Patent Publication Number: US-2002011669-A1

Title: Semiconductor device

Description:
BACKGROUND OF THE INVENTION  
       [0001] 1. Field of the Invention  
       [0002] The present invention relates to semiconductor devices and, more particularly to a semiconductor device having a bonding pad electrode.  
       [0003] 2. Description of the Background Art  
       [0004] Recently, as the integration degree of the semiconductor devices increases and the devices are provided with multiple functions, the interconnections thereof are increasingly fine patterned and formed with multiple layers. Thus, a multilayer interconnection technique is important. Such multilayer interconnection is connected to a bonding pad electrode, which is electrically connected to a lead pin by a bonding wire.  
       [0005]FIG. 8 is a cross sectional view showing a structure of a conventional bonding pad electrode. Referring to FIG. 8, an interlayer insulating film  102  is formed on a silicon substrate  101 . An interlayer insulating film  104  is formed on interlayer insulating film  102 . A large number of interconnection layers (not shown) are formed in interlayer insulating films  102  and  104 . A bonding pad electrode  106  which is electrically connected to these interconnection layers is formed on interlayer insulating film  104 . An interlayer insulating film  107  is formed on interlayer insulating film  104  to cover bonding pad electrode  106 . A via hole  105  is formed in interlayer insulating film  107  which exposes a part of a surface of bonding pad electrode  106 .  
       [0006] Recently, fine patterning is also required for such bonding pad electrode. Thus, a width and thickness of bonding pad electrode  106  as shown in FIG. 8 are increasingly reduced.  
       [0007]FIG. 9 is a cross sectional view showing a bonding pad electrode shown in conjunction with a problem associated with the conventional bonding pad electrode. As shown in FIG. 9, in a conventional semiconductor device, a test called a wafer test is performed before dicing the wafer. A probe needle  112  generally including tungsten is brought into contact with a bonding pad electrode  106  for an electrical test. As a thin oxide film (Al 2 O 3 ) is formed on a surface of bonding pad electrode  106 , a certain degree of load must be applied to probe needle  112  against bonding pad electrode  106  to break the oxide film, so that electrical conduction between bonding pad electrode  106  and probe needle  112  is ensured. At the time, no particular problem arises when a thickness of bonding pad electrode  106  is equal to or larger than 8000 Å. However, when the thickness of bonding pad electrode  106  is smaller than 8000 Å, an external force applied by probe needle  112  concentrates stress at one portion of interlayer insulating film  104  under bonding pad electrode  106 . Thus, a crack  111  appears in interlayer insulating film  104 .  
       [0008]FIG. 10 is a cross sectional view showing a bonding pad electrode shown in conjunction with a problem associated with connection of a bonding wire to the bonding pad electrode shown in FIG. 9. Referring to FIG. 10, if a bonding wire  114  is connected to the bonding pad electrode on interlayer insulating film  104  in which the crack is formed as shown in FIG. 9, a cracked portion  113  is formed in bonding pad electrode  116  from crack  111  when connecting bonding wire  114 . Cracked portion  113  causes a problem of unstable electrical connection. Further, moisture entering from cracked portion  113  disadvantageously reduces resistance to moisture of the semiconductor device.  
       [0009] Conventionally, a semiconductor device in which a bonding pad electrode and an interconnection layer positioned thereunder are in direct contact with each other has also been known. FIGS.  11  to  13  are cross sectional views showing a semiconductor device described in Japanese Patent Laying-Open No. 5-243320. Referring to FIG. 11, in the semiconductor device as a conventional example, a lower aluminum interconnection  206  is formed on an interlayer insulating film  205 . A lower via hole  211  leading to lower aluminum interconnection  206  is formed in interlayer insulating film  205 . A tungsten sidewall  212  is formed on a sidewall of lower via hole  211 . An upper aluminum interconnection  208  is formed as a bonding pad electrode in contact with tungsten sidewall  212  and lower aluminum interconnection  206 . An upper via hole  213  leading to upper aluminum interconnection  208  is formed in interlayer insulating film  205 . A tungsten sidewall  214  is formed in contact with a sidewall of upper via hole  213  and upper aluminum interconnection  208 .  
