Abstract:
The method for forming a metal line stacking structure according to a preferred embodiment of the present invention comprises: sequentially forming a first barrier metal and a first metal layer on a lower dielectric layer that is disposed over a semiconductor substrate, and performing a plasma treatment; forming a second barrier metal on the plasma-treated first metal layer; selectively etching the second barrier metal, the first metal layer, and the first barrier metal to form a metal line layer including the second barrier metal, the first metal layer, and the first barrier metal, which respectively have a predetermined width; and sintering the metal line layer to raise a reaction between the first metal layer and the second barrier metal, thereby generating a metal compound layer.

Description:
CROSS-REFERENCE OF RELATED APPLICATIONS 
   This application is a continuation of U.S. patent application Ser. No. 10/418,791, filed on Apr. 18, 2003 now U.S Pat No. 7,141,880, which is incorporated herein by reference. 

   FIELD OF THE INVENTION 
   The present invention relates to a method for manufacturing a semiconductor device, and more particularly, to a method for forming a metal line stacking structure in a semiconductor device. 
   DESCRIPTION OF THE RELATED ART 
   As semiconductor devices have become more highly integrated and multi-layered, a multi-layer line technology has been introduced as an important manufacturing technology. In such multi-layer line technology, a metal line and a dielectric layer are alternately formed over a semiconductor substrate on which electric circuit elements are formed. The metal line, which are divided by the dielectric layer, are electrically connected together through a contact or via, so that an electric circuit operates. 
   By applying the multi-layer line technology to a semiconductor device, cross lining has been achieved, so that a freedom of degree and an integration degree in semiconductor device design has been improved, and furthermore, it is possible to decrease a length of a line so that an operation time delay in the line can also be decreased, thereby increasing operation speed of the semiconductor device. 
   A conventional method for forming a stacking structure of metal lines in a semiconductor device will be explained in detail with reference to the attached drawings.  FIGS. 1   a  to  1   f  show the conventional method for forming a metal line stacking structure in a semiconductor device. 
   As shown in  FIG. 1   a , a metal stacking structure is formed by sequentially stacking a barrier metal (Ti) layer (hereinafter referred to as a first Ti layer)  2 , a metal (Al) layer (hereinafter referred to as an Al layer)  3 , a titanium (Ti) layer (hereinafter referred to as a second Ti layer)  4 , and a titanium nitride (TiN) layer (hereinafter referred to as a TiN layer)  5  on a dielectric layer  1 , which is disposed over a semiconductor device substrate and is provided with a contact. 
   Next, as shown in  FIG. 1   b , the metal stacking structure is patterned according to a predetermined design and is sintered to form a desired metal line layer. Consequently, TiAl 3    6  is generated in some regions between the Al layer  3  and the first and second Ti layers  2  and  4 . In the figures, the relative size of the TiAl 3    6  has been exaggerated for convenience of explanation. 
   As shown in  FIG. 1   c , a dielectric layer  7  is then formed through a HDP (High Density Plasma) method or an SOG (Spin On Glass) method, so that a gap between the metal line layer is filled. Then, an inter-level dielectric layer  8  is deposited over the dielectric layer  7 , and is then leveled. 
   Next, as shown in  FIG. 1   d , a contact hole  9  is formed in the inter-level dielectric layer  8 . In order to decrease the resistance of the contact hole  9  and a resistance change of the contact hole  9  in a wafer, in an etching process to form the contact hole  9 , the TiN layer  5  and the Ti layer  4  are over-etched, and etching is terminated after reaching the Al layer  3 . 
   Next, as shown in  FIG. 1   e , a barrier metal layer, which is a stacking structure of a titanium (Ti) layer  10  and a titanium nitride (TiN) layer  11 , is formed on the inter-level dielectric layer  8  and on an inner wall of the contact hole  9  through an in-situ method. 
   Because the contact holes are now formed deeper and narrower as the integration degree of semiconductor devices has increased, it is preferable that the TiN layer  11  is formed through a CVD (Chemical Vapor Deposition) method in order to increase the bottom step coverage of the barrier metal. Then, as shown in  FIG. 1   f , a metal (for example, tungsten) layer (hereinafter referred to as a tungsten layer) is deposited in the contact hole  9  through a CVD (Chemical Vapor Deposition) method such that the contact hole  9  is filled with the tungsten. Then, the tungsten layer is polished and leveled through a chemical mechanical polishing (CMP) method until the inter-level dielectric layer  8  is exposed. Therefore, a contact is realized by forming a tungsten plug  12 , which is a portion of the tungsten layer, inside the contact hole  9 . 
