring layer. The lower and upper wiring layers communicate with each other by a via-hole. A fluorine compound gas having a reducing function is supplied into the via-hole to clean the via-hole. After that, a W nuclei is formed in the via-hole, and a W main portion is formed in the via-hole by, for example, a CVD process.  
           [0017]    The fluorine compound gas has a cleaning function. The fluorine compound gas includes, for example, a WF 6  gas, a NF 3  gas, or a SiF 4  gas.  
           [0018]    According to a second aspect of the present invention, there is provided another improved method for manufacturing a semiconductor element. The semiconductor element has a lower wiring layer and an upper wiring layer. These layers communicate with each other by a via-hole. After the via-hole is formed, a fluorine compound gas having a reducing function and a cleaning function is supplied into the via-hole to clean the inside of the via-hole and to form a part of a W nucleus in the via-hole. Subsequently, the remainder of the W nucleus is formed. After the W nucleus is formed, a W main portion is formed in the via-hole by, for example, a CVD process. The fluorine compound gas includes, for example, a SiF 4  gas.  
           [0019]    According to a third aspect of the present invention, there is provided still another improved method for manufacturing a semiconductor element. The semiconductor element has a lower wiring layer and an upper wiring layer. These layers communicate with each other by a via-hole. After the via-hole is formed, a fluorine compound gas having a reducing function and a cleaning function is supplied into the via-hole to clean the inside Qf the via-hole and to form a part of a W nucleus. Subsequently, suitable gases, such as a SiH 4  gas and WF 6  gas, are supplied into the via-hole to form the remainder of the W nucleus. A W main portion is then formed by, for example, a CVD process.  
           [0020]    Since unnecessary substances are removed from the via-hole before the W nucleus is formed, the via-hole and the semiconductor element can have a low resistance and high reliability.  
           [0021]    Other objects, aspects and advantages of the present invention will become apparent to those skilled in the art from the following detailed description and the appended claims, taken in conjunction with the accompanying drawings. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0022]    [0022]FIG. 1 illustrates a cross sectional view of a semiconductor element fabricated according to an embodiment of the present invention;  
         [0023]    [0023]FIG. 2 is a flowchart showing a process for forming a W plug in a via-hole of the semiconductor element shown in FIG. 1 according to a first embodiment of the present invention;  
         [0024]    [0024]FIG. 3 is a flowchart showing a process for forming the W plug in the via-hole according to a second embodiment of the present invention;  
         [0025]    [0025]FIG. 4 illustrates a flowchart of a process for forming the W plug in the via-hole according to a third embodiment of the present invention;  
         [0026]    [0026]FIG. 5 illustrates a flowchart of a process for forming the W plug in the via-hole according to a fourth embodiment of the present invention;  
         [0027]    [0027]FIG. 6 is a cross sectional view of a conventional semiconductor element fabricated by a conventional method; and  
         [0028]    [0028]FIG. 7 illustrates a flowchart of a process for forming a W plug in a via-hole of the semiconductor element shown in FIG. 6. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0029]    Embodiments of the present invention will now be described in detail.  
         [0030]    A first embodiment of the present invention is described with reference to FIG. 1 and FIG. 2. FIG. 1 shows a cross sectional view of a semiconductor element of the first embodiment.  
         [0031]    As shown in FIG. 1, an insulating layer  12 , a first wiring layer  13 , and an interlayer dielectrics  14  are disposed on a Si substrate  11  in that order. The interlayer dielectrics  14  has a via-hole  15  formed by a photolithographic process and an etching process. The wall of via-hole  15  is covered with an adhesive layer  16 , and the via-hole  15  has a W plug  17  formed therein. The W plug  17  is created by vapor deposition. Reference numeral  18  represents a second wiring layer.  
         [0032]    The procedure of filling the via-hole  15  with the W plug  17  (i.e., process for forming the W plug  17 ) will be described with reference to FIG. 2.  
         [0033]    [0033]FIG. 2 is a flowchart of the process for forming the W plug with gases supplied into the via-hole  15 .  
         [0034]    After the via-hole  15  is formed, the inside (particularly the bottom) of the via-hole  15  is cleaned by a sputtering process using, for example, Ar gas. The adhesive layer  16  is then formed over the wall of the via-hole  15 . Subsequently, the inside (particularly the bottom) of the via-hole  15  is further cleaned by a pre-treatment (additional cleaning step). After the pre-treatment, the W plug  17  is formed by a CVD process to fill the via-hole  15 .  