       [0010] Referring to FIG. 12, as another conventional example, a first aluminum interconnection  221  is formed in contact with an interlayer insulating film  220 . A lower via hole  203  leading to first aluminum interconnection  221  is formed in an interlayer insulating film  220 . A tungsten sidewall  224  is formed in contact with a sidewall of lower via hole  203  and first aluminum interconnection  221 . A second aluminum interconnection  222  is formed in contact with tungsten sidewall  224  and first aluminum interconnection  221 . An upper via hole  204  leading to second aluminum interconnection  222  is formed in interlayer insulating film  220 . A diameter of lower via hole  203  is larger than that of upper via hole  204 . A tungsten sidewall  225  is formed in contact with a sidewall of upper via hole  204  and second aluminum interconnection  222 . A third aluminum interconnection  223  is formed as a bonding pad electrode in contact with tungsten sidewall  225  and second aluminum interconnection  222 .  
       [0011] Referring to FIG. 13, in still another embodiment of a semiconductor device, a diameter of lower via hole  203  is smaller than that of upper via hole  204 . In this respect, it is different from the semiconductor device shown in FIG. 12 in which the diameter of lower via hole  203  is larger than upper via hole  204 . Other parts of the structure are similar to those of the semiconductor device shown in FIG. 12.  
       [0012] As the bonding pad electrode and the interconnection layer thereunder are directly in contact with each other as shown in FIGS.  11  to  13 , the crack in the interlayer insulating film and the breakage of the bonding pad electrode as shown in FIGS. 9 and 10 can be prevented to a certain extent.  
       [0013] However, the semiconductor devices shown in FIGS.  11  to  13  still suffer from various problems. In the semiconductor device shown in FIG. 12, for example, as strengths of first to third aluminum interconnections  221  to  223  are relatively low, if an external force is applied to third aluminum interconnection  223  by a probe needle in a direction indicated by an arrow  301 , the external force concentrates stress at a portion  220   a  of interlayer insulating film  220  directly below third aluminum interconnection  223 . Thus, a crack is formed at portion  220   a  of interlayer insulating film  220 , whereby first to third aluminum interconnections  221  to  223  thereabove may be cracked.  
       [0014] Further, when the external force is applied to third aluminum interconnection  223  by the probe needle in a direction indicated by an arrow  302 , a crack is formed at a portion  220   b  of interlayer insulating film  220  directly below third aluminum interconnection  223 . The crack would also result in the problem described in conjunction with FIGS. 9 and 10.  
       [0015] In addition, when the probe needle is brought into contact with third aluminum interconnection  223  and then separated therefrom, third aluminum interconnection  223  may come off from second aluminum interconnection  222  as the probe needle and third aluminum interconnection  223  are in a tight contact. Thus, third aluminum interconnection  223  may come off from second aluminum interconnection  222  at an interface  222   a,  thereby disadvantageously causing a loose connection.  
       SUMMARY OF THE INVENTION  
       [0016] The present invention is made to solve the aforementioned problems. An object of the present invention is to provide a semiconductor device with high reliability capable of preventing cracking in a layer below an interconnection layer.  
       [0017] Another object of the present invention is to provide a semiconductor device with high reliability capable of preventing separation of conductive layers which are in contact with each other.  
       [0018] A semiconductor device according to one aspect of the present invention includes an interconnection layer, an intermediate layer and a bonding pad electrode layer. The interconnection layer is formed on a semiconductor substrate. The intermediate layer is formed in contact with the interconnection layer and includes at least one material selected from a group of titanium, molybdenum, tungsten, titanium silicide, molybdenum silicide, tungsten silicide, titanium nitride, molybdenum nitride and tungsten nitride. The bonding pad electrode layer is in contact with the intermediate layer.  