   The metal line stacking structure in a semiconductor device can be obtained according to the above processes. The above processes are repeated in proportion to a number of metal layers that are needed for a specific semiconductor device. 
   However, the above conventional method for forming the metal line stacking structure in a semiconductor device has some problems, as follows. 
   The temperature of the substrate is increased to between 400 and 470 degrees Celsius in order to form the TiN layer  11  in the contact hole  9  through the chemical vapor deposition method. During the process of forming the TiN layer  11  on the high-temperature substrate, thermal energy of the substrate is transmitted to the metal layer, and thereby the metal layer upwardly extrudes through the bottom of the contact hole  9 . The extruded metal layer reacts with the Ti layer  10 , so that impurities are generated. 
   For example, if Al is used as the metal layer, TiAl 3  is generated, so that a loss of Ti occurs. Therefore, the thickness of a portion of the TiN layer  11  corresponding to this area is relatively thin when compared to other portions. 
   Such an up-extrusion of the metal layer also occurs in the process of forming the Ti layer  10  if the temperature of the substrate is 280 degrees Celsius or higher. 
   The thin TiN layer  11  of the barrier metal cannot act as a barrier for a source for forming the metal layer  12 . For example, when tungsten is used for the metal layer, the thin TiN layer  11  cannot act as a barrier for an F radical of WF 6 . Therefore, a TiAl x F y  composition, which causes high resistance of the contact hole, is disposed under the TiN layer  11 . Thus, the resistance of the contact hole increases, and this may degrade performance of a semiconductor device and cause the same not to operate. If the temperature of the substrate is decreased in order to solve the above problem, productivity lowers. For example, if the temperature of the substrate is decreased to 400 degrees Celsius from 450 degrees Celsius during the formation of the TiN layer of the barrier metal layer, throughput is decreased by more than 55%, so that efficiency of use of facilities and productivity are decreased. 
   SUMMARY OF THE INVENTION 
   The present invention has been made in an effort to solve the above problems. 
   It is a motivation of the present invention to provide a method for forming a stacking structure of metal lines in a semiconductor device, in which an up-extrusion of a metal layer of a metal line can be prevented, without lowering the temperature of a substrate during the formation of a barrier metal. 
   In a preferred embodiment of the present invention, the method for forming a metal line stacking structure in a semiconductor device comprises: sequentially forming a first barrier metal and a first metal layer on a lower dielectric layer that is disposed over a semiconductor substrate, and performing a plasma treatment; forming a second barrier metal on the plasma treated first metal layer; selectively etching the second barrier metal, the first metal layer, and the first barrier metal to form a metal line layer including the second barrier metal, the first metal layer, and the first barrier metal, which respectively have a predetermined width; and sintering the metal line layer to raise a reaction between the first metal layer and the second barrier metal, thereby generating a metal compound layer. 
   Preferably, the method for forming a metal line stacking structure further comprises: depositing an inter-level dielectric layer over all the metal line layer and the lower dielectric layer, after the step of sintering the metal line layer; selectively etching the inter-level dielectric layer to form a contact hole; and forming a third barrier metal on an inner wall of the contact hole, and forming a second metal on the third barrier metal to form a metal plug charging the contact hole. 
   It is preferable that when forming the contact hole, etching is terminated in the metal compound layer such that a bottom surface of the contact hole is positioned within the metal compound layer. 
   It is also preferable that the second barrier metal includes a titanium (Ti) layer and a titanium nitride (TiN) layer that are sequentially deposited over the first metal layer. 
   Preferably, a thickness of the titanium layer is between 100 and 300 angstroms, and wherein a thickness of the titanium nitride layer is between 200 and 600 angstroms. 
   It is further preferable that a thickness of the first metal layer is between 3000 and 8000 angstroms. 
   It is preferable that the first metal layer is made of a material selected from the group consisting of aluminum, an aluminum-copper (0.2 to 1.0% copper) alloy, an aluminum-copper-silicon (0.2 to 1.0% copper, and 0.5 to 2% silicon) alloy, and an aluminum-silicon (0.5 to 2.0% silicon) alloy. 
   It is preferable that the metal compound layer comprises TiAl 3  that is generated by a reaction between aluminum of the first metal layer and titanium of the second barrier metal. 
   It is further preferable that the metal compound layer is formed by a reaction of an upper portion of the first metal layer and the titanium layer, and it is formed on the first metal layer. 