         [0035]    In the first embodiment of the invention, as shown in FIG. 2, the WF 6  gas is used to perform the pre-treatment cleaning step (sub-step S 11 ) prior to the nucleation step (sub-steps S 12  and S 13 ). Subsequent to the pre-treatment (sub-step S 11 ), the nucleation step (sub-steps S 12  and S 13 ) is conducted using SiH 4  and WF 6 , and the W deposition step (Step S 14 ) is then conducted using H 2  and WF 6  in the same manner as the conventional method.  
         [0036]    Specifically, a wafer (Si substrate) is placed in a chamber (device for forming the W plug) and is then heated to a temperature suitable for the W plug formation. Subsequently, the gas SiH 4  is fed to the chamber to form a Si layer on the adhesive layer, and then another raw material gas WF 6  is additionally fed to the chamber to form the thin W film on the Si layer. After that, the gas SiH 4  is stopped, and the WF 6  gas and the H 2  gas are supplied to the chamber to deposit the W.  
         [0037]    Since the sub-step S 11  is employed, the first embodiment has the following advantages, when compared with the conventional method.  
         [0038]    As shown in FIG. 6, the substances  9  including TiOx, which result in high resistance, exist at the bottom of the via-hole  5  after the via-hole  5  is created. It is assumed that the substances  9  are formed on the first wiring layer  3  during the process of making the via-hole  5 . In the first embodiment of the present invention (FIG. 2), the Ar gas is supplied into the via-hole  5  to remove the substances  9  (sputtering process). However, the removal of the substances  9  by the Ar gas is often insufficient. Therefore, the WF 6  gas is introduced into the via-hole  15  in the first step (sub-step S 11 ) before formation of the W plug  17 . The substances  9  are therefore completely removed from the via-hole  15  by a cleaning effect of the WF 6  gas having a strong reducing function. Since the substances  9  do not exist inside the via-hole  15  (FIG. 1), the product (semiconductor element) has a low resistance.  
         [0039]    Next, a second embodiment of the present invention will now be described with reference to FIG. 1 and FIG. 3.  
         [0040]    A semiconductor element fabricated in accordance with the second embodiment is the same as the semiconductor element shown in FIG. 1. Thus, the structure of the semiconductor element will not be redundantly described here. The second embodiment is different from the first embodiment with respect to the process for forming the W plug  17  in the via-hole  15 . Therefore, the following description principally deals with the process for forming the W plug  17 .  
         [0041]    [0041]FIG. 3 is a flowchart showing the process for forming the W plug  17  with the gases supplied into a via-hole  15 .  
         [0042]    After the via-hole  15  is formed, the interior (particularly the bottom) of the via-hole  15  is cleaned by a sputtering process using, for example, Ar gas, and an adhesive layer  16  is then formed over the wall of the via-hole  15 . Subsequently, the interior (particularly the bottom) of the via-hole  15  is further cleaned by a pre-treatment step. A W portion  17  is then formed by a CVD process to fill the via-hole  15 . The pre-treatment step is performed using a NF 3  gas in this embodiment. The NF 3  gas has a strong reducing and cleaning function.  
         [0043]    As mentioned above, the NF 3  gas is fed to a W forming chamber (sub-step  21 ) prior to the CVD process. This pretreatment cleaning step completely removes the substances  9  from the via-hole  15 . Subsequent to the cleaning step, a nucleation step (sub-steps S 22  and S 23 ) and a W deposition step (sub-step S 24 ) are conducted in that order in the same manner as the conventional method (FIG. 6 and FIG. 7).  
         [0044]    Since the above procedure is employed, the following advantages can be obtained as compared with the conventional method (FIG. 6 and FIG. 7).  
         [0045]    According to a conventional method, the substances  9  such as TiOx, which create a high resistance, remain at the bottom of the via-hole. As a result, the semiconductor element has a high resistance at the via-hole. According to the second embodiment, however, the Ar gas is supplied into the via-hole  5  to remove the substances  9  before the adhesive layer is formed, and the NF 3  gas is fed into the via-hole  5  to completely clean the substances  9  (sub-step S 21 ) before the via-hole  15  is filled with the W portion  17 . Therefore, the substances  9  do not remain in the via-hole at the time of sub-steps S 22  and S 23 . The NF 3  gas has a cleaning effect with a strong reducing function. Thus, the product (semiconductor element) can have a low resistance.  
         [0046]    Next, a third embodiment of the present invention will be described with reference to FIG. 1 and FIG. 4. A semiconductor element fabricated in accordance with the third embodiment is the same as the semiconductor element shown in FIG. 1. Thus, the structure of the semiconductor element will not be described here. The third embodiment is different from the first and second embodiments with respect to the process for forming the W plug  17  in the via-hole  15 . Therefore, the following description principally deals with the process for forming the W plug  17 .  