       [0019] In the semiconductor device having the above described structure, a strength of the intermediate layer is high as it includes at least one material selected from a group of titanium, molybdenum, tungsten, titanium silicide, molybdenum silicide, tungsten silicide, titanium nitride, molybdenum nitride and tungsten nitride. Thus, even when a significant force is applied to a portion of the bonding pad electrode layer by a probe needle, the force is dispersed in the intermediate layer. As the force is dispersed generally to the interconnection layer below the intermediate layer, cracking of the layer below the interconnection layer is prevented. As a result, the semiconductor device with high reliability is provided.  
       [0020] Further, as titanium, molybdenum, tungsten, titanium silicide, molybdenum silicide, tungsten silicide, titanium nitride, molybdenum nitride and tungsten nitride included in the intermediate layer form tight connections with other materials, the interconnection layer and bonding pad electrode layer which are both in contact with the intermediate layer are more tightly connected. Thus, separation of the interconnection layer and intermediate layer or the bonding pad electrode layer and intermediate layer are prevented. As a result, the semiconductor device with high reliability is provided.  
       [0021] More preferably, the semiconductor device further includes a first insulating layer. The first insulating layer is provided with a first hole which exposes a part of a surface of the interconnection layer and formed to cover the interconnection layer. The bonding pad electrode layer is formed in the first hole to be connected to the surface of the interconnection layer with the intermediate layer interposed.  
       [0022] More preferably, a diameter of the first hole is at least 50 μm and at most 120 μm. A depth of the first hole is not larger than 1 μm.  
       [0023] More preferably, the semiconductor device further includes a second insulating layer covering the bonding pad electrode layer. A second hole leading to the bonding pad electrode layer is formed in the second insulating layer. In this case, a bonding wire can be provided in the second hole leading to the bonding pad electrode layer.  
       [0024] More preferably, the bonding pad electrode layer and intermediate layer are in contact with each other directly below the hole, and the intermediate layer and interconnection layer are also in contact with each other. In this case, even when a significant force is applied to the bonding pad electrode layer, it is dispersed generally to the interconnection layer which is positioned therebelow, so that cracking of the layer below the interconnection layer is efficiently prevented.  
       [0025] More preferably, the intermediate layer includes first and second intermediate layers. The first intermediate layer is in contact with the interconnection layer. The second intermediate layer is in contact with the bonding pad electrode layer and has a composition which is different from that of the first intermediate layer. In this case, for example, if layers which are high particularly in mechanical strength and in adhesion are respectively used for the first and second intermediate layers, the intermediate layer is provided with two different characteristics. As a result, a structure with high reliability can be provided.  
       [0026] More preferably, the first and second intermediate layers include titanium (Ti) and titanium nitride (TiN), respectively.  
       [0027] More preferably, the interconnection layer and a bonding pad electrode layer are formed of layers including aluminum. A high adhesion is obtained between aluminum and the intermediate layer in the interconnection layer and bonding pad electrode layer, separation of the interconnection and intermediate layers as well as the bonding pad electrode layer and the intermediate layer are prevented. Further, the intermediate layer serves to prevent diffusion of aluminum.  
       [0028] A semiconductor device according to another aspect of the present invention includes an interconnection layer, intermediate layer and bonding pad electrode layer. The interconnection layer includes a conductive material formed on a semiconductor substrate. The intermediate layer is formed in contact with the interconnection layer and includes at least one material selected from a group of titanium, molybdenum, tungsten, titanium silicide, molybdenum silicide, tungsten silicide, titanium nitride, molybdenum nitride and tungsten nitride. The bonding pad electrode layer is formed in contact with the intermediate layer and includes the conductive material which is the same as that of the interconnection layer.  
       [0029] In the semiconductor device having the above described structure, a strength of the intermediate layer is high as it includes at least one material selected from a group of titanium, molybdenum, tungsten, titanium silicide, molybdenum silicide, tungsten silicide, titanium nitride, molybdenum nitride and tungsten nitride. Thus, even when a significant force is applied to a portion of the bonding pad electrode layer by a probe needle, the force is dispersed in the intermediate layer. Thus, the force is dispersed generally to the interconnection layer formed below the intermediate layer, so that cracking in a layer formed below the interconnection layer is prevented. As a result, the semiconductor device with high reliability is obtained.  