   It is still further preferable that during the plasma treatment, power is supplied to the substrate at 50 to 500 W with a frequency of 1 to 999 MHz, and power is supplied to a chamber side wall at 50 to 500 W with a frequency of 1 to 999 KHz. 
   Preferably, the plasma treatment is performed using gas selected from the group consisting of argon (Ar), neon (Ne), krypton (Kr), xenon (Xe), and a mixture of hydrogen (H 2 ) and nitrogen (N 2 ), with a flow rate of 1 to 99 sccm, for 1 to 99 seconds. 
   It is preferable that the sintering is performed within a temperature range of 350 to 450 degrees Celsius. 
   Preferably, the sintering is performed for 20 to 60 minutes in a nitrogen-bearing atmosphere within an electric furnace. 
   It is preferable that the sintering is performed for 10 to 60 seconds using a rapid thermal process method. 
   It is further preferable that the method for forming a metal line stacking structure further comprises forming a lower dielectric layer charging a gap between the metal line layer through a high density plasma method or a spin on glass method before depositing the inter-level dielectric layer. 
   In another preferred embodiment of the present invention, the metal line stacking structure in a semiconductor device comprises: a metal line layer, a metal compound layer, an inter-level dielectric layer, a contact hole, and a metal plug. 
   The metal line layer is formed on a lower dielectric layer being disposed over the semiconductor device, and the metal line layer has a predetermined width and includes a first barrier metal, a first metal layer, and a second barrier metal that are sequentially stacked. 
   The metal compound layer is formed between the first metal layer and the second barrier metal. The inter-level dielectric layer is formed over all the lower dielectric layer and the metal line layer. The contact hole is formed in the inter-level dielectric layer, a bottom of which is located within the metal compound. The metal plug is charged into the contact hole. 
   It is preferable that the second barrier metal includes a titanium (Ti) layer and a titanium nitride (TiN) layer, wherein the TiN layer is formed on the Ti layer, and wherein a thickness of the Ti layer is between 100 and 300 angstroms, and a thickness of the TiN layer is between 200 and 600 angstroms. 
   It is also preferable that the first metal layer is formed of a material selected from the group of aluminum, an aluminum-copper (0.2 to 1.0% copper) alloy, an aluminum-copper-silicon (0.2 to 1.0% copper, and 0.5 to 2silicon) alloy, and an aluminum-silicon (0.5 to 2.0% silicon) alloy, and wherein a thickness of the first metal layer is between 3000 and 8000 angstroms. 
   Preferably, the metal compound layer comprises TiAl 3  that is generated by a reaction between aluminum of the first metal layer and titanium (Ti) of the Ti layer. 
   It is preferable that the metal line stacking structure further comprises a third barrier metal formed on an inner wall of the contact hole. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The accompanying drawings, which are incorporated in and constitute a part of the specification, illustrate an embodiment of the invention, and, together with the description, serve to explain the principles of the invention: 
       FIGS. 1   a  to  1   f  are schematic cross-sectional views showing a method for forming a stacking structure of metal lines in a semiconductor device according to a prior art; and 
       FIGS. 2   a  to  2   h  are schematic cross-sectional views showing a method for forming a stacking structure of metal lines in a semiconductor device according to a preferred embodiment of the present invention. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   Preferred embodiments of the present invention will now be described in detail with reference to the accompanying drawings.  FIGS. 2   a  to  2   h  show a method for forming a metal line stacking structure in a semiconductor device according to the preferred embodiment of the present invention. 
   First, as shown in  FIG. 2   a , a barrier metal  21  and a metal layer  22  are sequentially stacked on a dielectric layer  20 . The dielectric layer  20  may be disposed over a semiconductor substrate, and a contact or via is formed in the dielectric layer  20 . 
   Next, as shown in  FIG. 2   b , the metal layer  22  is plasma-treated and the size of the grain on the surface of the metal layer  22  is decreased. 
   Next, as shown in  FIG. 2   c , a titanium (Ti) layer (hereinafter referred to as a Ti layer)  23  and a titanium nitride (TiN) layer (hereinafter referred to as a TiN layer)  24  are stacked in order on the plasma-treated metal layer  22 . In this manner, a metal stacking structure including the barrier metal  21 , the plasma-treated metal layer  22 , the Ti layer  23 , and the TiN layer  24  is obtained. 
   This metal stacking structure can be applied to all multi-metal line layer structure except at a highest-positioned metal line layer. 
   If the above-stated metal stacking structure corresponds to a lowest-positioned metal line layer structure, the dielectric layer  20  is a pre metal dielectric (PMD) including a contact being filled with a metal plug. 