         [0047]    [0047]FIG. 4 is a flowchart showing the process for forming the W plug  17  with the gases supplied into a via-hole.  
         [0048]    After the via-hole  15  is formed, the interior (particularly the bottom) of the via-hole  15  is cleaned by a sputtering process using, for example, Ar gas, and an adhesive layer  16  is then formed over the wall of the via-hole  15 . Subsequently, the interior (particularly the bottom) of the via-hole  15  is further cleaned by a pre-treatment step. A W portion  17  is then formed by a CVD process to fill the via-hole  15 . The pre-treatment step is performed using a SiF 4  gas in this embodiment.  
         [0049]    Before the CVD process is conducted, the SiF 4  gas is fed to the chamber in the first step (sub-step  31 ). Subsequently, a nucleation step (sub-steps S 32  and S 33 ) and a W deposition step (sub-step S 34 ) are conducted in that order in the same manner as the conventional method (FIG. 6 and FIG. 7).  
         [0050]    Since the above procedure is employed, the following advantages can be obtained as compared with the conventional method.  
         [0051]    The substances  9  (FIG. 6) such as TiOx which create a high resistance remain at the bottom of the via-hole immediately after the formation of the via-hole. The Ar gas is supplied into the via-hole  5  to remove the substances  9  prior to the formation of the adhesive layer. However, the removal of the substances  9  by the Ar gas is often insufficient. Therefore, before the via-hole  15  is filled with the W portion  17 , the SiF 4  gas is supplied into the via-hole  15  (sub-step S 31 ) so as to completely remove the substances  9  from the via-hole  15 . The SiF 4  gas has a strong reducing function. Thus, the resulting semiconductor element (FIG. 1) has a low resistance.  
         [0052]    Next, a fourth embodiment of the present invention will be described with reference to FIG. 1 and FIG. 5. A semiconductor element fabricated in accordance with the fourth embodiment is the same as the semiconductor element shown in FIG. 1. Thus, the structure of the semiconductor element will not be described here. The fourth embodiment is different from the foregoing embodiments with respect to the process for forming the W plug  17 . Therefore, the following description principally deals with the process for forming the W plug  17 .  
         [0053]    [0053]FIG. 5 is a flowchart showing the process for forming the W plug  17  with the gases supplied into a via-hole  15 .  
         [0054]    After the via-hole  15  is formed, the interior (particularly the bottom) of the via-hole  15  is cleaned by a sputtering process using, for example, Ar gas, and an adhesive layer  16  is formed over the wall of the via-hole  15 . Subsequently, the interior (particularly the bottom) of the via-hole  15  is further cleaned by a pre-treatment step. A W portion  17  is then formed by a CVD process to fill the via-hole  15 . The pre-treatment cleaning step is performed using a SiF 4  gas in this embodiment.  
         [0055]    Before the CVD process is conducted, the SiF 4  gas is fed to the chamber in the first step (sub-step  41 ) to conduct the pre-treatment cleaning. When the SiF 4  gas removes the unnecessary substances  9 , the SiF 4  gas also creates a Si layer. In other words, the pre-treatment and part of the nucleation step (i.e., formation of the Si layer) are carried out at the same time. After the pre-treatment and Si layer formation, the feeding of the SiF 4  gas is stopped, and the SiH 4  gas and the WF 6  gas are fed into the chamber to complete the nucleation step (sub-step S 42 ). The CVD step for filling the via-hole  15  with W (sub-step S 43 ) is then conducted.  
         [0056]    Since the fourth embodiment uses the above procedure, the following advantages can be obtained.  
         [0057]    The substances  9  (FIG. 6) such as TiOx which create a high resistance often remain at the bottom of the via-hole after the via-hole is created. The Ar gas is supplied into the via-hole  5  to remove the substances  9  prior to the formation of the adhesive layer. However, the removal of the substances  9  by the Ar gas is often insufficient. Therefore, before the via-hole is filled with the W portion, the SiF 4  gas is fed into the via-hole (sub-step S 41 ) to completely remove the substances  9  from the via-hole bottom. The SiF 4  gas has a strong reducing function. Thus, the resulting semiconductor element has a low resistance.  
         [0058]    Furthermore, in the fourth embodiment, the Si layer is formed in the via-hole by the SiF 4  gas while the inside of the via-hole is being cleaned by the SiF 4  gas. That is, the cleaning can be performed together with part of the nucleus forming process. Subsequently, the remainder of the nucleus forming process is done, and the W deposition step is conducted.  
         [0059]    It should be noted that the present invention is not limited to the illustrated and described embodiments. Various modifications and changes can be made within the scope of the present invention and such modifications are also included in the scope of the present invention.