       [0030] In addition, as titanium, molybdenum, tungsten, titanium silicide, molybdenum silicide, tungsten silicide, titanium nitride, molybdenum nitride and tungsten nitride included in the intermediate layer are high in adhesion with other materials, separation of the interconnection intermediate layers as well as that of the intermediate and bonding pad electrode layers are prevented. Thus, the layers are provided with enhanced adhesion and the semiconductor device with high reliability can be provided.  
       [0031] More preferably, the conductive material includes aluminum. As adhesion between aluminum in the conductive material and the intermediate layer is high, adhesion between the interconnection intermediate layers as well as that between the intermediate and bonding pad electrode layers are increased. As a result, separation of the interconnection and intermediate layers as well as that of the intermediate and bonding pad electrode layers are prevented, and the semiconductor device with high reliability can be provided.  
       [0032] A semiconductor device according to still another aspect of the present invention includes an interconnection layer, a first insulating layer, an intermediate layer, a sidewall conductive layer and a bonding pad electrode layer. The interconnection layer is formed on a semiconductor substrate. The first insulating layer covers the interconnection layer and includes a first hole. The first hole allows a portion of a surface of the interconnection layer to be exposed. The first hole also has a sidewall. The intermediate layer covers a surface of the first insulating layer, a sidewall of the first hole and the exposed portion of the surface of the interconnection layer, and includes at least one material selected from a group of titanium, molybdenum, tungsten, titanium silicide, molybdenum silicide, tungsten silicide, titanium nitride, molybdenum nitride and tungsten nitride. A sidewall conductive layer is formed on the sidewall of the first hole with the intermediate layer interposed. The bonding pad electrode layer is formed in the first hole to be connected to the surface of the interconnection layer with the intermediate layer interposed.  
       [0033] In the semiconductor device having the above described structure, a strength of the intermediate layer is increased as it includes at least one material selected from a group of titanium, molybdenum, tungsten, titanium silicide, molybdenum silicide, tungsten silicide, titanium nitride, molybdenum nitride and tungsten nitride. Thus, a significant force is applied to a portion of the bonding pad electrode layer by a probe needle, which force is transmitted to the intermediate layer through the first hole provided in the first insulating layer. Thus, the force is dispersed generally to the interconnection layer formed below the intermediate layer, so that cracking in a layer formed below the interconnection layer is prevented. As a result, the semiconductor device with high reliability can be provided.  
       [0034] As titanium, molybdenum, tungsten, titanium silicide, molybdenum silicide, tungsten silicide, titanium nitride, molybdenum nitride and tungsten nitride in the intermediate layer have high adhesion with other materials, adhesion between the interconnection and intermediate layers as well as that between the intermediate and bonding pad electrode layers are increased. As a result, separation of the interconnection and intermediate layers and that of the intermediate and bonding pad electrode layers are prevented, so that the semiconductor device with enhanced reliability is provided. In addition, the sidewall conductive layer formed on the sidewall of the first hole prevents cracking at the sidewall of the first hole.  
       [0035] More preferably, the interconnection and bonding pad electrode layers include aluminum. In this case, as adhesion between aluminum and the intermediate layer is high, the adhesion between the interconnection and intermediate layers as well as that between the bonding pad electrode and the intermediate layers can be further increased. As a result, separation of the interconnection and intermediate layers and that of the intermediate and the bonding pad electrode layers are prevented, so that the semiconductor device with high reliability can be provided.  
       [0036] The foregoing and other objects, features, aspects and advantages of the present invention will become more apparent from the following detailed description of the present invention when taken in conjunction with the accompanying drawings. 
     
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
     [0037]FIG. 1 is a top view of a semiconductor device according to the present invention.  
     [0038]FIG. 2 is a view showing a cross section taken along the line II-II in FIG. 1.  
     [0039] FIGS.  3  to  7  are cross sectional views showing first to fifth steps of a method of manufacturing the semiconductor device shown in FIGS. 1 and 2.  