   In addition, if the above-stated metal stacking structure corresponds to a metal line layer structure other than the highest-positioned layer or the lowest-positioned layer, the dielectric layer is a inter-level dielectric layer (ILD) including a via being filled with a metal plug.) on a multi metal line layer that is patterned according to a predetermined design and sintered. 
   In the metal stacking structure, the surface of the plasma-treated metal layer  22  having the small grain size reacts with the Ti layer  23  and is changed to TiAl 3  during the following sinter process. TiAl 3  acts as a etch stop layer and is disposed under the contact hole to prevent an up-extrusion of the metal layer  22 . 
   It has been found through experimentation that in order to prevent oxidation of the metal layer  22 , the plasma treatment of the metal layer  22  must be performed in-situ in a chamber for forming the metal stacking structure without vacuum break. 
   During the plasma treatment, electrical power is applied to the substrate at 50 to 500 W with a frequency of 1 to 999 MHz, and electrical power is applied to the chamber side wall at 50 to 500 W with a frequency of 1 to 999 KHz. 
   Gas used in the plasma treatment can be an inert gas such as argon (Ar), neon (Ne), krypton (Kr), xenon (Xe), or the like, or a mixture of hydrogen H 2  and nitrogen N 2 . The plasma treatment is performed using such gas at a flow rate of 1 to 99 sccm for a time period of 1 to 99 seconds, and the size of the grain of the metal layer  22  is then decreased to such a value at which TiAl 3  having a desired thickness and a desired uniformity can be formed. 
   In view of a gap-filling efficiency, the metal stacking structure should not be too thick, and furthermore, because resistance of a metal line increases if TiAl 3  is formed, the metal stacking structure should not be too thin. 
   Therefore, it is preferable that a thickness of the barrier metal  21  is within a range of 100 to 900 angstroms. In particular, if the barrier metal  21  is formed of a Ti layer only, a thickness thereof is preferably between 100 and 300 angstroms, and if the barrier metal  21  is made of a Ti layer and a TiN layer, a thickness of the Ti layer is preferably between 100 to 300 angstroms and that of the TiN is between 100 to 600 angstroms. 
   The metal layer  22  is preferably formed of a general conducting metal such as aluminum, an aluminum alloy, and copper, and a thickness thereof is preferably between 3000 to 8000 angstroms. A thickness of the Ti layer  23  is preferably between 100 to 300 angstroms, and that of the TiN layer  24  is preferably between 200 to 600 angstroms. 
   The aluminum alloy for use in the metal layer  22  can be an aluminum-copper alloy (preferably 0.2 to 1.0% copper), an aluminum-copper-silicon alloy (preferably 0.2 to 1.0% copper, and 0.5 to 2.0% silicon), or an aluminum-silicon alloy (preferably, 0.5 to 2.0% silicon). 
   As shown in  FIG. 2   d , in order to form a metal line layer, the metal stacking structure is patterned according to a predetermined design and is then sintered. 
   The sintering process is performed at 350 to 450 degrees Celsius, and it is preferable that the sintering process is performed for 20 to 60 minutes in a nitrogen-bearing atmosphere in an electric furnace, or it is performed for 10 to 60 seconds through a rapid thermal process (RTP) method. 
   During the sintering process at 350 to 450 degrees Celsius, TiAl 3  is formed as a result of a reaction of Ti and Al. Therefore, if the barrier metal  21  is formed of titanium (Ti) and the metal layer  22  is formed of aluminum (Al), TiAl 3    25  is formed in interface between the barrier metal  21  and the metal layer  22 . In  FIG. 2   d , for convenience of explanation of the invention, the relative size of the TiAl 3    25  is exaggerated. 
   Furthermore, because a grain size of the surface of the plasma-treated metal layer  22  has been decreased, an upper portion of the metal layer (in the case of an aluminum metal layer)  22  much more easily reacts with the Ti layer  23  than a lower portion thereof, so that a uniform and thick TiAl 3  layer  25 ′ is formed as a result of the reaction. 
   As shown in  FIG. 2   e , a dielectric layer is then formed over all the metal stacking structure and the semiconductor substrate. 
   Initially, a lower dielectric layer  26  that charges the gap in the spacing between the metal line layers is formed through a HDP (High Density Plasma) method or an SOG (Spin On Glass) method. Then an inter-level dielectric layer  27  is formed over the lower dielectric layer  26  such that it can cover a topology effect (irregular surface) of the lower dielectric layer  26 . The inter-level dielectric layer  27  is then under planarization through a chemical mechanical polishing process or through an etch back process. 