     [0040]FIG. 8 is a cross sectional view showing a structure of a conventional bonding pad electrode.  
     [0041]FIG. 9 is a cross sectional view showing a bonding pad electrode shown in conjunction with a problem associated with the conventional bonding pad electrode.  
     [0042]FIG. 10 is a cross sectional view showing the bonding pad electrode shown in conjunction with a problem associated with connection of a bonding wire to the bonding pad electrode shown in FIG. 9.  
     [0043] FIGS.  11  to  13  are cross sectional views showing a conventional semiconductor device described in the aforementioned Laying-Open Application. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
     [0044] An embodiment of the present invention will now be described with reference to the drawings.  
     [0045] Referring to FIGS. 1 and 2, an interlayer insulating film  2  including a silicon oxide film is formed on a silicon substrate  1 . An interconnection layer  3  including aluminum is formed on interlayer insulating film  2 . An interlayer insulating film  4  as a first insulating layer including a silicon oxide film is formed to cover interconnection layer  3 . A via hole  5  is formed in interlayer insulating film  4  as a first hole leading to interconnection layer  3 . A length of a side of the via hole (a length corresponding to W 1  in FIG. 1) is about 100 μm. A depth of the via hole is about 1 μm. Via hole  5  allows a surface of interconnection layer  3  to be exposed. A titanium (Ti) layer  9  as a first intermediate layer and a titanium nitride (TiN) layer  10  as a second intermediate layer are formed on the exposed surface of interconnection layer  3 , a sidewall of via hole  5  and a surface of interlayer insulating film  4 . Titanium layer  9  and titanium nitride layer  10  form the intermediate layer. Titanium layer  9  is in contact with interconnection layer  3  and titanium nitride layer  10 . A sidewall conductive layer  8  as a sidewall conductive layer including tungsten is formed in contact with titanium nitride layer  10 . A bonding pad electrode layer  6  is formed in contact with sidewall conductive layer  8  and titanium nitride layer  10 . Bonding pad electrode layer  6  includes aluminum. Bonding pad electrode layer  6  and titanium nitride layer  10  are directly in contact with each other. A passivation film  7  as a second insulating layer is formed to cover bonding pad electrode layer  6 . A via hole  11  is formed in passivation film  7  as a second hole leading to bonding pad electrode layer  6 . A bonding wire  14  for electrically connecting an external device and the semiconductor device is connected to bonding pad electrode layer  6 . Bonding wire  14  includes aluminum or gold.  
     [0046] Next, a method of manufacturing the semiconductor device shown in FIGS. 1 and 2 will be described. Referring to FIG. 3, an interlayer insulating film  2  including a silicon oxide film is formed on a silicon substrate  1  by CVD (Chemical Vapor Deposition). An aluminum film is formed on interlayer insulating film  2 . The aluminum film is patterned to form an interconnection layer  3 . An interlayer insulating film  4  including a silicon oxide film is formed to cover interconnection layer  3  and interlayer insulating film  2  by combining methods including plasma CVD, Spin on Glass and etch back by dry etching. A resist is applied on interlayer insulating film  4  for photolithographically patterning, so that a resist pattern having a via hole pattern is formed. Using the resist pattern as a mask, interlayer insulating film  4  is etched by RIE (Reactive Ion Etching). Thus, a via hole  5  is formed. Thereafter, the resist pattern is removed using oxygen plasma or the like.  
     [0047] Referring to FIG. 4, a titanium layer  9  is formed by sputtering. A titanium nitride layer  10  is formed on titanium layer  9  by sputtering. A tungsten layer  28  is formed by CVD to cover an entire surface of titanium nitride layer  10 . A thickness of tungsten layer  28  is about 5000 Å to about 10000 Å.  
     [0048] Referring to FIG. 5, an entire surface of tungsten layer  28  is etched back. At the time, as titanium nitride layer  10  must be left on the entire surface, a method which does not etch titanium nitride layer  10 , such as a stop on TIN method, is used for the etch back. Thus, in a sidewall portion of via hole  5 , the tungsten layer is left to form a sidewall conductive layer  8 , whereas a central portion of via hole  5  does not have any tungsten layer.  
     [0049] Subsequently, an aluminum film is formed to cover titanium nitride layer  10  and sidewall conductive layer  8 . At the time, in via hole  5 , interconnection layer  3  and the aluminum film are connected with titanium nitride layer  10  and titanium layer  9  interposed. As sidewall conductive layer  8  is formed in the sidewall portion of via hole  5 , the aluminum film is formed on sidewall conductive layer  8 . Then, the aluminum film is patterned by photolithography and RIE to form a bonding pad electrode layer  6 . It is noted that although a side coverage ratio a (=a ratio of a thickness b to a thickness c of bonding pad electrode layer  6  in FIG. 6: b/c) at an end of such wide opening is about 0.5 when a general sputtering is used, sidewall conductive layer  8  increases the side coverage ratio α up to at least 0.6. A silicon nitride film of passivation film  7  is formed on the entire surface of bonding pad electrode layer  6  by plasma CVD. A via hole  11  leading to bonding pad electrode layer  6  is formed in passivation film  7 .  
     [0050] Referring to FIG. 7, a probe needle  12  including tungsten is brought into contact with bonding pad electrode layer  6  for probing the device. After a prescribed test is performed, probe needle  12  is separated from bonding pad electrode layer  6 . Thereafter, a bonding wire  14  is connected to bonding pad electrode layer  6  to complete the semiconductor device shown in FIGS. 1 and 2.  
     [0051] In such semiconductor device, in the step shown in FIG. 7, a strong force is applied to a portion of bonding pad electrode layer  6  by probe needle  12  when probe needle  12  is brought into contact with bonding pad electrode layer  6 . The force is transmitted to titanium nitride layer  10  and titanium layer  9 . Titanium layer  9  and titanium nitride layer  10  are high particularly in mechanical strength as compared with aluminum, so that the force applied by probe needle  12  is dispersed in titanium nitride layer  10  and titanium layer  9 . Thus, the force is dispersed generally to interconnection layer  3  positioned below titanium layer  9 , whereby cracking of interlayer insulating film  2  below interconnection layer  3  is prevented. As a result, cracking of bonding pad electrode layer  6  would not be caused and the semiconductor device is provided with high reliability.  
     [0052] Further, in the step shown in FIG. 7, even when a force is applied by probe needle  12  in a direction indicated by an arrow  31 , a crack at a portion  4   a  in interlayer insulating film  4  is avoided as titanium nitride layer  10  and titanium layer  9  are also formed on interlayer insulating film  4 . As a result, the reliability of the semiconductor device is further increased.  
     [0053] Further, as titanium nitride layer  10  and titanium layer  9  are both high in adhesion with aluminum, bonding pad electrode layer  6  and interconnection layer  3  are tightly connected with titanium nitride layer  10  and titanium layer  9  interposed. Thus, when removing probe needle  12  from bonding pad electrode layer  6 , separation of bonding pad electrode layer  6  and interconnection layer  3  is prevented. Thus, the semiconductor device with enhanced reliability is provided.  
     [0054] Although the embodiment of the present invention has been described, various modifications can be added to the embodiment. For example, although titanium nitride and titanium are used as materials forming the intermediate layer in the embodiment, the materials are not limited to this and a metal with high melting point such as molybdenum (Mo), tungsten (W), titanium silicide (TiSi), molybdenum silicide (MoSi), tungsten silicide (WSi), molybdenum nitride (MoN) or tungsten nitride (WN) may be used.  
     [0055] Further, although the intermediate layer includes two layers in the present embodiment, it is not limited to this and may include only one layer, or include three or more layers. Moreover, although the interconnection layer and bonding pad electrode layer include aluminum in the present embodiment, the layers may include aluminum alloy, and any material may be used as long as it is high in adhesion with the intermediate layer.  
     [0056] Although the present invention has been described and illustrated in detail, it is clearly understood that the same is by way of illustration and example only and is not to be taken by way of limitation, the spirit and scope of the present invention being limited only by the terms of the appended claims.