   As shown in  FIG. 2   f , a contact hole  28  is then formed by etching the inter-level dielectric layer  27 , the lower dielectric layer  26 , the TiN layer  24 , and a predetermined depth of the TiAl 3  layer  25 ′, with a predetermined width. 
   At this time, in order to decrease resistance of the contact hole  28  and to decrease a change of a resistance of the contact hole in a wafer, the TiN layer  24  is over-etched, and etching is terminated in the TiAl 3  layer  25 ′. Further, more than 50 angstroms of the TiAl 3  layer  25 ′ under the contact hole  18  is preferably left not etched, and the remaining portion of the TiAl 3  layer  25  prevents the metal layer  22  from upwardly extruding. 
   As shown in  FIG. 2   g , a barrier metal having a stacking layer structure of a titanium (Ti) layer (hereinafter referred to as a Ti layer)  29  and a titanium nitride (TiN) layer (hereinafter referred to as a TiN layer)  30  is formed on the inter-level dielectric layer  27  and an inner wall of the contact hole  28  through an in-situ method. 
   Because the contact holes are now formed deeper and narrower as the integration degree of semiconductor devices has increased, it is preferable that the TiN layer  30  is formed through a CVD (Chemical Vapor Deposition) method in order to increase the bottom step coverage of the barrier metal. 
   That is, the Ti layer  29  is formed through a physical vapor deposition (PVD) method, and the TiN layer  30  is formed through the CVD method. During the formation of the Ti layer  29  through the PVD method, the temperature of the substrate is regulated to 100 to 300 degrees Celsius, and during the formation of the TiN layer  30  through the CVD method, the temperature of the substrate is regulated to be 400 to 450 degrees Celsius. 
   Since the TiAl 3  layer  25 ′, which is formed by the reaction of the plasma-treated metal layer  22  and the Ti layer  23 , prevents the up-extrusion of the metal layer  22 , the TiN layer  30  having a predetermined thickness is deposited on a inner wall of the contact hole  28 . 
   As shown in  FIG. 2   h , a metal layer acting as a metal plug  31 , which is formed of tungsten (W), Al, copper (Cu), a tungsten-silicon (W—Si) alloy, or an aluminum (Al) alloy, is formed on the TiN layer  30  through a Chemical Vapor Deposition (CVD) method such that an inside of the contact hole  28  is fully charged. 
   The deposited metal layer and the barrier metal (the Ti layer  29  and the TiN layer  30 ) are then under planarization through a chemical mechanical polishing (CMP) process until the inter-level dielectric layer  27  is exposed. Consequently, the metal layer is left remaining as a form of a metal plug  31 . 
   Because the TiN layer  30  particularly on the bottom of the contact hole to has a sufficient thickness for functioning as a barrier, impurities generated by a reaction of source material for the formation of the metal plug  31  and material of the metal layer  22  can be prevented so that a cause of an increase of the resistance of the contact hole can be removed. 
   For example, if the metal plug  31  is made of tungsten (W) and the metal layer  22  is made of aluminum (Al), a reaction between F of WF 6  that is used for the deposition of tungsten and aluminum can be prevented. 
   As another planarization method, an etch back process for the metal layer can be performed. 
   The metal line stacking structure in a semiconductor device is formed according to the above-stated method, and these processes are repeatedly performed according to a number of metal layers that are needed in a specific semiconductor device. 
   As stated above, in the method according to the preferred embodiment of the present invention, the uniform and thick TiAl 3  layer is formed during the sintering process due to the plasma treatment of the metal layer and the sintering process, and etching is finished in the TiAl 3  layer so that a predetermined thickness of the TiAl 3  remains under the contact hole. Therefore, the metal layer can be prevented from upwardly extruding while forming the barrier metal in the contact hole. 
   Furthermore, impurities generated by a reaction between the source material for the formation of the metal plug and the metal layer can be prevented. For example, TiAl x F y  generated by a reaction of WF 6  that is used for forming a tungsten plug and Al can be prevented. 
   Still furthermore, a formation of the contact hole void by outgassing during the formation of the metal plug can be prevented so that performance degradation of a semiconductor device can be prevented. 
   Although preferred embodiments of the present invention have been described in detail hereinabove, it should be clearly understood that many variations and/or modifications of the basic inventive concepts herein taught which may appear to those skilled in the present art will still fall within the spirit and scope of the present invention, as defined in the appended claims.